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The covalent linkage of catalytic units to aptamer sequence-specific nucleic acids exhibiting selective binding affinities for substrates leads to functional scaffolds mimicking native enzymes, nucleoapzymes. The binding of the substrates to the aptamer and their structural orientation with respect to the catalytic units duplicate the functions of the active center of enzymes. The possibility of linking the catalytic sites directly, or through spacer units, to the 5′-end, 3′-end, and middle positions of the aptamers allows the design of nucleoapzyme libraries, revealing structure–functions diversities, and these can be modeled by molecular dynamics simulations. Catalytic sites integrated into nucleoapzymes include DNAzymes, transition metal complexes, and organic ligands. Catalytic transformations driven by nucleoapzymes are exemplified by the oxidation of dopamine or l-arginine, hydroxylation of tyrosine to l-DOPA, hydrolysis of ATP, and cholic acid-modified esters. The covalent linkage of photosensitizers to the tyrosinamide aptamer leads to a photonucleoapzyme scaffold that binds the N-methyl-N′-(3-aminopropane)-4,4′-bipyridinium-functionalized tyrosinamide to the aptamer. By linking the photosensitizer directly, or through a spacer bridge to the 5′-end or 3′-end of the aptamer, we demonstrate a library of supramolecular photosensitizer/electron acceptor photonucleoapzymes mimicking the functions of photosystem I in the photosynthetic apparatus. The photonucleoapzymes catalyze the photoinduced generation of NADPH, in the presence of ferredoxin-NADP+-reductase (FNR), or the photoinduced H2 evolution catalyzed by Pt nanoparticles. The future prospects of nucleoapzymes and photonucleoapzymes are discussed.

Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents the recent advances of our laboratory towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid / electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.

The synthesis and applications of redox-responsive and photoresponsive hydrogels are introduced. One approach to synthesize redox-responsive hydrogels involves the crosslinking of polymers with nucleic acid duplexes and metal-carboxylate bridges. The second approach to assemble redox-responsive hydrogels includes the cooperative crosslinking of the polymers with duplex nucleic acids and donor-acceptor redox-active bridges. By reversible oxidation/reduction of the redox-active groups, switchable stiffness of the hydrogels is demonstrated. The use of redox-responsive hydrogels as shape-memory and self-healing materials is discussed. Photoresponsive hydrogels are introduced by the design of polymer matrices cooperatively stabilized by permanent crosslinking units, e.g. boronate ester/glucosamine, and trans/cis-photoisomerizable nucleic acid bridges. Alternatively, photoresponsive hydrogels crosslinked by nucleic acids and supramolecular complexes consisted of photoisomerizable host-guest or donor-acceptor complexes are introduced. Cyclic photoinduced formation/dissociation of the photoresponsive bridges lead to reversible stiffness of the hydrogels. In addition, Au nanoparticles (NPs) or nanorods (NRs) are immobilized in hydrogels. The light-induced thermoplasmonic melting of the nucleic acid bridges by Au NPs or NRs and switchable stiffness of the hydrogels are demonstrated. The stiffness-controlled hydrogels are applied as shape-memory and self-healing matrices and as controlled drug release materials. In addition, light-induced mechanical bending of bilayer hydrogels consisting of Au NPs/NRs is demonstrated.

This paper features the synthesis of thrombin-responsive, nucleic acid-gated, UiO-68 metal&ndash, organic framework nanoparticles (NMOFs) loaded with the drug Apixaban or rhodamine 6G as a drug model. Apixaban acts as an inhibitor of blood clots formation. The loads in the NMOFs are locked by duplex nucleic acids that are composed of anchor nucleic acids linked to the NMOFs that are hybridized with the anti-thrombin aptamer. In the presence of thrombin, the duplex gating units are separated through the formation of thrombin&ndash, aptamer complexes. The unlocking of the NMOFs releases the drug (or the drug model). The release of the drug is controlled by the concentration of thrombin. The Apixaban-loaded NMOFs revealed improved inhibition, as compared to free Apixaban, toward blood clot formation. This is reflected by their longer time intervals for inducing clot formation and the decreased doses of the drug required to affect clots formation. The beneficial effects of the Apixaban-loaded NMOFs are attributed to the slow-release mechanism induced by the NMOFs carriers, where the inhibition of factor Xa in the blood clotting cycle retards the formation of thrombin, which slows down the release of the drug.

Recent scientific efforts are directed to the coupling of biomolecules with semiconductor quantum dots (QDs) to yield hybrid nanomaterials. The biomolecule/QDs conjugates combine the unique optical and electrical properties of QDs with the recognition and catalytic functions of biomolecules and provide new materials for versatile bioanalytical applications. The article addresses different approaches that implement functional biomolecule–QD hybrid systems for sensing applications. QDs are implemented as fluorescent labels for biorecognition events, and the size-controlled luminescence features of QDs are used for the development of multiplexed analysis schemes. Also, fluorescence resonance energy transfer (FRET), electron transfer, and chemiluminescence resonance energy transfer (CRET) processes are used to probe the dynamics of biorecognition events and biocatalyzed transformations. Specifically, the incorporation of functional QDs into cells holds great promise for monitoring intracellular metabolic path...

