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Itamar Willner

Publications and source records attributed to Itamar Willner.

At least 19 recordsLinked to original sources
PubMed2004

Enzyme-catalyzed bio-pumping of electrons into au-nanoparticles: a surface plasmon resonance and electrochemical study.

The enzyme glucose oxidase (GOx) is reconstituted on a flavin adenin dinucleotide (FAD, 1) cofactor-functionalized Au-nanoparticle (Au-NP), 1.4 nm, and the GOx/Au-NP hybrid is linked to a bulk Au-electrode by a short dithiol, 1,4-benzenedithiol (2), or a long dithiol, 1,9-nonanedithiol (3), monolayer. The reconstituted GOx/Au-NP hybrid system exhibits electrical communication between the enzyme redox cofactor and the Au-NP core. Because the thiol monolayers provide a barrier for electron tunneling, the electron transfer occurring upon the biocatalytic oxidation of glucose results in the Au-NPs charging. The charging of the Au-NPs alters the plasma frequency and the dielectric constant of the Au-NPs, thus leading to the changes of the dielectric constant of the interface. These are reflected in pronounced shifts of the plasmon angle, theta(P), in the surface plasmon resonance (SPR) spectra. As the biocatalytic charging phenomenon is controlled by the concentration of glucose, the changes in the theta(P) values correlate with the concentration of glucose. The biocatalytic charging process is characterized by following the differential capacitance of the GOx/Au-NP interface and by monitoring the potential generated on the bulk Au-electrode. The charging of the GOx/Au-NPs is also accomplished in the absence of glucose by the application of an external potential on the electrode, that resulted in similar plasmon angle shifts. The results allowed us to estimate the number of electrons stored per Au-NP at variable concentrations of glucose in the presence of the two different thiol linkers.

Aspergillus niger↗
PubMed2004

Amplified chemiluminescence surface detection of DNA and telomerase activity using catalytic nucleic acid labels.

A G-rich nucleic acid sequence binds hemin and yields a biocatalytic complex (DNAzyme) of peroxidase activity, namely, the biocatalyzed generation of chemiluminescence in the presence of H(2)O(2) and luminol. The DNAzyme is used as a label for the amplified detection of DNA, or for the analysis of telomerase activity in cancer cells, using chemiluminescence as an output signal. In one configuration, the analyzed DNA is hybridized with a primer nucleic acid that is associated with a Au surface, and the DNAzyme label is hybridized with the surface-confined analyte DNA. The DNA is analyzed with a detection limit of approximately 1 x 10(-)(9) M. In the second system, telomerase from HeLa cancer cells induces telomerization of a primer associated with a Au surface and the complementary DNAzyme units are hybridized with the telomere to yield the chemiluminescence. The detection limit of the system corresponds to 1000 HeLa cells in the analyzed sample.

Base Sequence↗
PubMed2004

Magneto-mechanical detection of nucleic acids and telomerase activity in cancer cells.

The ultra-sensitive magneto-mechanical detection of DNA, single-base-mismatches in nucleic acids, and the assay of telomerase activity are accomplished by monitoring the magnetically induced deflection of a cantilever functionalized with magnetic beads associated with the biosensing interface. The analyzed M13phi DNA hybridized with the nucleic acid-functionalized magnetic beads is replicated in the presence of dNTPs that include biotin-labeled dUTP. The resulting beads are attached to an avidin-coated cantilever, and the modified cantilever is deflected by an external magnetic field. Similarly, telomerization of nucleic acid-modified magnetic beads in the presence of dNTPs, biotin-labeled dUTP, and telomerase from cancer cell extracts and the subsequent association of the magnetic beads to the cantilever surface results in the lever deflection by an external magnetic field. M13phi DNA is sensed with a sensitivity limit of 7.1 x 10(-20) M by the magneto-mechanical detection method.

Base Pair Mismatch↗
PubMed2003

Probing photoelectrochemical processes in Au-CdS nanoparticle arrays by surface plasmon resonance: application for the detection of acetylcholine esterase inhibitors.

