Electroaddressable selective functionalization of electrode arrays: Catalytic NADH detection using aryl diazonium modified gold electrodes

We report the application of 4-nitrophenyl diazonium modified electrodes towards the electrochemical detection of NADH. Selective activation of individual electrodes on a 5 element array by electro-addressable conversion of nitro groups to amines and subsequent EDC/NHS crosslinking to the NADH oxidant, pyrroloquinoline quinone (PQQ), is demonstrated. Inactivated electrodes retained nitro functionality and were protected against non-specific adsorption and mild chemical reactions. Electrodeposition conditions were used to control nitrophenyl film thickness and showed that while increased film thickness leads to greater functionalization density of PQQ, it also results in decreased electron transfer kinetics. The electrodeposition protocol can therefore serve as a method to control electrode functionalization density and film electron transfer kinetics. We believe this simple technique for selective electrode functionalization may facilitate the development of next generation multianalyte electrochemical sensors.