Abstract
Photoisomerizable nitrospiropyran (SP)/nitromerocyanine (MR) monolayer assembled on Au-electrodes provides active interfaces for controlling, by light electron transfer, reactions at the electrode surface. The functionalized electrodes act as 'photo-command' interfaces for the amperometric transduction and amplification of recorded optical signals. The nitrospiropyran monolayer, SP state, undergoes light-induced isomerization to the protonated nitromerocyanine monolayer, MRH+ state. The positively charged MRH+-monolayer interface, by means of electrostatic interactions, allows control of electrochemical transformation at the electrode interface. Electrooxidation of 3-hydroxytyramine (dopamine), (3), is ratarded at the MRH+-monolayer electrode as compared to its electrooxidation by the SP- monolayer electrode. In contrast, electrochemical oxidation of 3,4- dihydroxyphenylacetic acid, DHPAA, (4), is enhanced at the MRH+-monolayer electrode as compared to the SP-electrode state. By cyclic photoisomerization of the monolayer between the MRH+ and SP states, the amperometric responses of the electrode are tuned to high and low values in the presence of the two substrates. Another photo-command surface includes a mixed monolayer of pyrroloquinoline quinone, PQQ, and nitrospiropyran units. In the PQQ-SP- monolayer configuration, effective electrocatalyzed oxidation of NAD(P)H proceeds in the presence of Ca2+ ions. Photoisomerization of the monolayer to the PQQ-MRH+ state blocks the electrocatalytic oxidation of NADPH. The system is used for the cyclic amplified amperometric transduction of optical signals recorded by the monolayer. The SP/MRH+-monolayer electrode is also employed to control bioelectrocatalyzed transformations. Electrostatic attraction of ferrocene-modified glucose oxidase, Fc-GOx, by the MRH+- monolayer electrode, facilitates the electrocatalyzed oxidation of glucose, whereas in the presence of the SP-monolayer electrode the bioelectrocatalytic process is inhibited. The enzyme Fc-GOx, enables the cyclic, amplified amperometric transduction of optical signals recorded by the photoactive monolayer. A mixed monolayer consisting of nitrospiropyran and pyridine units assembled on a Au-electrode provides a functionalized interface that controls the binding of cytochrome c (Cyt. c) to the monolayer and the resulting electrical contact of Cyt. c with the electrode. With the pyridine-SP monolayer configuration, Cyt. c associates to the pyridine sites and reveals effective electrical communication with the electrode surface. In the pyridine-MRH+-monolayer state, Cyt. c is electrostatically repelled from the pyridine sites and its electrical contact with the electrode is blocked. The photostimulated association and dissociation of Cyt. c to and from the photoisomerizable monolayer is microgravimetrically analyzed by a quartz- crystal microbalance.
Original language | English |
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Pages (from-to) | 703-719 |
Number of pages | 17 |
Journal | Biosensors and Bioelectronics |
Volume | 12 |
Issue number | 8 |
DOIs | |
State | Published - Jul 1997 |
Event | Proceedings of the 1996 Workshop on Artificial Biosensing Interfaces, ABI - Tubingen, Ger Duration: 7 Oct 1996 → 12 Oct 1996 |
Keywords
- Charged monolayers
- Electrochemical transduction of optical signals
- Electrostatic interactions
- Light-induced electrocatalysis
- Photoactivated cytochrome c
- Photoactivated glucose oxidase
- Photoisomerizable monolayer electrodes
- Photoregulated antigen-antibody interactions
- Photostimulated electron transfer
- Photostimulation
- Reversible immunosensors
- Selective redox reactions