Detection immunosensors

There are mainly three types of transducers used in immunosensors electrochemical, optical, and microgravimetric transducers. The immunosensors may operate either as direct immunosensors or as indirect ones. For direct immunosensors, the transducers directly detect the physical or chemical effects resulting from the immunocomplex formation at the interfaces, with no additional labels used. The direct immunosensors detect the analytes in real time. For indirect immunosensors, one or multiple labeled bio-reagents are commonly used during the detection processes, and the transducers should detect the signals from the labels. These indirect detections used to need several washing and separation steps and are sometimes called immunoassays. Compared with the direct immunosensors, the indirect immunosensors may have higher sensitivity and better ability to defend interference from non-specific adsorption. 

This complex subsequently reacts with other reagents in the solution to produce either an insoluble dimer product, which also adsorbs on the AW device surface, or a massive ion (l3 was used) that inserts into an ionic binding site in the surface film. Thus, the areal mass increase per bound analyte is significantly amplified. While these and other immunosensor detection schemes can involve rather complex reagent and/or buffer systems, the relative advantages of piezoelectric sensors in terms of cost, speed, and safety make them attractive alternatives to radioimmunoassay and other standard assay techniques. 

Conventional bacterial detection methods generally require laborious procedures and many hours or even days for complete analysis. The relatively large mass of bacterial cells, combined with the availability of antibodies to most species means that Pz immunosensor detection offers a very attractive alternative to microbiological methods. Generally giving results in minutes, with adequate sensitivity and selectivity. The earliest Pz immunosensors for bacterial detection have already been discussed [65,68,70]. 

Shankaran DR, Gobi KV, Miura N (2007) Recent advancements in surface plasmon resonance immunosensors detection of small molecules of biomedical, food and environmental interest. Sens Actuators B Chem 121 158-177... 

The working conditions of the immunosensor (enzyme and antigen concentrations, dilutions of the antibodies, pH of the buffer solution) were found. The cholinesterase immobilized demonstrated the maximum catalytic activity in phosphate buffer solution with pH 8.0. The analytical chai acteristics of the sensor - the interval of the working concentrations and detection limit - have been obtained. The proposed approach of immunoassay made possible to detect 5T0 mg/ml of the bacterial antigen. 

A major disadvantage is that the direct sensor detection cannot distinguish between the sensor response to the specific analyte binding from the response to a possible nonspecific adsorption of other compounds. The nonspecific fouling from blood or blood serum seems to be one of the main barriers for practical application of immunosensors in medical diagnostics. 

Brynda E., Elouska M., Brandenburg A., Wikerstal A., Skvor J., The detection of human P2-microglobulin by grating coupler immunosensor with three-dimensional antibody networks, Biosens. Bioelectron. 1999 14 363-368. 

Rowe C.A., Scruggs S.B., Feldstein M.J., Golden J.P, Ligler F.S., An array immunosensor for simultaneous detection of clinical analytes, Anal. Chem. 1999 71 433-439. 

FIGURE 2.11 Schematic diagram of the separation-free immunosensor principle for pesticides (H2O2 detected at + 50 mV vs Ag/AgCl via direct enzymatic reduction of HRP) (adapted from [98]). 

M.A. Lopez, F. Ortega, E. Dominguez, and I. Katakis, Electrochemical immunosensor for the detection... 

There are many other examples of competitive electrochemical immunoassays and immunosensors for detecting clinically important analytes [12-14], Despite simplicity, a disadvantage of competitive immunoassays is that labeling the analyte may reduce, or totally remove, its binding affinity for antibody. This would occur if the analyte were labeled at a site that is closely associated with an epitope. 

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