From Raw Material Identification to Fine and Specialty Chemicals Analysis

The Global Chemical Industries Summit 

Trace Element Detection Limits: What Every Spectroscopist Should Know

Peak Shape and Closely Spaced Peak Convolution in Raman Spectra

Identifying Doxycycline Hydrochloride and Tylosin in Chicken Using SERS

Studying Inorganic Arsenic, Heavy Metals, and Iodine in Dried Seaweed

The Infrared Spectra of Polymers II: Polyethylene

I’ve got the STEM degree. Now, what’s next? How do I prepare for an interview? How do I land a leadership role? What do I do if I don’t want to work in a laboratory?

These are common thoughts that many people in science, technology, engineering, and math (STEM) fields face as they are deciding what steps to take to get to their ideal career. While navigating through school or the early stages of a STEM career, emphasis is typically placed on the technical aspects needed within the field. Countless hours are spent learning how to master a hands-on technique to exhibit expertise in a subject or discipline. However, advancing a STEM career and moving up the leadership ladder requires additional skills outside of the technical expertise needed for the laboratory.

Transitioning into a successful career demands skills outside of the knowledge, expertise, and research acquired through attending an academic institution. It requires gaining awareness about what is needed to be fulfilled at work and investing time in developing soft skills

interpersonal skills, behavioral traits, and personal competencies that go beyond technical and analytical skills. Soft skills help to facilitate effective engagement with others, drive employee satisfaction, and ultimately complement any technical requirements needed for a job. Managers often seek individuals who can harmonize technical and soft skills. Common soft skills include those related to:

Because these skills are so valuable, it is beneficial to think of them as “career assets” rather than a simple set of skills. Why is that? By definition, an asset is a useful or valuable thing, person, or quality—much like monetary assets. You should acquire a broad portfolio of these professional assets for your career to flourish.

As you navigate your career, keep a few of these suggestions in mind:

 Crafting a vision for what you need to feel fulfilled in life, both professionally and personally, is key to manifesting those dreams. Check in with yourself often about your needs, and write them down! This will help to ensure that all of the things that you are doing are leading you toward your definition of success.

Set S.M.A.R.T. goals and create an action plan.

 The S.M.A.R.T. framework is a great way to set goals so you can remain accountable. The acronym stands for specific, measurable, attainable or achievable, relevant or realistic, and time-bound. This method helps to clarify your goals, focus your efforts, and prioritize efficiently so that you can manage your time wisely. After crafting your goals, break down projects into manageable pieces to put your plan into action. Build your personal board of directors. Identify mentors, advisors, coaches, and sponsors to aid in your professional development and support you as you advance your career.

As the saying goes, it’s not what you know, it’s who you know. Practice networking as much as possible, and seize unconventional opportunities to connect with others. Networking is about planting seeds that can be cultivated into future relationships. As you engage with others, be sure to articulate who you are, what you do, and most importantly, where you see yourself going. Remember, your network equals your net worth.

Be prepared to navigate the job search and interview like a pro.

 When updating your CV or resume, focus on including statements of impact, and aligning them with keywords found in the job posting. Prepare for interviews by researching the company, and be ready to ask meaningful questions. If you are struggling with preparing for the interview, focus on who, what, where, when, why, and how. Who are you? What do you do or what can you do for the company? Where do you see your career going, or where do you see yourself fitting into the company? When can you start? Why should they hire you? And, how will you get the job done?

. Having a good sense of your emotions and how they influence your behavior and interactions with others can be the foundation to developing meaningful relationships with those around you.

 Get to know what your communication style is, and practice regularly. Focus on the 6 C’s of Communication: clarity, conciseness, credibility, candor, composure, and connection. As you engage with others, be mindful of non-verbal cues, and practice active listening to deepen conversations.

 Identify your greatest strengths (your “super powers”) and use them strategically. Don’t be afraid to lean into areas where you need improvement, to prevent weaknesses from becoming your “kryptonite.” Be open and receptive to feedback and critique.

Get comfortable with being uncomfortable; it’s where the growth is.

 As you navigate your career, remain agile, flexible, and resilient.

 Leaders inspire and motivate others by building authentic relationships and keeping a positive mental attitude. Embrace who you are and strive to keep growing into the best version of yourself.

Overall, the best thing to remember about your career is that you are in charge of determining the direction that it will head. Don’t be afraid to revisit your plans, and pivot as needed to make sure that you are being fulfilled. Along the way, make sure that you find ways to acknowledge and celebrate your “wins” to help you stay motivated. Set goals, and be intentional about your actions to achieve success on your own terms.

The “Beyond the Beaker” workshop that was originally scheduled for SciX 2021 had to be cancelled, but the SciX organizers look forward to offering this workshop at future SciX conferences. Dr. Pritchett’s article speaks to SciX’s strong support of students and early career professionals.

 is a Senior DEI Strategist and leadership coach within the federal government. She began her career as a research chemist working on developing standard reference materials for clinical, food, and forensics projects. Prior to her current role, she also worked as a scientific advisor in the federal government and an Embassy Science Fellow for Scifest Africa located in Makhanda, South Africa. Throughout her career, she has remained dedicated to STEM education and inspiring the next generation of STEM professionals. She created a career coaching program for post-doctoral researchers within her current organization to help them gain clarity about their goals and elevate them toward the next step in their careers. Since its inception in 2018, there have been over 60 participants in the career coaching program. She has over 15 years of experience teaching, and currently works as an Adjunct Lecturer of General Chemistry at Montgomery College in Rockville, Maryland. Direct correspondence to: 

Articles

Dr. Jeanita Pritchett offers insight on how science, technology, engineering, and math (STEM) students can transition into a successful scientific career after graduation.

Beyond the Beaker: How to Advance Your Scientific Career

To better understand biological processes, spectroscopists are developing innovative approaches that utilize the unique interactions between nanostructured materials and light for near field imaging and ultrasensitive label-free spectroscopic detection. Zac Schultz of The Ohio State University and his team have utilized techniques like tip-enhanced Raman spectroscopy (TERS) as well as surface-enhanced Raman spectroscopy (SERS) with gold nanostars, to demonstrate an approach to investigate chemical interactions involved in protein–ligand binding. 

 recently spoke to Schultz about this work. Schultz is the 2021 recipient of the Clara D. Craver Award from The Coblentz Society. This interview is part of an ongoing series of interviews with the winners of awards that are presented at the annual SciX conference, which will be held this year from September 26 through October 1, in Providence, Rhode Island.

Recently, you and your team conducted an experiment that demonstrated that gold nanostars (Au NSs) can be used to investigate the binding between the peptide chain arginine–glycine–aspartic acid (RGD) and α

integrin (1). What was the most important question that this experiment answered, and what other important questions remain?

Protein receptors are responsible for a wide range of biological activity—everything from communicating signals from the environment into the cell to being the docking sites for pathogens and viruses. The key is to understand the specificity of the binding interaction. In this experiment, we demonstrated that the Raman signal from an Au nanostar with a short peptide attached can provide chemical information about the protein receptor it binds with. The detected Raman signal originates from the protein, which allows us to differentiate specific binding to the desired protein from nonspecific, or random, binding that may trigger other biological activity. We believe this is an important tool in understanding protein signaling–related applications like drug targeting.

