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Biomedical subjects

Itamar Willner

Publications and source records attributed to Itamar Willner.

At least 37 records · Page 2Linked to original sources
PubMed2006

Biomolecule-nanoparticle hybrid systems for bioelectronic applications.

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.

Animals↗
PubMed2006

Following aptamer-thrombin binding by force measurements.

The rupture forces between an aptamer (1)-functionalized AFM tip and a thrombin-modified Au surface are analyzed. The rupture force for a single aptamer/thrombin complex is determined as approximately 4.45 pN. The analysis of the system reveals that the rupture forces correspond to the melting of the G-quadruplex structure of the aptamer bound to the thrombin. This melting of the G-quadruplex leads to the dissociation of the aptamer/thrombin complex.

Aptamers, Nucleotide↗
PubMed2006

Nucleic acid-functionalized Pt nanoparticles: Catalytic labels for the amplified electrochemical detection of biomolecules.

Nucleic acid-functionalized Pt nanoparticles (Pt-NPs) act as catalytic labels for the amplified electrochemical detection of DNA hybridization and aptamer/protein recognition. Hybridization of the nucleic acid-modified Pt-NPs with a sensing nucleic acid/analyte DNA complex associated with an electrode enables the amperometric, amplified, detection of the DNA by the Pt NP electrocatalyzed reduction of H2O2 (sensitivity limit, 1 x 10(-11) M). Similarly, the association of aptamer-functionalized Pt- NPs to a thrombin aptamer/thrombin complex associated with an electrode allowed the amplified, electrocatalytic detection of thrombin with a sensitivity limit corresponding to 1 x 10(-9) M.

Aptamers, Nucleotide↗
PubMed2006

Two coupled enzymes perform in parallel the 'AND' and 'InhibAND' logic gate operations.

The coupled activation of two enzymes: glucose dehydrogenase (GDH) and horseradish peroxidase (HRP), is used to construct the parallel-operating AND and InhibAND logic gates. The added substrates for the respective enzymes, glucose and H(2)O(2), act as the gate inputs, while the biocatalytically generated NADH and gluconic acid provide the output signals that follow the operations of the gates. The two gates are generated in the same vial, thus allowing the logic operations to take place in parallel, and the simultaneous readout of the functions of the gates.

Glucose 1-Dehydrogenase↗
PubMed2006

Controlling chemical reactivity at solid-solution interfaces by means of hydrophobic magnetic nanoparticles.

Hydrophobic magnetic nanoparticles are employed to reversibly regulate the hydrophobic/hydrophilic properties of surfaces and to control the electrochemistry and bioelectochemistry at chemically modified electrodes. Selective bioelectrocatalytic transformations at relay-functionalized electrodes are accomplished by the magnetic attractions of the hydrophobic magnetic nanoparticles with coadsorbed hydrophobic redox relays to the electrode. The selective activation of one of two biocatalysts solubilized in the aqueous electrolyte solution in the absence or presence of hydrophobic magnetic nanoparticles results in the specific activation of bioelectrocatalytic processes. The magnetic attraction and retraction of hydrophobic magnetic nanoparticles to and from semiconductor nanoparticle (CdS)-functionalized electrodes enable the control of the photocurrent directions at the electrode from cathodic to anodic directions, respectively. The magnetic attraction of the hydrophobic magnetic nanoparticles to the surfaces is also employed to control biorecognition and biocatalytic transformations at solid supports. The magnetic attraction and retraction of the hydrophobic magnetic nanoparticles to and from the surfaces allow the blockage and activation of DNA hybridization, polymerization, and enzymatic digestion, respectively.

Electrochemistry↗
PubMed2006

Switchable surface properties through the electrochemical or biocatalytic generation of Ag0 nanoclusters on monolayer-functionalized electrodes.

The electroswitchable and the biocatalytic/electrochemical switchable interfacial properties of a Ag(+)-biphenyldithiol (BPDT) monolayer associated with a Au surface are described. Upon the application of a potential corresponding to -0.2 V the Ag(+)-BPDT is reduced to the Ag(0)-BPDT interface, and silver nanoclusters are generated on the interface. The application of a potential that corresponds to 0.2 V reoxidizes the monolayer to the Ag(+)-BPDT monolayer. The reversible electrochemical transformation of the Ag(+)-BPDT monolayer and of the Ag(0)-BPDT surface was followed by electrochemical means and surface plasmon resonance spectroscopy (SPR). The SPR experiments enabled us to follow the kinetics of nanoclustering of Ag(0) on the surface. The hydrophobic/hydrophilic properties of the surface are controlled by the electrochemically induced transformation of the interface between the Ag(+)-BPDT and Ag(0)-BPDT states. The Ag(0)-BPDT monolayer reveals enhanced hydrophilicity. The hydrophobic/hydrophilic properties of the interface were probed by contact angle measurements and force interactions with a hydrophobically-functionalized AFM tip. The Ag(0)-BPDT interface was also biocatalytically generated using alkaline phosphatase, AlkPh, and p-aminophenyl phosphate as substrate. The biocatalytically generated p-aminophenol reduces Ag(+) ions associated with the surface to Ag(0) nanoclusters. This enables the cyclic biocatalytic/electrochemical control of the surface properties of the modified electrode.