Metallic nanoparticles (NPs) of unique electronic and catalytic properties, or supramolecular nucleic acid-based nanostructures, provide new materials for electroanalytical applications. Metallic NPs are used for the electrical contacting of redox enzymes with electrodes and as electrocatalysts for the development of amperometric biosensors. DNA is used as a template for electroanalytical applications, such as the electrical contacting of enzymes with electrodes. Finally, an electrochemical method to synthesize molecularly imprinted Au NPs composites on surfaces is described, and the imprinted composites enable the selective and ultrasensitive detection of explosives, or their use as electrochemically triggered sponges for the uptake and release of substrates.

Biomolecule-nanoparticle (or carbon nanotube) hybrid systems provide new materials that combine the unique optical, electronic, or catalytic properties of the nanoelements with the recognition or biocatalytic functions of biomolecules. This article summarizes recent applications of biomolecule-nanoparticle (or carbon nanotubes) hybrid systems for sensing, synthesis of nanostructures, and for the fabrication of nanoscale devices. The use of metallic nanoparticles for the electrical contacting of redox enzymes with electrodes, and as catalytic labels for the development of electrochemical biosensors is discussed. Similarly, biomolecule-quantum dot hybrid systems are implemented for optical biosensing, and for monitoring intracellular metabolic processes. Also, the self-assembly of biomolecule-metal nanoparticle hybrids into nanostructures and functional nanodevices is presented. The future perspectives of the field are addressed by discussing future challenges and highlighting different potential applications.

The electrical contacting of redox enzymes with electrodes is the most fundamental requirement for the development of amperometric biosensors and biofuel cell elements. For the effective electrical communication of redox enzymes with electrodes the use of electron relay units that transport the electrons between the enzyme redox center and the conducting surface is essential. Also, the structural alignment of the redox enzyme units in respect to the electrode in a configuration where the enzyme redox center is in close proximity to the conductive surface is needed. The present report summarizes the reconstitution paradigm developed by our laboratory in the last decade as a versatile method to electrically contact redox enzymes with electrodes, and as a generic approach to develop amperometric biosensors and biofuel cell elements. The process is based on the reconstitution of the apo-enzyme on a relay-cofactor monolayer on thin film-functionalized electrode. Different relay units were used to electrically communicate flavin adenine dinucleotide (FAD)-containing enzymes (flavoenzymes) or pyrroloquinoline quinone (PQQ)-containing enzymes with electrodes. This included molecular redox-active relays, molecular redox-active ‘shuttles’, redox-active polymers (e.g., polyaniline), Au nanoparticles, and carbon nanotubes. The reconstitution of different apo-enzymes on these relay-cofactor-functionalized electrodes led to unprecedented efficient electrical contacting between the redox centers of the enzymes and the electrodes. Besides very sensitive amperometric biosensors that emerged from this method, the resulting amperometric biosensors revealed high selectivity and specificity. A related approach to establish electrical contact between redox enzymes dependent on diffusional cofactors and electrodes and to develop an integrated bioelectrocatalytically active enzyme electrode was developed. The method involved assembly of a relay-cofactor diad on the electrode, and the surface crosslinking of an affinity complex generated between the enzyme and the surface-confined cofactor units. This method was successfully applied to electrically contact nicotinamide adenine dinucleotide (phosphate) NAD(P)+-dependent enzymes and cytochrome c-dependent enzymes. For example, enzyme-modified electrodes for the bioelectrocatalyzed oxidation of alcohol, lactate and malate were fabricated by the electrical contacting of the respective NAD(P)+-dependent dehydrogenases. Similarly, the bioelectrocatalytic reduction of O2 was accomplished by an integrated cytochrome c/cytochrome oxidase-functionalized electrode. The electrically contacted enzyme electrodes were also used to develop noncompartmentalized biofuel cell elements. Biofuel cell elements consisting of electrically contacted reconstituted enzyme electrodes were constructed. Glucose or alcohol were used in these systems as fuel substrates and O2 as oxidizer.

Machinelike operations are common functions in biological systems, and substantial recent research efforts are directed to mimic such processes at the molecular or nanoscale dimensions. The present Feature Article presents three complementary approachscate the present es to design machinelike operations: by the signal-triggered mechanical shuttling of molecular components; by the signal-triggering of chemical processes on surfaces, resulting in mechanical motion of micro/nanoscale objects; and by the fuel-triggered motility of biomolecule-metal nanowire hybrid systems. The shuttling of molecular components on molecular wires assembled on surfaces in semirotaxane configurations using electrical or optical triggering signals is described. The control of the hydrophilic/hydrophobic surface properties through molecular shuttling or by molecular bending/stretching processes is presented. Stress generated on microelements, such as cantilevers, results in the mechanical deflection of the cantilever. The deposition of a redox-active polyaniline film on a cantilever allows the reversible electrochemically induced deflection and retraction of the cantilever by the electrochemical oxidation or reduction of the polymer film, respectively. A micro-robot consisting of the polypyrrole (PPy) polymer deposited on a multi-addressable configuration of electrodes is described. Au magnetic core/shell nanoparticles are incorporated into a polyaniline film, and the conductivity of the composite polymer is controlled by an external magnet. Finally, the synthesis of a hybrid nanostructure consisting of two actin filaments tethered to the two ends of a Au nanowire is described. The adenosine triphosphate (ATP)-fueled motility of the hybrid nanostructure on a myosin monolayer associated with a solid support is demonstrated.

