Ocean Optics

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We describe how a manufacturer of antimicrobial-impregnated catheters has traded HPLC for reflectance spectroscopy to streamline its quality control processes.

Quality Control Testing for Catheters

	There are two primary methods of blending ethanol into gasoline: match blending and splash blending. Match blending aims to achieve some specified boiling point for the mixture and is primarily done with aromatics, resulting in a dirtier emission profile versus splash blending. Splash blending is the primary method used in the United States and is based on percent volume, specifically aiming to achieve 10% ethanol by volume in the final mix (Environmental and Energy Study Institute, 2014). In this study, we look at the Ocean Optics MZ5 MIR Spectrometer's ability to determine volume fraction of ethanol in a splash-blended fuel mixture using MIR spectroscopy.

	In the world of fuel octane ratings, the 0-mark is set by 

-octane, also known as 2,2,4-trimethylpentane (Compound Interest, 2016). Focusing on the latter, mixtures were made using 

-octane (99.8%) and 200-proof ethanol from Millipore Sigma. The following volume fractions were prepared:

	Sample fluids were placed onto the crystal and measured. The MZ5's Mirror software saved the processed absorbance spectra.

	The MZ5-MIR-ATR spectrometer offers excellent spectral response from 910-1810 cm

 and is a robust measurement system for petroleum products and general process organics. Its simplified fixed-crystal design eliminates fiber connections and the movement/vibrational issues that come with their use.

	Figure 1 shows the resulting spectra for the ethanol mixtures described in Table I, along with some explanations for the activities and how they relate to the organic structures.


	Figure 1: Absorbance of i-octane/EtOH mixtures.

	The ethanol activity is clearly the dominant influencer to these spectra, which is highly useful in determining its concentration both in the lab and on the process line. While there are two regions of large alcohol activity, the C-O stretch band is both the largest and the most independent of the 

-octane profile. Plotting the volume fraction versus this absorbance trend provides a strong correlation (Figure 2).


	Figure 2: Absorbance trend of C-O stretch band.

	The MZ5 is more than a spectrometer-it is a window into the molecular structures and concentrations of the chemicals in your process stream. In addition, Ocean Optics can provide users with algorithm development and machine learning tools that derive additional insight from the spectral data the MZ5 collects. Tools can be developed and refined to handle complex fuel mixtures and account for interference issues to provide readings that are robust and trusted.


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Volume Fraction Determination of Ethanol in Splash-Blended Fuel Mixture

	Modular spectrometers and accessories can be configured into small-footprint systems for measuring the color and absolute or relative irradiance of light sources and displays. Ocean Optics systems are compact, flexible, and simple to deploy in various settings.

	At a recent trade show, we showcased an experiment demonstrating the effectiveness of our Flame model spectrometer to monitor the color and spectral irradiance of digital displays.

	For the demo, we collected a handful of commercially available digital photo frames, taking care to select a combination of backlit LCD and LED displays, each with different dimensions and screen resolution performance (Figure 1). A radiometrically calibrated spectrometer (model Flame-S-RAD) with cosine corrector attached measured the output of the displays. OceanView spectroscopy software calculated color values, color difference, and power and photometry values.


	Figure 1: In this demonstration, a radiometrically calibrated spectrometer with cosine corrector attached (foreground) measures the spectral output and color consistency of emissive displays.

	As with a relative or absolute irradiance measurement, the spectrometer must be calibrated first. In the demo, our emissive color measurement began with an absolute irradiance measurement. Establishing an accurate scale for the spectrometer's response at each wavelength is essential to calculating color and power.

	Color consistency within samples requires color measurements that are repeatable from measurement to measurement. A well-defined method of comparing reflective or emissive color, either within a batch or to an acceptable standard, is also required. Ocean Optics color measurement systems offer both, providing the flexibility to configure the measurement system for various sample types and needs, as well as the software to perform quantifiable color comparisons.

	Delta E is used to quantify the difference between two colors. A delta E (dE) less than or equal to 1.0 indicates that the human eye will perceive two colors as the same. As the dE increases above 1.0, the perceived difference in color increases. The calculation of delta E takes a subjective comparison of color and provides a quantitative value indicating how different the colors appear to the human eye. In some cases, depending on the application, less rigorous dE limits are set where the perception of slight differences in color is acceptable.

	For this demo, we calculated the L*a*b* color difference of different locations within an emissive display as compared to a reference location within the same display (Figure 2). Also, that reference display could have been compared to the other displays in the demo setup. We could easily update the color reference reflection spectrum at any time during the measurements to calculate dE relative to a different color reference.


