Label-Free Biosensing Using Thin-Film Amorphous Silicon Photodiodes Integrated with Microfluidics

A hydrogenated amorphous silicon p-i-n photodiode was optimized for enhanced sensitivity in the 200300 nm wavelength range, in particular at 215 nm, 260 nm and 280 nm, which are absorbance peaks for key biomolecules. The UV-optimized photodiode was characterized in terms of its dark current density-voltage characteristics; its external quantum efficiency as a function of incident light wavelength; photocurrent density as a function of incident photon flux and wavelength; and the noise equivalent power at the identified key UV wavelengths. A dark current of 1 x 10(-10)Acm(-2) was obtained at 0 V. An external quantum efficiency of 6%, 7% and 8% and noise equivalent power of 7.49 x 10(-13)W, 5.33 x 10(-13)W and 5 x 10(-13)W were obtained at 215 nm, 260 nm, and 280 nm, respectively. The UV absorbance spectrum between 205-355 nm was determined for thiolated single-stranded DNA (SH-ssDNA), bovine serum albumin (BSA) and ascorbic acid with the UV-optimized photodiode coupled with a microfluidic structure. Limits of detection of 9.97 mu M and 0.18 mu M were obtained for BSA and SH-ssDNA, respectively. The absorbance of ascorbic acid at 215 nm was successfully detected.