Biomolecule-metal or semiconductor nanoparticle (NP) hybrid systems combine the recognition and catalytic properties of biomolecules with the unique electronic and optical properties of NPs. This enables the application of the hybrid systems in developing new electronic and optical biosensors, to synthesize nanowires and nanocircuits, and to fabricate new devices. Metal NPs are employed as nano-connectors that activate redox enzymes, and they act as electrical or optical labels for biorecognition events. Similarly, semiconductor NPs act as optical probes for biorecognition processes. Double-stranded DNA or protein chains that are modified with metallic nanoclusters act as templates for the synthesis of metallic nanowires. The nanowires are used as building blocks to assemble nano-devices such as a transistor or a nanotransporter.

Recent advances in nanobiotechnology involve the use of biomolecule-nanoparticle (NP) hybrid systems for bioelectronic applications. This is exemplified by the electrical contacting of redox enzymes by means of Au-NPs. The enzymes, glucose oxidase, GOx, and glucose dehydrogenase, GDH, are electrically contacted with the electrodes by the reconstitution of the corresponding apo-proteins on flavin adenine dinucleotide (FAD) or pyrroloquinoline quinone (PQQ)-functionalized Au-NPs (1.4 nm) associated with electrodes, respectively. Similarly, Au-NPs integrated into polyaniline in a micro-rod configuration associated with electrodes provides a high surface area matrix with superior charge transport properties for the effective electrical contacting of GOx with the electrode. A different application of biomolecule-Au-NP hybrids for bioelectronics involves the use of Au-NPs as carriers for a nucleic acid that is composed of hemin/G-quadruplex DNAzyme units and a detecting segment complementary to the analyte DNA. The functionalized Au-NPs are employed for the amplified DNA detection, and for the analysis of telomerase activity in cancer cells, using chemiluminescence as a readout signal. Biomolecule-semiconductor NP hybrid systems are used for the development of photoelectrochemical sensors and optoelectronic systems. A hybrid system consisting of acetylcholine esterase (AChE)/CdS-NPs is immobilized in a monolayer configuration on an electrode. The photocurrent generated by the system in the presence of thioacetylcholine as substrate provides a means to probe the AChE activity. The blocking of the photocurrent by 1,5-bis(4-allyldimethyl ammonium phenyl)pentane-3-one dibromide as nerve gas analog enables the photoelectrochemical analysis of AChE inhibitors. Also, the association CdS-NP/double-stranded DNA hybrid systems with a Au-electrode, and the intercalation of methylene blue into the double-stranded DNA, generates an organized nanostructure of switchable photoelectrochemical functions. Electrochemical reduction of the intercalator to the leuco form, -0.4 V vs. SCE, results in a cathodic photocurrent as a result of the transfer of photoexcited conduction-band electrons to O(2) and the transport of electrons to the valance-band holes by the reduced intercalator units. The oxidation of the intercalator, E 0 V (vs. SCE), yields in the presence of triethanolamine, TEOA, as sacrificial electron donor, an anodic photocurrent by the transport of conduction-band electrons, through intercalator units, to the electrodes, and filling the valance-band holes with electrons supplied by TEOA. The systems reveal potential-switchable directions of the photocurrents, and reveal logic gate functions.

This feature article addresses the implementation of catalytic nucleic acids as functional units for the construction of logic gates and computing circuits, and discusses the future applications of these systems. The assembly of computational modules composed of DNAzymes has led to the operation of a universal set of logic gates, to field programmable logic gates and computing circuits, to the development of multiplexers/demultiplexers, and to full-adder systems. Also, DNAzyme cascades operating as logic gates and computing circuits were demonstrated. DNAzyme logic systems find important practical applications. These include the use of DNAzyme-based systems for sensing and multiplexed analyses, for the development of controlled release and drug delivery systems, for regulating intracellular biosynthetic pathways, and for the programmed synthesis and operation of cascades.

This feature article addresses the implementation of catalytic nucleic acids as functional units for the construction of logic gates and computing circuits, and discusses the future applications of these systems. The assembly of computational modules composed of DNAzymes has led to the operation of a universal set of logic gates, to field programmable logic gates and computing circuits, to the development of multiplexers/demultiplexers, and to full-adder systems. Also, DNAzyme cascades operating as logic gates and computing circuits were demonstrated. DNAzyme logic systems find important practical applications. These include the use of DNAzyme-based systems for sensing and multiplexed analyses, for the development of controlled release and drug delivery systems, for regulating intracellular biosynthetic pathways, and for the programmed synthesis and operation of cascades.

