Manganese dioxide nanosheet-modulated ratiometric fluoroprobe based on carbon quantum dots from okra for selective and sensitive dichlorvos detection in foods

Herein, we developed a ratiometric fluoroprobe by integrating okra-derived carbon quantum dots (CQDs) with amplex red (AR) using manganese dioxide nanosheets (MnO 2 NSs) as a medium. Fluorescence intensities (FIs) of CQDs were sharply quenched by MnO 2 NSs via an inner-filter effect processes, whereas the FIs of AR were significantly enhanced due to oxidation of AR to AR-ox by the oxidase-mimetic activity of MnO 2 NSs. Acetyrylcholinesterase hydrolyzed acetylthiocholine to produce thiocholine, and the decomposition of MnO 2 NSs to Mn 2+ by thiocholine led to the FI recovery of CQDs, but decreased FIs of AR-ox. Based on the above phenomenon and the inhibitory effect of dichlorvos (DDVP) on acetyrylcholinesterase activity, a novel ratiometric fluoroprobe for DDVP quantification was pioneered. Under optimized conditions, this fluoroprobe gave a wide linear range (4–120 μg/L), low detection limit (1.2 μg/L), and satisfactory fortification recoveries (90.0–110.0%), thereby providing good prospects for routine DDVP monitoring in foods.