UV-induced, nonenzymatic, H₂O₂-free colorimetric detection of Dopamine using MXene-based quasi-quantum dots

This study presents a UV-activated, nonenzymatic, and hydrogen peroxide–independent colorimetric sensing strategy for the highly sensitive and selective detection of dopamine (DA), utilizing MXene-derived quasi-quantum dots (MQQDs) as photoactive nanozymes. The MQQDs demonstrate pronounced UV-activated oxidase-mimetic catalytic activity, facilitating the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) into its blue oxidized form (oxTMB) in the absence of H₂O₂. Upon the introduction of dopamine (DA), the absorbance intensity of oxTMB at 652 nm decreases progressively with increasing DA concentration. This attenuation is attributed to the redox interplay between DA and the photoexcited MQQDs, wherein DA acts as an electron donor, reducing oxTMB back to its colorless TMB form and thereby inhibiting the oxidation reaction. This electron-transfer-mediated inhibition mechanism enables quantitative colorimetric detection of DA with a detection limit of 65.4 nM. Spectroscopic analysis and kinetic fitting confirm the UV-triggered oxidase-mimetic behavior of MQQDs following Michaelis–Menten kinetics. The developed H₂O₂-free photoenzymatic platform offers a facile, stable, and environmentally benign route for DA quantification, with promising applicability in point-of-care diagnostics and neurochemical sensing. • Developed a nonenzymatic, H₂O₂-free colorimetric assay for dopamine. • UV-activated MXene quasi-quantum dots function as efficient nanozymes. • MQQDs show strong UV-triggered peroxidase-mimetic activity toward TMB. • Assay provides high sensitivity, low detection limit, and excellent selectivity.