Sensitivity portable instrumentation

The detector in a spectrometer must produce a signal related to the intensity of the radiation falling on it. For instruments operating in the visible region a photovoltaic or barrier-layer cell is the simplest and cheapest available. Current produced when radiation falls on a layer of a semiconductor material, e.g. selenium, sandwiched between two metallic electrodes, is proportional to the power of the incident radiation and can be monitored by a galvanometer. Barrier layer cells are robust and are often used in portable instruments but they are not very sensitive and tend to be unstable during extended use. 

Optical fiber detectors (OFD) are devices that measure electromagnetic radiation transmitted through optical fibers to produce a quantitative signal in response to the chemical or biochemical recognition of a specific analyte. Ideally, an OFD should produce a specific and accurate measurement, continuously and reversibly, of the presence of a particular molecular species in a given sample medium. Additionally, OFD should pro vide maximum sensitivity and minimal interferences fromsuperfluous ions or molecules to obtain low detection limits. Other attractive features include the miniaturization of the fiber s tip to accommodate single-cell analysis and portable instrumentation to allow in situ analysis. 

Experiments to date have shown that a portable instrument incorporating a thoughtfully chosen array of sensors can detect, identify, and quantify a wide variety of chemicals in air. Also, pattern recognition techniques are being used to understand the information content of the arrays and to focus future experimental work. Development of smaller, more sensitive, and more reliable electrochemical sensors will expand the applications of the system described here. 

Metal labels have been proposed to resolve problems connected with enzymes. Metal ions [13-16], metal-containing organic compounds [17,18], metal complexes [19-21], metalloproteins or colloidal metal particles [22-28] have served as labels. Spectrophotometric [22,25], acoustic [25], surface plasmon resonance, infrared [24] and Raman spectroscopic [28] methods, etc. were used. A few papers have been dealing with electrochemical detection. However, electrochemical methods of metal label detection may be viewed as very promising taking into account their high sensitivity, low detection limit, selectivity, simplicity, low cost and the availability of portable instruments. 

Beside different kinds of nanocrystals (or QDs) AuNPs are showing a special interest in several applications. Electrochemical methods used for AuNPs label detection may be very promising taking into account their high sensitivity, low detection limit, selectivity, simplicity, low cost and availability of portable instruments. 

Arduini, F., Amine, A., Moscone, D., Ricci, F., Palleschi, G. (2007). Fast, sensitive and cost-effective detection of nerve agents in the gas phase using a portable instrument and an electrochemical biosensor. Anal. Bioanal. Chem. 388 1049-57. 

The application of the ASV technique to the analysis of seawater has been reviewed (6-9). Its advantages over other trace-metal methods are several (1) sea salts do not interfere (2) a high degree of sensitivity and selectivity can be achieved through electrolytic preconcentration, thus the analysis can be carried out directly in seawater, and few or no reagents need to be added (3) the measurement is easily automated (4) relatively inexpensive, rugged, and portable instrumentation can be built for field use (5) more than one metal may be measured at one time with a sensitivity approaching parts per trillion. 

A more recent, and very promising, development is due to Cohen and James, who adapted a position-sensitive proportional counter to stress measurement. This counter has the great advantage that it can measure the 29 position of a diffracted beam without a 29 movement of the counter (Sec. 7-5). Preliminary work was done with the counter mounted on a standard diffractometer [16.10]. Later a portable instrument was made, in which the counter and a miniature, air-... 

Rb, Mo, Ag. Ba, Tb). In this way a number of excitation lines can be produced. The advantages of these radioactive sources lie in their simplicity and small size as well as their independence ofelectrical power. Thus they are suited to portable instruments. Spectra obtained from fluorescent emission show much better resolution than primary X-ray spectra as they lack the continuum background, figure 8.27. Consequently sensitivity and precision are rather better for fluorescence methods than they are for electron excitation techniques. ... 

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