Localized Temperature Monitoring in Mouse Brain during Light Delivery via a Non-Planar Tapered Fiber-Integrated µRTD Sensor.

Monitoring local brain temperature with high spatial precision is essential to understanding neurophysiological processes and managing the side effects of optical neuromodulation techniques. We present a novel multifunctional neural interface integrating a microscale resistance temperature detector (µRTD) onto the curved surface of a tapered optical fiber (TF), enabling co-localized light delivery and thermal sensing with minimal footprint. The µRTD, patterned via an unconventional two-photon polymerization (TPP)-based process on the fiber surface, exhibits thermal sensitivity <0.1°C and low self-heating under physiologically-safe bias conditions. We demonstrate the system's capacity to resolve subtle temperature changes induced by optogenetic stimulation/inhibition protocols (the latter requiring illumination periods of hundreds of milliseconds up to several seconds), revealing significant thermal accumulation only under long, high-intensity illumination. This integration resolves the spatial mismatch of multimodal probes and reduces implant cross-section compared to coaxial or side-by-side configurations. Furthermore, the TPP approach is modular, allowing integration with additional functionalities (i.e., electrophysiological recording or thermoplasmonics). By uniting photonic and thermal readout into a minimally invasive probe, our technology offers a powerful tool for studying thermally mediated neural processes, enhancing the safety and interpretability of optical neurotechnologies. Its integration potential positions this platform as a complementary technology for next-generation multifunctional neural interfaces.