Unlocking the Unknown with Applied Spectral Knowledge.

KEYWORDS• Illicit drugs

• SERS

• Nanoparticles

TECHNIQUES• Raman

APPLICATIONS• Security screening

• Substance

identification

ApplicationNote

Identifying Illicit Drugs using Surface Enhanced Raman SpectroscopySERS Methods Detect Trace Levels of Co-caine, Heroin, Methamphetamine and THCSurface Enhanced Raman Spectroscopy (SERS) is an exten-sion of Raman spectroscopy in which gold or silver nanopar-ticles 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 ex-cited, 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).

IntroductionTo test how well Ocean Insight SERS technology can de-tect trace drugs, measurements were performed using gold nanoparticles with an Ocean Insight 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.

Unlocking the Unknown with Applied Spectral Knowledge.

Sample PreparationHeroin hydrochloride, cocaine hydrochloride, Δ9-tetrahydrocannabinol and (±)-methamphet-amine were prepared in 100 ppm, 10 ppm and 1 ppm solutions in methanol.

For the Ocean Insight SERS technology, which comprises analyte-sensitive nanoparticle chem-istries, we used 50 μL of 100 ppm, 10 ppm and 1 ppm solutions of several illicit drugs. We tested these concentrations to determine feasibility, al-though results suggest lower concentrations are possible.

Experimental SetupFor measurements with the gold nanoparticles, we used a modular Raman system comprising the QE Pro high-sensitivity spectrometer, a 785 nm laser for Raman excitation and sampling op-tics. 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 materi-als.

As demonstrated in the spectra, SERS methods utilizing Ocean Insight nanoparticles can detect ppm levels of illicit drugs, which Raman tech-niques alone would not be able to accomplish.

Also, 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. Here are the experiment results:

Cocaine

Heroin

Figure 1. The enhanced Raman spectrum of cocaine.

Figure 2. The enhanced Raman signal of heroin reveals distinct spectral features.

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Gold Nanoparticles + CocaineRaman excitation: 785 nm, 3 s, 350 mW

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Gold Nanoparticles + HeroinRaman excitation: 785 nm, 3 s, 350 mW

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Unlocking the Unknown with Applied Spectral Knowledge.

Methamphetamine

THC

ConclusionsWhen compared with other SERS substrates on the market, the Ocean Insight nanoparticles show better sensitivity for a wide range of low concentrations of commonly used molecules for benchmarking SERS performance. Additionally, Ocean Insight nanoparticles are far more robust and simpler to use, with sample preparation and measurement taking seconds as opposed to minutes or hours.

Figure 4. Strong Raman response is observed in THC despite the potentialfor interference from fluorescence.

Figure 3. The enhanced Raman signal of methamphetamine shows a strong peak near 1000 cm-1.

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