Biomolecule–nanoparticle (NP) [or quantum-dot (QD)] hybrid systems combine the recognition and biocatalytic properties of biomolecules with the unique electronic, optical, and catalytic features of NPs and yield composite materials with new functionalities. The biomolecule–NP hybrid systems allow the development of new biosensors, the synthesis of metallic nanowires, and the fabrication of nanostructured patterns of metallic or magnetic NPs on surfaces. These advances in nanobiotechnology are exemplified by the development of amperometric glucose sensors by the electrical contacting of redox enzymes by means of AuNPs, and the design of an optical glucose sensor by the biocatalytic growth of AuNPs. The biocatalytic growth of metallic NPs is used to fabricate Au and Ag nanowires on surfaces. The fluorescence properties of semiconductor QDs are used to develop competitive maltose biosensors and to probe the biocatalytic functions of proteases. Similarly, semiconductor NPs, associated with electrodes, are used to photoactivate bioelectrocatalytic cascades while generating photocurrents.

Redox enzymes in bioelectronic devices usually lack direct electrical contact with electrodes, owing to the spatial separation of their redox centers from the conductive surfaces by the protein shells. The reconstitution of apo-enzymes on cofactor-functionalized nanostructures associated with electrodes provides a means to align the biocatalysts on the conductive surface and to electrically contact redox enzymes with electrodes. The reconstitution of apo-enzymes on cofactor-functionalized gold nanoparticles or carbon nanotubes has led to effective electrical communication between the redox proteins and the electrodes. Alternatively, the reconstitution of redox enzymes on molecular wires that enable electron tunneling or dynamic charge shuttling represent supramolecular biocatalytic nanostructures exhibiting electrical contact. The bioelectrocatalytic activities of the electrically wired reconstituted enzymes on electrodes have allowed the development of amperometric biosensors and biofuel cell elements.

Enzymes act as catalysts for the growth of metallic nanoparticles (NPs). The enzyme-mediated growth of metallic NPs provides a general means to follow biocatalyzed transformations, and to develop optical sensors for different substrates such as glucose, L-DOPA, alcohols, lactate or nerve gas analogs. Enzymes modified with Au NPs act as biocatalysts for the fabrication of metallic nanowires. The dip-pen nanolithography of NP-functionalized enzymes on Si surfaces yields biocatalytic templates that enable the orthogonal evolution of nanowires consisting of different metals.

Vectorial electron transfer (ET) is a central feature of many biological transformations such as the photosynthetic apparatus or the biocatalytic oxygen assimilation. The present essay summarizes recent studies directed to the chemical modification of biomaterials to yield new photoactive materials that mimic natural photosynthesis to the extent that photoinduced directional ET leads to charge separation of the photogenerated redox products. Specifically, the reconstitution of proteins with photosensitizer–electron-acceptor units is addressed. One example involves the reconstitution of apo-myoglobin with a bis-bipyridinium Zn(II)-protoporphyrin dyad. Vectorial photoinduced ET initiated by the photoactive protein in the presence of the secondary electron acceptor Ru(NH3)63+ leads to substantial stabilization of the redox products. A second example includes the reconstitution of apo-β-hemoglobin with Co(II)-protoporphyrin IX as catalytic redox center and the chemical functionalization of the cysteine-93 residue with the eosin chromophore. The photogenerated redox species Eo− β-HbCo(I) are stabilized against back ET, kb=370 s−1. The modified protein acts as a photoenzyme for the photoinduced hydrogenation of acetylene to ethylene. A different approach to accomplish photoinduced vectorial ET involves the organization of layered Au-nanoparticle arrays crosslinked by the oligocationic bis-bipyridinium-Zn(II)-protoporphyrin IX (1), acting as a photosensitizer–electron-acceptor dyad. Photoinduced ET assembly leads to the transport of electrons through the conductive Au-nanoparticle array and to the generation of a photocurrent. A further approach to stimulate photoactivated vectorial ET involves the use of a photoisomerizable monolayer associated with an electrode as a command interface for the photochemical activation and deactivation of the electrical contact between cytochrome c (Cyt. c) and the electrode. A photoisomerizable monolayer consisting of pyridine and nitrospiropyran units is used to control the electrical contact between Cyt. c and the electrode. The electrically contacted Cyt. c activates the biocatalyzed reduction of O2 by cytochrome oxidase (COx). The integrated system, consisting of the photoisomerizable monolayer-functionalized electrode and the Cyt. c/COx/O2 components, provides a system for the amplified electrical transduction of photonic signals recorded by the monolayer interface. The system duplicates functions of the vision process.