The photoelectrochemical charging of Au-nanoparticles (NP) in a Au-nanoparticle/CdS-nanoparticle array assembled on a Au-coated glass surface is followed by means of surface plasmon resonance (SPR) spectroscopy upon continuous irradiation of the sample. The charging of the Au-NPs results in the enhanced coupling between the localized surface plasmon of the Au-NP and the surface plasmon of the bulk surface, leading to a shift in the plasmon angle. The charging effect of the Au-NPs is supported by concomitant electrochemical experiments in the dark. Analysis of the results indicates that ca. 4.2 electrons are associated with each Au-nanoparticle under steady-state irradiation. The photoelectrochemical charging effect of the Au-NPs in the Au-CdS NP array is employed to develop a SPR sensor for acetylcholine esterase inhibitors.

Animals↗
PubMed2003

Au nanoparticle-enhanced surface plasmon resonance sensing of biocatalytic transformations.

N-(3-Aminopropyl)-N'-methyl-4,4'-bipyridinium is coupled to tiopronin-capped Au nanoparticles (diameter ca. 2 nm) to yield methyl(aminopropyl)viologen-functionalized Au nanoparticles (MPAV(2+)-Au nanoparticles). In situ electrochemical surface plasmon resonance (SPR) measurements are used to follow the electrochemical deposition of the bipyridinium radical cation modified Au nanoparticles on an Au-coated glass surface and the reoxidation and dissolution of the bipyridinium radical cation film. The MPAV(2+)-functionalized Au nanoparticles are also employed for the amplified SPR detection of NAD(+) and NADH cofactors. By SPR monitoring the partial biocatalyzed dissolution of the bipyridinium radical cation film in the presence of diaphorase (DP) NAD(+) is detected in the concentration range of 1x10(-4) M to 2x10(-3) M. Similarly, the diaphorase-mediated formation of the bipyridinium radical cation film on the Au-coated glass surface by the reduction of the MPAV(2+)-functionalized Au nanoparticles by NADH is used for the amplified SPR detection of NADH in the concentration range of 1x10(-4) M to 1x10(-3) M.

Biotransformation↗
PubMed2003

Magnetic control of electrocatalytic and bioelectrocatalytic processes.

Bioelectronics is a rapidly progressing interdisciplinary research field that has important implications for the development of biosensors, biofuel cells, biomaterial-based computers, and bioelectronic devices. Magneto-controlled molecular electronics and bioelectronics are new topics that examine the effect of an external magnetic field on electrocatalytic and bioelectrocatalytic processes of functionalized magnetic particles associated with electrodes. In this article we describe the progress in the developments of magneto-switchable electrocatalytic and bioelectrocatalytic transformations, and the effects of the rotation of the magnetic particles on the electrocatalytic and bioelectrocatalytic processes are discussed. Finally, the implications of the results on the development of biosensors, amplified immunosensors, and DNA sensors are described.

Biosensing Techniques↗
PubMed2003

A biofuel cell with electrochemically switchable and tunable power output.

An electroswitchable and tunable biofuel cell based on the biocatalyzed oxidation of glucose is described. The anode consists of a Cu(2+)-poly(acrylic acid) film on which the redox-relay pyrroloquinoline quinone (PQQ) and the flavin adenine dinucleotide (FAD) cofactor are covalently linked. Apo-glucose oxidase is reconstituted on the FAD sites to yield the glucose oxidase (GOx)-functionalized electrode. The cathode consists of a Cu(2+)-poly(acrylic acid) film that provides the functional interface for the covalent linkage of cytochrome c (Cyt c) that is further linked to cytochrome oxidase (COx). Electrochemical reduction of the Cu(2+)-poly(acrylic acid) films (applied potential -0.5 V vs SCE) associated with the anode and cathode yields the conductive Cu(0)-poly(acrylic acid) matrixes that electrically contact the GOx-electrode and the COx/Cyt c-electrode, respectively. The short-circuit current and open-circuit voltage of the biofuel cell correspond to 105 microA (current density ca. 550 microA cm(-2)) and 120 mV, respectively, and the maximum extracted power from the cell is 4.3 microW at an external loading resistance of 1 kOmega. The electrochemical oxidation of the polymer films associated with the electrodes (applied potential 0.5 V) yields the nonconductive Cu(2+)-poly(acrylic acid) films that completely block the biofuel cell operation. By the cyclic electrochemical reduction and oxidation of the polymer films associated with the anode and cathode between the Cu(0)-poly(acrylic acid) and Cu(2+)-poly(acrylic acid) states, the biofuel cell performance is reversibly switched between "ON" and "OFF" states, respectively. The electrochemical reduction of the Cu(2+)-polymer film to the Cu(0)-polymer film is a slow process (ca. 1000 s) because the formation and aggregation of the Cu(0)-clusters requires the migration of Cu(2+) ions in the polymer film and their reduction at conductive sites. The slow reduction of the Cu(2+)-polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell. The electron-transfer resistances of the cathodic and anodic processes were characterized by impedance spectroscopy. Also, the overall resistances of the biofuel cell generated by the time-dependent electrochemical reduction process were followed by impedance spectroscopy and correlated with the internal resistances of the cell upon its operation.

