A carbon quantum dot–gold nanoparticle system as a probe for the inhibition and reactivation of acetylcholinesterase: detection of pesticides

Abstract

In this work, fluorescence (FL) quenching (turn-off) and recovery (turn-on) of carbon quantum dots (CQDs) in the presence of dispersed and aggregated gold nanoparticles (AuNPs) was used as a probe for monitoring the inhibition and reactivation of acetylcholinesterase (AChE). The FL of CQDs is quenched due to fluorescence resonance energy transfer (FRET) between the CQD donor and AuNP acceptor. The catalytic hydrolysis of acetylthiocholine (ATCh) by AChE produces thiocholine, which induces aggregation of the AuNPs. The turn-off FL signals of CQDs were measured in the presence of pesticides due to the inhibition of the catalytic activity of AChE. The activity of AChE was recovered using an oximate (1-dodecyl-4-(hydroxyimino)methyl)pyridinium bromide (4-C₁₂-PyOx⁻) reactivator, and the turn-on FL signal of the CQDs was measured. The % inhibition and % reactivation of AChE by pesticides and the reactivator have been obtained. Inhibitory protocols have been utilized for the detection of pesticides and limits of detection of 0.05 nM (paraoxon), 0.10 nM (malathion), 0.12 nM (methamidophos), and 0.13 nM (carbaryl) were obtained. This method has been successfully applied for the detection of pesticides in real water samples (tap water and river water) and apple juice samples. Furthermore, we investigated the CQD–AuNP sensing method with logic gates (INHIBIT and OR) that simply optimize the system.