Chemical Sensors Based Upon Metal Nanowires and Nanogaps in Metal Nanowires Transduced Using Impedance

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With support from the Chemical Measurement and Imaging (CMI) program in the Division of Chemistry, Professor Reginald Penner at the University of California, Irvine is developing new concepts for configuring gold nanowires as chemical sensors. Over the last twenty five years, nanoscience has provided new building blocks - nanomaterials - for constructing small and highly sensitive chemical sensors and biosensors. Such “nano-enabled” sensors have been used for the measurement of heavy metals in aqueous solutions, and metabolites in bodily fluids like blood and urine. The most important nanomaterials have been carbon nanotubes, semiconductor (e.g., silicon) nanowires, and polymer (e.g., polyaniline) nanofibers. In contrast, almost no role for metal nanowires in chemical sensing has been demonstrated. The only exception is for hydrogen gas sensing, where palladium nanowires have been successfully applied. The applicability of metal nanowires as sensors is limited because the significant electrical conductivity of these structures is hardly affected by the composition of the metal surface. The Penner research group has described two new concepts for configuring gold nanowires as chemical sensors. The key for both concepts is the application of an alternating current measurement of the nanowire resistance that is designed to probe the composition of a solution in close proximity to the nanowire surface. This project seeks to redefine the capabilities of metal nanowires for functioning as sensors for analytes such as metal ions (Fe3+), proteins (e.g., thrombin binding protein), and pH.Chemical and bio-sensors based upon carbon nanotubes, semiconductor nanowires, and metal oxide nanowires have each been described in thousands of publications, but virtually no applications of analogous metal nanowire-based sensors have been reported. In this project, two new types of chemical sensors based upon single metal nanowires will be developed. The two types are solid metal nanowires (1), and metal nanowires containing a single nanogap (2). Nanogaps in metal nanowire, with widths of 5 – 40 nm, will be produced using automated, feedback-controlled, electromigration. The concept of metal nanowire-based sensing is made possible by a new modality for transducing the signal produced by analyte species captured at the surfaces of these metal nanowires, involving the use of through-wire electrical impedance spectroscopy (EIS). EIS measures the perturbation of the capacitance of these metal nanowire structures when analyte species are present at wire surfaces. A single “universal” equivalent circuit describes the EIS response of both types of nanowire sensors under investigation. This project is designed to elucidate the fundamental capabilities of these two metal nanowire architectures, but also to develop practical nanowire-based sensors for analytes such as metal ions (Fe3+), proteins (e.g., thrombin binding protein), and pH.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.