A pressure pulse wave sensor inspired by light-reflecting skin structures in atherinid fish

The human dermis and epidermis provide inspiration for the development of next-generation wearable devices for on-skin sensing. The dermis contains complex microvascular and lymphatic networks that are essential for tissue homeostasis; however, real-time visualization of dermal microfluid dynamics in vivo remains technically challenging. Here, I report that three species of Atherinidae exhibit rapid flashing ("twinkling") spots on their skin that function as optical reporters of dermal microcirculation. Spatiotemporal analyses reveal that fluid-pressure fluctuations associated with circulatory networks adjacent to chromatophore complexes are accompanied by rapid tilting of guanine platelets within iridophores. These platelets are organized into a honeycomb-like membrane structure, enabling coordinated platelet motion to modulate reflected light intensity. A prototype surface light-reflection pressure sensor patch containing guanine platelets demonstrated the conversion of applied fluid-pressure pulses into optical signals, suggesting potential applications in noninvasive physiological pulse waves monitoring. These findings reveal a previously unrecognized biological mechano-optical transduction mechanism and provide a biomimetic framework for visualizing dermal microfluid dynamics and developing wearable optical biosensing technologies.