Tailored sensoric, electronic, photoelectrochemical, and bioelectrocatalytic functions can be designed by organized molecular or biomolecular nanoparticle hybrid configurations on surfaces. Layered receptor-cross-linked Au nanoparticle assemblies on electrodes act as specific sensors of tunable sensitivities. Layered DNA-cross-linked CdS nanoparticles on electrode supports reveal organized assemblies of controlled electronic and photoelectrochemical properties. Au nanoparticle-FAD semisynthetic cofactor units are reconstituted into apo-glucose oxidase (GOx) and assembled onto electrodes. The resulting enzymes reveal effective electrical contacting with the electrodes, and exhibit bioelectrocatalytic functions toward the oxidation of glucose to gluconic acid. Magneto-switchable electrocatalysis and bioelectrocatalysis are accomplished by the surface modification of magnetic particles with redox-relay units. By the attraction of the modified magnetic particles to the electrode support, or their retraction from the electrode, by means of an external magnet, the electrochemical functions of the magnetic particle-tethered relays can be switched between "ON" and "OFF" states, respectively. The magneto-switchable redox functionalities of the modified particles activate electrocatalytic transformations, such as a biocatalytic chemoluminescence cascade that leads to magneto-switchable light emission or the activation of bioelectrocatalytic processes.

The base sequence in nucleic acids encodes substantial structural and functional information into the biopolymer. This encoded information provides the basis for the tailoring and assembly of DNA machines. A DNA machine is defined as a molecular device that exhibits the following fundamental features. (1) It performs a fuel-driven mechanical process that mimics macroscopic machines. (2) The mechanical process requires an energy input, "fuel." (3) The mechanical operation is accompanied by an energy consumption process that leads to "waste products." (4) The cyclic operation of the DNA devices, involves the use of "fuel" and "anti-fuel" ingredients. A variety of DNA-based machines are described, including the construction of "tweezers," "walkers," "robots," "cranes," "transporters," "springs," "gears," and interlocked cyclic DNA structures acting as reconfigurable catenanes, rotaxanes, and rotors. Different "fuels", such as nucleic acid strands, pH (H⁺/OH⁻), metal ions, and light, are used to trigger the mechanical functions of the DNA devices. The operation of the devices in solution and on surfaces is described, and a variety of optical, electrical, and photoelectrochemical methods to follow the operations of the DNA machines are presented. We further address the possible applications of DNA machines and the future perspectives of molecular DNA devices. These include the application of DNA machines as functional structures for the construction of logic gates and computing, for the programmed organization of metallic nanoparticle structures and the control of plasmonic properties, and for controlling chemical transformations by DNA machines. We further discuss the future applications of DNA machines for intracellular sensing, controlling intracellular metabolic pathways, and the use of the functional nanostructures for drug delivery and medical applications.

The base sequence in nucleic acids encodes substantial structural and functional information into the biopolymer. This encoded information provides the basis for the tailoring and assembly of DNA machines. A DNA machine is defined as a molecular device that exhibits the following fundamental features. (1) It performs a fuel-driven mechanical process that mimics macroscopic machines. (2) The mechanical process requires an energy input, "fuel." (3) The mechanical operation is accompanied by an energy consumption process that leads to "waste products." (4) The cyclic operation of the DNA devices, involves the use of "fuel" and "anti-fuel" ingredients. A variety of DNA-based machines are described, including the construction of "tweezers," "walkers," "robots," "cranes," "transporters," "springs," "gears," and interlocked cyclic DNA structures acting as reconfigurable catenanes, rotaxanes, and rotors. Different "fuels", such as nucleic acid strands, pH (H⁺/OH⁻), metal ions, and light, are used to trigger the mechanical functions of the DNA devices. The operation of the devices in solution and on surfaces is described, and a variety of optical, electrical, and photoelectrochemical methods to follow the operations of the DNA machines are presented. We further address the possible applications of DNA machines and the future perspectives of molecular DNA devices. These include the application of DNA machines as functional structures for the construction of logic gates and computing, for the programmed organization of metallic nanoparticle structures and the control of plasmonic properties, and for controlling chemical transformations by DNA machines. We further discuss the future applications of DNA machines for intracellular sensing, controlling intracellular metabolic pathways, and the use of the functional nanostructures for drug delivery and medical applications.

Bioelectronics is a progressing interdisciplinary research field that involves the integration of biomaterials with electronic transducers, such as electrodes, field-effect-transistors or piezoelectric crystals. Surface engineering of biomaterials, such as enzymes, antigen-antibodies or DNA on the electronic supports, controls the electrical properties of the biomaterial-transducer interface and enables the electronic transduction of biorecognition events, or biocatalyzed transformation, on the transducers. Bioelectronic sensing devices, biosensors of tailored sensitivities and specificities, are being developed.

