Sublithographic vertical gold nanogap for label-free electrical detection of protein-ligand binding

Abstract

Label-free electrical detection of protein-ligand binding using a vertical gold nanogap is presented. A sublithographic nanogap was created using a sacrificial ultrathin film deposited by atomic layer deposition (ALD) in a process similar to the formation of a cantilever in microelectromechanical system processing. Due to the atomic precision of the sacrificial Al2O3 thickness by ALD, a 7nm nanogap was successfully fabricated. After binding streptavidin to biotin on the gold surface, an electrical current was measured for various voltages. A dramatic current increase was observed in the case of biotin-streptavidin binding in comparison with the other two cases: a control group filled with air and a biotin-only binding group. There was a minimal current change in the cases of the biotin-PBST group, the biotin-BSA group, and the biotin-saturated streptavidin group, as compared with the biotin-streptavidin group. At a 0.1μg∕ml concentration of streptavidin (1.5nM), the current difference before and after the protein binding was amplified by approximately 3000-fold with 17nm nanogap. Also, the detection sensitivity of the vertical nanogap as the gap size varied was investigated. As the size of biotin-streptavidin binding is the most comparable to 12nm nanogap, the highest sensitivity was shown in the 12nm gap device. 7nm nanogap can be used to detect smaller size of biomolecule than that of biotin streptavidin. This arrayable, two-terminal microdevice could be tested for use on a wide range of other biomolecules.