Surface-enhanced Raman spectroscopy for detection of fentanyl and its analogs by using Ag-Au nanoparticles

The problem of opioid abuse has become a global problem. Thus, creating an urgent need for highly sensitive detection of opioid substances. In this work, we developed a method for the controllable preparation of Ag@Au nanocrystals (Ag@Au NCs) for highly sensitive SERS detection of fentanyl and its analogs. By regulating the concentration of ligands on the surface of silver seed, we successfully prepared Ag@Au NCs with three different morphologies, including core-satellite, yolk shell and hollow structure. Firstly, we explored the SERS-enhancing effect of Ag@Au NCs with different morphology using rhodamine 6G as the molecule to be tested. The results show that the core-satellite Ag@Au NCs has the best SERS effect, and the lowest detection concentration for R6G reached to 10^-10 M. Furthermore, we used the prepared core-satellite Ag@Au NCs to detect fentanyl and its five analogs, including carfentanyl, furanylfentanyl, thiofentanyl, 4-fluorobutyrfentanyl and N-4-piperidylacetanilide. Trace detection was achieved for the above six substances. For the environmental water samples spiked with fentanyl, the calculated recovery was 89.2% with an RSD value of 7.3%. Moreover, in order to realize the qualitative analysis of the characteristic peaks of different fentanyl analogs, we performed DFT calculations on the Raman spectra of the above-mentioned 6 substances. By analyzing the DFT calculation results, conventional Raman spectroscopy and SERS spectroscopy, we realized the distinction of six fentanyl analogs with similar structures.