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 elec- tron transfer between molecular redox-species or redox-proteins. The systems use a photon- ic input for the generation of an electronic output and act as information processing assem- blies. Programmed arrays of photosensitizer/electron acceptor cross-linked Au-nanoparticle arrays are assembled on indium tin oxide (ITO) for photoelectrochemical applications. The miniaturization of devices to molecular or nanoscale dimensions represents a challenging research topic in modern science (1,2). Photonic activation of electronic functions in nanostructured assemblies may have important implications in designing molecular-based logic gates (3), information storage and processing devices (4), and in the tailoring of new sensors (5), optical switches (6), and solar cells (7). Several basic features should characterize photoactivated molecular arrays that act as electronic devices: (i) Photoactive molecular or nanoparticle architectures must be integrated with electronic trans- ducers such as electrodes, piezoelectric crystals or field-effect-transistors; (ii) The photonic signal should trigger a chemical or physical function in the nanostructured array. This may include the pho- tonic activation of a binding process (8), molecular translocation (9), redox-functions (10), electron transfer (11), wettability (12), or sol-gel transitions (13); (iii) The photonic activation of the device functions should be reversible. (iv) The photonically triggered chemical functions in the organized molecular or nanoparticle architectures should be electronically transduced in the form of current, volt- age, or other electronic outputs. The present account describes novel methods to organize photoactive molecular (14), biomolecular (15), and nanoparticle arrays (16) on electronic transducers, and address- es the possible applications of these systems as "smart interfaces" for information storage and process- ing, sensing and the control of the electron-transfer properties at electrodes. Scheme 1A shows a general scheme for the amperometric transduction of photonic information recorded by a photoisomerizable monolayer-interface associated with the electrode. State A of the monolayer is redox-inactive and does not electronically communicate with the electrode. Photoisomerization of the interface to state B results in a redox-active species, and the recorded optical signal is amperometrically transduced. Irradiation of the redox-active monolayer at another wavelength regenerates the redox-inactive monolayer, and the primary photonic information recorded by the sys- tem is erased. Thus, the system describes a "Write-Read-Erase" system. Figure 1A shows the assembly of a photoisomerizable phenoxynaphthacene quinone monolayer-electrode that acts as a photochemical switch according to Scheme 1A (17). The carboxymethyl phenoxy naphthacene quinone (1) was cova

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.

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.

Layered functionalized electrodes are used as optoelectronic assemblies for the electronic transduction of recorded photonic signals. Functionalization of a Au electrode with a photoisomerizable redox-activated monolayer enables the amperometric transduction of the photonic information recorded by the interface. This is exemplified with the organization of a phenoxynaphthacenequinone monolayer (1a). Organization of a photoactivated command layer on an electrode can be used to control interfacial electron transfer and might be applied for the electrical transduction of recorded optical signals. This is addressed with the assembly of a nitrospiropyran photoisomerizable monolayer (2a) on a Au electrode which acts as a command surface for controlling by light interfacial electron transfer. The monolayer undergoes photoisomerization between the neutral state (2a) and the positively charged protonated merocyanine state (2b). The charged interface controls the oxidation of dihydroxyphenylacetic acid, DHPAA (3), and of 3-hydroxytyramine, DOPA (4), and the system is used for the electrochemical transduction of optical signals recorded by the monolayer. Functionalization of electrodes with a β-cyclodextrin monolayer or with an eosin π-donor layer enables the light-stimulated association or dissociation of the photoisomerizable N,N′-bipyridinium azobenzene (5t) and of bis-pyridinium azobenzene (8t) to or from the modified surfaces. Association and dissociation of the surface-associated supramolecular complexes are transduced by electrochemical or piezoelectrical signal outputs. The organization of a supramolecular system where a molecular component is translocated by light-signals between two distinct positions enables one to design ‘molecular machines’. This is exemplified by the organization of a molecular assembly consisting of a ferrocene-functionalized β-cyclodextrin (11) threaded onto an azobenzene-alkyl chain wire and stoppered with an anthracene barrier which acts as a nanoscale molecular machine, a light-stimulated ‘molecular train’. The ferrocene-functionalized β-cyclodextrin is reversibly translocated between the trans-azobenzene and the alkyl chain by cyclic light-induced isomerization of the photoactive monolayer. The position of the β-cyclodextrin receptor is transduced by its chronoamperometric response.

Tailoring of electrically contacted enzyme electrodes provides the grounds for bioelectronic and biosensor systems. Redox-enzymes organized onto electrodes as monolayer assemblies, and chemically functionalized by redox-relay groups, yield electrically contacted enzyme electrodes exhibiting bioelectrocatalytic features. The sensitivity of the enzyme electrode can be enhanced, or tuned, by the organization of multilayer enzyme electrodes and the application of rough metal supports. Enzyme electrodes of extremely efficient electrical communication with the electrode are generated by the reconstitution of apo-flavoenzymes onto relay-FAD monolayers associated with electrodes. The reconstitution process results in an aligned enzyme on the surface, and its effective electrical contact with the electrode yields selective enzyme electrodes of unprecedented high current responses. Integrated electrodes consisting of relay-NAD(P)+-cofactor and enzyme units are generated by the reconstitution of NAD(P)+-dependent enzymes onto a relay-NAD(P)+ monolayer assembly followed by lateral crosslinking of the enzyme network.

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.

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.

