Branched nanotrees with immobilized acetylcholine esterase for nanobiosensorapplications

Abstract

A novel lab-on-a-chip nanotree enzyme reactor is demonstrated for the detection of acetylcholine.The reactors are intended for use in the RISFET (regional ion sensitive field effect transistor)nanosensor, and are constructed from gold-tipped branched nanorod structures grown onSiNx-covered wafers. Two different reactors are shown: one with simple, one-dimensionalnanorods and one with branched nanorod structures (nanotrees). Significantly higherenzymatic activity is found for the nanotree reactors than for the nanorod reactors, mostlikely due to the increased gold surface area and thereby higher enzyme bindingcapacity. A theoretical calculation is included to show how the enzyme kinetics andhence the sensitivity can be influenced and increased by the control of electricalfields in relation to the active sites of enzymes in an electronic biosensor. Thepossible effects of electrical fields employed in the RISFET on the function ofacetylcholine esterase is investigated using quantum chemical methods, which showthat the small electric field strengths used are unlikely to affect enzyme kinetics.Acetylcholine esterase activity is determined using choline oxidase and peroxidase bymeasuring the amount of choline formed using the chemiluminescent luminol reaction.