Silicon thin film photodetectors for multi‐channel fluorescence detection in a microfluidic point‐of‐care testing device

Abstract

Fluorescence spectroscopy is a highly sensitive detection method widely used in analytical chemistry, bioanalytics, and medicine. The here presented amorphous silicon (a‐Si:H) based thin film photodetector arrays contribute to the miniaturization of this measurement method and thereby enable integration of a point‐of‐care testing (POCT) device. Revealed from photocurrent decay measurements, the limit of detection of the photodiodes with an active area A = 36.3 mm2 is in the 100 fA‐range. Dark current analysis at zero bias voltage yields a standard deviation σ = 4.4 fA for the thermally generated noise of the nip photodiodes. In the context of the desired application, a minimum detectable fluorescence radiation intensity Umin = 4.5 pW cm−2 with a dynamic range DNR = 78 dB is estimated. At the emission peak wavelength λem = 667 nm and with a bandwidth Δf = 0.25 Hz the photodiodes reach a noise equivalent power NEP = 54.6 fW Hz−1/2 and therewith a specific detectivity D* = 1.1 × 1013 Jones. Fluorescence measurements with the dye DY‐636 diluted in pure water with a molar concentration c = 1.31 μM demonstrate the suitability of the multi‐channel photodetectors for high‐sensitivity fluorescence spectroscopy.Low‐signal a‐Si:H photodetector multi‐channel chips in different geometrical layouts with an active area of up to 36.3 mm2 per diode.