Electrical communication of the redox-active center of enzymes with an electrode surface is a fundamental element for the development of amperometric biosensor devices. Different methods to assemble enzyme-electrodes exhibiting electrical contact between the redox protein and electrode surface are discussed with specific examples for tailoring glucose sensing electrodes. By one approach, a multilayer array of glucose oxidase is assembled on a Au-electrode. The number of enzyme layers is controlled by the synthetic methodology to assemble the electrode. Electrical contact between the enzyme array and the electrode is established by chemical modification of the protein layer with N -(2-methyl-ferrocene)-caproic acid, acting as an electrode is established by chemical enzyme layers associated with the electrode allows one to control the sensitivity of the resulting enzyme electrode. A further means of enhancing the sensitivities of enzyme electrodes involves the application of rough Au-electrodes as base-support to assemble the enzyme network. The high surface area of these electrodes (roughness factor ≈ 20) allows the increase of the biocatalyst content in a single monolayer, and the resulting amperometric responses of the electrodes are ca. 8-fold enhanced compared to enzyme layers assembled on smooth electrodes of identical geometrical areas. A novel method to electrically wire flavoenzymes with electrode surfaces was developed by reconstitution of the apo-flavoenzyme with a ferrocene-tethered FAD diad. Reconstitution of apo-glucose oxidase with the ferrocene-FAD diad yields an active bioelectrocatalyst of direct electrical communication with the electrode, ‘electroenzyme’. The reconstitution methodology was further applied to tailor enzyme-electrodes of superior properties for electrical contact with the electrodes. A pyrroloquinoline quinone-FAD diad monolayer was assembled on a Au-electrode. Apo-glucose oxidase was reconstituted on the surface with the FAD-cofactor site to yield the aligned biocatalyst on the electrode. The pyrroloquinoline quinone. PQQ, redox unit acts as an electron relay that electrically contacts the FAD redox-site of the enzyme with the electrode. The surface reconstituted enzyme exhibits direct electrical communication with the electrode and acts as bioelectrocatalyst for the oxidation of glucose. The electrical communication of the reconstituted glucose oxidase on the PQQ-FAD monolayer is extremely efficient. The experimental current density at a glucose concentration of 80 mM is 300 ± 100 μ A · cm −2 . This value overlaps the theoretical current density of glucose oxidase electrode (290 ± 60 μ A · cm −2 ) taking into account the limiting turnover-rate of the enzyme, 900 ± 150 s −1 (at 35°C). The extremely efficient electrical contact of the reconstituted enzyme and the electrode yields an enzyme-electrode that is insensitive to oxygen and is not affected by glucose-sensing interferants such as ascorbic acid. The application of the different enzyme-electrode configurations as bioelectronic devices for the determination of glucose is addressed.

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.

DNA/nanoparticle hybrid systems combine the unique electronic and optical properties of nanomaterials with the recognition and catalytic properties of nucleic acids. These materials hold great promise for the development of new sensing platforms, the programmed organization of nanoparticles, the switchable control of plasmonic phenomena in the nanostructures, and the controlled delivery of drugs. In this Perspective, we summarize recent advances in the application of DNA/nanoparticle (NP) hybrids in these different disciplines. Nucleic acid-semiconductor quantum dot hybrids are implemented to develop multiplexed sensing platforms for targeted DNA. The chemiluminescence resonance energy transfer mechanism is introduced as a new transduction signal, and the amplified detection of DNA targets through the biocatalytic regeneration of analytes is demonstrated. DNA machines consisting of catenanes or tweezers, and modified with fluorophore/Au NP pairs are used as functional devices for the switchable "mechanical" control of the fluorescence properties of the fluorophore. Also, nucleic acid nanostructures act as stimuli-responsive caps for trapping drugs in the pores of mesoporous SiO2 nanoparticles. In the presence of appropriate biomarker triggers, the pores are unlocked, leading to the controlled release of anticancer drugs. Selective cancer-cell death is demonstrated with the stimuli-responsive SiO2 nanoparticles.

The information encoded in the base sequence of DNA provides substantial structural and functional information for the instructive self-assembly of one-dimensional (1D) functional DNA nanostructures. The hybridization chain reaction (HCR) and the formation of HCR-stimulated DNAzyme nanochains are presented, as a means to develop amplified DNA sensors and aptasensors. Similarly, the rolling circle amplification (RCA) process is implemented to generate 1D DNA nanochains consisting of constant repeat units being implemented for the amplified sensing (using DNAzymes as repeat units) and for the switchable control of electron transfer at electrodes. 1D DNA nanostructures are used as templates for the programmed positioning of enzymes that enable the activation of enzyme cascades and the biocatalytic growth of metallic nanowires. The future perspectives of the self-assembly mechanisms are discussed.

