Microfluidic genetic and amino acid analysis using an integrated a-Si:H detector

Hydrogenated amorphous silicon (a-Si:H) PIN photodiodes are used as fluorescence detectors for microfluidic biochemical and chemical analysis devices. A hybrid- integrated detector consisting of a half-ball lens, a ZnS/YF₃ multilayer optical interference filter with a pinhole, and an annular a-Si:H photodiode is developed that allows the laser excitation to pass up through the central aperture in the photodiode. Using this integrated device, the limit of detection for fluorescein flowing in a 50-μm deep channel is 17 nM (S/N = 3). Furthermore, analysis of PCR amplicons generated from Staphylococcus aureus and chiral analysis of glutamic acid are successfully demonstrated. The a-Si:H detector exhibits high sensitivity at the emission wavelengths of commonly used fluorescent dyes and is readily microfabricated and integrated at low cost making it ideal for portable microfluidic bioanalyzers.