Project Update Archive
Project 5: Nanotechnology-based environmental sensing
2009
The goal of Project 5 is to develop easier, smaller, and/or less expensive methods to detect and quantify toxic chemical species found at current or potential Superfund sites. Improved sensors and diagnostics could reduce the cost of monitoring, help improve remediation methods, and more accurately assess the health risks associated with these hazardous and toxic species.
We focus on the use of engineered nanotechnology-based sensing methods using gold and silver nanoparticles of various sizes and shapes. These engineered nanomaterials (with dimensions of less than 100 nanometers) have unique properties that differ from conventional bulk materials, especially in their interactions with light. Developing new and more complex nanostructures also increases our understanding of how localized surface plasmons are affected by the shape, symmetry, proximity, and size of the nanoparticles.
We continue progress towards a functional detector for groundwater contaminants such as arsenic species. We have now developed a new method to chemically control the shape of silver nanocrystals by using a highly anisotropic etching process. Tuning of the etchant strength and reaction conditions allows the preparation of novel nanoparticle shapes in high yield and purity, which cannot be synthesized with conventional nanocrystal growth methods. The fine control of this process affords access to drastically modified plasmonic characteristics of these particles, making possible wavelength-tunable, single-particle Surface Enhanced Raman Spectroscopy (spSERS). These etched particles possess unique structural features and have been shown to exhibit spSERS signal 30 times stronger than the parent unmodified structures, making them very appealing for Raman tagging application. Importantly, these spSERS active nanoparticles are highly sensitive towards non-resonant analytes. The development of such spSERS active nanostructures represents an important step toward a general sensing platform which could be used to sense multiple analytes simultaneously using different excitation sources.
We also continued work on developing mercury detectors using gold nanorods. Nanorods with dimensions on the order of 40 nm long and 15 nm wide have shown the greatest sensitivity to elemental mercury, with concentrations of 3 ng/l of mercury in water producing a shift of approximately 20 nm in the surface plasmon resonance peak, a change easily seen with a relatively simple ultraviolet spectrometer system. We developed a method to coat single layers of these nanorods onto quartz substrates, which stabilizes the particles, especially after exposure to mercury. The particles remain isolated on the substrate, which prevents coagulation of the rods that affects their spectral properties.
2008
Drs. Catherine Koshland and Donald Lucas research objective is to develop easier, smaller, and/or less expensive methods to detect and quantify toxic and/or hazardous chemical species found at existing or potential Superfund sites. New sensors and diagnostics could reduce the cost of monitoring, help improve remediation methods, and more accurately assess the health risks associated with these hazardous and toxic species. Their focus is on the use of nanotechnology-based sensing methods, since nanomaterials often have unique properties that differ from conventional bulk materials.
Project researchers have made significant progress towards a functional arsenic detector in ground water using a nanostructured SERS substrate. Using close-pack arrays of octahedral shaped silver nanocrystals, the researchers demonstrated the chemical sensing of arsenic ions with detection limits as low as 1 part per billion in solution. Their sensor is based on surface-enhanced Raman spectroscopy (SERS), where analyte molecules near nanostructured metallic surfaces experience huge enhancements in Raman scattering cross-sections, typically orders of magnitude higher than expected. The nature of vibrational spectroscopy allows them to simultaneously probe for arsenic in both of the commonly found oxidation states and discriminate between the two. This is important since the different oxidation states have different toxicities.
The detection is performed directly on the substrate by placing a droplet of the analyte solution onto the nanocrystal monolayer, with no additional sample preparation required. These substrates have been verified to work in the presence of known competing anions, and have been used to accurately characterize the arsenic levels in polluted well water obtained by collaborators in Nevada. Future work in this direction will include characterization of differently shaped nanocrystals and optimization of the SERS enhancement factor on each of these substrates.
The group continued work on developing elemental mercury detectors using gold nanoparticles. They have successfully used different techniques to immobilize the 5 nm diameter gold nanoparticles on a substrate using organosilanes to link the gold to the silica surface; this prevents coagulation and improves the sensor performance. The detector works for mercury in both the vapor phase and in the aqueous phase. The reserachers have determined that the attachment of the mercury to the gold nanoparticles is reversible at temperatures that do not damage the sensor. This finding opens a potential means of practical filtering of mercury from waste streams, since the nanoparticles have an extremely high surface area to volume ratio, and can be produced at reasonable costs. Additional work on avoiding cross-sensitivity to other pollutant species continues, using either physical or chemical barriers to prevent other species from reaching the gold surface.
The researchers also use microfabricated channels to detect and characterize individual cells based on their cell-surface receptors. The method involves measuring a current pulse generated when an individual cell passes through an artificial pore. When the pore is functionalized with proteins, specific interactions between a cell-surface marker and the functionalized proteins retard the cell, leading to an increased pulse duration that indicates the presence of that specific biomarker. The researchers successfully screened murine erythrolukemia cells based on their CD34 surface marker in both a single and mixed population of cells.