One of your recently published research articles mentions that TERS and SERS can be used to investigate the interaction between proteins and ligands by selectively detecting the Raman signals of integrin from not only the purified receptor but from intact cell membranes as well (1). Can you elaborate on how the TERS signal differs from the SERS Au NS signal and why one technique may be more advantageous than the other?

Both TERS and SERS amplify the Raman signal from molecules in close (within a nanometer or so) proximity. TERS has the advantage that you can position the enhancement with high spatial precision (a few ~10 nm). SERS generates a comparable enhanced signal, but in SERS, it is typically difficult to say where the signal came from within the laser spot (typically ~1 µm). The improved spatial resolution of TERS provides a more controlled experiment to understand where the signal originates and how many receptors are probed, but this control comes at the significant cost of speed and limited scan areas. In SERS, we can probe an entire cell (20 x 20 µm) in the same time it takes to acquire a 1 x 1 µm TERS image.Interestingly, in our prior TERS work on RGD and integrins we detected nearly identical signals to our SERS work with Au nanostars. The SERS work would not have been as definitive without the earlier TERS work, but SERS enables higher throughput for this kind of characterization.

It is described in the Sloan-Dennison paper that chemometric analysis was used to analyze the spectral differences between Au-RGDFC and Au-RGDFC–α

 NSs (1). Why was multivariate curve resolution (MCR) applied, and what were you able to demonstrate using this data analysis technique?

Multivariate analysis enables us to use the entire Raman spectrum as the signature for the molecule. In univariate analysis, a single peak could arise from different molecules containing similar components; however, by using multivariate analysis, we are able to differentiate signals that might share a common peak and extract data associated with whole spectrum. We use MCR because it generates components that more closely resemble the spectra of molecules that comprise the observed signals. One of the more compelling findings is the MCR component from a purified integrin receptor in solution is nearly identical to the component determined in cells, providing confidence to the molecular basis of our work.

In another recent study you collaborated on, you and your team used the liquid chromatography (LC)–SERS technique to detect metabolites (2). Metabolomics, which is the large-scale study of small molecules, is a powerful systems biology approach that monitors changes in biomolecule concentrations to diagnose and monitor health and disease. What challenges did you face in using this technique and what surprised you about the results obtained?

Metabolomics is an incredibly complex field and analyzing metabolites from cellular samples means there are many molecules present that can interfere with detection. A common problem in SERS is that the molecules stick to the surface, which complicates sequential detection of molecules; but we were able to statistically validate unique signals in our SERS chromatogram, which really opened the door to our work in this area. Honestly, the level of reproducibility from the cellular samples was impressive. I expected that we would identify one or two key signals, but our analysis showed patterns in a larger number of metabolites from cellular samples.

Metabolomics has emerged as a promising avenue in cancer research and diagnostics. What results have you achieved so far in this field using LC–SERS?

publication, the metabolites detected by LC–SERS appear to be specific to the genetics of the tumor model. We examined normal tissue, and several mouse-tumor models of breast cancer, and observed unique metabolite patterns in each biological sample. This supports the idea that metabolomics can be used to monitor cancer progression and, potentially, response to therapy. This is not specific to SERS; however, the instrumentation costs associated with SERS are significantly lower than with many other techniques. These reduced costs may facilitate access. We are hopeful our work may enable point-of-care metabolomics to assist in the diagnosis and treatment of cancer and other diseases.

Has receiving the Coblentz Society Clara D. Craver Award been an encouragement for you? Will you continue with your current research plans moving forward or do you see a change in your research topic emphasis?

It is always nice to be recognized for the work you are doing. While I get to accept the award, it also validates the hard work and contributions of my students, postdocs, and collaborators. Recognition like the Clara Craver Award provides motivation to continue that work and further advance science. Moving forward, we plan to continue advancing Raman detection for biomedical applications. We are also interested in energy applications and hope to develop new vibrational spectroscopy–based approaches to address these and other challenges.

(2) L. Xiao, C. Wang, C. Dai, L.E. Littlepage, J. Li, and Z.D. Schultz, 

, 1–6 (2020). DOI: 10.1002/anie.201912387.

 is an associate professor at The Ohio State University. Direct correspondence to: 

Zac Schultz of The Ohio State University and his team used tip-enhanced Raman spectroscopy (TERS) and surface-enhanced Raman spectroscopy (SERS) with gold nanostars to investigate chemical reactions involved in protein–ligand binding. He recently spoke with Spectroscopy about his findings.

Investigating Protein Receptors and Other Biomolecules Using SERS and TERS

Jerome Workman Jr. serves on the Editorial Advisory Board of Spectroscopy and is currently with Unity Scientific LLC. He is also an adjunct professor at Liberty University and U.S. National University. He can be reached at jworkman04@gsb.columbia.edu.

Bhavya Sharma is an assistant professor of chemistry at the University of Tennessee in Knoxville, where she is conducting research to detect active and important biomolecules related to hormone regulation, neurological health, and disease diagnosis. For this work, she is applying various forms of Raman spectroscopy, including surface-enhanced Raman spectroscopy (SERS) spatially offset Raman spectroscopy (SORS), and surface-enhanced spatially offset Raman spectroscopy (SESORS). She is the winner of the 2021 Emerging Leader in Molecular Spectroscopy Award, which is presented by Spectroscopy magazine. This annual award recognizes the achievements and aspirations of a talented young molecular spectroscopist, selected by an independent scientific committee. We recently interviewed her about her work.

As a postdoctoral researcher, you were able to combine SERS and SORS into a hybrid analytical technique referred to as SESORS (1). Would you explain to our readers how this concept came about, and what is the ultimate purpose of this technique?

I was not actually the first person to combine SERS and SORS. This was done by Pavel Matousek, Nick Stone, Karen Faulds, and Duncan Graham in the United Kingdom. Karen is the person who came up with the acronym SESORS. My contribution to innovative applications of SESORS was to be the first person to apply it towards Raman detection through bone. When President Obama announced the Brain Initiative in 2013, I started thinking about how we could apply Raman spectroscopy to looking at the brain. I used to have discussions with my postdoctoral advisor about this, but it seemed that everything would require removing pieces of the skull or drilling holes into the skull to take Raman measurements. I was familiar with SORS, which had been used to measure signals through skin and tissue, and I thought, why not through bone? I wasn’t actually sure it would work. Bone is dense; it is more difficult to get light through it, and more importantly, to get the Raman scattered light back out. I decided to start trying to take measurements, and I didn’t tell my postdoctoral advisor about it. I wanted to see if I could make it work before I told him about it. My first test was actually to use eggs, since an eggshell has a similar chemical composition as bone. I thought if I could detect a SERS signal through the eggshell, then maybe I could do it through bone, and it worked! I moved onto to bone after that.

The ultimate purpose of this technique is to develop a way to measure neurochemicals related to neurological disease and brain injury in the brain without having to drill holes in or remove pieces of the skull. Many neurological conditions and diseases are not diagnosed until a person starts displaying symptoms. By that point, it may be too late to treat the actual disease because of degeneration of neurons, which do not grow back. We are working to develop methods for noninvasive detection of early onset neurological disease.

By combining Raman techniques and chemometrics, you were able to directly detect important biomolecules, such as cortisol, for the first time (2). Why is this research important? What were the major analytical hurdles you encountered when developing a rapid non-invasive method to detect cortisol at physiological concentrations?

