Photoisomerizable dinitrospiropyran

Since the photoisomerizable dinitrospiropyran units tethered to the redox enzyme act as photoisomerizable antigen sites for the anti-dinitrophenyl antibody DNP-Ab, the light-controlled association and dissociation of the antibody to and from the antigen-functionalized redox enzyme layer may control the bioelectrocatalytic functions... 

Scheme 18 Photochemical patterning of a photoisomerizable dinitrospiropyran monolayer associated with a glass support with agarose beads functionalized with DNP-Ab.

FIG. 7.32 Preparation of a photoisomerizable dinitrospiropyran monolayer on a transducer and the reversible senstrig of DNP-Ab. 

Fig. 17 Pattern of DNP-Ab-functionalized agarose beads on a glass support functionalized with a dinitrospiropyran photoisomerizable layer.

Fe(CN)6] , electrochemically contacted at a photoisomerizable command interface (lla/llb). Figure 7.15 shows the impedance features (as Nyquist plots) of the nitrospiropyran (11a) and protonated nitromerocyanine (lib) electrodes in the presence of [Fe(CN)6] as a redox probe. The impedance spectra show a larger resistance to interfacial electron transfer when the monolayer is in the neutral dinitrospiropyran state (Ret = 60 kll) than when it is in the positively charged protonated merocyanine state (Ret = 48 kQ) (Figure 7.15, curves b and a). The heterogeneous rate constants for electron transfer between the electrode and the redox probe were calculated to be 0.82 X 10" and 1.1 x 10" cm s" for the 11a and 1 lb-monolayer modified Au-electrodes, respectively. 

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. 

FIG. 7.37 (A) Cyclic voltainmograms of (a) The dinitrospiropyran-tediered GOx monolayer dec-trode. (b) The protonated dinitromerocyanine-tethered GOx monol r electrode, (c) The dinftro-spiropyran-tethered GOx monolayer electrode in the presence of the DNP-Ab. Data were recorded in the presence of ferrocene-carboxylic acid 4x 10 M, as diffusionai electron mediator and jocose, 5 X 10" M, scan rate 2 mV seer. (B) Biphasic switchable amperometric transduction of photonic si ls recorded by the photoisomerizable-GOx/DNP-Ab system ( ) The electrode in the dinitrospiropyran-GOx state. ( ) The electrode in the protonated dinitromerocyanine-state. (A) The electrode in the presence of the dinitrospiropyiwi-GOx monolayer with associated DNP-Ab. (Adapted from r rence 143, Figures I and 3. Reproduced by permission ofThe Royal Society of C3iemlstry.)... 

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