Detection and screening of basic amino acids using the luminescence switching of a WS2 nanosheet–Ag2O nanoparticle composite

Abstract

The Förster resonance energy transfer (FRET) pair-based detection has gained considerable attention due to its promising sensitivity and selectivity. Herein, we report a turn-on sensor for detecting basic amino acids utilizing the fluorescence emission properties of WS₂ nanosheets (WS₂ NSs). The sensor functions based on a FRET dyad. The addition of AgNO₃ into an alkaline solution of WS₂ NSs leads to the in situ formation of silver oxide nanoparticles (Ag₂O NPs). The negative surface charge and the presence of sulphur vacancies, together with the possibility for a multiplexed adsorption platform of WS₂ NSs, account for the formation Ag₂O NPs on their surface. In the WS₂ NS–Ag₂O NP system (termed as a 0D–2D composite), the fluorescence emission of the nanosheets became subdued due to the FRET. This 0D–2D composite is proven to be an excellent turn-on sensor for basic amino acids. Histidine, lysine and arginine can induce the aggregation of the Ag₂O NPs, which shuts the FRET pathway, along with the regeneration of the fluorescence of WS₂ NSs. The aggregation of Ag₂O NPs occurs in a sensor solution with pH below the isoelectric points of the amino acids to help to discriminate them. The dynamic range and limit of detection of the sensor have been evaluated. The protein detection capability of the sensor was verified using a lysine containing protein, ubiquitin, and by real sample analysis, using biological fluids.