SPECTROSCOPY
Rob Morris explores Raman spectroscopy for life sciences RAMAN THE POWER OF F
rom health issues associated with ageing populations to the growing demand for faster, more accurate diagnostic tools, today’s
life sciences professionals seek analytical instrumentation and application insight that’s simpler, smarter and more robust with each successive generation. Here, we’ll focus on Raman spectroscopy. Recently, Ocean Insight experts Yvette
Mattley, lab services manager, and Amy Bauer, principal applications scientist, shared their insights on the power of Raman analysis.
When asked about Raman and recent
developments, Bauer comments: “Any pure material has a unique Raman spectrum, and can be used for identification in cases where there’s not fluorescence in the way and there is adequate signal level.” Mattley says: “Although Raman is still out of reach for some prospective users, there are newer options that are less expensive and nearly as high-performing as scientific-grade Raman systems. For example, the Ocean HDX 785nm Raman spectrometer is accessible to a wide range of users, including university labs, budget-limited start-ups and product integrators. Te user can add a laser, Raman probe and sample holder to measure the Raman response of life sciences samples including biomolecules, cannabinoids and human tissue.”
ON CHOOSING RAMAN EXCITATION WAVELENGTHS Bauer says that, “It can be difficult to tell which laser excitation wavelength is going to work best. Raman signals scale strongly with the wavelength of the excitation light and get stronger with shorter excitation wavelengths.” She explains: “As the Raman signal is scaling positively with decreased wavelength, the principal problem that we encounter when we perform Raman spectroscopy is also scaling that way. Of course, I am discussing our evil nemesis, fluorescence. As the wavelength of the
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FIG. 1. With SERS analysis, spectral differences among cannabinoids are observed as Raman shifts vary by functional group. Shown at 10ppm dilution are cannabidiolic acid (CBDA), cannabidiol (CBD), cannabigerolic acid (CBGA), cannabigerol (CBG), tetrahydrocannabinolic acid (THCA) and tetrahydrocannabinol (THC)
exciting light decreases, the Raman signal increases, but so does fluorescence. And fluorescence can overtake signals with the shorter wavelength lasers. People measuring biological samples, for example, are using 785 nm and 1064 nm lasers because they are worried about seeing fluorescence.” With regard to challenging Raman applications, Mattley says: “Low concentration samples are challenging, especially if you have a complex analyte matrix, like biological fluids including blood or saliva. However, with techniques such as surface-enhanced Raman spectroscopy (SERS), which uses nanoparticles to enhance sensitivity, even complex matrices can be analysed.” Bauer adds: “In the case of complicated mixtures, using computer software, chemometrics and machine learning can help, or in the case of thin films, careful sample preparation and presentation improves with a microscope.”
Mattley observes that, “We have been successful in quantifying results in analysing human blood. We used the intensity of one of the main Raman peaks for the analyte of interest. We then corresponded it to the amount of the material present, so that we were able to get a good concentration curve from those measurements. “I’ve been making Raman measurements
for a few years, and what really comes through is the specificity and sensitivity of Raman, especially when you’re using SERS substrates. And that you need to spend the necessary time to optimise the setup and make sure you’re getting the best data. But the effort is worth it,” she concludes.
Rob Morris is with Ocean Insight
www.oceaninsight.com
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