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 7 nm 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 0.1 mu g/ml concentration of streptavidin (1.5 nM), the current difference before and after the protein binding was amplified by approximately 3000-fold with 17 nm 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 12 nm nanogap, the highest sensitivity was shown in the 12 nm gap device. 7 nm 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. (c) 2007 American Vacuum Society.