Detection using 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. 

G.H. Kim, A.G. Rand, and S.V. Letcher, Impedance characterization of a piezoelectric immunosensor. Part II Salmonella typhimurium detection using magnetic enhancement. Biosens. Bioelectron. 18, 91-99 (2003). 

A Displacement Flow Immunosensor for Explosive Detection Using Microcapillaries, Anal. Chem. 1997, 69, 2779. 

Immunotechniques have recently been developed to detect food contaminants, e.g., toxins, growth hormone, antibiotics, pesticides, and herbicides. Penicillin (62) in milk, aflatoxins and mycotoxins (63, 64, 65) in milk, cheeses, yogurt, corn have been detected by immunosensors. Characteristics of protein and receptors in or on the cell surface were used in detecting pathogens such as Listeria and Salmonella by immunosensors (11, 66). The principle of immunosensors has also been applied in pesticide determinations (67, 68). 

Western blot and ELISA tests [63,64]. Besides the higher sensitivity, an improved selectivity has also been observed using the optical fiber immunosensor. Anti-E2 antibodies in all sera positive for anti-HCV (anti-core, NS3 and NS5) and HCV RNA (100% sensitivity) could be detected. Using Western blot tests, only 69% of anti-HCV (anti-core, NS3 and NS5) positive samples could be detected [63,64]. Furthermore, standard test for anti-HCV antibodies requires the use the three cited antigens (core, NS3 and NS5) because of its limited sensitivity. The high sensitivity of the optical fiber immunosensor, containing only the HVC E2 envelope protein, allows the identification of all RNA positive patients. 

The presented examples of recent achievements in immunosensor development show the tremendous progress in this field. Detection limits lower continuously, miniaturized setups by keeping the possibility of automated production progressed, and procedures for detection are constantly simplified. Direct immobilization of the receptor antibody by photochemical reactions enables the production of ready to use immunosensors in few steps. With photovoltaic components, time consuming and expensive labeling procedures of the analyte can be avoided. 

A disposable immunosensor for AFBi determination in barley has been reported [203], this time using an SPCE bearing surface-immobilised AFBi antigen conjugated to BSA. After incubation of the sensor with the sample and an anti-AFBi monoclonal antibody, the addition of a secondary antibody labelled with alkaline phosphatase, enabled the generation of 1-naphthol from 1-NP, and its detection using DPY. The assay had a reported detection limit of 30pgml 1 in barley. 

Valera, E., J. Ramon-Azcon, A. Rodriguez, et al. 2007. Impedimetric immunosensor for atrazine detection using interdigitated [mu]-electrodes (ID[mu]E s). Sens. Actual B Chem. 125 526-537. 

Ochratoxin-A (OTA), a mycotoxin produced in unstored food and beverages has recently been detected using CH-Fe304 nanobiocomposite modified indium-tin oxide (ITO) electrode [73], This immunosensor shows a specific response to OTA detection in the range of 0.5 - 6 ng/dL with a detection limit of 0.5 ng dL 1. The sensitivity of the bioelectrode has been found to be 36 pA/ng dL"1 cm 2 with response time of 18s [101],... 

Narang U., Gauger P. R., Ligler F. S., A displacement flow immunosensor for explosive detection using microcapillaries, A a/. Chem., 69, 2779-2785, 1997. 

The simultaneous measurements of SPR and electrochemical impedance were carried out using a flow injection analysis (FIA) cell by Bart et al. [5]. The FIA system was tested for interferon-y detection using liposome bounded to the secondary antibody to increase the amount of mass for SPR detection. Liposome binding did not yield an impedance shift, but the different concentrations of interferon caused an increase in the impedance signal. In this way, it was possible to use the impedance-SPR measurements in this system. This immunosensor indicates the usefulness of the FIA cell for investigations of the ESPR method as a biosensor development. 

Mass-based immunosensors have been developed, owing to their advantages of label-free and real-time detection. Microbalances of piezoelectric crystals are the most widely used immunosensors, although it is a challenge to detect small molecules on the piezoelectric sensor surface with a high sensitivity. In Figure 32, Jin and coworkers have... 

Neves, M.M.P.S., Gonzilez-Garcfa, M.B., Nouws, H.P.A. and Costa-Garcfa, A. (2012) Celiac disease detection using a transglutaminase electrochemical immunosensor fabricated on nanohybrid screen-printed carbon electrodes. Biosens. Bioelectron., 31, 95-100. 

Kim DJ, et al. Organic electrochemical transistor based immunosensor for prostate specific antigen (PSA) detection using gold nanoparticles for signal amplification. Biosensors Bioelectronics 2010 25 2477-82. http //dx.doi.Org/10.1016/j.bios.2010.04.013. 

PAHs are always found as a mixture of individual compounds with similar molecular structure, similar electron density, and a lack of side groups. Therefore, an immunosensor based on SPEs was developed for PAH detection using a co-exposure competition assay. The immunosensor displayed cross-reactivities of varying degrees towards 16 important PAH compounds. ... 

Valera E, Azcon JR, Rodriguez A, CastantaaLM, Sanchez FJ, Marco MP (2007) Impedimetiic immunosensor for atrazine detection using interdigitated p-electrodes (ID iE s). Sensor Actuator B 125 526-537... 

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