Chemical nose for discrimination of opioids based on unmodified gold nanoparticles

Abstract

Considering the need for detection of opioids, a colorimetric sensor array based on unmodified gold nanoparticles (AuNPs) was developed for the first time in order to sensitively detect and identify multiple structurally similar opioids including morphine, codeine, oxycodone, noroxycodone, thebaine, tramadol and methadone in aqueous media. Size dependency of assembly process encouraged us to employ AuNPs with four distinct particle sizes as sensing elements and visual differentiation tools to construct a colorimetric nanoarray. The target opioids seem to act as “molecular bridges”, shortening the interparticle distance and inducing the aggregation of AuNPs. This aggregation produces changes in both the color and UV–vis spectra of AuNPs generating a visual molecular fingerprint of each analyte. The cumulative array responses were differentiated by principal component analysis (PCA) and hierarchical cluster analysis (HCA) with 100% classification accuracy demonstrating the versatility of this simple nanoarray platform. Furthermore, color difference maps were created to provide a visual tool for classifications and semi-quantitative analysis without exploiting any statistical techniques. Finally, we demonstrated the ability of the constructed array to identify the various opioids in urine sample. The obtained results suggest that the proposed colorimetric nanoarray has promising perspective in the clinical toxicology and forensic cases for the on-spot detection of illegal drugs.