A compact fluorescence detection system integrated with LED and PIN Photodetector for Microfluidic application

Laser Induced Fluorescence (LIF) is the most sensitivity and widely used detection method in microfluidic chip. However the tranditional LIF detection has the disadvantage of bulky which limits the promotion and widely use of microfluidic chip. A novel compact fluorescence detection system which can be generally used in glass based micro-fluidic chip is proposed. The high-powered light emitting diode (LED) is used as the exciting light source, and multimode optical fiber is also used as transmission channel to transmit exciting light into the detection window. The filter is a specially designed thin film with the thickness of only 2-3 microns and is integrated on the bottom of the glass based microfluidic chip. PIN silicon based chip is chosen as the photodetector, and is integrated on the microfluidic chip by silicon and glass bonding. The integrated microfluidic chip is packaged in a specially designed cavity to shield external stray light. Experiment results show that the best working current for LED is 200mA; the distance between optical fiber tip and detection spot is 1.5mm; the transmittance of the thin film filter of emission light can reach up to 90% at the wavelength of 520nm; the detection limits for FITC labeled Phenylalanine is 10-7mol/L, and the on-line electrophoresis detection is also achieved.