Thomas Kubic

Nondestructive identification of natural and synthetic organic colorants in works of art by surface enhanced Raman scattering.

We present a new method based on surface-enhanced Raman scattering (SERS) for the nondestructive identification of organic colorants in objects whose value or function precludes sampling, such as drawings, prints, historic and archeological textiles, handwritten or printed documents, and forensic evidence. A bead of a polymer hydrogel loaded with a solution containing water, an organic solvent, and a chelating agent is used to extract minimal amounts of the colorants from the work of art for SERS analysis. Using a gel as a medium for the solvent mixture confines its action only to the areas of the work of art covered by the gel bead. The gel bead is then removed from the work of art, covered with a drop of Ag colloid, and examined with a Raman microscope. Transfer of the dye from the substrate to the gel does not require removing a sample from the work of art, therefore preserving the physical integrity of the object. Spectrophotometric color measurements confirm that color change is below the limit perceivable by a human observer. Finally, the size of the polymer bead can be reduced to a fraction of a millimeter in order to further minimize any impact on the work of art, without detriment to the effectiveness of the method. The technique has been successfully used for the analysis of a mordant dye on the 15th century Netherlandish tapestry, The Hunt for the Unicorn, and of a synthetic lake pigment on a Meiji period Japanese woodblock print.

Surface-enhanced Raman Spectroscopy for Trace Identification of Controlled Substances: Morphine, Codeine, and Hydrocodone

Abstract:u2002 We obtain the normal Raman and surface‐enhanced Raman spectrum of three controlled substances: morphine, codeine, and hydrocodone. The spectra are assigned with the aid of density functional theory. Because of rather intense fluorescence, normal Raman spectra suffer from poor signal‐to‐noise, even when differential subtraction techniques are employed. On the other hand, surface enhancement by Ag nanoparticles both enhances the Raman signal and suppresses the fluorescence, enabling far more sensitive detection and identification. We also present a set of discriminant bands, useful for distinguishing the three compounds, despite the similarities in their structures.

Application of Raman Spectroscopy, Surface-Enhanced Raman Scattering (SERS), and Density Functional Theory for the Identification of Phenethylamines

We evaluated the normal Raman (NR) and the surface-enhanced Raman scattering (SERS) of three sympathomimetic amines: phenethylamine, ephedrine, and 3,4-methylenedioxymethamphetamine (MDMA). In addition, quantum mechanical calculations–geometry optimization and calculations of the harmonic vibrational frequencies–were performed using the density functional theory (DFT) approach. Vibrational assignments were made by comparing the experimental and calculated spectra. The study found that both NR and SERS provided excellent spectra for the drugs tested. Certain conditions, such as response to various laser wavelengths and background fluorescence of the analyte, could be easily managed using SERS techniques. The DFT-calculated spectra could be correlated with the experimental spectra without the aid of a scaling factor. We also present a set of discriminant bands, useful for distinguishing the three compounds, despite their structural similarities.

An Alternative Method to Screen for Pepper Spray Residue

A method was developed to screen for pepper spray residue using instruments and methods other than those techniques commonly employed to analyze chemical residue (i.e.. gas chromatography mass spectrometry-GCMS or liquid chromatography mass spectrometry-LCMS). The method employed gas chromatography (GC), thin layer chromatography (TLC), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to screen for dried pepper spray stains. Pepper sprays from nine different manufacturers were investigated. Capsaicin and dihydrocapsaicin were identified and unique IR reflectance spectra are presented. An additional five compounds were presumptively found. Results showed that a particular stain could be characterized as a pepper-based stain.

EXPRESS: Competitive binding investigations and quantitation in surface enhanced Raman spectra of binary dye mixtures

This research presents a study in surface-enhanced Raman quantitation of dyes present in mixtures of alizarin and purpurin using standard calibration curves and Langmuir isotherm calibration models. Investigations of the nature of competitive adsorption onto silver nanoparticles by centrifugation indicates that both dyes in the mixture interact with the nanoparticles simultaneously, but only the stronger adsorbing one is seen to dominate the spectral characteristics. Calibration can be carried out by careful selection of peaks characteristic to each dye in the mixture. Comparisons of peak height and peak area calibrations reveal that peak heights, when selected by the maximum value and accounting for peak shifts, prove the better model for quantitation. It is also shown that the microwave nanoparticle synthesis method produces stable nanoparticles with a shelf-life of at least one year that give very little variation within and between uses.

Detection and Quantitation of Trace Fentanyl in Heroin by Surface-Enhanced Raman Spectroscopy

The identification of fentanyl, a main culprit in opioid overdose deaths, has become critical. Whereas Raman spectroscopy is an effective tool for detecting illicit drugs, the weak intensity of Raman scattering can make it difficult to distinguish trace materials. This shortcoming is addressed by surface-enhanced Raman spectroscopy (SERS), which produces strong signal enhancements when target compounds are near metal nanoparticles. This work examines the use of a paper-based substrate impregnated with silver nanoparticles for the detection of trace quantities of fentanyl alone and as an adulterant in heroin. In addition, intensity ratios of diagnostic peaks associated with each substance were fitted to a Langmuir isotherm calibration model and used for the quantitative analysis of fentanyl in heroin mixtures. Linearity was observed at <6% fentanyl, a significant finding that is consistent with concentrations found in drugs seized during law enforcement efforts. In addition, swabbing with these paper-based SERS substrates facilitated the recovery of fentanyl from surfaces, showing this to be applicable for crime scene investigations. However, assessment using the calibration model proved difficult for swabbed samples. Overall, this work demonstrates a potentially simple and sensitive technique for the forensic analysis and quantitation of fentanyl in trace amounts.