After the last year and a half, everyone knows what high stress levels feel like. We are working to develop methods for detecting cortisol in noninvasively collected biofluids, particularly to help monitor cortisol in people with high stress jobs, like first responders, military personnel, and so forth. We want something that can be used in the field, so that a person can be evaluated in the middle of a high stress situation, and a decision can be made if they need some time away. High levels of cortisol in your system for extended periods of time can have long-term negative health consequences.

The major hurdle we encountered is that cortisol is not very soluble! The body is amazing. Somehow, we have cortisol in our systems, which are primarily made of water, salts, and proteins. It took us a while to figure out how to get cortisol into physiologically relevant solvents.

Some of your most influential and instructive research publications may very well be in your recent review articles on the explanations and applications of Raman phenomena (3–5). What are the main takeaways you have learned from researching and writing these review articles?

For me, it is just so great to see such vast applications of Raman spectroscopy. We have so many great researchers around the world developing new substrates for SERS, to help increase enhancement, as well as new Raman spectroscopy-based methods for solving a range of problems from biological, environmental, and energy, to name a few. It is really exciting to read about and highlight all of the Raman spectroscopy-related research efforts.

You have also published recent work measuring volatile organic compound (VOC) detection using a porous-silicon-oxide coated disc-on-pillar array (6). Can you explain the significance and meaning of this work?

We collaborated with researchers at Oak Ridge National Laboratory to utilize these disc-on-pillar arrays for SERS gas sensing. We were interested in developing a SERS-based method for detecting VOCs in two ways, one for industrial applications where you could monitor VOCs at low concentrations; the other, which was somewhat of a crazy idea, was for human health monitoring. It turns out that, depending on your health, you can exhale something like a thousand different chemicals on your breath, some of which are VOCs. The idea was to create a SERS-based sensor for some of these human health-related VOCs. The work you mention here was a first step towards developing these sensors. This is something we’re still working on developing.

What were some of the key challenges you have encountered during your work? What would you consider to be the most useful contributions of your work?

The main experimental challenges we’ve faced have centered around the idea of how do we detect biological molecules of interest at the concentration ranges that are physiologically relevant. Resolving these challenges is where SERS comes in, because it allows us to get to the low concentration ranges. However, we’ve run into issues with SERS where some molecules will not get close enough to the surface to be enhanced, so then we need to come up with ways to address that. Luckily, we have the literature to find ways to address these issues, including things like using antibodies or other capture molecules to help bring the analyte molecules within the sensing range of the SERS substrates. Other issues challenges have included things like how to detect signals through thicker areas of bone. The human skull is between 3–14 mm thick depending on where you measure on the skull, so we’ve demonstrated SESORS detection through almost 3 mm of bone. How do we push that detection through thicker areas? This question is one thing we’re currently working on answering.

I think the most useful contributions of our work include showing that you can use SESORS to measure Raman scattering through bone. Other groups have followed us in this, particularly for detection of glioblastomas, an aggressive type of cancer, in the brain. We also published an extensive study of SERS detection of neurotransmitters on two different metals (gold and silver) at three different excitation wavelengths, which we thought would be helpful for researchers in the field since, when we first started looking at neurotransmitters, the literature contained either older studies or conflicting results.

What are some key aspects in science that motivate you? Would you share some of your work and organizational habits that have helped you be productive and successful professionally?

I’m really motivated by the problem-solving aspect of science. There are so many issues in this world that need creative solutions. I am driven by being part of the solution. I also am a huge proponent of Raman spectroscopy. I sometimes think it can be used to solve anything; it really can’t, but I definitely like to try to solve various problems applying different forms of Raman spectroscopy. Another thing that motivates me is helping students learn. My group always has a large number of undergraduate researchers contributing to our work. I encourage undergraduate students to pursue research, and if I don’t have space in my group, I try to help them find research positions in other groups. I think being part of a research group is an invaluable experience for an undergraduate student.

One of the first things I learned as a new assistant professor was to turn the notifications from my email off. I try to set aside specific times to look at email, otherwise it can be overwhelming and really distracting. My group also implemented the use of Slack before the pandemic. I had tried to use it early in my career when I had two graduate students, and it didn’t really work well. Now, however, with five graduate and eight undergraduate students, it has provided us with a great tool for communicating, particularly while we were all working from home. We’ve also implemented different project management tools to help people keep track of timelines. Another thing I learned personally during the pandemic that has really helped me be more productive is that I need to set aside time to just think, which sounds weird to say, but it is really easy to get caught up in emails, teaching, talking to students about research, and so on. But to come up with new ideas or to solve problems we’re having; I need quiet time to read literature or just think about things.

What can you share with our readers regarding your next area of interest for your research? 

We’re still working on improving methods for non-invasive detection of neurochemicals in the brain. This will be something we’re working on for the foreseeable future. We also are always looking for new ways to combine analytical techniques with Raman spectroscopy to help improve things like limits of detection.

Do you have any words of advice for young people desiring a career in science?

Find what makes you really excited and happy. Try out different things to figure that out. Get involved in undergraduate research; if you’re still in high school or just starting college, don’t think you need to wait until your senior year to do this. You can start even as a freshman.

(1) A.S. Moody, P.C. Baghernejad, K. Webb, and B. Sharma, 

(3) T.J. Moore, A.S. Moody, T.D. Payne, G.M. Sarabia, A.R. Daniel, and B. Sharma, 

(4) B. Sharma, R.R. Frontiera, A.I. Henry, E. Ringe, and R.P. Van Duyne, 

(5) M.D. Sonntag, J.M. Klingsporn, A.B. Zrimsek, B. Sharma, L.K. Ruvuna, and R.P. Van Duyne, 

(6) T.J. Moore, and B. Sharma, “Volatile Organic Compound Detection using Porous-Silicon-Oxide Coated Disc-on-Pillar Arrays, In Optical Sensors” (pp. SeTu4E-4). Optical Society of America (July, 2018). https://doi.org/10.1364/SENSORS.2018.SeTu4E.4

 is an assistant professor of chemistry at the University of Tennessee in Knoxville. She has developed novel Raman spectroscopy methods for neurochemical detection, including surface-enhanced spatially offset Raman spectroscopy (SESORS). Her group has demonstrated detection of neurochemicals through the skull, down to nanomolar concentration ranges. Additionally, she is developing methods to demonstrate direct detection of molecules, such as cortisol, for the first time by combining SERS and multivariate analysis. ●

Bhavya Sharma is the winner of the 2021 Emerging Leader in Molecular Spectroscopy Award. We recently interviewed her about her work conducting research to detect active and important biomolecules related to hormone regulation, neurological health, and disease diagnosis.

Exploring Neurochemistry Using Raman Spectroscopy

Throughout his career, Mark Meyerhoff, the Philip J. Elving Professor of Chemistry at the University of Michigan, has been exploring chemical sensors for biomedical applications. Recent work has involved the development of novel nitric oxide (NO)–releasing implantable sensors or monitoring important analytes continuously in vivo. For his work Meyerhoff has been awarded the 2021 ANACHEM award, which is presented annually to an outstanding analytical chemist based on activities in teaching, research, administration or other activity which has advanced the art and science of the field. Meyerhoff spoke to us about this work, his career, and what being presented this award at this fall’s SciX event means to him.

Would you comment on the meaning of being this year’s recipient of the ANACHEM Award, and some descriptive words about the impact of past recipients?

