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 200-300 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 1×10
^-10
Acm
^-2
was obtained at 0 V. An external quantum efficiency of 6%, 7% and 8% and noise equivalent power of 7.49 × 10
^-13
W, 5.33 × 10
^-13
W and 5 × 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 μM and 0.18 μM were obtained for BSA and SH-ssDNA, respectively. The absorbance of ascorbic acid at 215 nm was successfully detected.