Photoisomerizable Monolayer Research Articles

Dynamic photo-control of kinesin on a photoisomerizable monolayer – hydrolysis rate of ATP and motility of microtubules depending on the terminal group

The reversibly and repeatedly altered gliding motility of microtubules driven by kinesin on the photoresponsive monolayer surface is studied. It was confirmed that an azobenzene monolayer surface needs to have free amino terminal groups for the successful dynamic control of the motility of microtubule. The surface of the azobenzene monolayer with terminal amino groups can dynamically control the ATP hydrolysis activity of kinesin which resulted in the change in motility of the microtubules.

Optically Activated Uptake and Release of Cu2+ or Ag+ Ions by or from a Photoisomerizable Monolayer-Modified Electrode

Di-(N-butanoic acid-1,8-naphthalimide)-piperazine dithienylethene was covalently linked to a cysteamine monolayer associated with a Au surface to yield a photoisomerizable monolayer composed of the open or closed dithienylcyclopentene isomers (3a or 3b), respectively. Electrochemical and XPS analyses reveal that the association of metal ions to the monolayer is controlled by its photoisomerization state. We find that Cu(2+) ions reveal a high affinity for the open (3a) monolayer state, K(a) = 4.6 × 10(5) M(-1), whereas the closed monolayer state (3b) exhibits a substantially lower binding affinity for Cu(2+), K(a) = 4.1 × 10(4) M(-1). Similarly, Ag(+) ions bind strongly to the 3a monolayer state but lack binding affinity for the 3b state. The reversible photoinduced binding and dissociation of the metal ions (Cu(2+) or Ag(+)) with respect to the photoisomerizable monolayer are demonstrated, and the systems may be used for the photochemically controlled uptake and release of polluting ions. Furthermore, we demonstrate that the photoinduced reversible binding and dissociation of the metal ions to and from the photoisomerizable electrode control the wettability properties of the surface.

Photoswitchable Electrocatalysis and Catalyzed Chemiluminescence Using Photoisomerizable Monolayer-Functionalized Surfaces and Pt Nanoparticles

A photoisomerizable monolayer consisting of carboxypropyl nitrospiropyran (1a) linked to an aminopropyl siloxane layer associated with an indium tin oxide surface is used to photoswitch the electrocatalyzed reduction of H2O2 in the presence of Pt nanoparticles (NPs) or to photostimulate the generation of chemiluminescence in the presence of Pt NPs, H2O2, and luminol. Photoisomerization of 1a to the protonated merocyanine, 1b, layer results in the electrostatic attraction of the negatively charged Pt NPs to the surface. This facilitates the electrocatalyzed reduction of H2O2 or the catalyzed generation of chemiluminescence in the presence of H2O2/luminol. Further photoisomerization of the 1b monolayer results in the formation of the nitrospiropyran layer that allows the washing off of the surface-bound Pt NPs. The resulting 1a-modified surface is inactive toward the reduction of H2O2 or toward the generation of chemiluminescence.

An electrochemical/photochemical information processing system using a monolayer-functionalized electrode

An electroactive and photoisomerizable monolayer associated with a Au electrode acts as a Write-Read-Erase information processing system and as a flip-flop Set/Reset memory element.

Molecular and biomolecular optoelectronics

Abstract Reversible electronic transduction of photonic processes occurring on electrodes is the conceptual method to develop molecular and biomolecular optoelectronic systems. Cyclic photochemical activation of molecular or biomolecular monolayer redox-functions provides a general methodology for the amperometric transduction of photonic information that is recorded by the chemical assembly. Alternatively, photoisomerizable monolayers associated with electrodes act as "command interfaces" for controlling the interfacial electron transfer between molecular redox-species or redox-proteins. The systems use a photonic input for the generation of an electronic output and act as information processing assemblies. Programmed arrays of photosensitizer/electron acceptor cross-linked Au-nanoparticle arrays are assembled on indium tin oxide (ITO) for photoelectrochemical applications.