It is a great honor to be selected as this year’s recipient of the ANACHEM Award. Two very famous University of Michigan (U of M) Analytical Chemistry professors, Hobart H. Willard and Philip J. Elving, who both had an enormous impact in the field of analytical chemistry, won this award in 1953 and 1957, respectively. Indeed, my current collegiate professorship is titled the Philip J. Elving Professor of Chemistry. I overlapped with Elving for nearly five years, and he gave me great advice to help me succeed in academics and in running my research group. Two other outstanding U of M analytical professors, Mike Morris and Richard Sacks, were also winners of this award (1999 and 2006, respectively), and they also were great role models for me. To win an award won by these and many other stars in the field of analytical chemistry is very special.

Your career has demonstrated a lifelong interest in exploring using chemical sensors for biomedical applications. Why did you select electrochemical and optical sensor methodologies to explore biological systems?

As an undergraduate chemistry major (at Herbert Lehman College, CUNY system), I originally thought I would pursue a career in nuclear magnetic resonance (NMR) or mass spectrometry (MS). I was fortunate to have hands-on experience with these “big” instruments in the early 1970s in a qualitative organic analysis course. We were given four unknown organic compounds and had to identify what those molecules were, using infrared (IR), MS, and NMR. However, when taking an instrumental analysis course, one of the experiments was to use a fluoride ion-selective membrane electrode to determine the fluoride concentration in New York City drinking water. It was such a relatively simple method, given the selectivity of the sensing chemistry (LaF

 crystal develops a different voltage in response to the activity of fluoride in the sample) that I immediately became very interested in pursuing my PhD in this area. I decided to go to SUNY-Buffalo to work with one of the leaders in the field of ion-selective electrodes (ISE) and biosensors at that time, Professor Garry A. Rechnitz.

Your research team has developed novel nitric oxide (NO) releasing implantable sensors or monitoring important analytes continuously in vivo. What has been your motivation to get involved in this challenging area?

In the mid-1990s, my laboratory started to work on developing sensors that can emit nitrogen oxide (NO) to prevent clotting on the surface of sensors implanted in blood vessels for continuous monitoring of oxygen, carbon dioxide, and glucose, among other blood analytes. This had been the “holy grail” in the field of sensors for some time. However, such devices would often fail and give erroneous results, because platelets in blood would become activated and stick to the surface of the sensors. Platelets are metabolically active, consuming O

, so platelet adhesion on the sensors would cause false analytical results. I went to a lecture on the U of M campus by Michael Marletta, and learned that NO is produced by endothelial cells that line the walls of all blood vessels, and NO levels near the surface of these cells prevent platelet activation and clotting. So, I wrote an NIH RO1 grant to pursue the idea of using NO release compounds (diazeniumdiolates back then) on the surface of various sensors to greatly improve their in vivo analytical performance. That grant was funded and renewed multiple times. Most importantly, in every in vivo sensor experiment (in animals) we have conducted over the past 20 years, there has always been a very significant improvement in the accuracy of the analyte measurements with NO release sensors vs. control sensors (without NO release) implanted in the blood vessels of the same animals. This has been true no matter what chemistry is used to generate the increase in NO locally at the surface of the in vivo sensing devices.

At what age did you realize that analytical science would be your career choice?

Probably in my second year of college at age 18, when I had a quantitative analysis class. I really loved getting “unknown” samples and then doing some measurements (including titrations and spectrophotometry) to determine the concentration of a given species. Grading back then was based almost completely on accuracy, so that meant you had to be really careful. That was when I decided to pursue a career in analytical chemistry, but as described above, it was a year later when I took instrumental analysis, and we did a fluoride ion-selective experiment, that I found my passion for this given subfield (sensors) of analytical chemistry.

What were some of the most challenging problems you have encountered during your research career?

One of them was perhaps finding the right project that would motivate a given graduate student or post-doc to become truly passionate about their research. I typically would give a student or post-doc one or two side projects, often via collaboration with other labs on campus. Many times, it was one of these side projects, not the main one that I originally assigned, that evolved into the main part of a student’s thesis, or a post-doc’s primary publications.

What would you consider to be the most meaningful contributions of your work?

This is a difficult question, since there are so many research publications that I feel were very meaningful and important. However, I have to say that as I approach my retirement years, the thing that stands out most to me is the training of so many graduate PhD students (68) and post-docs (38 or so) who are now very successful in academics (big and small schools around the world), as well as in industrial and governmental jobs. Without a doubt, this is the most gratifying part of being a professor at a major research university.

Would you share with our readers your work ethic, philosophy, and how you plan your daily or weekly work schedule?

Well, I am not the kind of person who can do things at the last minute. When it comes to preparing new lectures for class, or a seminar at a conference or university, I generally start way in advance, so that I have plenty of time to recheck the content, find spelling errors, make sure the substance of the lecture flows well, and so forth. The same is true for proposals and publications. In the case of proposals, I generally try to start two months in advance and try to write at least one paragraph or more most days of the week. Before you know it, the proposal is mostly done, and I have plenty of time to spend editing, getting figures inserted, and take other steps to make the proposal nearly perfect. This approach has worked well for me over many years.

What words of wisdom do you have for any young people interested in a scientific research career?

“Don’t Major in Minor Things.” I read those words in a little booklet that was given to me as a gift titled “Life’s Little Instruction Book: 511 Suggestions, Observations, and Reminders on How to Live a Happy and Rewarding Life.” I would often say to students that majoring in chemistry is not a minor thing, and that there are more career paths available by majoring in chemistry and biochemistry than almost any other science. Indeed, chemistry majors can easily obtain an industrial job after their four years in undergraduate school. They also are quite attractive candidates for medical and dental schools. Of course, if they enjoy conducting research, they can go on to obtain MS and PhD degrees and actually be paid during their graduate school years, with no tuition costs (now the stipends are in excess of $30,000 per year, whereas, when I was a graduate student, it was about $3000 per year).

 is currently Philip J. Elving Professor of Chemistry in the Department of Chemistry at the University of Michigan, Ann Arbor. His long-term research interests have been in the field of analytical chemistry, particularly the development of new ion-, gas-, and bio-selective electrochemical/optical sensors suitable for measurements of clinically and environmentally important analytes. An active consultant or is on the Scientific Advisory Boards for several biomedical companies, he is cofounder of NOTA Laboratories and NitriCap Medical, two companies that are focused on developing novel NO-releasing chemistries and devices for medical applications.●

Mark Meyerhoff has been exploring chemical sensors for biomedical applications. Because of his work, Meyerhoff has been awarded the 2021 ANACHEM award. Meyerhoff spoke to us about his work, his career, and what being presented this award at this fall’s SciX event means to him.

Developing Electrochemical and Optical Sensors to Measure Analytes in Physiological Samples

Surface-enhanced Raman scattering (SERS) is used to improve Raman scattering, often allowing the detection of single molecules. It generates molecularly specific fingerprints of analytes and, with carefully controlled experimental conditions, can be highly quantitative. Roy Goodacre, a professor of biological chemistry at the University of Liverpool in the United Kingdom, first used this technique to achieve whole-organism fingerprinting of bacteria and then explored SERS in a variety of other applications, including within biotechnology, disease diagnostics, quantitative detection, imaging, food security, and more. Goodacre is the 2021 winner of the Charles Mann Award for Applied Raman Spectroscopy. This interview is part of an ongoing series of interviews with the winners of awards that are presented at the annual SciX conference, which will be held this year from September 26 through October 1, in Providence, Rhode Island.

