Detection of molecular tags with an integrated amorphous silicon photodetector for biological applications

Abstract A hydrogenated amorphous silicon micro-photodiode is used to optically detect the presence, in solution, of species which can be used as molecular labels for biomolecules. These molecular labels are a fluorescent molecule and an enzyme. The light emitted by the fluorophore (Alexa Fluor 430) in solution is detected by the photodiode through an amorphous silicon carbon filter which absorbs the excitation light. The enzyme (horseradish peroxidase) is used with two different substrates (luminol and tetramethylbenzidine) to produce chemiluminescent and light absorbent products, respectively. Sensitivities down to picomolar level (corresponding to 1 attomole of molecular labels in solution) have been obtained.