A Cooled ICCD System For Biochip Detection

Biochip technologies are widely used in drug research, disease diagnosis, gene structure and function research, and other fields. Biochip is a micro-array composed of base molecules which is fixed on the solid plane using micro-processing technology. Base molecules can be labeled because of specific interactions between the fluorescent dye molecules and base molecules. By detecting the distribution and strength of the fluorescence signal from excited fluorescent molecules, biochip can be detected, and the results can be converted to analyble image or data.The detection instrument is an important component of biochip technology. In this paper, we studied a method to detect the biochips labeled with Cy3 fluorescent molecules using optical fiber-coupled ICCD(Intensified Charge Coupled Device) system. To improve the detection sensitivity of the system, the CCD chip and image intensifier tube are cooled.We studied weak signal detection limits of cooled CCD, lens coupled ICCD and optical fiber-coupled ICCD through comparison experiment. Based on the experimental results, we determine that the image intensifier can amplify the weak signal, thus greatly improve the detection sensitivity. The different detection results of different coupled ICCDs show that lens coupled ICCD increased detection sensitivity but lost too many photons, while optical fiber-coupled ICCD had high energy utilization and increased both detection sensitivity and signal intensity, shortening the exposure time. Besides, by comparing the properties of the image intensifier before and after cooling, it is found that cooling can be used to reduce image intensifier background noise and improve the signal-to-noise ratio.The detection limits of the cooled ICCD for biochip detection is 1500 flours/um~2, below to its weak light signal detection limits. This is resulting from the high background noise. Based on the experimental results, we analysed the sources and the proportion of background noise in biochip detection. The noise can be divided into four parts: CCD dark current and readout noise, image intensifier background noise, the fluorescence from the base-plate of biochip and the scattered light issued from indoor objects. The former two can be reduced by cooling the CCD and the image intensifier or by average detection. The third one can be effectively lowered by using a base-plate with less fluorescent impurities. The last one can be cut down by optimizing the image formation.