Current low-level light detection technologies for biomedical applications such as DNA microarray sensors use charge-coupled devices or photomultiplier tubes which cannot be easily integrated with electronic circuits on a chip. Complementary metal-oxide semiconductor (CMOS) image sensors do allow for the integration of photosensitive and signal processing elements on the same chip. However, more research is required if optimized low-level light detectors in standard CMOS technologies are to be developed. In this research, we have investigated different photosensitive devices, including vertical, lateral, and avalanche photodiodes and two floating gate-well-tied phototransistors with different gate oxide thicknesses. The photodetectors were fabricated in a commercial 0.18μm CMOS technology, and their optoelectronic characteristics were measured to determine the optimum configuration for low-level light detection.