	Figure 2: With spectral monitoring of emissive displays, the calculation of color parameters and blue light intensity is possible using Ocean Optics spectrometers and software.

	Irradiance is the amount of energy at each wavelength emitted from a radiant sample. From that data, more specific photopic values can be calculated, including lumens, lux, and candela.

	Measurements in absolute irradiance mode require calibration using a source with known power output. For the demo, we used a spectrometer that was radiometrically calibrated at the Ocean Optics calibration lab. The spectrometer came with a calibration file that allowed us to work in absolute irradiance mode.

	The calibration process generates a file with energy response data for each pixel in the CCD, given in µJ/count. Factoring in the surface area of the sampling optic and the integration time allows irradiance measurements in µW/cm

	Why use a cosine corrector as a sampling optic for a diffuse emissive source like a digital photo frame? The cosine corrector has a 180° field of view and samples any light incident on the diameter of its white diffusing surface, and specifically in that plane. Cosine correctors work well for measuring the power incident on a surface like a screen, in which case the corrector should be placed flush with that surface.

	For the demo, we used the Absolute Irradiance mode in OceanView and selected the Photometry, Photons, Power and Energy wizard to calculate power and a range of other values. For calculating photometry values (lumens, lux, candela), the distance from the display surface must be taken into account.

	As part of our emissive displays demo, we monitored blue light in the 400–500 nm range. Blue light has shorter wavelengths and higher energy output than other visible light, so it reaches deeper into the eye. The cumulative effect of this exposure can cause damage to the eyes over time. Blue light exposure has increased with the move from incandescent lighting to compact fluorescent and LED lighting and with our constant exposure to digital screens.

), a Cincinnati, Ohio-based company that provides systems for protection from harmful blue light, we adjusted our spectrometer integration time to cover the blue light range and then reported the power values in uW for three criteria (Figure 2):

		Fatigue range (400–420 nm): eyes can become irritated, strained and tired

		Macular damage range (400–440 nm): may cause permanent damage to the retina

		Sleep range (460–484 nm): nighttime exposure can hinder melatonin production, disrupt circadian rhythms, and lead to trouble sleeping

	Accurate measurement of spectral irradiance and emissive color of digital displays is an important application of spectroscopy, with several use cases:

		Maintaining color consistency in LEDs, LCDs, and other displays

		Calculating color differences within and among displays

		Determining the output of emissive devices at wavelengths associated with blue-light hazards

		Calculating photometry values (lumens, lux, candela)

		Determining the power output of emissive sources

Monitoring Spectral Irradiance and Color in Digital Displays

	Surface enhanced Raman spectroscopy (SERS) is an extension of Raman spectroscopy in which gold or silver nanoparticles amplify the Raman signals. The technique works via an electromagnetic effect where molecules come into proximity with gold or silver particles. When incident laser light strikes the nanoparticulate surface, localized surface plasmons can be excited, greatly enhancing Raman signals. The enhancement can be significant, making SERS well-suited to trace level detection of illicit drugs such as cocaine, heroin, methamphetamine, and tetrahydrocannabinol (THC).

	To test how well Ocean Optics SERS substrates can detect trace drugs, measurements were performed using gold and silver nanoparticles with an Ocean Optics modular Raman setup. As we discovered, detection of several illicit drugs using gold nanoparticles is a rapid, reliable technique that requires only a few milliwatts of laser power.

	Heroin hydrochloride, cocaine hydrochloride, Δ

-tetrahydro-cannabinol, and (±)-methamphetamine were prepared in 100 ppm solutions in methanol.

	For the Ocean Optics SERS substrates, which comprise analyte-sensitive nanoparticle chemistries applied to a treated glass surface, we used 15 µL of 100 ppm solutions for the gold and silver nanoparticle substrates. We tested at 100 ppm to determine feasibility, although results suggest lower concentrations are possible.

	For measurements with the gold and silver SERS substrates, we used a modular Raman system comprising the QE Pro high-sensitivity spectrometer, a 785 nm laser for Raman excitation, and sampling optics. The 785 nm excitation produces excellent Raman spectra for most chemicals, with limited interference from fluorescence. These systems also offer very good spectral resolution, making them a preferred wavelength choice for Raman spectroscopy of chemicals and organic materials. Three measurements for each sample were taken from multiple spots on the same substrate, which then were averaged.

	As demonstrated in the spectra, SERS methods utilizing Ocean Optics substrates can detect ppm levels of illicit drugs, which Raman techniques alone would not be able to accomplish.

