Hydrogel-confined Fe-MOF nanozyme sensor chip for matrix-tolerant colourimetric screening of malathion in Chinese medicinal matrices

Abstract

Matrix-induced colour drift remains a major barrier to translating nanozyme-based colourimetric assays from buffer systems to Chinese medicinal matrices. Here, we report a sodium alginate (SA)-confined iron-based metal–organic framework (Fe-MOF) nanozyme chip, denoted as the Fe-MOF/SA chip, for smartphone-assisted screening of malathion in pretreated herbal extracts. The hydrogel does not merely carry the Fe-MOF catalyst; rather, it confines the Fe-MOF within a more stable H2O2-TMB chromogenic microenvironment, thereby converting a drift-prone inhibition response in the dispersed nanozyme system into a more reproducible colour readout based on the b* coordinate of the Commission Internationale de l’Éclairage L*a*b* (CIE L*a*b*) colour space, where b* represents the blue–yellow component. Under optimised conditions, the chip provided a linear response from 10 to 500 ng mL−1 with an LOD of 4.4 ng mL−1. Relative to free Fe-MOF, the hydrogel-confined format markedly reduced matrix-dependent response deviations in chrysanthemum, honeysuckle and coptis extracts. Standard-addition recoveries of 93.5–108.3% with RSDs of 2.7–3.7% were obtained, and HPLC analysis of the same spiked extracts gave comparable concentrations. These results support the use of the Fe-MOF/SA chip as a portable front-end screening platform for malathion in chemically heterogeneous herbal matrices.