Colorimetric sensor for nitrite in water samples based on the light-driven oxidase-mimicking activity of bio-derived flavin adenine dinucleotide

Bio-derived FAD acts as a small-molecule light-driven oxidase mimic. • FAD exhibits wavelength-selectivity by responding only to blue and UV light. • Oxygen-dependent blue-light-driven and oxygen-independent UV-driven modes. • H 2 O 2 -free, metal-free colorimetric sensor achieves visual detection of nitrite. • A sensor enables sensitive detection with precise spatiotemporal control. Natural enzymes are constrained by poor stability and structural fragility, while existing enzyme mimics predominantly exhibit an “always-on” mode lacking spatiotemporal controllability. Herein, it was discovered that bio-derived flavin adenine dinucleotide (FAD), the core cofactor of natural photoenzymes, exhibits intrinsic light-driven oxidase-mimicking activity under blue and ultraviolet (UV) light. Notably, FAD operates in an oxygen-dependent mode under blue light and an oxygen-independent mode under UV light, enabling its application in various complex scenarios. Leveraging the superior biocompatibility and application potential of the blue-light mode, a novel colorimetric sensor for nitrite detection was successfully constructed. FAD catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB under blue light, and nitrite triggers the diazotization of oxTMB to generate yellow diazo-TMB, enabling visual detection for nitrite through color change. The colorimetric sensor achieves a wide linear range of 40–440 μM, with a low limit of detection (LOD) of 1.93 μM. Moreover, the sensor exhibits excellent anti-interference capability and satisfactory recoveries (85.0%–103.5%) in real water samples. This work establishes FAD as a bio-derived light-driven oxidase mimic, providing a new strategy for designing efficient, wavelength-selective enzyme mimic and opening a new avenue for advanced light-driven sensors with precise spatiotemporal control. A facile strategy employs bio-derived flavin adenine dinucleotide (FAD), which exhibits intrinsic light-driven oxidase-mimicking activity, enabling the construction of a metal-free, spatiotemporally controllable colorimetric sensor for nitrite detection. Download: Download high-res image (105KB) Download: Download full-size image