	Also, the gold nanoparticles appear to work best for detecting these drugs. Certain peaks have higher Raman cross-sections, and each peak is enhanced by the gold nanoparticles differently depending on how the molecule is oriented with respect to the gold surface.

SERS Methods Detect Trace Levels of Cocaine, Heroin, Methamphetamine, and THC

In this application note, we evaluate the effectiveness of surface enhanced Raman spectroscopy (SERS) to measure trace levels of imidacloprid, one of a class of insecticides linked to honeybee loss.

	In recent years, high rates of honeybee loss have prompted investigation by government regulators and other researchers. Early in 2016, the U.S. Environmental Protection Agency cited the insecticide imidacloprid as a threat to commercial honeybee colonies (1). Imidacloprid is widely used for pest control in agriculture, turf management and home protection applications.

	We tested the effectiveness of Ocean Optics gold and gold-silver nanosponge substrates, the former using 785 nm as the Raman laser excitation wavelength and the latter using 638 nm as the excitation wavelength. For the 785 nm Raman excitation setup we used a QE Pro-Raman spectrometer and for 638 nm excitation we used the IDRaman reader. Both configurations also included a Raman laser, a Raman probe, and a sample holder.

	For the measurements using gold substrates we prepared 1000 ppm, 100 ppm, 10 ppm, and 1 ppm solutions of imidacloprid in acetone, added 10 µL of each solution per substrate, and let the substrate dry completely. For solutions preparation, faster-drying acetone is a better choice than water.

	For the gold-silver nanosponge substrate measurements we prepared a 100 ppm solution of imidacloprid in acetone, added 10 µL of the solution per substrate, and let the substrate dry completely.

	We made a series of measurements using the gold (AU) substrates, in a setup with 785 nm Raman laser excitation at 15 mW of power and the spectrometer integration time set for 3 s (Figure 1). The gold substrates work best for imidacloprid concentrations >4 pg, primarily because the gold substrates have a stronger background signal, making lower concentration measurements challenging.

	For very low level imidacloprid concentrations, our new gold-silver (SP) nanosponge substrates are most effective. These substrates are based on a plasma-phase deposition of the gold-silver alloy onto a unique glass surface, and are distinguished by high sensitivity with low background noise. The low background noise makes it easier to discern Raman peaks at very low concentration levels. To test this, we used the gold-silver substrates in a setup with 638 nm Raman excitation at 21.2 mW of power and the spectrometer integration time set for 1 s (Figure 2).

	The lowest imidacloprid concentration we measured was 4 pg, which converts to 0.4 ppb. This is well within the 25 ppb concentration level that the U.S. EPA reports is harmful to honeybee populations.

	In our imidacloprid measurements, we observed some differences in Raman peaks between substrates, most likely the consequence of different binding mechanisms of the analyte with the substrate material (nanoparticles for the gold and thin film for the gold-silver alloy), but also because the chemistries enhance certain transitions differently (2). In addition, some molecules will exhibit shifts in their Raman peaks depending on how they are oriented on the SERS-active surface.

	As our testing has demonstrated, SERS substrates are a viable option for trace level detection. And, unlike many existing SERS products on the market, Ocean Optics SERS substrates are easy to use, affordable and can be mass produced with high repeatability for routine deployment in the laboratory or field.

		“Pesticide is threat to bees, EPA says,” Los Angeles Times, January 7, 2016.

Pesticide Detection Using SERS Techniques

	We tested the effectiveness of Ocean Optics gold and gold-silver nanosponge substrates, the former using 785 nm as the Raman laser excitation wavelength and the latter using 638 nm as the excitation wavelength. For the 785 nm Raman excitation setup we used a QE Pro-Raman spectrometer and for 638 nm excitation we used the IDRaman reader. Both configurations also included the Raman laser, a Raman probe and a sample holder.

	For the measurements using gold substrates we prepared 1000 ppm, 100 ppm, 10 ppm and 1 ppm solutions of imidacloprid in acetone, added 10 µL of each solution per substrate, and let the substrate dry completely. For solutions preparation, faster-drying acetone is a better choice than water.

	In our imidacloprid measurements, we observed some differences in Raman peaks between substrates, most likely the consequence of different binding mechanisms of the analyte with the substrate material (nanoparticles for the gold and thin film for the gold-silver alloy), but also because the chemistries enhance certain transitions differently. In addition, some molecules will exhibit shifts in their Raman peaks depending on how they are oriented on the SERS-active surface.

