Characterisation of hydrogenated silicon–carbon alloy filters with different carbon composition for on-chip fluorescence detection of biomolecules

Absorption filters based on hydrogenated amorphous silicon–carbon alloys are developed for application as fluorescence filters in microarray and lab-on-a-chip systems. The carbon content of the thin film is varied by changing the amount of ethylene added to the ethylene/silane gas mixture during plasma-enhanced chemical vapour deposition. The optical properties of the films are characterised by transmittance measurements to obtain the refractive index, the optical bandgap, and the energy E04 of the films as a function of their carbon content. A set of filters that is appropriate for the detection of naturally fluorescent biomolecules is indicated. The system is used to demonstrate the detection of one of these naturally fluorescent biomolecules, the reduced form of nicotinamide adenine dinucleotide (NADH).