Fluorescence detection of DNA using an amorphous silicon p-i-n photodiode

A microdevice based on a thin-film hydrogenated amorphous silicon (a-Si:H) n-i-p photodiode is used to quantify the density of DNA oligonucleotides labeled with a fluorophore in solution, adsorbed, and hybridized on the device surface. Excitation of single-stranded DNA molecules tagged with the fluorophore Alexa Fluor 430 with near UV/blue light results in the emission of visible light at 539 nm. The emitted light produces an electrical signal in the photodetector, allowing the optoelectronic detection and quantification of the DNA molecules. An integrated high-pass filter cuts the excitation light while allowing the collection of the emission light by the photodiode. The detection limit of the present device is of the order of 5 nM in solution. A surface density of the order of 2 pmol/cm2 was measured for DNA targets hybridized to immobilized DNA probes. The sensitivity of the current device is limited by the efficiency of the filtering of the excitation light. The detection concept explored can enable o...