Immunosensor reversible

A comparison of the products of AP hydrolysis of HQDP (HQ), PP, and 1-NP using cyclic voltammetry revealed that HQ produced well-defined peaks, and that the oxidation of HQ is reversible. More importantly, no apparent passivation of the electrode surface was observed even at high millimolar concentrations after 50 scans. Following a series of investigations, this non-fouling nature of HQ was attributed to the non-accumulation of its oxidation products on the electrode surface and the good diffusional properties of HQ at the electrode-solution interface. Another positive feature of HQDP as a substrate for AP is a tenfold greater oxidation current response of HQ compared to those obtained in the presence of PP or 1-NP. Overall, HQDP provides a suitable and attractive alternative substrate system for AP in the development of amperometric immunosensors. 

S. Grant, F. Davis, K.A. Law, A.C. Barton, S.D. Collyer, S.P.J. Higson, and T.D. Gibson, Label-free and reversible immunosensor based upon an AC impedance interrogation protocol. Anal. Chim. Acta 537, 163-168 (2005). 

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). 

I. Willner and B. Willner, Electronic transduction of photostimulated binding interactions at photoisomerizable monolayer electrodes novel approaches for optobioelectronic systems and reversible immunosensor devices. Biotechnol. Prog. 15, 991-1002 (1999). 

A phenytoin energy transfer immunosensor has been reported that is reversible and direct, in which macromolecular reagents are retained within a short length of 200-/dialysis tubing cemented to the end of an optical fiber (Figure 14.18).018 119)A... 

A reversible, direct fluoroimmunosensor for human serum albumin (HS A) measurement has been described by Bright et al.(m> Antibody Fab fragments are first immobilized on small quartz plates by hinge-region thiols, and then dansylated. The immunosensor is formed by attaching the quartz plates with bound Fab to the distal end of a bifurcated fiber-optic probe, which transmits both the excitation and emission. Binding of ffSA to the immunosensor results in a three- to five-fold enhancement of dansyl fluorescence. The sensor can be reused up to 50 times, with a detection limit of about 1.8 x 10-8 M, and a somewhat limited dynamic range. 

An optical immunosensor for continuous T4 measurement has been described, in which the fluorescent indicator protein is separated from the sample flow chamber by a dialysis membrane.024) The indicator is T4-binding globulin (TBG), the intrinsic fluorescence (ex. 290 nm) of which is quenched by T4binding. Due to the high affinity of the TBG for thyroxine, the immunosensor is not reversible, but multiple measurements can be made until the TBG is saturated. Sensitivity is inadequate for clinically useful concentrations of T4, but suggestions for improvement of the method are made. 

J. R. Astles and W. G. Miller, Reversible fiber-optic immunosensor measurements, Sensors and... 

Enzyme immunosensors are employed for the determination of Hepatitis B surface antigen, IgG, alpha-fetoprotein, estradiol, theophylline, insulin [9004-10-8], and albumin (69,70). However, these immunosensors generally have slow response times and slow reversibility (57). 

Gonzalez-Martinez, M.A., R. Puchades, A. Maquieira, I. Ferrer, M.P. Marco, and D. Barcelo. (1999). Reversible immunosensor for the automatic determination of atrazine Selection and performance of three polyclonal antisera. Anal. Chim. Acta, 386 201-210. 

Scheme 14 Assembly of a reversible immunosensor using a photoisomerizable antigen-functionalized transducer.

Photoswitchable antigen/antibody (substrate/ receptor) complexes 1. Reversible immunosensors 2. Patterning of surfaces with biomaterials using antigen/antibody-biomaterial conjugates (Design of biosensor arrays, biochips) 1. Immobilization of systems on electronic transducers (electrodes, piezoelectric crystals, FET) or the assembly of biomaterials on inert supports by non-covalent interactions (eg. glass, polymers)... 

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 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. 

The determination of antigens and antibodies can be improved by immobilization of the appropriate immunochemical partner of the analyte. When the immunological reaction can be rendered reversible the immobilized ligand becomes reusable. Whereas in immunoreactors the immunosorbent is separated from the sensor, in immunosensors both elements are in intimate physical contact. We shall show below that these devices can be used to perform the classical functions of immunoassays. 

---