Light-driven motion of liquids on a photoresponsive surface

The macroscopic motion of liquids on a flat solid surface was manipulated reversibly by photoirradiation of a photoisomerizable monolayer covering the surface. When a liquid droplet several millimeters in diameter was placed on a substrate surface modified with a calix[4]resorcinarene derivative having photochromic azobenzene units, asymmetrical photoirradiation caused a gradient in surface free energy due to the photoisomerization of surface azobenzenes, leading to the directional motion of the droplet. The direction and velocity of the motion were tunable by varying the direction and steepness of the gradient in light intensity. The light-driven motion of a fluid substance in a surface-modified glass tube suggests potential applicability to microscale chemical process systems.

Molecular and Biomolecular Assemblies Based on Photochromic Compounds

Photoswitchable redox-activated monolayers on electrode supports act as molecular electronic systems for the electronic transduction of recorded photonic information. Photoisomerizable monolayers assembled on electrodes may act as command interfaces for controlling interfacial electron transfer and thus act as interfaces for the amperometric transduction of photonic signals recorded by the monolayer. Photoswitchable biomaterials assembled on electronic transducers represent novel optobioelectronic systems. This is exemplified by the organization of a photoswitchable enzyme for the amplified amperometric transduction of photonic signals, and by the tailoring of reversible immunosensor systems.

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 "command interfaces" for controlling the binding interactions of biomaterials with the functionalized surfaces. The light-induced binding and dissociation of the biomaterials to and from the electrodes, respectively, are electronically transduced. Two systems, including the photostimulated binding and dissociation of cytochrome c (Cyt c) and of anti-DNP antibody to and from functionalized surfaces, are discussed. The application of the systems as optobioelectronic devices and reversible immunosensors is addressed. A mixed monolayer consisting of pyridine and nitrospiropyran (1a) photoisomerizable units assembled on a Au-electrode acts as a command interface for the light-controlled 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 (1b) results in the electrostatic repulsion of Cyt c and its dissociation from the electrode support. This blocks the electrical contact between Cyt c and the electrode. By the cyclic photoisomerization of the mixed monolayer between the 1a and 1b states, reversible "ON"-"OFF" amperometric transduction of the affinity interactions between the redox protein and the interface is accomplished. Coupling of the photostimulated electrical contact between Cyt c and the electrode surface to the Cyt c-mediated bioelectrocatalyzed reduction of O(2) by cytochrome oxidase provides a means to amplify the transduced electronic signal. A photoisomerizable thiolated dinitrospiropyran (2a) monolayer, assembled on solid supports, acts as a light-active antigen interface that enables the photocontrolled binding and dissociation of anti-dinitrophenyl antibody (DNP-Ab) to and from the interface. The dinitrospiropyran (2a) layer acts as an antigen for the DNP-Ab, whereas the protonated dinitromerocyanine (2b) lacks antigen features for the DNP-Ab. By reversible photoisomerization of the monolayer between the 2a and 2b states, cyclic binding and dissociation of DNP-Ab to and from the monolayer interface is accomplished. The association and dissociation of the DNP-Ab to and from the 2a- and 2b-monolayer states are electronically transduced, using amperometric, Faradaic impedance and microgravimetric, quartz crystal microbalance analyses. The photostimulated binding of an antibody to a photoisomerizable antigen monolayer provides a novel method to design reversible immunosensor devices.

Surface Plasmon Resonance Characterization of Photoswitchable Antigen−Antibody Interactions

Photostimulated association and dissociation of anti-dinitrophenyl antibody, anti-DNP-Ab, to and from a dinitrospiropyran photoisomerizable monolayer is probed by surface plasmon resonance (SPR). The anti-DNP-Ab binds to a dinitrospiropyran antigen monolayer, whereas the DNP-Ab dissociates from the protonated dinitromerocyanine monolayer. Reversible binding and dissociation of anti-DNP-Ab to and from the photoisomerizable monolayer was assayed by SPR spectroscopy. Analysis of the SPR data indicates that the average thickness of the antibody layer is ca. 70 Å which corresponds to a surface coverage of ca. 4.4 × 10-9 mol·cm-2.

