Performances of amorphous silicon photodiodes integrated in chemiluminescence based μ-TAS

A detailed characterization of the performances of amorphous silicon photodiodes in the detection of chemiluminescent signal is carried out. Comparison with commercial CCD acquisition system has been done as benchmark. The underlying idea is the development of stand-alone and compact micro-total-analysys-systems (mu-TAS) that do not need bulky and expensive equipment for their operation as external focusing optics and excitation sources. The photosensor is p-i-n structures deposited by Plasma Enhanced Chemical Vapour Deposition on a glass substrate covered with a transparent conductive oxide that acts as bottom electrode and window layer for the light impinging through the glass. A PDMS layer with wells has been fabricated using an aluminum mold and bonded on the glass substrate with a well aligned with a photosensor. The experiments have been performed by filling a well with solutions containing different quantities of horseradish peroxidase. A good linearity of the photosensor response is observed across the entire measurement range that spans over three orders of magnitude. The system detection limit is 70 fg/mu L. A very good agreement between results achieved with conventional off-chip CCD detection and the on-chip photodiode has been observed. Experiments with target molecules immobilized on a functionalized glass surface have been also performed in microfluidic regime, confirming the validity of the proposed integrated approach based on a-Si: H technology.