Stretchable physical sensors that can detect and quantify human physiological signals such as temperature, are essential to the realization of healthcare devices for biomedical monitoring and human-machine interfaces. Despite recent achievements in stretchable electronic sensors using various conductive materials and structures, the design of stretchable sensors in optics remains a considerable challenge. Here, an optical strategy for the design of stretchable temperature sensors, which can maintain stable performance even under a strain deformation up to 80%, is reported. The optical temperature sensor is fabricated by the incorporation of thermal-sensitive upconversion nanoparticles (UCNPs) in stretchable polymer-based optical fibers (SPOFs). The SPOFs are made from stretchable elastomers and constructed in a step-index core/cladding structure for effective light confinements. The UCNPs, incorporated in the SPOFs, provide thermal-sensitive upconversion emissions at dual wavelengths for ratiometric temperature sensing by near-infrared excitation, while the SPOFs endow the sensor with skin-like mechanical compliance and excellent light-guiding characteristics for laser delivery and emission collection. The broad applications of the proposed sensor in real-time monitoring of the temperature and thermal activities of the human body, providing optical alternatives for wearable health monitoring, are demonstrated.

In vivo imaging at high spatiotemporal resolution holds the key to the fundamental understanding of complex biological systems. Integrating an optical phase-locked ultrasound lens into a conventional two-photon fluorescence microscope, we achieved microsecond scale axial scanning, which enabled high-speed volumetric imaging. We applied this system to multicolor volumetric imaging of fast processes, including calcium dynamics in the cerebral cortex of behaving mice, and transient morphology changes and trafficking of immune cells.

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For in vivo deep imaging at high spatiotemporal resolutions, we developed Multi-Pupil Adaptive Optics (MPAO) which enables simultaneous wavefront correction over a large imaging field-of-view. The current implementation improves correction area by nine times over that of conventional methods. MPAO’s capability of spatially independent wavefront control further enables 3D nonplanar imaging. We applied MPAO to in vivo structural and functional imaging of biological dynamics in mammalian brain.