Photoswitchable Antigen−Antibody Interactions Studied by Impedance Spectroscopy

A thiolated dinitrospiropyran (1a) is assembled as a monolayer onto a Au electrode. The monolayer exhibits reversible photoisomerizable properties, and irradiation of the 1a monolayer state, 360 nm 495 nm, regenerates the 1a monolayer electrode. The 1a monolayer interface acts as antigen for the dinitrophenyl antibody, DNP-Ab, while the 1b state lacks an affinity for DNP-Ab. This stimulates the association of the antibody to the 1a monolayer interface, while photoisomerization of the monolayer to the 1b state allows one to wash off DNP-Ab and regenerate the 1a monolayer assembly by a secondary illumination process. The photoisomerization of the monolayer interface and the binding or dissociation of DNP-Ab to and from the photoisomerizable monolayer are studied by impedance spectroscopy, in the presence or absence of a solubilized redox probe. The derived equivalent circuits ena...

Gated molecular and biomolecular optoelectronic systems via photoisomerizable monolayer electrodes

Molecular and biomolecular optobioelectronic systems that yield the amperometric transduction of recorded optical signals are described. Phenoxynaphthacene quinone is assembled as a monolayer on an Au electrode. Photoisomerization of the monolayer between the redox-active trans-quinone state and the redox-inactive ‘ana’-quinone state provides a means to transduce electrochemically optical signals recorded by the monolayer. Coupling of the redox-active trans-quinone monolayer electrode to the secondary reduction of N,N′-dibenzyl-4,4′-bipyridinium, BV2+, provides a means to amplify the transduced current. As the redox potential of the trans-quinone monolayer is pH dependent, the electrocatalyzed monolayer-mediated reduction of BV2+ is controlled by light and the pH. The system represents an ‘AND’ gated molecular electronic assembly. A thiol nitrospiropyran monolayer was assembled on an Au electrode. The functionalized electrode acts as photo-triggered ‘command interface’ that controls the electrooxidation of dihydroxyphenylacetic acid (DPAA). The electrical properties of the monolayer are controlled by the photoisomer state of the monolayer and the pH of the medium. The monolayer in the nitromerocyanine state exists at pH 9.2 and 7.0 in zwitterionic or positively charged states, respectively. Electrooxidation of the negatively charged substrate, DPPA, is enhanced only in the presence of the protonated nitromerocyanine monolayer electrode. This permits the gated oxidation of the substrate by two complementary triggering signals, light and pH. A mixed monolayer consisting of nitrospiropyran and thiolpyridine units assembled on an Au electrode is applied as a photoisomerizable command surface for controlling the electrical contact of cytochrome c (Cyt c) with the electrode. In the nitrospiropyran–pyridine configuration electrical contact of Cyt c and the electrode is attained by the association of Cyt c to pyridine promoter sites. Photoisomerization of the monolayer to the protonated nitromerocyanine state results in the electrostatic repulsion of Cyt c from the monolayer, and the electrical contact of Cyt c with the electrode is blocked. Coupling of the electrically contacted Cyt c and nitrospiropyran–pyridine monolayer electrode configuration to the cytochrome oxidase biocatalyzed reduction of oxygen provides a means to amplify the transduced amperometric response. The photostimulated association and dissociation of Cyt c to and from the photoisomerizable monolayer were confirmed by microgravimetric, quartz crystal microbalance analyses. The system mimics the function of the native vision process. © 1998 John Wiley & Sons, Ltd.

