Surface-enhanced Raman spectroscopy (SERS) is a highly specific analytical tool in which incorporation of plasmonic nanoparticles increases the Raman signal due to electromagnetic (EM) field-enhancement-based mechanism. We previously demonstrated a toxicology drug assay in human plasma samples using a flexible plasmonic substrate in SERS. Herein, we report an advanced plasmonic substrate for detecting synthetic drugs, such as fentanyl, alprazolam, and their analogs in patient plasma samples. Due to metabolic processes, drugs are found at remarkably low concentrations in blood plasma within few hours of consumption. Therefore, a more ultrasensitive approach is necessary to improve drug testing in forensic toxicology and/or workplace drug testing. Exploring beyond SERS, tip enhanced Raman spectroscopy (TERS) further enhances the EM field at the tip-apex of a plasmonic metal-coated probe adjacent to the analyte upon laser irradiation. In our work, a TERS-analogous substrate of few micrometer diameter microneedles is fabricated using polydimethylsiloxane (PDMS) and coated with self-assembled plasmonic gold nanorods (AuNRs). The plasmonic AuNRs create “hot spots” due to the formation of a self-assembled standing structure of AuNRs at the microneedle tip. The hot-spot formation increases the Raman signal of the drug analytes. Furthermore, to maintain the working principle of a TERS inspired substrate, the target drug analytes are pre-concentrated on the microneedle tips through the utilization of a controlled droplet evaporation method driven by the hydrophobic salinization of PDMS microneedles. The surface modified, plasmonic microneedles are successfully used to detect alprazolam and fentanyl with the limit of detections (LODs) determined to be 28pM and 68fM, respectively. Our sharp tip microneedles serve as TERS-based substrates that offer advancements in real world applications, such as detecting drugs in highly diluted blood plasma samples from emergency departments.

Drug detection using a tip-enhanced Raman spectroscopy analogous plasmonic sharp tip substrate

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.