Electronic transduction of photostimulated binding interactions at photoisomerizable monolayer electrodes: Novel approaches for optobioelectronic systems and reversible immunosensor devices

Photoisomerizable monolayers assembled onto electrode supports act as "comm and interfaces" for controlling the binding interactions of biomaterials wi th the functionalized surfaces. The light-induced binding and dissociation of the biomaterials to and from the electrodes, respectively, are electroni cally transduced. Two systems,including the photostimulated binding and dis sociation of cytochrome c (Cyt c) and of anti-DNP antibody to and from func tionalized surfaces, are discussed. The application of the systems as optob ioelectronic devices and reversible immunosensors is addressed. A mixed mon olayer consisting of pyridine and nitrospiropyran (1a) photoisomerizable un its assembled on a Au-electrode acts as a command interface for the light-c ontrolled association and dissociation of Cyt c to and from the monolayer. Cyt c binds to the pyridine/1a-monolayer electrode, resulting in electrical contact between the redox protein and the electrode. Photoisomerization of the mixed monolayer to the pyridine/protonated merocyanine state (Ib) resu lts in the electrostatic repulsion of Cyt c and its dissociation from the e lectrode support. This blocks the electrical contact between Cyt c and the electrode. By the cyclic photoisomerization of the mixed monolayer between the la and Ib states, reversible "ON"-"OFF" amperometric transduction of th e affinity interactions between the redox protein and the interface is acco mplished. Coupling of the photostimulated electrical contact between Cyt c and the electrode surface to the Cyt c-mediated bioelectrocatalyzed reducti on of O-2 by cytochrome oxidase provides a means to amplify the transduced electronic signal. A photoisomerizable thiolated dinitrospiropyran (2a) mon olayer, assembled on solid supports, acts as a light-active antigen interfa ce that enables the photocontrolled binding and dissociation of anti-dinitr ophenyl antibody (DNP-Ab) to and from the interface. The dinitrospiropyran (2a) layer acts as an antigen for the DNP-Ab, whereas the protonated dinitr omerocyanine (2b) lacks antigen features for the DNP-Ab. By reversible phot oisomerization of the monolayer between the 2a and 2b states, cyclic bindin g and dissociation of DNP-Ab to and from the monolayer interface is accompl ished. The association and dissociation of the DNP-Ab to and from the 2a- a nd 2b-monolayer states are electronically transduced, using amperometric, F aradaic impedance and microgravimetric, quartz crystal microbalance analyse s. The photostimulated binding of an antibody to a photoisomerizable antige n monolayer provides a novel method to design reversible immunosensor devic es.