Ozlu Turk, GizemSoylu, Mehmet Cagri2026-03-012026-03-0120262079-637410.3390/bios160100542-s2.0-105028698073https://doi.org/10.3390/bios16010054https://hdl.handle.net/20.500.14720/29800Flexible biosensors offer rapid and low-cost diagnostics but are often limited by the mechanical and electrochemical instability of polymer-based designs in biological media. Here, we introduce a metallic flexible microcrack transducer that exploits the intrinsic deformability of superelastic nickel-titanium (NiTi) for label-free impedimetric detection. Mechanical bending of NiTi wires spontaneously generates martensitic-phase microcracks whose metal-gap-metal geometry forms the active transduction sites, where functional interfacial layers and captured analytes modulate the local dielectric environment and govern the impedance response. Our approach imparts a novel dielectric character to the alloy, enabling its unexplored application in the megahertz (MHz) frequency domain (0.01-10 MHz) where native NiTi is merely conductive. Functionalization with Escherichia coli (E. coli)-specific antibodies renders these microdomains biologically active. This effectively transforms the mechanically induced microcracks into tunable impedance elements driven by analyte binding. The gamma-bent NiTi sensors achieved stable and quantitative detection of E. coli ATCC 25922 in sterile human urine, with a detection limit of 64 colony forming units (CFU) mL-1 within 45 min, without redox mediators, external labels, or amplification steps. This work pioneers the use of martensitic microcrack networks, mimicking self-healing behavior in a superelastic alloy as functional transduction elements, defining a new class of metallic flexible biosensors that integrate mechanical robustness, analytical reliability, and scalability for point-of-care biosensing.eninfo:eu-repo/semantics/openAccessFlexible Nickel-Titanium (NiTi) BiosensorLabel-Free Impedimetric SensingMartensitic MicrocracksPoint-of-Care BiosensingSelf-Healing InterfacesFlexible Nickel–Titanium (NiTi) BiosensorArticle