Layered molecular optoelectronic assemblies

I. Willner and B. Willner, J. Mater. Chem., 1998, 8, 2543 DOI: 10.1039/A804135K

Light-controlled electron transfer reactions at photoisomerizable monolayer electrodes by means of electrostatic interactions: active interfaces for the amperometric transduction of recorded optical signals

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 retarded 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 Ca 2+ 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.

Photoswitchable biomaterials as grounds for optobioelectronic devices

Optobioelectronic systems provide a means for the electronic transduction of recorded optical signals. The methodologies to assemble optobioelectronic devices are reviewed. One method involves the chemical modification of redox enzymes with photoisomerizable units and their integration with electrode surfaces. In one photoisomer state the protein structure is perturbed and its bioelectrocatalytic activities are blocked. In the second photoisomer state, the tertiary structure of the protein is retained and the enzyme exhibits bioelectrocatalytic functions. This method is exemplified by the chemical modification of glucose oxidase (GOx) with photoisomerizable nitrospiropyran units and with the reconstitution of apo-GOx with the photoisomerizable nitrospiropyran-FAD (flavin adenine dinucleotide phosphate) cofactor. The two systems enable the cyclic amplified amperometric transduction of optical signals recorded by the photoactive proteins. The second approach to assemble optobioelectronic systems involves the organization of photoisomerizable monolayers on electrode surfaces acting as ‘optical command surfaces’ for the control of the electrical contact between redox proteins (or redox enzymes) and the electrode. This method is exemplified by the control of the electrical contact of cytochrome c (Cyt. c) with a functionalized electrode consisting of a mixed monolayer of pyridine/nitrospiropyran assembled onto an Au-electrode. The ON-OFF photostimulated electrical contact of Cyt. c with the electrode is coupled to mediated electron transfer cascades, i.e. bioelectrocatalyzed reduction of oxygen by cytochrome oxidase (COx). The systems allow the amplified amperometric transduction of optical signals recorded by the photoisomerizable monolayer-electrode. The photochemically-triggered activation or deactivation of the electrical communication between Cyt. c and the electrode, originate from the association or repulsion of the protein from the photoisomerizable monolayer-electrode interface. This enables the microgravimetric transduction of the optical signals recorded by the monolayer using a quartz crystal microbalance (QCM). The photostimulated electrical contact of Cyt. c and the electrode, and the subsequent activation of an electron transfer cascade via the electrobiocatalyzed reduction of oxygen by COx, allow the amplified amperometric transduction of optical signals recorded by the monolayer-functionalized-electrode. Reversible immunosensors based on photoisomerizable antigen monolayers assembled onto electrodes represent another configuration of an optobioelectronic device. Assembly of an antigen monolayer on electrodes yields an active interface for the amperometric transduction of the association of the complementary antibody (Ab) to the monolayer. Binding of the Ab to the monolayer blocks the electrical contact of a redox enzyme, i.e. ferrocene-modified glucose oxidase (Fc-GOx), with the electrode, and inhibits the electrobiocatalyzed oxidation of glucose. A photoisomerizable antigen assembled as a monolayer on an electrode allows the tailoring of reversible immunosensing interfaces. In one photoisomer state, the monolayer acts as an active interface for amperometric detection of the antibody. The complementary photoisomer state lacks affinity for the Ab and allows the washing-off of the antibody and the regeneration of the active antigen monolayer by a second illumination cycle. This approach is exemplified by the application of a dinitrospiropyran monolayer assembled onto an Au-electrode as a reversible sensing interface for the dinitrophenyl antibody (DNP-Ab). The dinitrospiropyran monolayer, SP-state, acts as an active interface for the association of the DNP-Ab. Photoisomerization of the monolayer to the dinitromerocyanine configuration, MRH +-state, allows the washing-off of the DNP-Ab and regeneration of the active SP-monolayer electrode by a secondary photoinduced isomerization. The reversible photostimulated binding and dissociation of DNP-Ab to and from the electrode is transduced by the application of Fc-GOx as redox probe and is further supported by microgravimetric QCM analyses.

