Impedance based sensing of the specific binding reaction between Staphylococcus enterotoxin B and its antibody on an ultra-thin platinum film.

Immunobiosensing techniques to measure specific antigen-antibody binding reactions are important in the development of biosensor applications in biotechnology, in vitro diagnosis, medicine and food technology. An immunobiosensor was constructed to measure the specific binding reaction between Staphylococcus enterotoxin B (SEB) and anti-SEB antibodies. The biosensor comprised an anti-SEB bioactive layer covalently immobilized on an ultra-thin platinum (Pt) film sputtered onto a 100 nm thick silicon dioxide layer on a silicon chip. The Pt film was discontinuous with a normal thickness of 25 A. The impedance of the Pt film decreased during the binding of the anti-SEB to SEB in phosphate buffered saline (PBS) at room temperature. The impedance decreases were irreversible in PBS before saturation of the specific binding sites. When saturated, the impedance at 100 Hz was 14% of the value obtained for the fresh anti-SEB layer in PBS. The magnitude of the impedance (Z) decrease followed a simple relationship with SEB concentration in the range between 0.389 and 10.70 ng/ml SEB. The specificity of the biosensor was demonstrated by showing that no irreversible impedance decreases occurred when the sensor was exposed to 100 ng/ml kappa-casein, or alpha-lactalbumin, in PBS.

Preliminary evaluation of an active end-of-service-life indicator for organic vapor cartridge respirators.

Data are presented on a microwatt chemiresistor microsensor for use with negative-pressure organic vapor respirators. This sensor would operate at or within a sorbent bed and detect parts per million levels of chemical vapors and/or gases as a function of sensor resistance. Sensors were evaluated against four challenge concentrations of ethyl acetate (750 ppm, 1000 ppm, 1500 ppm, and 2000 ppm). Direct comparison of breakthrough times and curves for the chemiresistor microsensor and a standard infrared (IR) detector system were made. The chemiresistor sensor responses were found to correlate well with the IR system. The evaluation showed that although the chemiresistor sensors were not as sensitive as the IR detectors, they could be used if located inside the charcoal bed. Thus, these sensors could function as organic-vapor detectors and could be used in cartridge applications. However, further improvements in stability and sensitivity of these chemiresistor sensors is necessary.

An optical waveguide acid vapor sensor.

An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths.

Use of the Curtis-Godson approximation in calculations of radiant heating by inhomogeneous hot gases.

Calculations of radiant heating by inhomogeneous hot gases require knowledge of spectral transmittances of inhomogeneous optical paths. Determination of these transmittances is a difficult problem that can be attacked by means of the Curtis-Godson approximation, which replaces each inhomogeneous optical path with a hypothetical homogeneous path that has the same transmittance. The authors have tested the accuracy of the Curtis-Godson approximation experimentally. Infrared spectral transmittances of inhomogeneous hot samples of H(2)O and CO(2) were measured. Each inhomogeneous hot gas specimen consisted of two or three homogeneous zones in series. The transmittance of each zone was measured, as was the transmittance of the entire multizone assembly. The measured transmittance of each inhomogeneous path was compared with a transmittance calculated from the homogeneous zonal transmittances, using the Curtis-Godson approximation in conjunction with a random band model. The measured and calculate inhomogeneous transmittances concurred to within about 0.02. The error appeared to be due more to the band model theory than to the Curtis-Godson approximation.