Redox polymers act as macromolecular interfaces that electrically communicate redox centers in proteins with their macroscopic environment. N-Methyl-N′-carboxyalkyl-4,4′-bipyridinium-derivatized polylysine (1) acts as an electron mediator from photoexcited Ru(bpy)32+ to the redox enzyme glutathione reductase (GR). The rate of electron transfer from the redox polymer to GR is controlled by the chain lengths linking the bipyridinium units to the polymer. Nitrate reductase (NR) immobilized in an acrylamide-N-methyl-N′-acrylamido-4,4′-bipyridinium copolymer (4) reveals electrical communication with photoexcited Ru(bpy)32+ and stimulates the photoinduced biocatalyzed reduction of nitrate (NO3−) to nitrite (NO2−). Electrobiocatalyzed reduction of nitrate to nitrite is accomplished by immobilization of NR in polythiophene-4,4′-bipyridinium associated with an Au electrode. The rate of electrocatalyzed reduction of NO3− relates to the bulk concentration of nitrate, and thus the enzyme electrode acts as a biosensor for NO3−. Photoelectrochemical biocatalyzed reduction of nitrate to nitrite is accomplished by electrostatic or covalent attachment of NR to a N-methyl-N′-propionyl-4,4′-bipyridinium-derivatized polyethyleneimine associated with semiconductor TiO2 colloids or powders. The polymer acts as electron trap of conduction band electrons and electrically communicates the semiconductor photocatalyst with nitrate reductase.

The base sequence encoded in nucleic acids yields significant structural and functional properties into the biopolymer. The resulting nucleic acid nanostructures provide the basis for the rapidly developing area of DNA nanotechnology. Advances in this field will be exemplified by discussing the following topics: (i) Hemin/G-quadruplex DNA nanostructures exhibit unique electrocatalytic, chemiluminescence and photophysical properties. Their integration with electrode surfaces or semiconductor quantum dots enables the development of new electrochemical or optical bioanalytical platforms for sensing DNA. (ii) The encoding of structural information into DNA enables the activation of autonomous replication processes that enable the ultrasensitive detection of DNA. (iii) By the appropriate design of DNA nanostructures, functional DNA machines, acting as "tweezers", "walkers" and "stepper" systems, can be tailored. (iv) The self-assembly of nucleic acid nanostructures (nanowires, strips, nanotubes) allows the programmed positioning of proteins on the DNA templates and the activation of enzyme cascades.

Artificial photosynthetic devices provide a means for the use of solar light in generating fuel materials and valuable chemicals and for the removal of environmental pollutants. Control of photosensitized electron transfer reactions and development of catalysts for utilizations of the intermediate electron transfer products are essential aspects in designing artificial photosynthetic systems. Homogeneous and heterogeneous catalysts as well as biocatalysts (enzymes and cofactors) can be coupled to photochemically induced electron transfer reactions and effect photosynthetic transformations such as hydrogen evolution, CO2-fixation, hydrogenation, and hydroformylation processes. The progress in tailoring artificial photosynthetic devices in the context of thermodynamic and kinetic limitations of such systems is described. Integrated systems, where catalytic performance and control of electron transfer reactions which occur in organized assemblies are specifically emphasized.

Surface-enhanced Raman scattering (SERS) from molecules adsorbed on rhodium-modified colloidal silver particles is reported for the first time. Deposition of thin layers of metallic rhodium on the silver surface led to fast aggregation of the sol and to modifications of its SERS spectrum. An intense new band, assigned to the RhO stretching vibration of citrate ions bound to rhodium sites, appeared at 530 cm −1 in the Raman spectrum after rhodium addition to the suspension. The spectra of acetylene adsorbed on both unmodified silver particles and silver modified by an overlayer of rhodium indicated that acetylene displaced the citrate ions from their adsorption sites. All acetylene spectra were characterized by weak bands at 1990, 2050 and 2150 cm −1 assigned to σ π-complexes between acetylene and silver, by a silver acetylide peak at 1800 cm −1 and by an intense band at 1550 cm −1 due to C=C containing species formed on the surface. However, on the rhodium-modified colloid an additional band, attributed to acetylene σ π-bound to rhodium sites, was observed at 1910–1920 cm −1 . The intensity of the new band was a direct function of the amount of rhodium deposited on the silver. It increased immediately after acetylene adsorption, and later slowly diminished, while simultaneously the 1550 cm −1 peak became more important. This time evolution was ascribed to a reaction taking place on the surface.

Electrical communication between the redox centres of enzymes and electrodes is an essential function for the development of enzyme electrodes for biosensors or biofuel cell elements.1–3 Redox proteins usually lack direct electrical communication between their redox sites and the electrode support. ...

Amplified detection of DNA is a central research topic in modern bioanalytical science. Electronic or optical transduction of DNA recognition events provides readout signals for DNA biosensors. Amplification of the DNA analysis is accomplished by the coupling of nucleic acid-functionalized enzymes or nucleic acid-functionalized nanoparticles (NP) as labels for the DNA duplex formation. This chapter discusses the amplified amperometric analysis of DNA by redox enzymes, the amplified optical sensing of DNA by enzymes or DNAzymes, and the amplified voltammetric, optical, or microgravimetric analysis of DNA using metallic or semiconductor nanoparticles. Further approaches to amplify DNA detection involve the use of micro-carriers of redox compounds as labels for DNA complex formation on electrodes, or the use of micro-objects such as liposomes, that label the resulting DNA complexes on electrodes and alter the interfacial properties of the electrodes. Finally, DNA machines are used for the optical detection of DNA, and the systems are suggested as future analytical procedures that could substitute the polymerase chain reaction (PCR) process.