Like the palladium chloride (PdCl2) films described in the immediately preceding article, gold nanowire sensors have been found to be useful for detecting airborne elemental mercury at concentrations on the order of parts per billion (ppb). Also like the PdCl2 films, gold nanowire sensors can be regenerated under conditions much milder than those necessary for regeneration of gold films that have been used as airborne-Hg sensors. The interest in nanowire sensors in general is prompted by the expectation that nanowires of a given material covering a given surface may exhibit greater sensitivity than does a film of the same material because nanowires have a greater surface area.

Four Gold-Nanowire-Mat Sensors were exposed to various concentrations of Hg in air at a temperature of 25 °C and a relative humidity of about 30 percent.
In preparation for experiments to demonstrate this sensor concept, sensors were fabricated by depositing gold nanowires, variously, on microhotplate or microarray sensor substrates. In the experiments, the electrical resistances were measured while the sensors were exposed to air at a temperature of 25 °C and relative humidity of about 30 percent containing mercury at various concentrations from 2 to 70 ppb (see figure). The results of this and other experiments have been interpreted as signifying that sensors of this type can detect mercury at ppb concentrations in room-temperature air and can be regenerated by exposure to clean flowing air at temperatures <40 °C.

The responses of the experimental sensors were found to be repeatable over a period of about 4 months, to vary approximately linearly with concentration from 2 to 20 ppb, and to vary somewhat nonlinearly with concentration above 20 ppb. Although mercury concentrations were found to be measurable down to 2 ppb, the limit of sensitivity may be lower than 2 ppb: Experiments at lower concentrations had not yet been performed at the time of reporting the information for this article.

This work was done by Margaret Ryan, Abhijit Shevade, Adam Kisor, and Margie Homer of Caltech; Jessica Soler of Glendale City College; and Nosang Myung and Megan Nix of the University of California, Riverside, for NASA’s Jet Propulsion Laboratory. NPO-44787

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Detecting Airborne Mercury By Use of Gold Nanowires

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NASA Tech Briefs Magazine

This article first appeared in the July, 2009 issue of NASA Tech Briefs Magazine (Vol. 33 No. 7).

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Overview

The document discusses a NASA project (NPO 44787) focused on detecting airborne mercury using gold nanowires, particularly in the context of the International Space Station (ISS). The concern arises from the presence of mercury in light bulbs aboard the ISS, where a broken bulb could expose astronauts to harmful levels of mercury. Traditional mercury detection methods have relied on amalgam formation with metals like gold, iridium, palladium, platinum, rhodium, and aluminum. However, these methods require high temperatures (up to 200 °C) for regeneration, which is not ideal for space applications.

To address this issue, researchers at the Jet Propulsion Laboratory (JPL) developed sensors made from gold nanowires. These nanowires were created at the Nano Electrochemical System Laboratory at the University of California, Riverside, and were designed to be deposited as a mat on JPL microhotplate or microarray sensor substrates. The sensors were tested for their response to mercury concentrations ranging from 2 to 70 parts per billion (ppb) in humidified air. The results showed that the gold nanowire sensors provided a repeatable response to mercury and could regenerate in flowing clean air at temperatures below 40 °C, significantly lower than traditional sensors.

The novelty of this approach lies in the ability of the gold nanowire sensors to operate at room temperature, offering a more efficient and lower power solution compared to conventional mercury sensors that require elevated temperatures and frequent replacements. Over a testing period of four months, the nanowire sensors demonstrated consistent performance, making them a promising candidate for inclusion in the 3rd Generation Electronic Nose, a project aimed at enhancing environmental monitoring in space.

The document emphasizes the potential broader applications of this technology beyond aerospace, highlighting its relevance in various fields where mercury detection is critical. For further inquiries, contact information for JPL's Innovative Technology Assets Management is provided, indicating the ongoing commitment to advancing research and technology in this area. Overall, the development of gold nanowire sensors represents a significant advancement in the safe monitoring of hazardous substances in confined environments like the ISS.