Three major causes of corrosion of steel in concrete are chloride ions (Cl-), temperature (T) and acidity (pH). Under normal operating temperatures and with pH above 13, steel does not undergo pitting corrosion. In presence of Cl-, if the pH decreases below 12, the probability of pitting increases. Acid rain and atmospheric carbon dioxide cause the pH to drop in concrete, often leading to corrosion of the structure with the concomitant cost of repair or replacement. Currently, the pH level in concrete is estimated through destructive testing of the structures. Glass ISFET, and other pH sensors that need maintenance and calibration cannot be embedded in concrete. In this paper, we describe an inexpensive solid state pH sensor that can be embedded in concrete, to detect pH changes at the early stages. It employs a chemical reagent, trinitrobenzenesulfonic acid (TNBS) that exhibits changes in optical properties in the 12 - 14 pH range, and is held in a film of a sol-gel/TNBS composite on an optically transparent surface. A simple LED/filter/photodiode transducer monitors pH-induced changes in TNBS. Such a device needs no periodic calibration or maintenance. The optical window, the light-source and sensor can be easily housed and encapsulated in a chemically inert structure, and embedded in concrete.
A new immunoaffinity fluorometric biosensor has been developed for detecting and quantifying aflatoxins, a family of potent fungi-produced carcinogens that are commonly found in a variety of agriculture products. They have also been cited as a biological agent under weapons development. The handheld, self-contained biosensor is fully automatic, highly sensitive, quick, quantitative, and requires no special storage. Concentration from 0.1 parts per billion to 50 ppb can be determined in less than 2 minutes with a 1 ml sample volume. Higher concentrations can be determined by simply reducing the sample volume. The device operates on the principles of immunoaffinity for specificity and fluorescence for a quantitative assay. The analytic procedure is flexible so that other chemical and biological analytes could be detected with minor modifications to the current device.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is designing, fabricating and testing a small, high resolution, time-of-flight mass spectrometer (TOFMS) suitable for biomedical applications requiring lightweight, low-powered and portable instrumentation. This instrument can be used to identify solids, liquids and gases of both chemical and biological origins to quantify the habitat environment and support biomedical research and medical care. The virtue of the JHU/APL TOFMS technology presented here, resides in the promise for a small, lightweight, low- power, device that can be used continuously with advanced signal processing diagnostics. To date, JHU/APL has demonstrated mass capability beyond 10,000 Atomic Mass Units in a very small, low power prototype for biological analysis. The JHU/APL approach, described in this paper, is to design the instrument for both wide mass range and fine mass resolution by the use of electronic control in a tandem mass spectrometer instrument. In this paper we will outline the principle behind the operation of the APL's miniaturized TOFMS system and present examples of the analysis of chemical and biological substances. In addition, we will also describe a novel method for the collection of airborne particles for TOFMS analysis suitable for automated collection and analysis applications.
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