Synergistic Effects of TiO₂ @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.