Vertically Oriented Assembly of a Few-Layer Ti 3 C 2 T x Grid by Electric Field Inducing and Freeze Drying for Wearable Levodopa Sensing in Sweat

Compared with the parallel assembly, the vertical assembly of MXene nanosheets on the substrate exhibits open three-dimensional porous structure, which is beneficial to the construction of high-performance electrodes. Herein, the vertically oriented assembly of Ti3C2Tx nanosheets is proposed by a novel preparation process of electric field inducing and freeze drying, resulting in the Ti3C2Tx grid with thin-wall and open porous structure. First, the electric field induces the formation of Ti3C2Tx hydrogel layer on the substrate. Second, freeze drying causes the growth of ice crystals for squeezing few-layer Ti3C2Tx nanosheets to stand up. More importantly, such a Ti3C2Tx grid with large surface area and intrinsic conductivity can effectively load electrocatalysts, resulting in the Au-Ti3C2Tx grid as a high-performance working electrode for the electrochemical detection of levodopa. The main parameters include 1-30 μM and 30-160 μM two-stage linear ranges and 37 nM detection limit. The structural advantages of Ti3C2Tx grid-based electrode materials are their three-dimensional conductive network and interconnected porous structure, which contribute to the penetration of the electrolyte, the diffusion of the analyte, and the electrocatalytic reaction. Furthermore, the self-adapting shape of the Ti3C2Tx grid leads to the fan-shaped Au-Ti3C2Tx grid collaborated with a self-designed leaf-like microfluidic. Ultimately, a wearable levodopa sensor composed of Au-Ti3C2Tx grid, microfluidic, flexible electronic system, and mobile phone client is established for detecting levodopa in human sweat, which is expected to help Parkinson's patients control the drug dosage. Our work proposes the vertically assembled Ti3C2Tx nanosheet loaded noble metal electrocatalysts to develop high-performance electrodes for electrochemical sensing.