Electrochemical immunosensor

FIGURE 1.3 Schematic drawing of a light addressable potentiometric sensor (LAPS) for pathogen detection. (Adapted from reference Gehring et al., 1998). 

A disposable electrochemical enzyme-amplified genosensor was described for specific detection of Salmonella (Del Giallo et al., 2005). A DNA probe specific for Salmonella was immobilized onto screen-printed carbon electrodes and allowed to hybridize with a biotinylated PCR-amplified product of Salmonella. The hybridization reaction was detected using streptavidin conjugated-AP where the enzyme catalyzed the conversion of electroinactive a-naphthyl phosphate to electroactive a-naphthol, which was detected by differential pulse voltammetry. 

1-2 X l(f cells, and the growth was detected at 10 h and 2.1 h, respectively. Though it was claimed to be more sensitive than PCR or immunoassay, it is highly unlikely to be specific because the specificity directly depends on the selectivity of the medium used. 

An electrochemical sensor using an array microelectrode was tested for the detection of allergens such as mite and cedar pollen (Okochi et ah, 1999). Blood was used in the assay and the release of serotonin, a chemical mediator of allergic response, which is electrochemically oxidized at the potential around 300 mV, was monitored for electrochemical detection by cyclic voltammetry. 

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Explain clearly how the use of enzymes can enhance the power of electrochemical immunosensors. 

The material is presented in 17 chapters, covering topics such as trends in ion selective electrodes, advances in electrochemical immunosensors, modem glucose biosensors for diabetes management, biosensors based on nanomaterials (e.g. nanotubes or nanocrystals), biosensors for nitric oxide and superoxide, or biosensors for pesticides. 

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

R.W. Keay and C.J. McNeil, Separation-free electrochemical immunosensor for rapid determination of... 

Competitive immunoassays may also be used to determine small chemical substances [10, 11]. An electrochemical immunosensor based on a competitive immunoassay for the small molecule estradiol has recently been reported [11]. A schematic diagram of this immunoassay is depicted in Fig. 5.3. In this system, anti-mouse IgG was physisorbed onto the surface of an SPCE. This was used to bind monoclonal mouse anti-estradiol antibody. The antibody coated SPCE was then exposed to a standard solution of estradiol (E2), followed by a solution of AP-labeled estradiol (AP-E2). The E2 and AP-E2 competed for a limited number of antigen binding sites of the immobilized anti-estradiol antibody. Quantitative analysis was based on differential pulse voltammetry of 1-naphthol, which is produced from the enzymatic hydrolysis of the enzyme substrate 1-naphthyl phosphate by AP-E2. The analytical range of this sensor was between 25 and 500pg ml. 1 of E2. 

The development of electrochemical immunosensors generally involves the immobilization of an immunocomplex on a single electrode, followed by detection via the... 

O.A. Sadik and J.M. van Emon, Applications of electrochemical immunosensors to environmental monitoring. Biosens. Bioelectron. 11, i-xi (1996). 

R.M. Pemberton, T.T. Mottram, and J.P. Hart, Development of a screen-printed carbon electrochemical immunosensor for picomolar concentrations of estradiol in human serum extracts. J. Biochem. Biophys. Methods 63, 201-212 (2005). 

S. Viswanathan, L.-C. Wu, M.-R. Huang, and J.-A.A. Ho, Electrochemical immunosensor for cholera toxin using liposomes and poly(3,4-ethylenedioxythiophene)-coated carbon nanotubes. Anal. Chem. 78, 1115-1121 (2006). 

M. Akram, M.C. Stuart, and D.K.Y. Wong, Signal generation at an electrochemical immunosensor via the direct oxidation of an electroactive label. Electroanalysis 18, 237-246 (2006). 

S.M. Wilson, Electrochemical immunosensors for the simultaneous detection of two tumor markers. Anal. Chem. 77, 1496-1502 (2005). 

Y.V. Plekhanova, A.N. Reshetilov, E.V. Yazynina, A.V. Zherdev, and B.B. Dzantiev, A new assay format for electrochemical immunosensors polyelectrolyte-based separation on membrane carriers combined with detection of peroxidase activity by pH-sensitive field-effect transistor. Biosens. Bioelectron. 19, 109-114(2003). 

M. Dijksma, B. Kamp, J.C. Hoogvliet, and W.P. van Bennekom, Development of an electrochemical immunosensor for direct detection of interferon- at the attomolar level. Anal. Chem. 73, 901-907 (2001). 

A.F. Chetcuti, D.K.Y. Wong, and M.C. Stuart, An indirect perfluorosulfonated ionomer-coated electrochemical immunosensor for the detection of the protein human chorionic gonadotrophin. Anal. Chem. 71, 4088-4094 (1999). 

J. Wang, B. Tian, and K.R. Rogers, Thick-film electrochemical immunosensor based on stripping poten-tiometric detection of a metal ion label. Anal. Chem. 70, 1682-1685 (1998). 

Liu et al. [140] have also used this interface for an electrochemical immunosensor for small molecules (Figure 1.26). In this sensor, one end of the molecular wire is attached to ferrocene dimethylamine with a covalent link formed between one of the amine group son the ferrocene and the carboxyl group on the wire. To the other amine is attached the antibody-binding epitope for the antibody, in this proof-of-concept study the epitope is biotin. Electron transfer can be readily achieved to the ferrocene molecule but upon antibody binding to this interface, the electrochemical signal is dramatically reduced. 

Electrochemical immunosensors are a powerful tool for the analysis of antibacterials in food and different configurations have been presented during recent years. For example, an amperometric immunosensor was reported by Wu et al. [182], for penicillin quantification in milk, with a linear range from 0.25 to 3 ng/ml and a limit of detection of 0.3 pg/L [182]. Other types of transduction have been also explored, like a label-free impedimetric flow injection immunosensor for the detection of penicillin G. 

Electrochemical immunosensors are the most numerous of immunosensors. Their suitability for use in flow systems is limited by the two factors commented on above in dealing with fibre optic-based sensors, viz. the need for an incubation period and exceedingly long response times. 

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