(A) study on nanogap devices for electric detection of biomolecules

Abstract

The electric detection of trace amounts of biomolecule is a key challenge in the development of diagnostic tools, because it has several advantages, including compatibility with electronic products, the possibility of their being developed into portable devices, and their high sensitivity in comparison with other methods. Nanogap devices, which are one of the recent advances in the electric biosensing field, have several favorable key features, such as simple operation mechanism, ultrahigh sensitivity, and design flexibility of device structures. In chapter 1 and 2, integrated nanogap electrodes with separations of several nanometers were fabricated to detect the biomoleucles by a simple and highly reproducible method of surface-catalyzed chemical deposition. By this method, multifingered nanogap electrodes of a few nanometers in separation were fabricated with a good yield (over 90%). The fabrication was achieved by immersing the initial gap electrodes obtained by conventional e-beam lithography into a stock solution containing Au ions and a mild reducing agent. After the surface-catalyzed chemical deposition, a rather wide initial gap distance of 18-52 nm was decreased to a few nanometers, showing a much narrower distribution. In chapeter 3, DNA hybridization was electrically detected by monitoring the electric conductance change of a nanodevice comprised of two electrodes separated by a narrow gap whose width was comparable to the size of a nanoparticle. Specific hybridization of a target DNA to the capture DNA on the electrode and the probe DNA on the gold nanoparticle (AuNP) resulted in the immobilization of AuNPs between the electrodes, which in turn led to a conductance jump across the gap. After fabrication of the device, the whole area except the gap region was passivated by e-beam resist to reduce a possible loss of target DNA. Two types of thiol-modified single-strand DNAs, which would specifically hybridize with portions of the target DNA, were...