A sensitive biosensor (cytosensor) has been developed based on color changes in the toxin-sensitive colored living cells of fish. These chromatophores are highly sensitive to the presence of many known and unknown toxins produced by microbial pathogens and undergo visible color changes in a dose-dependent manner. The chromatophores are immobilized and maintained in a viable state while potential pathogens multiply and fish cell-microbe interactions are monitored. Low power LED lighting is used to illuminate the chromatophores which are magnified using standard optical lenses and imaged onto a CCD array. Reaction to toxins is detected by observing changes is the total area of color in the cells. These fish chromatophores are quite sensitive to cholera toxin, Staphococcus alpha toxin, and Bordatella pertussis toxin. Numerous other toxic chemical and biological agents besides bacterial toxins also cause readily detectable color effects in chromatophores. The ability of the chromatophore cell-based biosensor to distinguish between different bacterial pathogens was examined. Toxin producing strains of Salmonella enteritis, Vibrio parahaemolyticus, and Bacillus cereus induced movement of pigmented organelles in the chromatophore cells and this movement was measured by changes in the optical density over time. Each bacterial pathogen elicited this measurable response in a distinctive and signature fashion. These results suggest a chromatophore cell-based biosensor assay may be applicable for the detection and identification of virulence activities associated with certain air-, food-, and water-borne bacterial pathogens.
Continuously tunable diode laser sources coupled to single-mode fiber are useful sources for fiber Bragg grating (FBG) strain sensors. A low-cost 1300 nm laser diode is anti-reflection coated making it nearly an LED. By coupling this coated laser to a short length of single-mode fiber containing a low-reflection FBG, which serves as
the new tunable laser output coupler, a tunable, fiber-coupled laser source is possible. The laser diode package is mounted in a temperature-controlled mount, and the FBG is mounted so it can be strained. By controlling both temperature and FBG strain, the laser can be continuously tuned across a 10 nm spectral range giving a narrow line laser source for use in strain sensors.
An optical fiber calcium ion sensor is developed through the exploitation of the natural selectivity of the Ca+2 binding
properties of the fluorescent probe Calcium Orange (Molecular Probes, Eugene, OR). A multi-mode optical fiber is used to detect calcium in solution. There is a two and a half fold increase observed between a 1 mM EGTA + buffer solution and a 1 mM Ca2+ solution. A variety of different methods of attaching the molecular probe to the end of the fiber are explored.
Research efforts in our department include work on novel GaAs/AlGaAs laser structures and photodetectors which could be used in fiber optic sensor applications. Brief descriptions are given of three such components: a HEMT- compatible, very low threshold diode laser; a high-gain traveling-wave amplifier or high-power, broad linewidth LED; and a MODFET photoconductor. A senior/graduate level course is also taught on guided wave optics. In this lecture/laboratory course, students do design projects on either fiber optic sensors or fiber communication systems. Two examples of student fiber sensor projects will be given: a pressure sensor and an interferometric temperature sensor.
The two-dimensional modeling of the
semi-insulating gallium arsenide (SI-GaAs) interdigitated
photodetectors is presented. The model considers full bipolar
transport, effects of nonuniform carrier generation, field
dependent mobilities, carrier diffusion, recombination and
includes the effects of the external circuit elements. Dynamic
simulation is performed after applying an ideal optical
impulse and the simulated response is compared with the
experimentally observed response.
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