Construction of a Label-Free Ratiometric Biosensor Based on Target Recycling Amplification and Hg-ZnSe QDs for Assay of BChE and OPs

Herein, we constructed a label-free ratiometric fluorescencebiosensingstrategy for the determination of butyrylcholinesterase (BChE) activityand organophosphorus (OPs) concentration. BChE promoted the hydrolysisof iodized s-butyrylthiocholine (BTCh) into a reducingsubstance thiocholine, which can decompose CoOOH nanosheets (CoOOHNSs) to Co2+. Subsequently, the single-stranded DNA (ssDNA)on the surface of CoOOH NSs was released. Then, ssDNA hybridized withhairpin DNA (h-DNA) and triggered the target recycling amplificationprocess, producing large amounts of G-quadruplex. After adding thioflavinT (ThT), the target BChE was converted into activatable G-quadruplex/ThTwith an amplified yellow fluorescence signal. The addition of OPscould significantly inhibit the hydrolysis of BTCh by BChE and thusunable to produce the yellow fluorescence G-quadruplex/ThT complex.Throughout the entire process, the fluorescence intensity of Hg-ZnSeQDs as a reference signal remained unchanged at 630 nm. Furthermore,this work provided an effective approach for detecting the BChE activityin serum samples and OPs in fruits and vegetables.

Automated summary

In this study, a label-free ratiometric fluorescence biosensing strategy was developed for the determination of BChE activity and OPs concentration. The strategy involved the hydrolysis of BTCh by BChE, releasing ssDNA which triggered target recycling amplification and produced G-quadruplex. The addition of OPs inhibited the hydrolysis, resulting in the absence of fluorescence signal.