Grantee Research Project Results
2003 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, 2003 through December 31, 2004
Project Amount: $400,000
RFA: Exploratory Research: Nanotechnology (2001) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
The 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 (PSi) and polysiloles. There are several research components to the problem. With luminescent PSi, surface functionalization as well as polymer coatings will be tested as methods 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 to impart chemical selectivity. Both approaches will be combined by encapsulating the polysilole in a nanotextured microcavity between two Bragg stacks constructed from PSi. 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. The focus on chromium (VI) and arsenic (V) detection is dictated by the redox quenching mechanism 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:
Colloidal solutions of functionalized tetraphenylsilole nanoparticles have been shown to detect carcinogenic chromium (VI) and arsenic (V) at low concentrations. The method of detection is based on the luminescence quenching of the silole by the electron accepting analyte. Although tetraphenylsilole is insensitive to simple inorganic oxidants, functionalization of the silole unit with hydrogen bonding substituents has been performed to incorporate binding regions for anionic oxidants, such as chromate and arsenate. Nanoparticle colloids of the silole show not only increased luminescence, but also much greater sensitivity in analyte detection. Fluorescence data were used to quantify analyte detection. During Year 2 of the project, we focused on characterizing the nanoparticles. We also focused on investigating the conditions that affect particle formation and yield the most sensitive chromium detection.
Fluorescence data were gathered on colloidal solutions of the nanoparticles and measured as a function of concentration, solvent composition, pH, and time. Nanoparticle solutions are prepared by adding water to a tetrahydrofuran solution of the silole, precipitating the colloid. A minimum of 75-80 percent water is necessary to affect any increase in luminescence based on silole aggregation, regardless of the concentration of silole or the pH of the solution. Higher silole concentrations have a sharper increase in luminescence between 70-99 percent water. It also was found that colloids precipitated from phosphate buffer solutions of pH 4, 7, or 10 show a twofold to fivefold increase in luminescence from those prepared with deionized water. In addition, luminescence intensity fluctuates over the first few hours, but it appears that after 5-10 hours, the particles stabilize and intensity decays slowly and steadily.
Several luminescence quenching experiments have been performed by adding a stock solution of chromium (VI) analyte to different colloidal silole solutions. It is clear that nanoparticle formation is necessary to detect any quenching by a small (0.1 ppm) amount of chromate. At least 80 percent water was necessary, correlating to the onset of aggregation. Highest quenching efficiencies were obtained with the 95 and 99 percent water concentration. A clearly detectable decrease in luminescence is achieved at the U.S. Environmental Protection Agency maximum contaminant level (MCL) of only 0.1 ppm chromium (VI). Photoluminescence quenching efficiencies were between 15.1 x 103 and 37.7 x 103 M-1. Linear Stern-Volmer plots were obtained. We will conduct fluorescence lifetime measurements to determine the quenching mechanism of the chromium and will repeat these measurements with arsenic.
We currently are performing dynamic light scattering experiments to determine the particle size of the colloid and how size varies with concentration, solvent composition, and pH. We already have performed these sizing experiments on the polysilole, a silole polymer capable of detecting TNT and other nitroaromatic explosives at ppb levels in water. The diameter of the polymer nanoparticles is on the order of 60-120 nm. It appears that they obtain some minimum size at 90 percent water and increase above or below that percentage. For a given water percentage, size does not depend heavily on concentration. As the dynamic light scattering experiment has been shown to be useful for the polysilole, we now will utilize this technique to determine particle size of the silole monomers. We then will be able to ascertain how particle size (i.e., extent of aggregation of monomer) is correlated to luminescence by comparing the data to previously gathered fluorescence data.
During this research project, we supported the following personnel: graduate students Steve Liu, Sarah Toal, Sarah Urbas, and Jamie Link; undergraduate student Jason Dorvee; and high school students Kelsey Jones and Pat Wang.
Future Activities:
We will develop a silole oligomer and polymer-based sensor with the analyte specific binding region to try and improve sensor selectivity and sensitivity at even lower concentrations. Fluorescence quenching studies will be performed with both chromium and arsenic. Light scattering and fluorescence lifetime studies will be performed on the monomer and then extended to these newly developed polymeric materials. Interfacing the PSi, metal, and polymer sensors is a future objective. The sensing platform (see Figure 1), which we have developed for the PSi sensors, is being adapted for use with the luminescent polymers.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 25 publications | 8 publications in selected types | All 6 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Cunin F, Schmedake TA, Link JR, Li YY, Koh J, Bhatia SN, Sailor MJ. Biomolecular screening with encoded porous-silicon photonic crystals. Nature Materials 2002;1(1):39-41. |
R829619 (2003) R829619 (Final) |
Exit |
Supplemental Keywords:
heavy metals, effluent, discharge, ecosystem, indicators, aquatic, nanotechnology, innovative technology, chemistry, optics, monitoring, analytical, measurement methods, electroplating industry, mining, groundwater, chromium (VI), Cr (VI) arsenic (V), As (V), porous silicon, PSi, luminescent polysiloles, nanoparticle colloids, fluorescence,, RFA, Scientific Discipline, Toxics, Water, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Sustainable Industry/Business, National Recommended Water Quality, Sustainable Environment, Physics, Environmental Chemistry, Chemistry, Arsenic, Technology for Sustainable Environment, Analytical Chemistry, Monitoring/Modeling, Biochemistry, New/Innovative technologies, Chemistry and Materials Science, Water Pollutants, Engineering, Environmental Engineering, 33/50, 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.