The goal of this dissertation was to develop a novel analytical scheme that can provide a more efficient, rapid, and sensitive method that will facilitate adoption in the laboratory and onsite in the field.
Forensic science relies on the use of multiple techniques in the assessment of evidence to increase the accuracy and reliability of the results; however, with the rapidly changing drug landscape due to the introduction of novel psychoactive substances, many traditional screening methods are no longer sensitive or selective enough for use. Additionally, many screening methods such as chemical color tests are prone to false positive and negative results and are subjective. To this end, electrochemistry and Raman spectroscopy were assessed independently for their use in orthogonal testing scenarios, and in tandem via spectro-electrochemical methods to improve both the sensitivity and selectivity of seized drug screening. A panel of 15 drug analytes and 15 diluent compounds comprising some of the most encountered analytes was considered. This panel was characterized via electrochemistry for use as the first tier in investigating a seized substance. Then normal Raman spectroscopy was explored as the second tier in an orthogonal analytical scheme. Both 785 nm and 1064 nm Raman systems were tested with the panel of analytes. The pure compounds were characterized prior to analysis of simulated mixture samples with binary mixtures prepared at 1:4, 1:7, 1:10, and 1:20 ratios. Finally, electrochemistry and Raman spectroscopy were combined into a third-tier technique: time-resolved spectro-electrochemistry. Both targeted and nontargeted electrochemical-surface enhanced Raman spectroscopy method (EC-SERS) was developed. The targeted EC-SERS method provided an analysis approach for fentanyl and fentanyl analogs, while also allowing for in situ generation of a SERS substrate with a silver electrode and simultaneous analysis of the sample. This method demonstrated excellent selectivity and sensitivity with a limit of detection for the most sensitive compound (4-ANPP) of 10 ng/mL. Additionally, differentiation of fentanyl analogs was demonstrated to be achievable. detection. To demonstrate the fit-for-purpose of this method, authentic seized samples were analyzed from a forensic laboratory including both true fentanyl positive and true fentanyl negative samples. Using GC-MS and LC-MS/MS as ground-truth, an overall accuracy of ~88% was achieved for the detection of fentanyl within the seized samples. More importantly, the power of this EC-SERS screening approach was demonstrated by the accurate identification of fentanyl even in mixtures containing 5 or more compounds. (Published abstract provided)
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