Two-dimensional CMOS-based image sensor system for fluorescent detection

The widespread use of DNA-based diagnostics requires the development of portable and low-cost DNA microarray testing instruments. One of the most popular methods for DNA detection is the use of fluorescent tags for target DNAs. Usually, charge-coupled device (CCD) detectors or photomultipliers are employed to detect the fluorescent emission of DNA targets, but they cannot be integrated with other electronic circuits on a chip in a standard silicon process. On the other hand, CMOS image sensors can be integrated with other electronic circuits to perform some processing on a chip and they also have lower power consumption, but their performance is not as good as that of the CCD detectors. In the project described in this paper, methods to enhance the quality of CMOS-based image sensors for fluorescent detection of DNA microarrays are being investigated. For this purpose, different types of photodiodes and phototransistors have been designed using two different technologies, namely, standard CMOS 0.35 mum and 0.18 mum technologies. Also, complete blocks of image sensors with photodiodes and phototransistors have been designed to investigate the response of an entire image system. Each block consists of a matrix of image sensors with an amplifier in each pixel, column amplifiers, and sample and hold circuits. The paper discusses in detail each component of these optical image sensors and provides simulations and experimental results on their performance.