Has your work with SERS solved some of the challenges commonly associated with Raman spectroscopy for quantitative analysis, such as native sample fluorescence and standardization of Raman intensity?

That’s a great question, and many people believe SERS to lack reproducibility. In fact, SERS can be made highly quantitative, which addresses the second half of your question in terms of standardization. Our group have developed SERS for quantitative analysis and embedded design of experiments in order to search the possible experimental landscape in terms of type of metal ions to reduce, how to perform the reduction (which dictates the “capping” agent on the nanoparticle surface), as well as conditions used to initiate aggregation (in terms of salts as well as controlling the pH of the environment). When you do this, you can come up with nice bespoke protocols that lead to high levels of standardization.

In terms of fluorescence, we very rarely see this. This is due I believe (I’m no physicist) to energy transfer occurring during the excitation. In fluorescence the molecules in the system absorb energy and are in the electronic excited state. After non-radiative decay fluorescence is seen as the emission of light at a longer wavelength to the incident radiation. However, in SERS which uses metallic nanoparticles, a type of FRET mechanism occurs where the light is not emitted but this energy is transferred to the metal. I might have that a bit wrong, but anyway SERS effectively quenches the normal fluorescence process. This is why a lot of people still use Rhodamine 6G which is a highly fluorescent dye to illustrate that their SERS conditions work. There are possibly more SERS spectra of this molecule in the literature than your readers have had hot diners!

In your paper “Recent developments in Quantitative SERS: Moving towards absolute quantification” (1) you and your colleagues critiqued the development of quantitative SERS from simple univariate assessment of single vibrational modes to multivariate analysis of the whole spectrum for improved quantification. What knowledge did you and your team gain from this study?

This was actually a review that I wrote along with my colleagues Professors Karen Faulds and Duncan Graham (from the University of Strathclyde in Scotland), rather than a primary paper. I’m glad you ask about this, as reviews are really good ways to synthesize knowledge and thus to refine concepts and to formulate new ideas. In this review, we specifically looked at how fellow scientists had developed SERS to be quantitative and thus used to provide reproducible and robust values for absolute levels of key analytes (or what we may term determinands). There are a number of things that can affect quantification, and these include (among others) variation in laser fluence during the experiment as well as the number of aggregated nanoparticles with associated molecules within the SERS/Raman collection voxel. At the end of this process, the CCD within a Raman spectrometer will give readouts of energy.

SERS is no different from using, say, liquid chromatography-mass spectrometry (LC–MS) to quantify drugs in athletes’ blood and urine during the Olympics. LC–MS only provides absolute levels of these drugs and their metabolites when the detector (the MS in this case) is calibrated appropriately. SERS is no different, one needs to calibrate the system, and once you do this then absolute quantification is readily achieved.

What we learned and reported in this review was that several groups had come to the conclusion that two general experimental strategies can be used to calibrate the whole system so that absolute quantification (for example, µM or ng/mL of a target in, as an example, blood or urine) could be accomplished. Rather interestingly, both these approaches have been borrowed from other fields including mass spectrometry!

The first method involves spiking the sample with a stable isotope of your molecule. This can be 13C or 15N, but what is particularly useful is the use of deuterium (2H or D) as the reduced mass changes (for example, substitution of C–H with C–D) cause very large shifts in vibrational frequencies. This method has been termed isotope dilution surface-enhanced Raman scattering (IDSERS) and the use of isotopologues of the target molecule overcomes any competitive co-adsorption or co-association with the metal surface, since the natural isotope and stable isotope have very similar physical properties. This also overcomes any laser power fluctuations as both analyte and internal standard are recording simultaneously. The isotope standards (isotopologues) can then be used as subtractions or as ratios if key peaks are clearly seen within the spectra for both natural and stable isotope. Alternatively, one can use multivariate analyses such as linear regression techniques like partial least squares (PLS) which uses the full spectrum, or multivariate curve resolution (MCR) which unmixes spectra to generate a series of ‘pure’ spectra as well as corresponding concentration values.

The second method is to use the standard addition method (SAM) where the standard here is the analyte you want to quantify. In SAM the standard is the natural isotope and so will have the same SERS spectrum as the molecule within the sample. The standard is then ‘spiked’ into the sample multiple times at different known levels. The areas of diagnostic peaks are then calculated and plots of these peak areas against the concentration of the spiked standard will yield a straight line. The key thing here is that the zero-level spike will still have a peak from the target molecule and so the “0” spike concentration will intercept the 

-axis. The slope can then be used to calculate the level of the molecule in the sample with high precision and accuracy.

These methods both give absolute quantification of targets and are excellent methods “borrowed” from other areas of analytical chemistry.

What are some of the newest uses of SERS for clinical diagnostics?

Well, let’s look at what effect the last 18 months or so have had on the SERS field. Many people have shifted their work towards detecting whether someone has Covid-19 or not. Some of these studies have been based on profiling a body fluid. For example, saliva has been used in a recent study by Carlomagno and colleagues (

https://doi.org/10.1038/s41598-021-84565-3

), where multivariate analysis was then used for identification of SERS patterns that are associated with infection. Alternatively, the virus can be measured directly using PCR-based approaches or via antibody detection and these methods are coupled with SERS where the read out is SERS of a specific target dye. These methods, including lateral flow devices, feature in a recent review by Saviñon-Flores 

I guess what this pandemic has achieved is to focus people’s minds on diagnostics. This proves that this area, and especially point of care diagnostics, is important and has allowed mass screening of populations. And of course, all these methods of diagnostics are embedded within excellent analytical science.

Do you see SERS being implemented in practical clinical diagnostics? And is quantitative analysis important?

In addition to Covid-19 detection discussed above, other developments of SERS for clinical application are highlighted in our review in 

) (1). I think one of the most interesting of these includes SERS methods for measuring drugs and their metabolites (xenometabolites) directly in human biofluids (for example, blood and urine). Because no chromatography is used, these methods are very rapid, with results generated in a few minutes. Here, quantification is very important and the measurement of drugs and their xenometabolites also allows one to calculate pharmacodynamics. In addition, SERS can also be used to know if someone has taken an illicit drug several days ago, because drug metabolites are generally cleared from the body at a slower rate than the drug itself.

The speed of analysis here is a huge advantage because many manufacturers are producing handheld and portable Raman instruments that can be taken to the patient, rather than shipping a sample to a central testing facility. I see the future of SERS being within diagnostic point-of-care applications.

In another paper, you described how SERS was used for simultaneous detection of multiple novel psychoactive substances (NPS) as an alternative to various hyphenated methods such as gas chromatography (GC) or liquid chromatography with mass spectrometry (LC–MS) (2). What advantages does the use of SERS have over these hyphenated methods for quantitative analysis of NPS?

The main advantages are similar to those articulated above. SERS can be made portable and is rapid, which means that the methods can be used for on-site for testing. This could be for testing someone for illicit use of these substances.

An alternative application would be to develop and deploy SERS within drug testing centers in large events like music festivals to check the authenticity of NPS. Unfortunately, some of these psychoactive drugs are impure or may contain NPS fentanyl analogs or indeed fentanyl itself. These can be lethal and there have, unfortunately, been several cases in the US, so authentication of drugs prior to use is really important.

