[Home Page] [Teaching]

RESEARCH

Work In Progress

My student colleagues and I are currently working in two fairly distinct areas: inorganic glass synthesis and thin metal film optical sensors.

Recent students in  my group include (Bold indicates currently active): 

The two major areas of research in my laboratories: 1. multi-mode surface plasmon sensing and 2. lanthanide-based electroluminescent materials.

The first area concerns an optical phenomenon called surface plasmon resonance (SPR).  In a typical SPR experiment, a light beam is reflected off of a 500Å gold film.  Under certain precisely defined conditions the reflectivity spectrum of this Au film is extremely sensitive to the presence or absence of molecular adsorbates on the gold film.  In this capacity, SPR has emerged as the premier tool for the measurement of biomolecular interactions.  If a biomolecule (probe) of interest can be tethered to the Au surface, then both kinetic and thermodynamic information for interaction with a target can be obtained.  SPR sensors respond through the extreme sensitive of the SPR effect to near surface refractive index changes (Dn_SURFACE).

We are exploring experimental and computational methods of performing SPR spectroscopy that add molecule-specific information, e.g. spectroscopic fingerprints, to the precise Dn_SURFACE information.  One way we have done this is by expanding the measurement from one dimension, i.e. reflectivity (R) versus wavelength (l) or angle (q), to two i.e. R(l,q).  Two-dimensional reflectivity surfaces encode far more information than one-dimensional spectra, and in favorable cases contain spectral signatures of the adsorbate. [1]  Currently we are exploring near- and mid-infrared frequency measurements in search of a set of conditions where both refractive index and spectroscopic signatures can be obtained simultaneously for target adsorbates.  Such an achievement would add tremendously to the SPR technique because it would allow both detection and identification of target analytes.

In the second experimental area, we seek to adapt the ideas of solid-state electrogenerated chemiluminescence to the area of lanthanide-ion based photonic devices.  The basic idea is this – electroactive molecules in the solid state behave similarly to semiconductors because they transport electrons along a fixed energy level related to the oxidation (or reduction) potential of the constituent molecules.  In 1996 Karolyn Maness and I demonstrated the electrochemical equivalent of the light emitting diode.[2]  This system was based on a ruthenium polypyridine and emitted in the red.  A far more interesting system would exploit the naturally narrow bandwidths of the lanthanide ions.  Our investigations to date have involved lanthanide ions in fluoride glasses – mixtures of metal fluorides that when quenched from a melt yield fluoride ion conducting glasses with excellent near IR transmission and lanthanide ion photophysics.