Flexible 3D-Printed Polydimethylsiloxane Microdevice with a Ternary Heterojunction-Engineered Photoanode for Sensitive Photoelectrochemical Detection of Tumor Necrosis Factor-α in Sweat

The detection of low-abundance biomarkers in sweat with high sensitivity is essential for wearable health monitoring applications. However, the performance of conventional photoelectrochemical (PEC) sensors is constrained by their rigid substrates, inefficient charge separation, and limited miniaturization capability. This study develops a flexible PEC sensor for the detection of tumor necrosis factor-alpha (TNF-α) in sweat by integrating functional nanomaterials with a 3D-printed microdevice. A hole transport layer of graphene oxide (GO) is introduced onto the surface of bismuth sulfide (Bi₂S₃) nanorods via an ultrasound-assisted method, followed by the loading of a Fe–Co bimetal-organic framework (MOF) to form a Bi₂S₃@GO/MOF ternary composite. Crucially, beyond conventional performance metrics, we directly visualize and quantify the enhanced interfacial charge transfer of Bi₂S₃@GO/MOF at the microscale through scanning photoelectrochemical microscopy (SPECM) and intensity-modulated photocurrent spectroscopy (IMPS) techniques. Furthermore, the MOF structure provides anchoring sites for immobilizing biotinylated aptamers, enabling specific capture of TNF-α molecules. Finally, integration with a custom 3D-printed polydimethylsiloxane (PDMS) microdevice results in a miniaturized analysis system. Our work provides a blueprint for next-generation wearable diagnostics, merging fundamental PEC insight with scalable 3D-printed device engineering.