Bioelectric Energy Sources↗
PubMed2003

"Plugging into Enzymes": nanowiring of redox enzymes by a gold nanoparticle.

The reconstitution of an apo-flavoenzyme, apo-glucose oxidase, on a 1.4-nanometer gold nanocrystal functionalized with the cofactor flavin adenine dinucleotide and integrated into a conductive film yields a bioelectrocatalytic system with exceptional electrical contact with the electrode support. The electron transfer turnover rate of the reconstituted bioelectrocatalyst is approximately 5000 per second, compared with the rate at which molecular oxygen, the natural cosubstrate of the enzyme, accepts electrons (approximately 700 per second). The gold nanoparticle acts as an electron relay or "electrical nanoplug" for the alignment of the enzyme on the conductive support and for the electrical wiring of its redox-active center.

Apoenzymes↗
PubMed2003

Highly sensitive amplified electronic detection of DNA by biocatalyzed precipitation of an insoluble product onto electrodes.

The amplified detection of a target DNA, based on the alkaline phosphatase oxidative hydrolysis of the soluble 5-bromo-4-chloro-3-indoyl phosphate to the insoluble indigo product as an amplification path, is addressed by two different sensing configurations. The accumulation of the insoluble product on Au electrodes or Au/quartz crystals alters the interfacial electron-transfer resistance at the Au electrode or the mass associated with the piezoelectric crystal, thus enabling the quantitative transduction of the DNA sensing by Faradaic impedance spectroscopy or microgravimetric quartz crystal microbalance measurements, respectively. One sensing configuration involves the association of a complex consisting of the target DNA and a biotinylated oligonucleotide to the functionalized transducers. The binding of the avidin/alkaline phosphatase conjugate to the sensing interface followed by the biocatalyzed precipitation provides the amplification path for the analysis of the target DNA. This analysis scheme was used to sense the target DNA with a sensitivity limit that corresponds to 5 x 10(-14) M. The second amplified detection scheme involves the use of a nucleic-acid-functionalized alkaline phosphatase as a biocatalytic conjugate for the precipitation of the insoluble product. Following this scheme, the functionalized transducers are interacted with the analyzed sample that was pretreated with the oligonucleotide-modified alkaline phosphatase, followed by the biocatalyzed precipitation as the amplification route for the analysis of the target DNA. By the use of this configuration, a detection limit corresponding to 5 x 10(-13) M was achieved. Real clinical samples of the Tay-Sachs genetic disorder were easily analyzed by the developed detection routes.

Alkaline Phosphatase↗
PubMed2003

Analysis of NAD(P)+/NAD(P)H cofactors by imprinted polymer membranes associated with ion-sensitive field-effect transistor devices and Au-quartz crystals.

Specific recognition sites for the NAD(P)+ and NAD(P)H cofactors are imprinted in a cross-linked acrylamide-acrylamidophenylboronic acid copolymer membrane. The imprinted membranes, associated with pH-sensitive field-effect transistors (ISFETs) or Au-quartz piezoelectric crystals, enable the potentiometric or microgravimetric analysis of the oxidized NAD(P)+ cofactors and the reduced NAD(P)H cofactors, respectively. The NAD+- and NADP+-imprinted membranes associated with the ISFET allow the analysis of NAD+ and NADP+ with sensitivities that correspond to 15.0 and 18.0 mVdecade(-1) and detection limits of 4 x 10(-7) and 2 x 10(-7) M, respectively. The NADH- and NADPH-imprinted membranes associated with the ISFET device enable the analysis of NADH and NADPH with sensitivities that correspond to 24.2 and 21.8 mV x decade(-1) and lower detection limits that are 1 x 10(-7) and 2 x 10(-7) M, respectively. The ISFET devices functionalized with the NADH and NADPH membranes are employed in the analysis of the biocatalyzed oxidation of lactic acid and ethanol in the presence of lactate dehydrogenase and alcohol dehydrogenase, respectively.

Binding Sites↗