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Stephen Brown

 

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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.