	(1) "Pesticide is threat to bees, EPA says," 


	830 Douglas Ave., Dunedin, FL 34698
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	We made a series of measurements using the gold (AU) substrates, in a setup with 785 nm Raman laser excitation at 15 mW of power and the spectrometer integration time set for 3 s (Figure 1). The gold substrates work best for imidacloprid concentrations >4 pg, primarily because the gold substrates have a stronger background signal, making lower concentration measurements challenging. 

	For very low level imidacloprid concentrations, our new gold-silver (SP) nanosponge substrates are most effective. These substrates are based on a plasma-phase deposition of the gold-silver alloy onto a unique glass surface, and are distinguished by high sensitivity with low background noise. The low background noise makes it easier to discern Raman peaks at very low concentration levels. To test this, we used the gold-silver substrates in a setup with 638 nm Raman excitation at 21.2 mW of power and the spectrometer integration time set for 1 s (Figure 2). 

	Figure 2: Gold-silver nanosponge substrates have less background signal, making them a good choice for measuring very low concentrations of insecticides such as imidacloprid.


	830 Douglas Ave., Dunedin, FL 34698
	tel. (727) 733-2447, fax (727)733-3962
	Website: 

Using modular spectroscopy, we calculate the color difference -- Delta E in the L*a*b* color space -- of Pantone® color guide samples compared with a color reference.

Determining Color Differences

Pesticide Detection using SERS Techniques

	In free space optics, light energy is collected from open beams and surfaces and sent on to the spectrometer. Free space optics can be used in various spectroscopy applications and are best deployed when the geometry between the light source and the spectrometer is defined and when these components are held in a rigid mechanical structure. Understanding how free space optics function within the spectrometer setup will help users to optimize experiments and obtain best results.

	Ocean Optics spectrometers are designed to project a spectrally convolved image of the input slit plane onto the detector (Figure 1). For example, if a light source comprising three monochromatic lines is projected onto the slit (aperture), then three distinct images of the slit would be seen at the detector plane. The images would be separated from each other by an amount determined by the wavelength dispersion of the system.


	Figure 1: Light enters the spectrometer at its entrance aperture.

	In free space coupling, an image of the subject is projected onto the slit. The details of the image projected onto the slit do matter. For example, if the image of a circular object is projected and greatly de-magnified onto the slit, the image of the object may be lesser in size than the slit and produce an effect similar to having a fiber smaller than the slit. In this case, the experimenter has to be careful with horizontal alignment of the image projected onto the slit. Horizontal shift will appear as a peak wavelength shift; however, the shift can never exceed the slit's original FWHM (full width at half maximum, an expression of spectrometer resolution).

	Moving the image vertically from the center of the slit will cause the apparent amplitude to change. Light entering the vertical center of the slit is most efficiently coupled through the system. Light entering at the top or bottom of the slit will not be routed to the detector as efficiently.

	Also, changing the angle of input causes the apparent intensity to change due to vignetting in the spectrometer. Light entering at 0° to the normal has the highest efficiency. To minimize these effects, ensure that the horizontal and vertical offsets, as well as horizontal and vertical angles, are fixed throughout the experiment.

	All of these alignment issues are greatly reduced if the projected image overfills the slit and overfills the numerical aperture of the spectrometer. This spatial and angular overfilling allows small angle changes and small offset changes to be irrelevant. If the image projected onto the slit plane is not properly focused then the field of view is not a well-defined region and will instead have fuzzy edges.

	The SMA bulkhead has an aperture that has been sized to restrict the angle of light entering the spectrometer (Figure 2). This has been designed to optimally fill the optical elements without overfilling, which would increase stray light. The full angle defined by a ray from the slit to the aperture is roughly 13.5°. The full angle defined by a ray from the opening of the SMA to the slit is greater than the 13.5°. This means that in a free space optical setup that is properly focused on the slit, the SMA connector is not restricting any light.


	Figure 2: An aperture in the spectrometer's SMA bulkhead restricts the angle of light entering the bench.


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Ocean Optics

Articles

Quality Control Testing for Catheters

Volume Fraction Determination of Ethanol in Splash-Blended Fuel Mixture

Monitoring Spectral Irradiance and Color in Digital Displays

SERS Methods Detect Trace Levels of Cocaine, Heroin, Methamphetamine, and THC

Pesticide Detection Using SERS Techniques

Pesticide Detection Using SERS Techniques

Pesticide Detection Using SERS Techniques

Determining Color Differences

Pesticide Detection using SERS Techniques

Free Space Coupling and Spectrometer Performance