What challenges do you think that SERS will have in sample presentation for quantitative detection and discrimination of a range of NPS?

The main challenges will be sample processing in order to extract NPS from body fluids and then ensuring that the NPS associates with the metal surface of the nanoparticles because the analyte needs to be close to or bound to the surface. Neither of these are straightforward, but we can again borrow approaches that we use in our mass spectrometry-based metabolomics. If we want to know the actual concentration in a biofluid then one can adjust for any variance in the extraction efficiency by spiking in isotopes of the NPS target molecule(s) directly into the sample being measured before any sample preparation has taken place. This means that any variation in sample preparation is accounted for as the NPS and its isotope equivalent have the same chemistries and so will be extracted with highly similar efficiencies. Any extraction and measurement errors can then be accounted for by using the ratios of the isotopes in the naturally occurring NPS and comparing this with any stable isotopes in the NPS spike. This approach is also discussed in our review published in 

For the discrimination of a wide range of NPS what we reported in (2) is that the SERS spectra contain vibrational features that reflect their core chemical structures. When we performed unsupervised cluster analysis using PCA (principal components analysis) we found that the NPS samples grouped into three distinct clusters that were identified as methcathinones, aminoindanes and diphenidines. This is potentially very exciting and could be exploited in the future. Clandestine chemists generate new NPS by modifying a designer drug by the addition of chemical groups to a core chemical structure, and that core reflects the psychoactive activity of the drug. Being able to identify the core structure of an NPS is as important as having a method that gives specific spectral fingerprints that allow for the identification of individual NPS.

Is there a specific direction you see this technique developing into over the next few years? In other words, are there unmet challenges to this technique that if resolved would bring broader applications?

SERS, at the moment, is mainly used within research laboratories. However, the realization that this method can be made to be robust, reproducible, highly quantitative, and that it is inherently portable suggests to me that it is only a matter of time before this technique can be translated from the laboratory to the clinical environment.

I’m not the only one to think this. Inspired by employing SERS for therapeutic drug monitoring, Professor Alois Bonifacio (from the University of Trieste in Italy) led a large-scale multi-instrument interlaboratory study, as part of the EU COST Action BM1401 Raman4Clinics to address whether equivalent data can be collected in different laboratories. This study was published last year in 

https://doi.org/10.1021/acs.analchem.9b05658

) and shows that SERS can indeed be standardized, and that once standard operating procedures (SOPs) are adopted, then SERS is robust enough to allow for the quantification of target molecules. Our group was proud to be part of this study which involved 15 different laboratories throughout Europe. Our study was one of the first multi-center SERS studies.

Of course, central to SERS is the instrument itself. In another study also published last year in 

https://doi.org/10.1021/acs.analchem.0c02696

) Professor Thomas Bocklitz (from the University of Jena in Germany) lead another Raman4Clinics study that was designed to address how Raman spectrometers can be configured to provide robust results and thus help improve inter-laboratory studies using Raman spectroscopy. This was also a large-scale round robin study involving 15 institutes within seven European countries and compared 35 Raman spectroscopic devices with different configurations. We were also involved in this study, and it led to a series of recommendations that we believe are worthy of future investigations to improve multi-laboratory studies.

I believe that both these studies are very important and show that SERS has great potential for adoption within clinical environments.

What are your next steps in your own work with Raman spectroscopy and SERS?

Lots, but I will just mention one very exciting area that we are developing.

Within the University of Liverpool’s Centre for Metabolomics Research (CMR) we are establishing a variety of Raman-based methods for chemical image analysis of tissues, cells, and bacteria. We have capabilities in spontaneous Raman spectroscopy from Renishaw, stimulated Raman spectroscopy (SRS), and coherent anti-Stokes Raman spectroscopy (CARS) from Leica. We also have a combined Optical Photothermal IR and Raman system from Photothermal Spectroscopy Corp.

Our group is very excited by these techniques, and we hope to combine vibrational spectroscopic imaging with mass spectrometry-based metabolomics. For those interested in the CMR please visit: 

https://www.liverpool.ac.uk/liverpool-shared-research-facilities/facilities/multi-omics/cmr/

Within these pages there are a few case studies, and to whet your reader’s appetites we have recently published papers on “metabolism in action” where we have been developing stable isotope probing using Raman and infrared imaging for understanding metabolic flux at the single bacterial cell level. This is really pushing the resolution limits of these platforms, and we’re very excited by the results.

Before we close out this interview, I would like to take this opportunity to thank FACSS for the Charles Mann Award. I was really shocked, absolutely thrilled and honored to find out about being given this award. There have been some exceptional scientists that I have looked up to (and indeed still do!) in the Raman field who have been bestowed this award, and I am amazed to be in their company. It’s a wonderful reflection of the work our fantastic research team has achieved over the last 20 years, and they are as deserving as I. Thanks to them all!

I'm also really hoping that I will be able to travel to Providencein September to meet up with friends and colleagues and of course to make new connections. I've certainly missed the international conference scene. I'm reminded of going to ICORS 2018 in Jeju and meeting Professor Luis Liz-Marzán (from CIC biomaGUNE in Spain) during a session or two on SERS. This chance meeting led to a substantial review by nearly 70 authors on SERS. A review that, while only being published two years ago, has already been cited over 500 times. If you’re really interested in SERS, then this tour-de-force in 

 on the “Present and Future of Surface-Enhanced Raman Scattering” (

(2) H. Muhamadali, A. Watt, Y. Xu, M. Chisanga, A. Subaihi, C. Jones, D.I. Ellis, O.B. Sutcliffe, and R. Goodacre, 

Roy Goodacre received his degree in microbiology from the University of Bristol (Bristol, England) and was awarded his PhD in 1992 in mass spectrometry applied to microbiological problems (also from Bristol). He is Professor of Biological Chemistry at the University of Liverpool and leads a team of around 20 researchers in the Department of Biochemistry and Systems Biology within the Institute of Systems, Molecular and Integrative Biology (ISMIB). Additionally, he is the Chair of the Institute's Research and Impact Committee, Deputy Head of Department, and a co-director of the Centre for Metabolomics Research. His research interests include analytical biotechnology and disease diagnostics, detection, imaging, food security, as well as systems and synthetic biology. He has more than 30 years of expertise in mass spectrometry (MS)-based metabolomics, Raman spectroscopy, and advanced multivariate data analysis.

https://en.wikipedia.org/wiki/Roy_Goodacre

https://scholar.google.com/citations?user=Dszi0U8AAAAJ&hl=en

Roy Goodacre, a professor of biological chemistry at the University of Liverpool in the United Kingdom, first used SERS to achieve whole-organism fingerprinting of bacteria and then explored SERS in a variety of other applications, including within biotechnology, disease diagnostics, quantitative detection, imaging, food security, and more. Goodacre is the 2021 winner of the Charles Mann Award for Applied Raman Spectroscopy. This interview is part of an ongoing series of interviews with the winners of awards that are presented at the annual SciX conference.

