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 µm wide and 25 µm deep. The elliptical microlenses have a major axis of 400 µm and a minor axis of 350 µm. The circular microlens diameters range from 280 µm to 350 µm. The apertures deposited on the outer chip surfaces are etched in a 3000-Å-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 e1.8 × 10 -4 % of the fluorescence light power emitted from one microchannel filled with a 50 µM 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.

Abstract-This

Abstract. Micro-optical systems based on refractive microlenses are investigated. These systems are integrated on a chemical chip. They focus an excitation beam into the detection volume (microliter or even submicroliter scale) and collect the emitted light from fluorescent molecules. The fluorescence must be carefully separated by spatial and spectral filtering from the excitation. This paper presents the ray tracing simulation, fabrication, and measurement of three illumination systems. The measurements show that an adroit placement and combination of microfabricated lenses and stops can increase the separation between the excitation light and the fluorescence light. Moreover we present the successful detection of a 20 nM Cy5™ (Amersham Life Science Ltd.) solution in a 100-m-wide and 50-m-deep microchannel (excitation volume Ϸ250 pL) using one of these illumination systems. The microchemical chip with the micro-optical system has a thickness of less than 2 mm.

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