Photochemically-, Chemically-, and pH-Controlled Electrochemistry at Functionalized Spiropyran Monolayer Electrodes

A photoisomerizable nitrospiropyran monolayer assembled on a Au electrode provides a functionalized interface for the photochemical, pH, and thermal control of electrochemical processes of charged electroactive redox probes. (Mercaptobutyl)nitrospiropyran 1 was assembled as a monolayer on a Au electrode. The monolayer exhibits reversible photoisomerizable features, and illumination of the nitrospiropyran monolayer, SP state, 320 nm < λ < 350 nm, yields at pH = 7.0 the protonated nitromerocyanine monolayer state, MRH+ state. Further irradiation of the MRH+ monolayer, λ > 495 nm, regenerates the SP state of the monolayer. The light-induced transformation of the monolayer between a neutral and a positively-charged interface allows the control of the electron transfer processes at the electrode interface. Electrooxidation of the negatively-charged (3,4-dihydroxyphenyl)acetic acid, DHPAA, is enhanced at the MRH+ monolayer electrode as compared to the SP-functionalized monolayer electrode. Electrooxidation of the positively-charged 3-hydroxytyramine (dopamine), DOPA, is inhibited at the MRH+ monolayer electrode as compared to its oxidation by the SP monolayer electrode. The control of the electrochemical oxidation of DHPAA and DOPA at the photoisomerizable monolayer electrode is attributed to the electrostatic interactions of the MRH+ monolayer electrode with the redox-active substrates. Electrostatic attraction of DHPAA and repulsion of DOPA by the MRH+ monolayer results in enhancement or inhibition of the electrochemical processes, respectively. By reversible isomerization of the monolayer between the SP and MRH+ states, cyclic amperometric transduction of the optical signals recorded by the monolayer is accomplished. In the presence of a mixture of oppositely-charged redox substrates, i.e. DHPAA and 2,5-bis[[2-(dimethylbutylammonio)ethyl]amino]-1,4-benzoquinone (3) or pyrroloquinoline quinone, PQQ, (4) and 3, photostimulated selective electrochemistry is accomplished in the presence of the photoisomerizable monolayer electrode. The transformation of the protonated nitromerocyanine monolayer, MRH+ state, generated at pH = 7.0, to the zwitterionic nitromerocyanine configuration, MR± state at higher pH, allows the pH-controlled electrooxidation of DHPAA and DOPA at the monolayer electrode. Similarly, thermal isomerization of the SP monolayer electrode, pH = 7.0, 60 °C, yields the MRH+ monolayer electrode. These thermochromic features of the monolayer are employed to respectively activate or deactivate the electrooxidation of DHPAA or DOPA at the functionalized electrode. By cyclic thermal isomerization of the SP monolayer to the MRH+ monolayer followed by photochemical isomerization of the MRH+ monolayer followed by photochemical isomerization of the MRH+ monolayer to the SP state, λ > 495 nm, the thermochromic and photochromic features of the monolayer are amperometrically transduced via the oxidation of DHPAA and DOPA, respectively. Electrochemical oxidation of DHPAA and DOPA is further accomplished by the application of a dinitrospiropyran monolayer (2) electrode in the presence of the dinitrophenyl antibody, DNP-Ab. (Mercaptobutyl)dinitrospiropyran 2 was assembled as a monolayer on a Au electrode. The dinitrospiropyran monolayer, SP state, exhibits antigen features for the DNP-Ab, where the protonated dinitromerocyanine monolayer, MRH+ state, lacks antigen features for the DNP-Ab. Association of the DNP-Ab to the SP monolayer electrode blocks the electrooxidation of DHPAA or DOPA. Photochemical isomerization of the SP monolayer to the MRH+ state, 320 nm < λ < 350 nm, results in the release of DNP-Ab and the activation of the electrooxidation of DHPAA and DOPA. By the reversible photoisomerization of the monolayer between the SP and MRH+ states in the presence of DNP-Ab, cyclic amperometric transduction of the optical signals recorded by the monolayer is accomplished.

