CombiMatrix’s CMOS arrays have 12,544 individually addressable electrodes that have been used for design of DNA chips for variety of applications including Influenza detection, human cancer research, and for spotting whole genome of several fungal species. Multiplexed immunoassays have also been developed on this platform by two different methods; a) linking antibodies with complementary DNA sequences that can be captured on specific electrodes containing complementary DNA sequence and b) biotinylated antibodies captured on streptavidin coated electrodes. However, antibodies being antibodies they are fragile at the electrodes and conjugated antibodies are difficult to produce reliably-this according to authors of recent paper in PLoS ONE. They have come up with a new method where they electrochemically deposit ‘protein friendly’ polypyrrole (Ppy) on selected electrodes followed by adsorption of antibodies on Ppy layers. For detection, they use sandwich immunoassay with Cy5 labeled 2nd antibody for fluorescent detection and HRP labeled 2nd Ab for enzyme enhanced electrochemical detection (ECD). Limit of detection (LOD) between 0.003 and 0.01pg/ml was achieved using ECD method.
Although, Ppy can be individually addressed on the electrodes, antibody adsorption is done using traditional spotting methods. In that sense this method is no different from traditional antibody arrays with fluorescent detection, with claimed LODs of sub pg/ml levels, except for ECD detection method.