Superresolution Line Scan Image Sensor for Multimodal Microscopy.

Abstract

A low-cost contact scanning microscope is presented which performs optical imaging of millimeter-scale samples with multiple sensory modalities at a spatial resolution better than the pixel size in both x and y dimensions. The 7.5 mm 3.2 mm 0.35m CMOS image sensor is comprised of 214 scanning lines of 256 pixels, each line horizontally shifted by 300 nm with respect to the adjacent lines. When scanning in the y dimension, this results in a staircase-like staggered-pixels organization with an effective spatial resolution in the x dimension of less than the pixel size, with a theoretical limit of 300 nm, subject to the light diffraction limit and to photodiode size-dependent spatial aliasing. The height of the resulting pixel "staircases" is capped at 2.5 mm by wrapping the 215th row back to the first row, yielding an approximately 2 mm 2.5 mm instantaneous scanning window size. The spatial resolution in the y dimension is set by the sample scanning rate and the frame rate, subject to the same limitations. Integration of multiple scanning lines naturally lends itself to the inclusion of multiple sensory modalities, with five modalities included as an example: High-resolution (up to 300 nm), fluorescence-sensitive, and triple-orientation light polarization-sensitive pixels. The resulting modified scanning pattern is digitized by on-chip column-parallel 2nd order Delta-Sigma ADCs with ENOB of 9.1 and is reconstructed into a full-resolution image in software. Experimental measurements, where contact-scanning is emulated by the sample image moving on an LCD monitor and projected through a lens, support the validity of the presented concept.