Photochemically-activated electrodes: application in design of reversible immunosensors and antibody patterned interfaces

Antigen monolayers assembled onto Au electrodes associated with a quartz crystal act as electrochemical or microgravimetric quartz-crystal-microbalance (QCM) sensing interfaces for the complementary antibody. Electrochemical analysis of the antibody (Ab) is based on the insulation of the antigen monolayer electrode by the associated Ab towards a redox probe in the electrolyte solution. Ferrocene-modified glucose oxidase (Fc-GOx) and glucose are employed as redox probes for the amperometric transduction of the Ab association to the electrode. Bioelectrocatalyzed oxidation of glucose provides an electrochemical route to amplify the antigen-Ab complex formation. Electrochemical analysis of the dinitrophenyl antibody, DNP-Ab, by a dinitrophenyl-lysine monolayer electrode is presented. QCM analysis of the Ab is based on the frequency changes of the quartz crystal resulting from the association of the Ab to the crystal assembly. This method is discussed with the analysis of the fluorescein antibody, Flc-Ab, using a fluorescein monolayer-modified quartz crystal. A novel method to tailor reversible immunosensor devices by the application of photoisomerizable antigen monolayers on electrodes is presented. The antigen is modified by photoactive units exhibiting reversible photoisomerizable properties. In one photoisomer state, the antigen exhibits affinity for the Ab and enables its electrochemical or QCM analysis. Photoisomerization to the complementary state perturbs the antigen structure and the monolayer lacks affinity for the Ab. This enables the washing-off of the Ab and the regeneration of the actively sensing interface by a second illumination process that restores the antigen monolayer-modified surface. This method is exemplified by the development of a reversible DNP-Ab sensing electrode. N-Mercaptobutyl dinitrospopyran was assembled as a photoisomerizable monolayer on a Au electrode. The dinitrospiropyran monolayer, SP-state, exhibits affinity for the DNP-Ab and enables the amperometric detection of the Ab using Fc-GOx and glucose as redox probe. The complementary photoisomerized protonated dinitromerocyanine monolayer, MRH +-state, lacks affinity for the DNP-Ab. By photoisomerization of the DNP-Ab associated with the SP-monolayer electrode to the MRH +-monolayer state, the DNP-Ab is washed-off, and by a second illumination process, the MRH +-monolayer is re-isomerized to the SP-monolayer assembly, which is the active interface for further analysis of the DNP-Ab. Cyclic amperometric detection of the DNP-Ab by the photoisomerizable dinitrospiropyran monolayer is demonstrated. The association of the DNP-Ab to the SP-monolayer electrode and the dissociation of the Ab from the MRH +-monolayer electrode are confirmed by QCM experiments using a dinitrospiropyran monolayer-modified quartz crystal. The insulating features of an antigen-Ab complex on a conductive surface and the photochemically controlled association of an antibody to a photoisomerizable monolayer assembled onto the surface were used to develop means for micropatterning of surfaces by the antibody. A dinitrospiropyran antigen monolayer was assembled onto conductive ITO glass. A DNP-Ab solution was used as ‘ink solution’ to pattern the surface. The Ab-pattern was imaged by electrochemical copper deposition onto the Ab-lacking surface domains. The dinitrospiropyran monolayer assembled onto ITO or Pyrex glass surfaces was employed as an active interface for the photolithographic patterning of the surface with the DNP-Ab. Irradiation of the dinitrospiropyran monolayer, SP-state, through a grid-mask generated surface domains of protonated dinitromerocyanine, MRH +-state, which lacks affinity for the DNP-Ab. The DNP-Ab covalently-linked to agarose beads (50 μm) was selectively associated to the SP-monolayer sites and the micro-pattern of the resulting antibody was imaged. Methods for employing this photolithographic patterning of DNP-Ab to generate microstructures of any biomaterial, and, specifically, neural networks, are discussed.

