Performance of an integrated microoptical system for fluorescence detection in microfluidic systems

This article presents a new integrated microfluidic/microoptic device designed for basic biochemical analysis. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar microfluidic systems, elements of the detection system are realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive circular or elliptical microlens arrays and chromium aperture arrays. The microfluidic channels are 60 pm,Aide and 25 pm deep. The elliptical microlenses have a major axis of 400 mum and a minor axis of 350 mum. The circular microlens diameters range from 280 mum to 350 mum. The apertures deposited on the outer chip surfaces are etched in a 3000-Angstrom-thick chromium layer. The overall thickness of this microchemical system is < 1.6 mm. A limit of detection of 3.3 nM for a, Cy5 solution in phosphate buffer (pH 7.4) was demonstrated. The crosstalk signal measured between two adjacent microchannels with 1 mm pitch was < 1:5600, meaning that less than or equal to1.8 x 10(-4)% of the fluorescence light power emitted from one microchannel filled with a 50 muM Cy5 solution reaches the photodetector at the adjacent microchannel. This performance compares very well with that obtainable in microchemical chips using confocal fluorescence systems, taking differences in parameters, such as excitation power into microchannels, data acquisition rates, and signal filtering into account.