Stephen Brown
Publications
R.
Stephen Brown
B.Sc., 1985, Dalhousie University;
M.Sc., 1988, University of Toronto
Ph.D., 1992, University of Toronto.
Chernoff Hall, CHE 404 (Office), CHE 330 (Lab)
(613) 533-6000 ext. 32655 (Office)
(613) 533-6000 ext. 74499 (Lab)
e-mail: browns@chem.queensu.ca
The main goal of my research group is the development of new methods of environmental
analysis, with emphasis on detecting small organic compounds in aqueous samples. This
requires development of instruments and chemical/biochemical assays to provide sensitive
and selective measurement of a particular contaminant.
Developing a complete analysis procedure occurs in three main steps:
- Design of the instrument;
- Development of the
chemistry and biochemistry to detect the contaminant;
- Combination of the
detection method with the instrument.
1) We mainly use optical signals for the analysis, so major components of the
instrument design are lasers, fibre-optics and light detectors. Our signal of choice is
fluorescence (compounds which absorb u.v. light but then emit visible light), because of
its sensitivity. The basic design of the instrument (see diagram)
uses a laser radiation source, a single optical fibre, a monochromator for separating the
different laser and sample wavelengths, and a photomultiplier light detector. A
‘perforated’ mirror (small hole in center) is used to redirect the signal
emerging from the optical fibre toward the detector. For different analysis methods, the
optimum components (laser type, wavelength, optical fibre material, etc.) must be
determined using various criteria. Since these instruments are generally not available
‘off the shelf’, we must also do custom assembling, electronics, computer
interfacing and programming.
2) For some environmental contaminants, there are simple chemical methods for detection
using coloured or fluorescent reagents. In these cases, we can adapt the standard methods
for remote or on-line measurements. Often, however, a method is not available, and we must
identify a scheme which will work for a sample of interest. The unique approach which our
group uses is the application of enzymes as selective catalysts for environmental
analysis. Currently, a great deal of research is proceeding in the characterization of
enzymes which degrade contaminants in the environment. As these enzymes are isolated and
purified, we can then develop biochemical enzyme assays which detect similar contaminants.
In methods which we have already developed, chlorinated phenols and polycyclic aromatic
hydrocarbons (PAHs) were detected, with the enzymes providing selectivity and increased
sensitivity to the analysis.
3) Combining steps 1) and 2) involves advancing from remote detection using the
environmental analysis methods to development of true fibre-optic chemical sensors. This
requires incorporating the detection method into the optical fibre light-guiding process.
For enzyme-based methods, this means immobilizing the enzyme (and possibly other reagents)
onto the optical fibre surface. There are many immobilization schemes available, but the
best one for a particular enzyme must be identified and possibly modified, considering
optical properties, enzyme stability and response. Working sensors can then be tested on
real samples for a final evaluation of overall performance.