Assembly of functionalized monolayers of redox proteins on electrode surfaces: novel bioelectronic and optobioelectronic systems

Functionalized monolayer electrodes provide the grounds for bioelectronic and optobioelectronic devices. Reconstitution of apo-glucose oxidase, apo-GOx, onto a pyrroloquinoline quinone-FAD diad, assembled as a monolayer on a Au-electrode, yields an aligned bioelectrocatalytically active enzyme on the electrode surface. The resulting reconstituted enzyme electrode exhibits superior electrical contact with the electrode surface and acts as an amperometric glucose sensing electrode. The enzyme electrode operates under oxygen and is unaffected by interfering substrates such as ascorbic acid. Photoswitchable redox proteins integrated with electrode surfaces act as active systems for the amplified amperometric transduction of recorded optical signals. Chemical modification of glucose oxidase by photoisomerizable nitrospiropyran units or reconstitution of apo-GOx with a photoisomerizable nitrospiropyran-FAD diad, yield photoisomerizable glucose oxidase with photoswitchable biocatalytic features. Assembly of the photoactive enzymes as monolayers on the Au-electrode results in functionalized surfaces for the cyclic ‘ON-OFF’ amplified amperometric transduction of recorded optical signals. A further method to photostimulate the electrical contact between a redox protein and an electrode involves the functionalization of the electrode with a photoisomerizable monolayer interface. A mixed monolayer consisting of pyridine and nitrospiropyran units was used to photoregulate the association and dissociation of cytochrome c to and from the monolayer assembly. The photostimulated electrical contact of cytochrome c with the monolayer electrode was employed to mediate the bioelectrocatalyzed reduction of oxygen in the presence of cytochrome oxidase, COx. The latter system provides an assembly for the cyclic amperometric transduction of recorded optical signals.

Amperometric Transduction and Amplification of Optical Signals Recorded by a Phenoxynaphthacenequinone Monolayer Electrode: Photochemical and pH-Gated Electron Transfer

A phenoxynaphthacenequinone photoisomerizable monolayer was assembled onto an Au electrode. The resulting “trans”-quinone monolayer exhibits poor electrochemical reversibility due to a nondensely-packed configuration. Treatment of the trans-quinone monolayer with 1-tetradecanethiol yields a densely-packed monolayer that exhibits electrochemical reversibility. The electrochemical response of the trans-quinone monolayer electrode is pH-dependent, consistent with a two-electron and two-proton redox process. Photoisomerization of the trans-quinone monolayer (305 nm 430 nm), the electroactivity of the monolayer is restored. By cyclic photoisomerization of the electrode between the ana- and trans-quinone states, reversible amperometric transduction of the recorded optical signals was accomplished. Coupling of redox-active materials, such as Fe(...

Patterning of surfaces by photoisomerizable antibody-antigen monolayers

A dinitrospiropyran antibody (DNP-Ab) photoisomerizable monolayer is assembled onto an indium tin oxide (ITO) conductive glass. The monolayer exhibits photoswitchable affinities for the DNP-Ab. The dinitrospiropyran monolayer state (SP) exhibits high affinity for the DNP-Ab, where the merocyanine photoisomer state (MR) lacks affinity for the Ab. Association of the Ab to the monolayer results in local insulation of the surface. The insulation of the ITO glass by the associated Ab and the photoswitchable binding of the DNP-Ab provides a means of mechanically patterning and photolithographically microstructuring the monolayer-modified surface. Application of the DNP-Ab solution as “ink” allows the mechanical patterning of the dinitrospiropyran monolayer (SP) and imaging of the pattern by electrodeposition of Cu onto the Ab-lacking domains. Photolithographic patterning of the dinitrospiropyran monolayer is accomplished by irradiation of the surface through a grid. Selective association of the agarose-bound DNP-Ab to the SP photolithographed pattern results in the microstructure of agarose particles containing the Ab.