Synergistic Effects of TiO ₂ @CdS Heterojunctions Enable High-Performance Blue-Light-Sensitive Photodetectors and Iontronic Synapse Fibers for Underwater Interactions

The development of high-performance blue-light-sensitive photodetectors for underwater applications faces significant challenges due to the limited absorption range and inefficient charge separation in conventional semiconductor materials. Here, we design a TiO₂@CdS core-shell heterojunction that synergistically combines the advantages of both materials, significantly enhancing blue-light absorption (450-495 nm) and charge carrier separation efficiency. The resulting fiber-shaped photoelectrochemical photodetector (FPPD) displays exceptional performance with a high responsivity of 101.87 mA W^-1, fast response time of <19 ms, and outstanding mechanical flexibility. Furthermore, our FPPD exhibits biomimetic synaptic functionalities including bilingual responses, short-term plasticity, and low energy consumption comparable to that of biological synapses, enabling neuromorphic information perception and computing capabilities. Practical applications in underwater optical communication, imaging, and human-machine interaction are successfully demonstrated, highlighting the FPPD's versatility in underwater environments. This work not only advances the design of high-performance underwater optoelectronic devices but also establishes a direct connection between traditional photodetection and emerging neuromorphic computing, laying the groundwork for innovative underwater systems and wearable technologies.