On-chip detection performed by amorphous silicon balanced photosensor for lab-on chip application

In this paper we have integrated a two-channel microfluidic network, fabricated by molding two polydimethilsiloxane channels, with a balanced photodiode constituted by two series-connected amorphous silicon/silicon carbide n-i-p stacked junctions, deposited by Plasma Enhanced Chemical Vapor Deposition on a glass substrate. The structure takes advantage of the differential current measurement to reveal very small variations of photocurrent in a large background current signal suitable for biomedical application. The microfluidic network has been fabricated with dimensions of 3 cm × 2 mm × 150 μm (L × W × H) for each channel. The experiments have been carried out measuring the differential current in several conditions. All the experiments have been executed under a large background light intensity to reproduce realistic operating conditions in biomedical applications. We have found that the proposed device is able to detect the presence or absence of water flow in the channel and the presence of fluorescent marker. In particular, under identical channel conditions the differential current is at least a factor 60 lower that the current flowing in each diode.