Antigen-monolayer electrode

I. Willner, R. Blonder, and A. Dagan, Application of photoisomerizable antigenic monolayer electrodes as reversible amperometric immunosensors. J. Am. Chem. Soc. 116, 9365-9366 (1994). 

Blonder, R., Levi, S., Tao, G., Ben-Dov, L, and Willnet I. Development of anaperometric and microgravimetric immunosensors and reversible immunosensors using antigen and photoisomerizable antigen monolayer electrodes. J. Am. Chem. Soc. 1997, 119, 10467-10478. 

The association of the DNP-Ab to the antigen-monolayer-functionalized electrode leads to the electrical insulation of the electrode support and to the introduction of an electron barrier at the electrode surface. Thus, in the presence of an electrically wired enzyme (e.g., ferrocene-tethered glucose oxidase), the bioelectrocatalytic current is inhibited upon the formation of... 

The combination of a photoisomerizable spiropyran and Ab-DNP was also applied in the development of reversible amperometric immunosensors.49 The amperometric immunosensor was based on a 6,8-dinitrospiropyran-assembled monolayer on an Au electrode (Figure 6b). When Ab-DNP associated with the spiropyran monolayer as the electrode, the electrode surface was insulated toward the solubilized redox probe, and its amperometric response decreased. After irradiation (360nmantigen monolayer that resulted in a dissociation of Ab-DNP from the monolayer. The rinsed electrode revealed a high amperometric response, indicating that the Ab-DNP was washed off. Thus, the two-step illumination of the monolayer enables its reversible cyclic performance, which would demonstrate a general means for cyclic operation of an amperometric immunosensor. 

Hapten monolayer electrode sensor assembly was used to detect triazine in a flow injection analysis mode. The interaction of the electrode with different antibody concentrations resulted in the formation of an antibody-antigen (Ab-Ag) complex which insulated the electrode towards the [Fe(CN)6] /Fe(CN)6] " redox probe and diis in turn resulted in no charge transfer. The extent of insulation depends on the antibody concentration and the time of exposure to the antibody solution. The decrease in amperometric response of the antigenic monolayer to corresponding antibody solution for a fixed time produces a quantitative measurement of the antibody concentration. Typical responses obtained for cyanazine-hapten monolayer electrode to different antibody concentrations is shown in Figure 4. The lowest detection limit achieved for cyanazine sensor was 4.0 pg/ml at a response time of few minutes and a less-than 2% cross-reactivity to atrazine, simazine and other metabolites. 

R. Blonder, E. Katz, Y. Cohen, N. Itzhak, A. Riklin, and I. Willner, Application of redox enzymes for probing the antigen—antibody association at monolayer interfaces development of amperometric immunosensor electrodes. Anal. Chem. 68, 3151—3157 (1996). 

Two examples of attachment of the cosubstrate to the electrode surface together with a monolayer of enzyme are shown in Figures 5.25 and 5.26, based on the avidin-biotin24 and antigen-antibody253 technologies, respectively. 

FIGURE 5.26. Antigen-antibody construction of a monolayer glucose oxidase electrode with an attached ferrocenium cosuhstrate and cyclic voltammetric response in a phosphate buffer (pH 8) at 25°C and a scan rate of 0.04 V/s. a Attached ferrocene alone, h Addition of the substrate, c Primary plots, d Secondary plot. The numbers on the curves in parts h and c are the values of the substrate concentration in mM. Adapted from Figure 2 in reference 24, with permission from the American Chemical Society. 

Still with an enzyme monolayer, the synthesis and current responses of a system that involves simultaneous attachment of the cosubstrate to the electrode coating are then described. The next step consists in constructing a multilayered coating constituted by successive layers of enzyme built thanks to antigen-antibody interactions. Sensing the diffusion of the cosubstrate through the film thus constructed provides evidence for spatial order and an estimate of the distances between layers. 

Blondeiv R., Katz, E., Cohen, Y., Itzhak, N., Riklin, A., and Willneg I. Application of redox enzymes for probing the antigen - antibody asseweiarion at monolayer interfaces Development of amperometric immunosensor electrodes. Ab[Pg.266]

Katz, E., and Willner, I. Amperometric amplification of antigen - antibody association at monolayer interfaces Design of immunosensor electrodes. J. Electroanal. Chem. 1996, 418,67-72. 

Bourdillon, C., Demaille, C., Gueris, J., Moiroux, J., Sav6ant, J.-M. (1993). A fully active monolayer enzyme electrode derivatized by antigen-antibody attachment, J. Am. Chem. Soc., 115 12264. 

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