Coencapsulating\nTMB Probes and Bimetallic MOF Nanozymes\nin a Hydrogel Patch for Fabricating Reusable Visual VC Sensors

As a typical chromogenic probe, 3,3′,5,5′-tetramethylbenzidine\n(TMB) has been widely applied in the field of visual detection due\nto its low toxicity and highly sensitive response. Due to the hydrophobic\nnature of TMB, encapsulating it into a hydrogel, which serves as an\nideal matrix for wearable sensors, presents significant challenges\nthat complicate the fabrication of visual wearable devices. Herein,\nthe TMB probe and bimetallic MOF nanozymes are coencapsulated in a\nhydrogel patch for the fabrication of reusable visual sensors. Hydrophobic\nTMB is oxidized to hydrophilic ox-TMB by a bimetallic MOF (CuFe-MOF),\nallowing its diffusion into a hydrophilic agarose hydrogel patch,\nwhere it is reduced back to TMB. This process allows the coimmobilization\nand coencapsulation of CuFe-MOF and TMB within the hydrogel patch.\nLeveraging the color change between TMB and ox-TMB, as a proof-of-concept\napplication, a reusable visual “On–Off–On”\nsensor is simply constructed and successfully applied to detect vitamin\nC in human sweat. Color changes can be quickly read by the naked eye\nor by smart devices without the need for external equipment. Meanwhile,\nbased on the reversible conversion relationship between TMB and ox-TMB,\na reusable sensor construction strategy is proposed. This approach\nnot only facilitates the use of a TMB probe in hydrogel applications\nbut also offers inspiration for the development of point-of-care testing\nequipment, demonstrating significant application potential.