Superfund Research Program
Nanotechnology-Based Environmental Sensing
Studies and Results
The nanotechnology-based environmental sensing project was designed primarily to develop a sensor to detect mercury in environmental samples. Heavy metals such as mercury continue to pose significant human and environmental health risks and are found in many Superfund sites. Development of cheap, sensitive mercury sensors that can be used in remote locations and developing countries could reduce the exposure of humans and animals. Research, testing, and analysis was completed and an Administrative Supplement was obtained to support the development and manufacture of the sensor.
Based on previous research in the nanotechnology-based environmental sensing project, this Administrative Supplement Core's aim was to develop and manufacture a cheap and effective sensor of environmental mercury contamination. They looked at peaks in absorbance caused by localized surface Plasmon resonance (LSPR). Mercury causes changes in the composition and refractive index of nanoparticles, causing a shift in observable peak absorbance.
Their research led to the development, design, construction, and testing of a robust mercury-sensing prototype device. With this device, they were able to measure ng/m3 concentrations of mercury in samples they obtained. They tested the prototype for interferences from possible co-existing contaminants. On a heated stage the nanoparticle film shows no response to water vapor, carbon dioxide (20%), sulfur dioxide (2000 ppm), and NOx (501 ppm). This is a key advantage of the technology compared to other spectrometry techniques for mercury measurement that show interferences from all of these contaminants. The levels tested were based on the high levels found in untreated coal exhaust. The Core manufactured films using the Langmuir-Blodgett method because it allows control over the packing density and produces uniform batches. Regenerating the films is easily done by heating them above 212 degrees farenheit, which vaporizes the mercury and frees space on the surface for repeated measurement.
The optical response of the sensor is directly proportional to the absorbed mercury mass, which is the intrgral of the vapor concentration. To return a value of concentration, the Core tracks the time derivative of the response. The tested dynamic range spans 4 orders of magnitude. By controlling the sample flow rate, they can provide equivalent time resolutions across a range of concentrations. They adapted EPA method 1631 for use with their plasmonic sensor. After oxidation/reduction, the elemental mercury vapor is collected and measured by the nanoparticle film. They showed the feasibility of aqueous detection with gold nanoparticle plasmonic transducer and directly detected mercury in ranges below the EPA limit. The mass limit of detection is ~5 pg, with only 2 atoms of absorbed mercury needed per particle for a measurable change in absorbance.
The cost of gold needed is miniscule, $0.0001 of gold per sensor chip. Operational costs are pennies per hour with low power requirements. The sensor can be built with off-the-shelf components. The advantages of their sensor are:
- Mercury vapor is collected and measured in a single step using a regenerating film of gold nanpoarticles, reducing contamination and measurement errors,
- Oxygen does not interfere with the measurement, so no inert gas is required,
- Uses solid state components and has a small footprint,
- Measures ambient mercury without sample preconcentration .
Gold nanoparticle-based mercury sensing is an inexpensive, simple, and robust technique for ultra-sensitive, continuous mercury detection. Cheap, sensitive sensors for measuring both elemental and total mercury concentrations would allow more measurements of these species in the environment, and could reduce the exposure of humans and animals.