We present a fluorescence detection system for capillary analysis. It is designed using a CMOS BDJ (Buried Double p-n Junction) detector which can be operated either as a photodiode or as a wavelength-sensitive device. Noise-reduction techniques such as signal pre-amplification and synchronous detection are implemented to boost the sensitivity of measurements. The system indicates fluorescence intensity for concentration determination, and average wavelength of fluorescence spectrum for molecular discrimination. The system has been tested by measuring two widely used fluorophores (FITC and Rhodamine B) in different concentrations. A 407-nm blue laser diode and a 532-nm green YAG compact laser have been respectively employed for their excitation. The illuminated volume inside the capillary is about 5 nl. The best results have been obtained with FITC, enabling as low as 10-10 M to be detectable.
KEYWORDS: Sensors, CMOS sensors, Signal detection, Electronics, Optical amplifiers, Fluorescence spectroscopy, Signal to noise ratio, Photodiodes, Photodetectors, Linear filtering
CMOS photodiodes have increasingly been used for biomedical purposes. They offer many technical and economic advantages for their on-chip integration and system miniaturization. With the aim of developing portable instruments for micro-analysis, we have investigated the CMOS BDJ detector for fluorescence detection. Like conventional photodidoes, the CMOS BDJ detector can be used as a photodetector. In addition to that, it can also be employed as a wavelength-sensitive device.
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