Raster-scanning two-photon endomicroscopy with ultra-compact, low-voltage electrothermal MEMS scanning mirror

Two-photon endomicroscopy (2PEM) is an advanced optical biopsy technique that provides high-resolution, label-free, depth-resolved imaging. Developing a 2PEM with low driving voltage is essential for clinical applicability. This study presents a raster-scanning 2PEM that employs an ultra-compact, low-voltage electrothermal microelectromechanical system (MEMS) scanning mirror. The probe features separate designs for excitation and collection optical paths, integrating an electrothermal MEMS scanner for high-uniformity raster scanning. The system achieves an imaging resolution of ∼1.69 μm, a field of view of 103 μm × 103 μm at driving voltages below 4 V, and a frame rate of ∼0.5 frames per second (256 × 256 pixels). Imaging results of unstained skin tissue sections and ex vivo mouse rectum tissues demonstrate the system's capability for label-free two-photon fluorescence and second-harmonic generation endomicroscopic imaging.