Extramural Research
Publications
Grantee Research Project Results
Investigators: William C. Trogler and Michael J. Sailor
Institution: University of California, San Diego
ABSTRACT: Selective solid-state sensors for chromium(VI) and arsenic(V)
based on redox quenching of the luminescence from nanostructured porous
silicon and polysiloles will be reported. Tetraphenyl(polysiloles), copolymers,
and corresponding germanium derivatives have been shown to sense electron
acceptor molecules such as nitroaromatics either in the vapor phase or in
aqueous solution. Detection at ppt levels is achieved by quenching of the
intense green luminescence of the polymers by excited state electron transfer
to analyte. Colloidal nanoparticulate (~120 nm by atomic force microscopy)
suspensions of these polymers materials display increased sensitivity toward
chromate detection; however, nitrate and perchlorate show only a weak quenching
ability. Colloidal suspensions of luminescent tetraphenylsiloles and functionalized
tetraphenylsilole monomers have been prepared. The detection sensitivity
can be enhanced to determine sub ppm levels of analyte by addition of surface
ionizable groups, such as amines. Arsenate, another drinking water contaminant
of concern, can also be detected using this approach. Work has also focused
on surface functionalization as a means to enhance binding of the chromate
and arsenate anions to nanostructured porous silicon photonic crystals,
and to stabilize the material towards oxidation in air and water environments.
In the present funding period we showed that replacing residual Si-H species
on the surface with methyl groups could increase the chemical stability
of porous silicon. We found that functionalized porous silicon surfaces
can be reductively coupled with iodomethane (CH3I), resulting in replacement
of most of the remaining Si-H bonds. 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.
The use of the modified nanostructures as concentrators for environmental
pollutants will be discussed.