Integrating peroxidase-mimicking activity with photoluminescence into one framework structure for high-performance ratiometric fluorescent pesticide sensing

We develop a robust ratiometric fluorescent nanosensor based on bifunctional Fe-based metal-organic frameworks (NH2-MIL-101(Fe)) for high-performance pesticide determination. The NH2-MIL-101(Fe) plays dual roles: the 2-aminoterephthalic acid ligand endows the framework with a photoluminescence at 428 nm, and the Fe node exhibits peroxidase-mimetic catalytic activity to oxidize the o-phenylenediamine substrate to diaminophenazine (DAP) with a fluorescence at 556 nm, which in turn suppresses the intrinsic signal (428 nm) of NH2-MIL-101(Fe) due to inner filter effect. When acetylcholinesterase is introduced for hydrolyzing acetylthiocholine chloride to thiocholine, the product with certain reducibility can inhibit the o-phenylenediamine oxidation, resulting in the DAP signal suppression (556 nm) and the NH2-MIL-101(Fe) one recovery (428 nm). Since pesticide residues effectively inhibit the activity of acetylcholinesterase, their presence can increase the formation of DAP and its fluorescence at 556 nm, thus the inherent signal of NH2-MIL-101(Fe) at 428 nm is suppressed again. By taking carbaryl as a pesticide model, the ratiometric nanosensor exhibits good sensitivity for carbaryl sensing in the scope of 2-100 ng/mL with a 1.45 ng/mL detection limit. No notable interferences from other species are observed for target detection. Moreover, our nanosensor is confirmed to be reliable for carbaryl analysis in real samples.