2007
The goal of The Nanotechnology-based Environmental Sensing project is to develop easier, smaller, and/or less expensive methods to detect and quantify toxic and/or hazardous chemical species found at existing or potential Superfund sites. New sensors and diagnostics could reduce the cost of monitoring, help improve remediation methods, and more accurately assess the health risks associated with these hazardous and toxic species. Dr. Catherine Koshland and Dr. Donald Lucas have focused on the use of nanotechnology-based sensing methods, since nanomaterials often have unique properties that differ from conventional bulk materials.
Kishland and Lucas have made significant progress towards a functional arsenic detector in ground water using a nanostructured SERS substrate. Using close-pack arrays of octahedral shaped silver nanocrystals, they demonstrated the chemical sensing of arsenic ions with detection limits as low as 1 part per billion in solution. The sensor is based on surface-enhanced Raman spectroscopy (SERS), where analyte molecules near nanostructured metallic surfaces experience huge enhancements in Raman scattering cross-sections, typically orders of magnitude higher than expected. The nature of vibrational spectroscopy has allowed the research group to simultaneously probe for arsenic in both of the commonly found oxidation states and discriminate between the two. This is important since the different oxidation states have different toxicities.
The detection is performed directly on the substrate by placing a droplet of the analyte solution onto the nanocrystal monolayer, with no additional sample preparation required. These substrates have been verified to work in the presence of known competing anions, and have been used to accurately characterize the arsenic levels in polluted well water obtained by collaborators in Nevada. Future work in this direction will include characterization of differently shaped nanocrystals and optimization of the SERS enhancement factor on each of these substrates.
Kishland and Lucas continued work on developing elemental mercury detectors using gold nanoparticles. The investigators have successfully used different techniques to immobilize the 5 nm diameter gold nanoparticles on a substrate using organosilanes to link the gold to the silica surface; this prevents coagulation and improves the sensor performance. The detector works for mercury in both the vapor phase and in the aqueous phase. Research has determined that the attachment of the mercury to the gold nanoparticles is reversible at temperatures that do not damage the sensor. This finding opens a potential means of practical filtering of mercury from waste streams, since the nanoparticles have an extremely high surface area to volume ratio, and can be produced at reasonable costs. Additional work on avoiding cross-sensitivity to other pollutant species continues, using either physical or chemical barriers to prevent other species from reaching the gold surface.
The Berkeley research team also uses microfabricated channels to detect and characterize individual cells based on their cell-surface receptors. The method involves measuring a current pulse generated when an individual cell passes through an artificial pore. When the pore is functionalized with proteins, specific interactions between a cell-surface marker and the functionalized proteins retard the cell, leading to an increased pulse duration that indicates the presence of that specific biomarker. Murine erythrolukemia cells have been successfully screened based on their CD34 surface marker in both a single and mixed population of cells.
2006
The goal of the Nanotechnology-based Environmental Sensing project is to develop easier, smaller, and/or less expensive methods to detect and quantify toxic and/or hazardous chemical species found at existing or potential Superfund sites. New sensors and diagnostics could reduce the cost of monitoring, help improve remediation methods, and more accurately assess the health risks associated with these hazardous and toxic species. The project researchers’ focus is on the use of nanotechnology-based sensing methods, since nanomaterials often have unique properties that differ from conventional bulk materials.
Charged particles are needed for most aerosol nanoparticle measuring techniques. Project researchers have achieved considerable success in developing a method for charging nanoparticles so they all have the same type of charge. This unipolar charger significantly improves particle detection for the smallest nanoparticles (less than 10 nanometers in diameter) that are the hardest to accurately measure.
In new work under this project, the researchers used small (typically less than 5 nm diameter) gold particles to detect elemental mercury. The gold nanoparticles absorb visible light and the absorption increases and shifts in color when mercury containing vapor is bubbled through the solution. The change in absorption is readily quantified using a simple UV/Vis spectrometer. A color change is observed in a few minutes when mercury vapor is present at the parts-per-million level. Project researchers also place the gold nanoparticles on glass surfaces to reduce their coagulation and improve the stability of the sensor. The glass surface can then be used as a simple mercury detector simply by exposing the glass to mercury-contaminated air. As the exposure to mercury vapor increases, the absorption peak shifts to the blue end of the spectrum and the absorbance increases.
The project researchers examined coated silver nanoparticles to detect arsenic, especially the arsenate ion. The method uses different shapes and sizes of silver to improve the detection of metals using surface enhanced Raman spectroscopy – in the best cases, detection limits can be improved by over a factor of a trillion. Project researchers are examining methods to improve the interaction of arsenate with the silver surface by modifying the surface of the silver nanostructures. So far cubes with 3.2, 1.6, and 0.8 nm coatings of Al2O3 have been isolated and characterized.
The researchers use microfabricated channels to detect particles as they pass through the small pores. As the particles pass the electrical properties change, giving us a method to measure properties such as concentration and size. Project researchers have used this resistive-pulse technique of particle sizing to measure the size of individual soot particles made in their laboratory. The overall range in size, from 150 nm to 500 nm is in good agreement with data obtained with the electron microscopy (150 – 650 nm). Similar techniques will be used in future experiments to measure biomolecules proposed for use in remediation of at Superfund sites.