Wavelength Tech Forum: Raman Spectroscopy

June 28, 2007

This month's Technology Forum looks at the topic of Raman spectroscopy and the trends and issues surrounding it. Joining us for this discussion are Andrew Whitley with Horiba Jobin Yvon, Joe Hodkiewicz with Thermo Fisher Scientific, and Antoinette O'Grady, with Princeton Instruments/Acton.

This month's Technology Forum looks at the topic of Raman spectroscopy and the trends and issues surrounding it. Joining us for this discussion are Andrew Whitley, with Horiba Jobin Yvon, Joe Hodkiewicz, with Thermo Fisher Scientific, and Antoinette O'Grady, with Princeton Instruments/Acton.

How have hybrids such as Raman/FT-IR and Raman/AFM instruments changed the Raman industry?

(Whitley) The biggest change to the Raman industry that hybrid Raman systems have brought about is to bring the technique to the attention and use of many more people. This has helped increase the popularity of the Raman technique in general. Thinking back one can think of Raman microscopy as the first Raman hybrid; first developed in the early 1970’s this type of Raman instrument is now seeing a huge growth with the introduction of fast Raman mapping (hyperspectral imaging) techniques by a number of companies including ours. The combined information from two techniques on the same platform provides a better understanding of materials - critically from the same sampling point. In some cases the combined technique also enhances the Raman measurement, in the case of Raman/AFM it enhances the spatial resolution. The number of different hybrid Raman systems available illustrates the importance and popularity of getting multiple types of information from the same spot. As well as those mentioned in the question there are also systems combining Raman/PLM, Raman/SEM, Raman/PL, Raman/CL and Raman/TCSPC Fluorescence Lifetimes.

(Hodkiewicz) The fact that people are interested in combining Raman with other techniques is a testament to the value of the Raman technique. As of this point the hybrid systems involving Raman have not demonstrably changed the industry. There are a number of these systems available commercially, but many of them are still rather experimental in nature and this is lessening the impact that these systems can have.

(O’Grady) They have allowed increased visibility of Raman in other science areas besides the traditional spectroscopy segment. This has helped to expand the popularity of Raman overall as an analysis technique.

What do you think portable Raman devices will look like in 5 years?

(Whitley) Raman systems can be made very small. They can therefore be packaged in a form suitable for the application and expectations in a particular field. The trick in portable Raman devices is in the sampling – being able to deliver safely the laser light to the sample and collect the Raman scattered light efficiently. Of course this is most often, but not always, done using fiber optics. It is clear that point-and-shoot type probes will become common. Surface enhanced Raman spectroscopy (SERS) techniques are developing rapidly and this could drive the sale of portable Raman devices. These devices need to interface with the SERS delivery system whether this is solution based or some type of sniffing technique. Raman microscopes will also become smaller and more portable, this will mean that they will be deployed in hazmat and medical applications much the same way that FT-IR microscope have been used recently.

(Hodkiewicz) The portable industry is driven by the applications. Over the years there have been a number of attempts to make portable instruments as lower cost alternatives to traditional laboratory instruments. These have not met with much success in the marketplace. More recently we have seen portable instruments being developed to meet new applications that have not previously been addressed – true field applications where the portable aspect of the instrument is critical to its function. Applications like these are most likely where we will see portable Raman applied in the future. Many of these instruments may be difficult to recognize as Raman. They will be dedicated analyzers reporting results rather than spectra.

(O’Grady) Portable Raman devices are shifting towards a handheld design and will become very application specific. The screen display will be a yes/no or go/no response, a list of chemical components and their concentrations. The form factor will be that of a multimeter. Probes will be direct contact in many applications or direct coupling to in-situ probes in process and environmental monitoring applications.

What advances do you see on the horizon for Raman mapping/imaging?

(Whitley) Historically Raman mapping/imaging has been thought of as a slow technique, however all that is changing with the introduction of fast Raman mapping techniques. It is now possible to measure the data at each pixel in a Raman image in 20ms or less. All this has been made possible through faster and more sensitive detectors CCD's, ICCD's and EMCCD's, faster scanners and faster readout methods. The detectors will continue to improve as will the scanning methods and this will only make the measurements faster. The signal to noise lost, through the faster acquisition times, can not be totally made up for through higher sensitivity, especially at the very fast measurement times; however the use of clever data processing can often pull very good images from even the noisiest data.

(Hodkiewicz) Raman imaging provides remarkable insights into a wide range of materials. Analysis of these images, however, is often still primitive compared with other imaging techniques. I expect that there will be considerable integration and expansion of image analysis tools in Raman systems in the coming years, which will greatly enhance the value of the technique.

(O’Grady) Coherent anti-Stokes Raman imaging is developing very rapidly and will open new diagnostic applications that the classical raster methods can not handle.

Do you see Raman growing in popularity or could another technology phase it out in the near future?

(Whitley) Fast Raman imaging, hybrid Raman and the introduction of lower priced Raman systems will see Raman continuing to grow in popularity in the near and far future. It is more likely that Raman will effect the popularity of some other techniques not the other way around.

(Hodkiewicz) Raman is definitely growing in popularity. Raman is extremely versatile and it is rapidly filling in the gaps between other more mature analysis techniques. Raman has been growing at a steady pace for the last 10 years or so. The technique could probably be growing even faster, except that the instrumentation has not matured as quickly as it has grown. Many of the commercially available Raman systems still require highly specialized users to operate them. Today most people who are using Raman are excited by the information that Raman can offer, but not particularly thrilled about the effort that they need to put into extracting it. As Raman technology continues to mature, it will become more accessible to a wider audience and we will see it applied in more routine analysis applications.

(O’Grady) For over 20 years, Raman has been the up and coming technique. The newer solid-state lasers and enhanced detectors make the technique very portable and non-destructive. Its inherent high specificity and ability to work in aqueous environments makes Raman unique. Classes of application specific compounds are rapidly being collected and multivarient mathematical data treatments add strong quantitative and predictive elements.

What application areas for Raman remain unexplored?

(Whitley) There are some pretty amazing things being done with Raman these days. Raman measurements are being done on semiconductor and biological materials with a spatial resolution of less than 20nm. Raman is going into space and to the bottom of our oceans. I am most excited about the use of Raman in the biological and biomedical fields, using Raman to help diagnose and treat disease, including cancer is something that may still be many years away; none the less it is a very real possibility. There are now endoscopic Raman probes that are being developed to be able to make Raman measurements inside the body.

(Hodkiewicz) There are many potential uses for Raman that remain underdeveloped today. Routine applications are one group that I have already mentioned. Another large area is the life sciences arena. There has been a lot of work done that demonstrates that Raman can be extremely useful in a number of areas of life sciences. I expect to see considerable expansion of Raman in these areas in the years to come.

(O’Grady) There is a great deal of exploration in the use of Raman techniques for biomedical diagnostic procedures. Real-time monitoring of process and structural changes are in the infancy stage of development for many application areas such as chemical and semiconductor.

What do you think?

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