Microring Resonator Based Disposable Ultrasound-sensing Chronic Cranial Window

Abstract

Chronic cranial window (CCW) has been widely used to provide optical access to the brain cortex for longitudinal imaging, while preserving the physiological environments of the brain. Various optical imaging modalities have been demonstrated with CCW for longitudinal brain imaging, including single-photon and multi-photon fluorescence microscopy, optical coherence tomography, and photoacoustic microscopy (PAM). However, sophisticated surgeries and windows designs are still required for chronic imaging and direct cellular recording or manipulation because the surgical implantation of CCW precludes direct physical access to the brain other than optical access. Here, we report an active CCW with integrated ultrasound sensor based on a transparent microring resonator (MRR). The MRR is fabricated on a quartz substrate by using low-cost soft nanoimprinting lithography (sNIL) and then integrated on a glass window with optical fibers for disposable ultrasound-sensing CCW (usCCW). Encapsulating MRR inside an acoustic impedance matched protection layer further improves its reliability for in vivo applications over the observed period of a month. The functions of the active usCCW are experimentally validated through longitudinal (PAM) imaging of cortical vasculature in live mice over a 28-days period.