Colorimetric detection of molecular recognition reactions with an enzyme biolabel using a thin-film amorphous silicon photodiode on a glass substrate

A hydrogenated amorphous silicon photodiode microfabricated on a glass substrate is used to optically detect and quantify the concentration of an enzyme (horseradish peroxidase, HRP) which can be used to label biomolecules such as DNA and proteins. HRP is used with tetramethylbenzidine substrate to produce a light absorbent product, and the variation of the optical transmission light through the solution is detected by the photodiode. Sensitivities below the picomolar level have been obtained for HRP in solution. When HRP was immobilized on a polymeric surface, minimum density in the range of 1 × 109 HRP molecules per cm2 was detected. The photodiode was successfully used to detect the molecular recognition of a surface-immobilized primary antibody with an HRP-labeled secondary antibody.