Quantitative Analysis Using Surface-enhanced Raman Scattering (SERS): Roy Goodacre, the 2021 winner of the Charles Mann Award for Applied Raman Spectroscopy

In cancer, the tissue microenvironment is an important determinant of disease progression and development. Spectroscopic imaging offers promise to reveal important information about what is happening in these microenvironments, with the potential to better predict tumor behavior. Professor Rohit Bhargava and his team at the University of Illinois, where they have established the Cancer Center at Illinois, are advancing research in this area, using techniques such as high-definition Fourier transform infrared (HD-FT-IR) coupled with machine learning. 

 recently spoke to Bhargava about this work. Bhargava is the 2021 recipient of the Ellis R. Lippincott Award. This interview is part of an ongoing series of interviews with the winners of awards that are presented at the annual SciX conference, which will be held this year from September 26 through October 1, in Providence, Rhode Island.

You and your team focused greatly on studying the spatial constraint that is measured by the shape and structure of tumors and how this affects how individual tumor cells interact with the tumor cellular microenvironment. Particularly, you and your team believed that high-definition Fourier transform infrared (HD-FT-IR) spectroscopic imaging, coupled with machine learning can accurately identify tumor microenvironment components in tissue images. What makes this an important question to solve and what is its significance to medical research and development?

Despite significant advances in cancer biology, we still need to understand cancer progression in its entirety. A greater understanding of its spatial and biochemical composition can lead to new opportunities in diagnostics and therapeutics, for example. We believe that this could be an area where spectroscopic imaging provides a solution. FT-IR imaging offers a full spectral range and, with HD optics, an orderly means to minimize the volume from which high-quality data can be obtained. Machine learning takes this extensive data set and provides insights that are difficult to appreciate manually, while being objective and consistent in assessment. Together, these techniques can help characterize the tumor microenvironment and its influence on cancer progression. There is also a significant opportunity for spectroscopists to drive new technologies, balancing speed, spectral detail, and spatial resolution to provide integrated solutions that can help analyze the complexities of tissue and their microenvironments. In fact, the tissue microenvironment is a general determinant of disease progression and development. We now have a National Institutes of Health (NIH) supported training program in which we educate the next generation at this interface of imaging, computation, and molecular content.

In your article, you and your team talked about a high-definition infrared imaging–based organizational measurement framework (INFORM) that leverages intrinsic chemical contrast of tissue to label unique components of the tumor and its microenvironment.

Why is INFORM a great technique for the analysis you are doing?

INFORM is an early-stage tool to show that leveraging the microenvironment information through IR imaging can add value to our ability to distinguish between potentially more and less aggressive colon cancer. The ability to predict the potential lethality of the disease at the time of initial diagnoses can potentially allow us to intervene quickly in those with the greatest need, discover new factors that can help predictions and guide further research. Now that we have this technological demonstration, we can build on this, refine the technique, and translate it to test on patient populations. I should also point out that this study is just the latest example of using the microenvironment to study disease progression. We and other groups have previously also reported association of microenvironmental changes with disease progression. The need now is to further develop technology and explore its use in specific problems, which this study attempted to do.

In your study on predicting tumor behavior, what did you do in this study that is different from what other researchers have done?

The major difference between our work and that of others is that we have championed imaging a diversity of tissue samples, using a tissue microarray format, now with HD FT-IR imaging. This is a time-consuming and onerous task but essential to motivate the development of faster imaging techniques. To our knowledge, this is also the most extensive study (in terms of number of patients) reported thus far with HD-IR imaging. Next, we developed a computational pipeline to utilize this data and explicitly derive parameters from different cell types of the tumor microenvironment. Finally, we translated the development to surgical samples and demonstrated predictive capability from parts of the tumor. Thus, the work establishes a technological pathway from laboratory to clinical samples.

Will varying types of tumor tissue prove to be more difficult to discriminate?

Yes, indeed. The more normal a tumor is, both biochemically and morphologically, the tougher it will be for any technique. However, given the vast potential of spatial-spectral IR data, I think the question we should be asking is: How accurately and optimally can we recognize disease for almost all cancers?

What challenges did you face in developing and implementing microenvironment-based imaging?

The main challenges are the complexity of the microenvironment and a lack of a priori information on which components can be measured in IR with sufficient accuracy to allow us to use them for predictions. These analytical considerations are confounded by the heterogeneity and variation of the disease itself.

Is HD-FT-IR being used for patient treatment at this time? What are the barriers to fully implementing this technique in medical practice?

No FT-IR imaging technique is being used for patient treatment at this time. That is a somewhat premature step for this field. After many years of fundamental progress, we have contributions by many groups to different types of instruments, novel analysis techniques, and demonstrations of various applications. Together, these three areas come together to provide useful solutions that then need to be validated in large patient cohorts. I should caution that, while the data quality of HD-IR is high, high imaging quality (often at the expense of time or signal to noise ratio) is not an automatic technological solution for every problem. A careful matching of the needs, technology development, and validation is needed for a few use cases. This remains the main barrier to further, translational development.

You received the Ellis R. Lippincott Award because of your contributions to the fundamental physics and instrument engineering of mid-IR microscopy and its applications to medical imaging. What are your next steps in furthering your research and what do you think is the future of medical imaging?

I am deeply honored to have received this recognition. It is a testament to the growing field of IR imaging that the work of my research group has been recognized. The last 10 years have seen an accelerating trend of progress with new theoretical understanding, the availability of quantum cascade lasers, many new instrument configurations, and application of IR imaging to a much broader range of problems. Our research continues to push some of these directions as well as engage a broad group of practitioners. We are planning to focus on the development of fast imaging systems, with expanded information content arising from higher quality spatial and spectral data and using it to study the microenvironment in a variety of cancers. We believe that this technology can contribute to medical research and practice by offering a new source of information that is particularly suited to the examination of complex tissues.

 is a Founder Professor of Engineering and serves as the Director of the Cancer Center at Illinois of the University of Illinois at Urbana-Champaign. Bhargava graduated with a dual-degree B.Tech. (1996) from the Indian Institute of Technology in New Delhi, India, and received a doctoral degree from Case Western Reserve University in Cleveland, Ohio, in 2000. After a stint at the National Institutes of Health, he has been at the University of Illinois as an Assistant (2005–2011), Associate (2011–2012) and Full (2012–) professor. Bhargava is widely recognized for his research on chemical imaging and advances in theory, instrumentation, and applications in cancer pathology. His innovative teaching and mentoring have also been consistently recognized by the success of his students. He directs the NIH T32-supported Tissue Microenvironment training program and founded the cancer scholars program. In addition to his research and educational activities, Bhargava has served to connect the research community in new and exciting ways to address basic science and engineering questions that surround cancer. He proposed and has served to develop the Cancer Center at Illinois—a basic science center at the convergence of science, engineering, and oncology. Direct correspondence to: 

Professor Rohit Bhargava and his team at the University of Illinois, where they have established the Cancer Center at Illinois, are advancing research in tumor microenvironments, using techniques such as high-definition Fourier transform infrared (HD-FT-IR) coupled with machine learning. We recently spoke to Bhargava about this work. 

High-Definition Fourier Transform Infrared Spectroscopic Imaging of the Tumor Microenvironment

Analytical chemists are continually striving to advance techniques to make it possible to observe and measure matter and processes at smaller and smaller scales. Professor Vartkess Ara Apkarian and his team at the University of California, Irvine have made a significant breakthrough in this quest: They have recorded the Raman spectrum of a single azobenzene thiol molecule. The approach, which breaks common tenets about surface-enhanced Raman scattering/spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS), involved imaging an isolated azobenzene thiol molecule on an atomically flat gold surface, then picking it up and recording its Raman spectrum using an electrochemically etched silver tip, in an ultrahigh vacuum cryogenic scanning tunneling microscope. For the resulting paper detailing the effort [1], Apkarian and his associates are the 2021 recipients of the William F. Meggers Award, given annually by the Society for Applied Spectroscopy to the authors of the outstanding paper appearing in the journal 

. We spoke to Apkarian about this research, and what being awarded this honor means to him and his team. This interview is part of an ongoing series with the winners of awards that are presented at the annual SciX conference. The award will be presented to Apkarian at this fall’s event, which will be held in person in Providence, Rhode Island, September 28–October 1.

