Electron tunneling through thin (similar to 1-50 nm), insulating materials can provide information regarding their band structure, density of states, surface and bulk defect densities and their energy levels and distributions. While electron tunneling has been used in thin inorganic insulating materials for nearly 7 decades, its applications in organic and biological materials, with exceptions of deoxyribonucleic acid and a few other materials, are not extensively explored. Here we report room temperature electron tunneling studies to differentiate between aptamers designed to attach to the capsid proteins on Zika viruses and the aptamer-Zika complexes. We show that the electron tunneling induced by the current versus voltage (I-V) measurements through these materials contain information that enable identification of the Zika virus without any need for DNA sequencing or additional molecular labels. The electron tunneling measurements were carried out using a conducting atomic force microscope, a home-made vertical tunneling junction and an electromigration-induced nanogap in a microfabricated 1 mu m-wide gold line on silicon nitride bridges. The current through aptamers and aptamer-Zika complexes all have a threshold voltage just before the exponential increase in the junction current. Below this voltage, the leakage currents are different for the aptamer and aptamer-Zika samples. The tunnel nanogap device is suitable for detecting viruses that are nanometer-scale biomaterials.
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