A Mechanically Flexible, Implantable Neural Interface for Computational Imaging and Optogenetic Stimulation Over 5.4×5.4mm² FoV

Subdural CMOS optical probe (SCOPe) for bidirectional neural interfacing

“…S3. We compared our SPAD sensor with other SPAD arrays (19,(27)(28)(29)(30)(31) (see Table S2). At 200 fps, our sensor shows higher dynamic range and lower power consumption than other comparable SPAD imaging systems (30,31).…”

“…The imager is 5.1 mm × 6.8 mm and is comprised of a 3×4 array of macros, each consisting of 14 blocks of 16×16 SPAD pixels with a pitch of 25 μm, and 12.5% of the array is removed for μLED bond pads and drivers. Unlike an earlier design( 19 ) in which detected photon counts are stored in shared-row counters, this design( 69 ) supports 10-bit pixel-level counters and a global shutter, improving the ratio of integration time to frame period 100-fold from 0.625% to 99.6%, while supporting frame rates of up to 200 fps with a 100 MHz reference clock. The chip’s frame rate is 200fps, when reading the entire array, or 400fps, when reading half the array (128×192); the latter allows for the imaging of fast state-of-the-art voltage indicators( 70 ).…”

“…The bias transistor operates as a large resistor, discharging the anode of the SPAD until there is a photon-induced avalanche current triggering a pulse that can be registered as a count in the external circuitry. In first implementations ( 18, 19 ), we designed a custom SPAD-based image sensor to enable time-gated (TG) fluorescence imaging through single-photon counting. Time gating uses the design of a high-speed active-quench, active-reset pixel circuit, which necessitates the implementation of a rolling shutter, shared off-pixel counter in order to maintain a small pixel pitch.…”

“…(A) We evaluated various types of computational imaging masks on the basis of working distance, reconstruction with LED blocks, light collection efficiency, flexibility, 3D capabilities, and ease of integration. (B) Comparison of working distances of the angle pixel( 49 ), amplitude mask( 16, 19 ), phase mask( 17 ), and fiber optic plate. (C) Numerical aperture, comparing amplitude and phase masks.…”

“…This radical improvement in volumetric efficiency is achieved through the design of a custom complementary metal-oxide-semiconductor (CMOS) application-specific integrated circuit (ASIC) which is capable of both fluorescence imaging and optogenetic stimulation. The integrated circuit chip, thinned to less than 15 µm so as to be mechanically flexible (18)(19)(20) and conform to the cortical surface, is packaged on a flexible polyimide printed circuit board along with the heterogeneous integration of the light sources, filters, and lens-less masks required for a high-performance optical neural interface. We demonstrate basic functionality of the SCOPe device for imaging and optical stimulation in vivo in the mouse model over a subset of the array.…”