(A) study of label-free electrical detection of protein-ligand binding with vertical gold nanogap

Abstract

In this thesis, label-free electrical detection of protein-ligand binding using a vertical gold nanogap is presented. A sub-lithographic vertical gold nanogap was created using a sacrificial ultra-thin film deposited by atomic layer deposition (ALD) in a process similar to the formation of a cantilever in MEMS processing. Due to the atomic precision of the sacrificial $Al_2O_3$ thickness by ALD, a 7-nm nanogap was successfully fabricated. After binding streptavidin to biotin on the gold surface, a DC electrical current was measured for various DC voltages. A dramatic DC current increase was observed in the case of biotin-streptavidin binding in comparison with the other two cases: a control group filled with air in nanogap and a biotin-only binding group. There was 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 (1.5 nM), the current difference before and after the protein binding was amplified by approximately 3000-fold. Also, the detection sensitivity of the vertical nanogap as the gap size varied was investigated. This arrayable, two-terminal microdevice can be used for a wide range of detection applications in the analysis of other biomolecules and for nucleic acid hybridization.