Immunosensors principle

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]). 

P.B. Luppa, L.J. Sokoll, and D.W. Chan, Immunosensor principles and applications to clinical chemistry. Clin. Chim. Acta 314, 1-26 (2001). 

Vo-Dinh T, Sepaniak MJ, Griffin GD, Alarie JP (1993) Immunosensors principles and applications. Immunomethods 3 85-92... 

M.-I. Mohammed, M.RY. Desmulliez, Lab-on-a-chip based immunosensor principles and technologies for the detection of cardiac biomarkers a review. Lab on a Chip 11 (2011)569-595. 

Luppa PB, Sokoll LJ, Chan DW. Immunosensors - principles and applications to clinical chemistry. Clinica Chimica Acta 2001 314 1-26. http //dx.doi.org/ 10.1016/s0009-8981(01)00629-5. 

J. Zeravik, T. Ruzgas, and M. Franek, A highly sensitive flow-through amperometric immunosensor based on die peroxidase chip and enzyme-channeling principle. Biosens. Bioelectron. 18,1321—1327 (2003). 

FIGURE 16.9 Principle of reagentless amperometric immunosensor based on immobilized antigen, competitive immunological reaction, and direct electrochemistry of HRP label (adapted from [138]). 

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... 

The amperometric immunosensors reported so far rely on various methodological principles including use of a Clark electrode for detecting oxygen formation or depletion, an electrochemically active product yielded in an enzyme reaction or an antigen labelled with an electroactive species. 

Figure 3.31 — (A) Continuous monitoring of analytes in a fermentation medium. In the absence of analyte, the analyte enzyme conjugate binds predominantly to sensor 1 (left). At high analyte concentrations in the medium, the signal shifts to sensor 2 (right). (B) Principle of the membrane immunosensor. (Reproduced from [225] and [226] with permission of VCH Publishers).

Immunosensors have been designed which use both direct and indirect immunoassay technology to detect specific analytes within a minute or less in a variety of matrices (see Fig. 9). Indirect immunosensors may employ ELA, FLA, or CLIA principles whereby enzyme-, fluorophore- or chemiluminescent-labeled analyte competes with the target (nonlabeled) analyte for binding sites on the immobilized antibody. Unbound (free) labeled analyte is then quantitated using an electrochemical, optical, or electromechanical transducer and compared to the amount of target analyte in the sample. 

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). 

---