Portable identification of fentanyl analogues in drugs using surface-enhanced Raman scattering

North America's opioid epidemic has created a need for drug checking technologies (DCT) that can detect potent opioids such as fentanyl and its analogues in drugs, and thus reduce the risk of accidental overdose. Here, a novel silver surface-enhanced Raman scattering (SERS) substrate is evaluated on its suitability for use as a DCT in point-of-care harm reduction applications. These substrates are assembled by electrochemically reducing silver (Ag) ions onto a silicon (Si) chip imprinted with gold (Au) microelectrodes, forming SERS-active Ag nanostructures. SERS analysis of lab-grade fentanyl analogues found that the substrates produced spectra of fentanyl, furanylfentanyl, and carfentanil that could be distinguished using principal component analysis (PCA). The limit of detection of fentanyl on the substrates was determined to be within a practical range, however estimations of fentanyl concentrations to an order of magnitude were achieved with 70% accuracy. The substrates also demonstrated the ability to detect trace fentanyl in high concentrations of heroin and caffeine, respectively. Notably, the substrates are compatible with handheld Raman spectrometers, allowing for powerful chemical detection on a compact, portable device. The performance and usability demonstrated by these SERS substrates validates their potential for use as DCTs that could be vital to the safety of people who use drugs.