Micro/Nanophotonic Ultrasound Sensors for in Vivo Photoacoustic Imaging

Photoacoustic imaging (PAI) has emerged as a powerful in vivo imaging modality for probing biological morphology, functional dynamics, and biochemical composition across spatial scales ranging from subcellular structures to organs. However, further progress in in vivo PAI is fundamentally constrained by the performance of photoacoustic wave detectors, which must simultaneously satisfy stringent requirements for optical transparency, extreme miniaturization, and high acoustic sensitivity. These requirements are difficult to reconcile using conventional piezoelectric technologies. In recent years, micro/nanophotonic ultrasound sensors have been widely investigated as promising alternatives. These sensors use photonic transduction mechanisms to enable sensitive ultrasound detection, smaller device footprints, and better compatibility with optical imaging geometries. Rapid advances in the design, fabrication, and system integration of micro/nanophotonic sensors have led to an increasing number of in vivo demonstrations and expanding biomedical applications. This review provides a comprehensive overview of micro/nanophotonic ultrasound detection technologies for in vivo PAI, summarizing fundamental sensing principles, representative device architectures, emerging applications, and key technical challenges, and discussing future development directions toward next-generation PAI systems.