Dual-mode, enhanced dynamic range CMOS optical sensor for biomedical applications

Silicon photodetectors and CMOS image sensors are widely used in biological sensing and medical imaging, where modern CMOS processes provide sufficient sensitivity and noise performance at a lower cost than traditional CCD sensors. At low light intensity, which is increasingly needed for single-molecule and low concentration biosensing, silicon photodetectors are limited by low photocurrent, commensurate with dark current magnitude. In this paper, we present a method to extend the optical dynamic range of a CMOS-integrated photodiode by operating alternately in linear mode and single-photon Geiger-mode using a single p-n junction diode sensor. The architecture was implemented in a commercial 130 nm CMOS process, and measured results are reported across a range of illumination intensities from 30-3000 lux. Results from an optical transmission experiment are provided to demonstrate utility for quantifying chromogenic reactions in lab-on-CMOS immunoassays.