Comparison of aggregating agents for the surface-enhanced Raman analysis of benzodiazepines

Abstract

Benzodiazepines are among the most prescribed compounds and are commonly present in many toxicological screens. They are also of concern forensically in cases of drug facilitated sexual assault. Currently these compounds are predominantly analyzed using immunoassay techniques; however more specific screening methods are needed. This paper demonstrates the applicability of surface enhanced Raman spectroscopy as a method for the analysis and detection of benzodiazepines. The procedure involves mixing urine extracts with gold nanoparticles and appropriate aggregating agents for trace detection of these compounds and their metabolites. In this paper we will discuss the optimization of various parameters of this technique as well as its application to screening urine samples. Eleven different benzodiazepines and metabolites were examined, including 1,2-triazolo-benzodiazepines and 1,4-benzodiazpines. Experiments were performed using four different chloride salts, MgCl₂, CaCl₂, KCl, and NaCl, as aggregating agents for the colloidal gold nanoparticles. Overall it was found that each aggregating agent produced different levels of signal enhancement for each drug. MgCl₂ provided the lowest limit of detection at 2.5 ng mL⁻¹, and linearity over a wide range of concentrations for a variety of drugs chosen. It was also determined that the optimum MgCl₂ concentration was 1.67 M. This method has shown the applicability of SERS for the detection of trace quantities of benzodiazepines in aqueous solutions as well as the optimization of the technique over a wide range of compounds. This technique can be utilized in the detection of trace benzodiazepines in toxicological samples following extraction of the analyte.