Device immunosensors

Immunosensors promise to become principal players ia chemical, diagnostic, and environmental analyses by the latter 1990s. Given the practical limits of immunosensors (low ppb or ng/mL to mid-pptr or pg/mL) and their portabiUty, the primary appHcation is expected to be as rapid screening devices ia noncentralized clinical laboratories, ia iatensive care faciUties, and as bedside monitors, ia physicians offices, and ia environmental and iadustrial settings (49—52). Industrial appHcations for immunosensors will also include use as the basis for automated on-line or flow-injection analysis systems to analyze and control pharmaceutical, food, and chemical processing lines (53). Immunosensors are not expected to replace laboratory-based immunoassays, but to open up new appHcations for immunoassay-based technology. 

Conductometric transducers, as the oldest electrochemical devices, seem not to enjoy wide applications due to their poor selectivity. For example, Yagiuda et al. proposed a conductometric immunosensor for the determination of methamphetamine (MA) in urine [89], The decrease in the conductivity between a pair of platinum electrodes might result from the direct attachment of MA onto the anti-MA antibodies immobilized on the electrode surface. The system was claimed to be a useful detection technique of MA in comparison with a gas chromatography-mass spectrometry method. 

I. Willner and B. Willner, Electronic transduction of photostimulated binding interactions at photoisomerizable monolayer electrodes novel approaches for optobioelectronic systems and reversible immunosensor devices. Biotechnol. Prog. 15, 991-1002 (1999). 

The developed sensor was used for ultrathin-film measurement. The reflection spectrum was shifted during the deposition of thin films (e.g., self-assembly of polyelectrolyte layers) onto the sensor end. The reflection between the thin film and the fiber endface was neglected because of their similar refractive indices. As the film increased its thickness, the length of the fiber cavity changed. The amount of change was estimated by the phase shift of the interferogram. The device could also be used as an immunosensor in which the optical thickness changes were used to... 

CNTs also have promising applications in the immunosensing field and many examples of such sensor devices can be found in the literature. For example, immunosensors with an electrochemiluminescence readout signal have been designed using CNTs as support of the immunorecognition systems [167]. 

Non-labelled immunosensors rely on various principles (Fig. 3.27.A). Either the antibody or the antigen is immobilized on the solid matrix to form a sensing device. The solid matrix should be sensitive enough at the surface to detect immunocomplex formation. Electrode, membrane, piezoelectric and optically active surfaces may in principle be used to construct non-labelled immunosensors. The antigen or antibody to be determined is dissolved in a solution and reacted with the complementary matrix-bound antibody or antigen to form an immunocomplex that alters the physical e.g. the electrode potential or intrinsic piezofrequency) or optical properties of the... 

Types of biosensors can be named either by the biological components, physical transducing devices, or the measured analytes. Researchers were originally using biological components to define types of biosensors (Table 2). Types of transducers had also been included in the name to identify the physical transducing device, i.e., enzyme electrodes, acoustic-immunosensors, optical biosensors, piezoelectric-immunosensors, and biochips. 

Very few immunosensors are commercially available. The commercial immunosensors are either the detector or bioanalyzer types. The PZ 106 immunosensor from Universal Sensors Inc. (New Orleans, LA) has been used as a detector to measure antibody-antigen reaction. Ohmicron (Newtown, PA) developed a series of pesticide immuno-bioanalyzers that have been used in field tests. Pharmacia Biosensor USA (Piscataway, NJ) recently introduced BIAcore immunodetection system. A combination of a unique flow injection device and surface plasmon resonance (SPR) detection technique provides a real time analysis. A carboxylmethyldextran layer added to plasmon generating gold film is a hydrophobic, activatable, and flexible polymer that provides high antibody and low non-specific bindings. System demonstration at the Institute of Food Technologists (IFT) 1994 meeting in Atlanta drew attention of food scientists. It should easily be adapted for food protein characterization. 

Immunosensors are affinity biosensors and are defined as analytical devices that detect the binding of an antigen to its specific antibody by coupling the immunochemical reaction to the surface of a device... 

Electrochemical immunosensors are valid tools for the measurement of environmental pollutants such as PCBs. These devices are based on the principles of solid-phase immunoassays and couple the specificity of the immunoassay test to the sensitivity of electrochemical techniques. Screen-printed electrodes are used in the immunosensor development, because they can have a field use and their technology allows mass production at low cost. 

For OTA detection, the optimized immunosensors and the protocol that was implemented on the electrochemical device allowed the detection of 0.4 pg/kg, with within- and between-assay variability less than 5% and 10%, respectively. The method was evaluated with respect to a reference instrumental method (HPLC/immunoaffinity clean-up method based on the AOAC Official Method 2000.03) obtaining good agreement (r — 0.9992). 

The development of immunosensors for the detection of diseases has received much attention lately and this has largely been driven by the need to develop hand-held devices for point-of-care measurements [67,68]. Immunosensors can incorporate either the antigen or the antibody onto the sensor surface, although the latter approach has been used most often [67]. Optical [69,70] and electrochemical [70] detection methods are most frequently used in immunosensors [67]. Detection by... 

Indeed, different immunosensor devices based on the frequency changes of the crystal have been reported.166,671... 

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