Alkaline Phosphatase↗
PubMed2005

Fluorescence resonance energy transfer in CdSe/ZnS-DNA conjugates: probing hybridization and DNA cleavage.

Nucleic-acid-functionalized CdSe/ZnS quantum dots (QDs) were hybridized with the complementary Texas-Red-functionalized nucleic acid. The hybridization was monitored by following the fluorescence resonance energy transfer from the QDs to the dye units. Treatment of the QD/dye DNA duplex structure with DNase I resulted in the cleavage of the DNA and the recovery of the fluorescence properties of the CdSe/ZnS QDs. The luminescence properties of the QDs were, however, only partially recovered due to the nonspecific adsorption of the dye onto the QDs. Similarly, nucleic-acid-functionalized Au nanoparticles (Au NPs) were hybridized with the complementary Texas-Red-labeled nucleic acid. The hybridization was followed by the fluorescence quenching of the dye by the Au NPs. Treatment of the Au NP/dye DNA duplex with DNase I resulted in the cleavage of the DNA and the partial recovery of the dye fluorescence. The incomplete recovery of the dye fluorescence originated from the nonspecific binding of the dye units to the Au NPs. The nonspecific binding of the dye to the CdSe/ZnS QDs and the Au NPs is attributed to nonprotected surface vacancies in the two systems.

Base Sequence↗
PubMed2005

Temperature-dependent and friction-controlled electrochemically induced shuttling along molecular strings associated with electrodes.

The temperature and solvent composition dependence of the electrochemically stimulated rate of shuttling of the redox-active cyclophane, cyclobis(paraquat-p-phenylene), on a molecular string has been studied. The molecular string includes a pi-donor diiminebenzene-site that is associated on one side with an electrode, and stoppered on the other side with an adamantane unit. The cyclophane rests on the pi-donor site, owing to stabilizing pi-donor-acceptor interactions. Electrochemical reduction of the cyclophane units, to the bis-radical cation cyclophane, results in the shuttling of the reduced cyclophane towards the electrode, a process that is driven by the removal of the stabilizing donor-acceptor interactions, and the electrostatic attraction of the reduced product by the electrode. The latter process is energetically downhill, and is temperature-independent. Upon oxidation of the reduced cyclophane that is associated with the electrode, the energetically uphill shuttling of the oxidized cyclophane to the pi-donor site proceeds. The rate of this translocation process has been found to be temperature-dependent, and controlled by the solvent composition. The experimental results have been theoretically analyzed in terms of Kramers' molecular friction model. The theoretical fitting of the experimental results, using solutions of variable composition, reveals that the rate-constants for the uphill reaction in a pure aqueous solution follow the temperature-dependence of the viscosity of water. The results demonstrate the significance of friction phenomena in shuttling processes within molecular machines.

Journal Article↗
PubMed2005

Endonuclease-based logic gates and sensors using magnetic force-amplified readout of DNA scission on cantilevers.

The endonuclease scission of magnetic particles functionalized with sequence-specific DNAs, which are associated on cantilevers, is followed by the magnetic force-amplified readout of the reactions by the nano-mechanical deflection/retraction of the cantilevers. The systems are employed to develop AND or OR logic gates and to detect single base mismatch specificity of the endonucleases. The two endonucleases EcoRI (E(A)) and AscI (E(B)) are used as inputs. The removal of magnetic particles linked to the cantilever by the duplexes 1/1a and 2/2a via the simultaneous cleavage of the DNAs by E(A) and E(B) leads to the retraction of the magnetically deflected cantilever and to the establishment of the "AND" gate. The removal of the magnetic particles linked to the cantilevers by the duplex 3/3a by either E(A) or E(B) leads to the retraction of the magnetically deflected cantilever and to the establishment of the "OR" gate. The magnetic force-amplified readout of endonuclease activities is also employed to reveal single base mismatch specificity of the biocatalysts.

Biosensing Techniques↗