Development and evaluation of a nontargeted electrochemical surface-enhanced Raman spectroscopy (EC-SERS) screening method applied to forensic seized drug casework samples

Abstract

Screening tests in forensic laboratories are a critical step in ensuring an efficient and effective analytical scheme for presumptive identification. Electrochemical surface-enhanced Raman spectroscopy (EC-SERS) represents a novel workflow that can be applied both in the laboratory and on-site as a fast, inexpensive, and selective approach to seized drug screening. Using cyclic voltammetry and a 785 nm Raman spectrometer, a nontargeted screen was developed using silver screen-printed electrodes and tested on a panel of common drugs of abuse and adulterants. Following characterization of the analyte panel, in-house binary and tertiary mixtures were assessed and the effectiveness of the developed EC-SERS method was tested using common score-based algorithms including correlation, hit-quality-index, spectral angle mapper, and correlation of the 1st derivative. For in-house blind samples, this approach allowed for positive identification of at least one compound in 100 % of samples. Identification of all compounds was lower at 52 %. Seized drug samples from adjudicated casework were tested on-site at the Maryland State Police laboratory as a fit-for-purpose study. EC-SERS provided an accurate screening result of 86 % using the 1st derivative correlation. Applying knowledge of both the local drug landscape and the prevalence of specific adulterants, this value improved to a positive screening of 93 % for the authentic samples. EC-SERS represents a novel approach to drug screening that could impact forensic laboratories, customs and border patrol, public health, and scene investigations. Future work should focus on improved data processing and chemometric tools for data generated in EC-SERS methods.