What is the significance to the scientific community of obtaining a Raman spectrum from a single molecule?

Improvement of spatial resolution has driven advances in optical microscopy, which has a history of over 1000 years. As far as molecular matter is concerned, seeing its smallest constituent, namely atoms, would be the ultimate limit. We have demonstrated this experimentally for the first time, by showing optical microscopy with a spatial resolution of 1.6 Å, equal to the radius of a silver atom (2). Beyond seeing single molecules, it is possible to wire molecules to photons (3), to use single molecules as complete opto-electronic devices (4), and, more generally, to access the sub-nano frontier in science.

Were there any previous efforts that you found especially useful in advancing this work further, be it a particular scientific approach or merely motivation or inspiration?

Surface-enhanced Raman scattering/spectroscopy (SERS) was discovered in 1974 by noting that the Raman intensity of molecules adsorbed on a roughened silver electrode were ~1 million times stronger than anticipated. Despite the very large literature on principles and applications of SERS, the subject remains a source of fascination, and we are only now reaching a rigorous understanding because of experimental advances. Perhaps the most incisive of these advances is SERS combined with scanning tunneling microscopy (STM) carried out under ultrahigh vacuum (UHV) conditions and cryogenic temperatures (5 K), exemplified by the current paper (1). This was the first direct demonstration that the spectrum of a single molecule can be observed on roughened silver by STM imaging of the molecule, and then picking it up by the tip and recording its spectrum. The observations, which were rigorously analyzed, went against many tenets as stated in the last line of the paper’s abstract: "Tips decorated with asperities break the rules and give unique insights on Raman driven by cavity modes of a plasmonic junction".

Our motivation and inspiration were the years of indirect experimental observations that had generated significant folklore about the subject. Decisive experimental observations were necessary to break through. It took us ~10 years to build the instrument and reach the point where we could carry out the definitive measurements. There are now a handful of laboratories in the world that have built up the same capabilities, such as Zenchao Dong's group in USTC and Martin Wolf's group at the Max Planck in Berlin, and Nan Jiang’s group at University of Illinois, Chicago and the number is growing as the tools become more accessible.

What motivated you to focus on this specific approach to this challenging problem?

The concept that light can be super-focused on a plasmonic wedge (5) or cone was well-established theoretically (6), and the approach of tip-enhanced Raman had already been taken by several groups starting circa 2000. The definitive experiments required atomic control of tip morphology, sub-Å resolution in scanning, and Å-scale stability in the substrate, which could be achieved by combining precision optics and a UHV cryogenic scanning tunneling microscope. This required significant instrumental development, and our earlier reports of atom-resolved optical imaging involved photo-tunneling (7) and electroluminescence with submolecular resolution (8).



What was your process to devise a method to measure the spectrum of a single molecule?

The combination of optics with high collection efficiency and ultrahigh vacuum scanning tunneling microscope operating at 5 K under pristine conditions was necessary to learn the governing physics, and to be able to definitively image a single molecule and record its Raman spectrum.



How was your approach different from what others have previously tried?

Precision instruments were necessary to learn that general notions of tip-enhanced Raman scattering (TERS) were misguided. We developed TERS in the atomistic near-field, by recognizing that on atomically sharp silver needles, the photon converts to charge.



Do you think that your method may be broadly used in laboratories, or will it be a specialized research project for some time to come?

I expect it to be broadly used, and already many new efforts are starting around the world.

Any word whether your findings were incorporated in other efforts? What sort of feedback did you receive

I find it somewhat ironic that previously the work was rejected twice. One criterion used to that end was that the described work could not be duplicated elsewhere. The body of the work carried by the team is now being recognized and adapted, as evident by the citations of the subsequent works (2-4).



Were there any particularly difficult challenges you encountered in your research?

The effort, which involved significant instrument development and the creation of a dedicated laboratory, required significant marshaling of resources and a long-time commitment, was only possible through Center type support provided by the National science Foundation (NSF). We first proposed the work to NSF in 2007, and created the Center for Chemistry at the Space-Time limit (CaSTL) for the expressed purpose of observing molecular motions with atomistic resolution. The Center had a 10-year lifespan, and delivered on its lofty promise of creating the Chemists' microscope.

Can you elaborate on the strengths that each member of the team bought to the project?

Joonhee Lee has been the team leader (project scientist) from inception to sunset of the CaSTL Center. He has led all aspects of the work, from construction of the instrument to execution of experiments to theoretical analysis, and now has started his own group at the University of Nevada to continue along the same general line of research. Nick Tallarida and Laura Rios were graduate students at the time. They were engaged in the execution of the very intensive experimental work and modeling, both in this project and several other joint publications on related work. The Mars mission is in Nick's good hands who is now at NASA, Jet Propulsion Laboratory (JPL), and the education of next generation scientists is Laura's good hands, as she is now on the faculty at the California Polytechnic Institute.



What are the next steps regarding this research?

This work has already led to a significant body of developments reflected in (2,3,4) and a series of papers in the making, addressing the sub-nano scale in microscopy, molecular devices, molecular electronics, with the key development being the confinement of the photon. Just like the confinement of the electron, which seeded nanoscience, the atomically confined photon (attained at the apex of an atomically sharp STM tip) has opened up the frontier of picoscience, another order of magnitude in miniaturization of devices.



What does being awarded the William F. Meggers award mean to you?

A tremendous amount of dedication and effort was expended by all team members in carrying out the work that appears on several pages of the journal. The cryo-UHV-STM-SERS/TERS work is complex and demanding. The experiments usually demand 24/7 operation over weeks on end. It is therefore satisfying to see an appreciation of the fruit of that labor by the Meggers Award.

(1) J. Lee, N. Tallarida, L. Rios, and V.A. Apkarian, 

Analytical chemists are continually striving to advance techniques to make it possible to observe and measure matter and processes at smaller and smaller scales. Professor Vartkess Ara Apkarian and his team at the University of California, Irvine have made a significant breakthrough in this quest: They have recorded the Raman spectrum of a single azobenzene thiol molecule. The approach, which breaks common tenets about surface-enhanced Raman scattering/spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS), involved imaging an isolated azobenzene thiol molecule on an atomically flat gold surface, then picking it up and recording its Raman spectrum using an electrochemically etched silver tip, in an ultrahigh vacuum cryogenic scanning tunneling microscope. For the resulting paper detailing the effort [1], Apkarian and his associates are the 2021 recipients of the William F. Meggers Award, given annually by the Society for Applied Spectroscopy to the authors of the outstanding paper appearing in the journal Applied Spectroscopy. We spoke to Apkarian about this research, and what being awarded this honor means to him and his team. This interview is part of an ongoing series with the winners of awards that are presented at the annual SciX conference. The award will be presented to Apkarian at this fall’s event, which will be held in person in Providence, Rhode Island, September 28–October 1.