Grantee Research Project Results
2002 Progress Report: Nanostructured Porous Silicon and Luminescent Polysiloles as Chemical Sensors for Carcinogenic Chromium(VI) and Arsenic(V)
EPA Grant Number: R829619Title: Nanostructured Porous Silicon and Luminescent Polysiloles as Chemical Sensors for Carcinogenic Chromium(VI) and Arsenic(V)
Investigators: Trogler, William C. , Sailor, Michael J.
Institution: University of California - San Diego
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 2002 through December 31, 2004
Project Period Covered by this Report: January 1, 2002 through December 31, 2003
Project Amount: $400,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The main objective of this research project is to develop new selective solid state sensors for chromium(VI) and arsenic(V) based on redox quenching of the luminescence from nanostructured porous silicon and polysiloles. There are several research components to the problem. The focus on chromium(VI) and arsenic(V) detection is dictated by the redox quenching mechanism that is being used, as well as by the importance of chromium(VI) and arsenic(V) as regulated chemicals under the Safe Drinking Water Act.
Progress Summary:
Tetraphenyl(polysiloles), copolymers, and corresponding germanium derivatives have been developed as excellent sensor materials for electron acceptor nitroaromatics, such as trinitrotoluene (TNT), either in the vapor phase or in aqueous solution. Detection at ppt levels is achieved by quenching the intense green luminescence of the polymers via excited state electron transfer to analyte. The hydrophobic nature of polysiloles precludes the detection of ionic oxidants, such as chromate, which have no affinity for these hydrophobic materials. Colloidal nanoparticulate (~120 nm by atomic force microscopy) suspensions of these polymeric materials display increased sensitivity toward chromate; however, nitrate and perchlorate show only a weak quenching ability. Colloidal suspensions of luminescent tetraphenylsiloles and functionalized tetraphenylsilole monomers, which are analogues of solid state particulate and quantum dot sensors, have been prepared. The detection sensitivity can be enhanced to determine sub-ppm levels of analyte by the addition of surface-ionizable groups, such as amines. Even arsenate, another drinking water contaminant of great concern, can be detected by this approach. Stabilization of nanoparticles by coating with SiO2 is being explored. A novel dehydrocoupling route to the synthesis of polysiloles and polygermoles has been developed, which improves the yield by two- to three-fold. It employs tetrakis-(triphenylphosphine)palladium(0) or Wilkinson’s catalyst in refluxing toluene and the corresponding silole or germole dihydride as monomer.
In the current period of funding, our work has focused on surface functionalization as a means to enhance the binding of the chromate and arsenate anions to porous silicon, and to stabilize the material against oxidation in air and water environments. In the present funding period, we showed that the chemical stability of porous silicon can be increased by replacing residual Si-H species on the surface with methyl groups (see Equation 1). Reacting a previously modified surface with a smaller reagent to "cap off" sites left unreacted by larger moieties has been used successfully in the synthesis of silica-based packings for reversed-phase chromatography. We found that functionalized porous silicon surfaces can be reductively coupled with iodomethane (CH3I), resulting in the replacement of most of the remaining Si-H bonds. The high degree of surface coverage obtained by methylation has been previously reported, but the extension to mixed surfaces has not been explored. Several experiments designed to quantify the stability of the modified porous silicon samples were performed, involving the use of chemical oxidants and solutions that mimic those used in bioassay applications or that might be encountered in environmental sensor applications.
Equation 1:
The microporous material will readily admit small inorganic analytes, such as chromate and arsenate, and exclude biomolecules that might confound the measurements. The sensors need to be compatible with silicon microcircuit fabrication technology. Subtasks accomplished during Year 1 of the research project included the development of an etching tool for automated preparation of multilayer porous silicon structures (Bragg stacks), development of the chemistry to stabilize PSi films in harsh environments, and construction of a prototype device for pollutant detection. The etching tool has been completed, and the prototype is still under construction.
Future Activities:
Future work will focus on continuing the development of sensors for chromate and arsenate begun during Year 1 of the project as outlined in detail in the accomplishments section. The main objective for Year 2 of the project is to interface the porous silicon and polymer sensors.
With luminescent porous silicon (PSi), surface functionalization, as well as polymer coatings, will be tested as ways to enhance binding of the chromate and arsenate anions. Highly luminescent polysiloles that are chain-terminated with anion binding regions also will be explored as chromate and arsenate sensors. Chemical modification to vary the redox potential of the polysilole excited state will be used as a way to impart chemical selectivity. Both approaches will be combined by encapsulating the polysilole in a nanotextured microcavity between two Bragg stacks constructed from porous silicon. Such devices have been shown to provide significant detection sensitivity enhancements. The nanoporous material will readily admit small inorganic analytes, such as chromate and arsenate, and exclude biomolecules that might confound the measurements.
Journal Articles:
No journal articles submitted with this report: View all 25 publications for this projectSupplemental Keywords:
heavy metals, effluent, discharge, ecosystem, indicators, aquatic, nanotechnology, innovative technology, chemistry, optics, monitoring, analytical, measurement methods, electroplating industry, mining, groundwater., RFA, Scientific Discipline, Toxics, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Sustainable Industry/Business, National Recommended Water Quality, Physics, Environmental Chemistry, Sustainable Environment, Arsenic, Chemistry, Technology for Sustainable Environment, Monitoring/Modeling, Analytical Chemistry, Biochemistry, New/Innovative technologies, Chemistry and Materials Science, Water Pollutants, Engineering, 33/50, Environmental Engineering, biosensing, nanosensors, environmental monitoring, chemical sensors, chromium & chromium compounds, nanotechnology, environmental sustainability, polysiloles, environmentally applicable nanoparticles, chemical sensor, nanostructured porous silicon, carcinogens, sustainability, water quality, innovative technologiesRelevant Websites:
http://www-chem.ucsd.edu/Faculty/bios/trogler.html Exit
http://www-chem.ucsd.edu/Faculty/bios/sailor.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.