Amorphous silicon sensors for single and multicolor detection of biomolecules

In this paper, we report on a system for single and multicolor detection of biomolecules based on amorphous silicon photosensors. The system promises to be compact, portable, and low cost. It allows the quantitative detection without using optics for focusing both the excitation and the emitted radiation. The revealed biomolecules can be chemi- or naturally luminescent or can be labeled with fluorochromes. Here, we focus on the detection of DNA molecules labeled with a single or with two fluorochromes by using a p-i-n and a p-i-n-i-p amorphous silicon stacked structure, respectively. The device design has been optimized in order to maximize the signal-to-noise ratio and to match the sensor spectral response with the emission spectra of the fluorochromes. This optimization process has been carried out by means of a numerical device simulator, which takes into account the optical and electrical properties of the amorphous silicon. Detection limit in the order of a few nmol/l have been achieved for both the single and the two-color photosensors. Comparison with commercial measurement equipment shows the suitability of our system for practical applications.