Fluorescence Detection of DNA Hybridization Using an Integrated Thin-Film Amorphous Silicon n-i-p Photodiode

This paper presents the fluorescence detection of DNA hybridization with a surface immobilized probe using a hydrogenated amorphous silicon (a-Si:H) photosensor. This sensor integrates a SiO2 layer for DNA probe immobilization, a p-i-n a-Si:H photodiode for fluorescence detection and a fluorescence filter of hydrogenated amorphous silicon carbide (aSiC:H) to cut the excitation light. With this integrated photosensor system, a five order of magnitude difference was obtained in the signal measured at the emission wavelength and that measured at the excitation wavelength for the same incident photon flux. The fluorophore Alexa Fluor 430 was used to label the DNA target molecules and a laser at 405 nm and a photon flux of 5.7x10(16)cm(-2).s(-1) was used as the excitation light source. The detection limit achieved for fluorophores in solution in contact with the device and for fluorophores immobilized on the device surface is 5x10(-9) M and 0.4 pmol/cm(2), respectively. The hybridization of the tagged DNA target with a covalently or electrostatically immobilized probe was successfully detected at a surface density of similar to 3 pmol/cm(2)