Crystal Facet Engineering Modulated Electron Transfer Mechanisms: A Self-Powered Photoelectrochemical Sensing Platform for Noninvasive Detection of Uric Acid

Crystal facet engineering is a pivotal strategy to design high-performance photoelectrodes and suppress electron and hole complexation, thus enhancing photoelectrochemical (PEC) activity through carrier enrichment at specific crystal facets. However, there is still a lack of systematic resolution on the intrinsic principles of crystal facet tuning energy band structure and the specific adsorption of signaling molecules. In this work, a multidimensional synergistic optimization strategy was proposed to achieve precise prediction and targeted crystal facet design of photoelectrodes by establishing a quantitative structure–activity relationship (QSAR) model of “crystal configuration-molecular recognition-carrier transport”. A three-dimensional hierarchical TiO₂ nanoflower (3D HTNF) photoelectrode dominated by the {110} facet exhibited a significant positive photocurrent toward uric acid (UA). Integrated with a microelectromechanical system (MEMS), a miniaturized self-powered PEC biosensor provided an innovative solution for high-throughput, noninvasive UA monitoring in saliva and displayed a linear range of 0.01–50 μM with a detection limit of 8.76 nM. In addition, the advantages of photoelectrodes in light harvesting, charge separation and migration, molecular adsorption, and surface reactions were verified by density functional theory (DFT) calculations to reveal the path selectivity and carrier transport mechanisms of the photo-oxidation reactions on specific crystal surfaces. This study elucidates the interplay mechanism of the crystal surface tuning energy band structure and the interfacial kinetics of response. The program can be extended to precisely detect biomarkers in complex biological matrices, promoting the leapfrog development of noninvasive health monitoring technology.