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Biomedical subjects

Itamar Willner

Publications and source records attributed to Itamar Willner.

At least 73 records · Page 4Linked to original sources
PubMed2004

Electromechanics of a redox-active rotaxane in a monolayer assembly on an electrode.

A rotaxane monolayer consisting of the cyclophane, cyclobis(paraquat-p-phenylene) (2), threaded on a "molecular string" that includes a pi-donor diiminobenzene unit and stoppered by an adamantane unit is assembled on a Au electrode. The surface coverage of the electroactive cyclophane unit, E degrees = -0.43 V vs SCE, corresponds to 0.8 x 10(-10) mol.cm(-2). The cyclophane (2) is structurally localized on the molecular string by generating a pi-donor-acceptor complex with the diiminobenzene units of the molecular string. The cyclophane (2) acts as a molecular shuttle, revealing electrochemically driven mechanical translocations along the molecular wire. Reduction of the cyclophane (2) to the respective biradical-dication results in its dissociation from the pi-donor site, and the reduced cyclophane is translocated toward the electrode. Oxidation of the reduced cyclophane reorganizes 2 on the pi-donor-diiminobenzene sites. The positions of the oxidized and reduced cyclophane units are characterized by chronoamperometric and impedance measurements. Using double-step chronoamperometric measurements the dynamics of the translocation of the cyclophane units on the molecular string is characterized. The reduced cyclophane moves toward the electrode with a rate constant corresponding to k(1) = 320 s(-1), whereas the translocation of the oxidized cyclophane from the electrode to the pi-donor binding site proceeds with a rate constant of k(2) = 80 s(-1). Also, in situ electrochemical/contact angle measurements reveal that the electrochemically driven translocation of the cyclophane on the molecular string provides a means to reversibly control the hydrophilic and hydrophobic properties of the surface. The latter system demonstrates the translation of a molecular motion into the macroscopic motion of a water droplet.

Journal Article↗
PubMed2004

Integrated nanoparticle-biomolecule hybrid systems: synthesis, properties, and applications.

Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

DNA↗
PubMed2004

Amplified detection of telomerase activity using electrochemical and quartz crystal microbalance measurements.

Telomerase is considered as an important biomarker for cancer cells. Two different methods for the amplified electrochemical and microgravimetric quartz-crystal-microbalance detection of telomerase activity originating from HeLa cancer cells are described. One method involves the telomerization of a primer (1) linked to the electrode, in the presence of telomerase from HeLa cell extract and dNTP, followed by the hybridization of a biotin-labeled nucleic acid (2) that is complementary to the telomere repeat units. The subsequent binding of an avidin-alkaline phosphatase conjugate (3) that catalyzes the oxidative hydrolysis of 5-bromo-4-chloro-3-indolyl phosphate (4) results in the precipitation of the insoluble product (5) on the electrode. The second method involves the telomerization of the primer (1) associated with the electrode, in the presence of the telomerase-containing HeLa cell extract and the dNTP nucleotide mixture that includes biotin-labeled dUTP. The telomerization leads to the labeling of the telomeres with biotin labels. The association of the avidin-alkaline phosphatase conjugate (3) to the biotin labels results in the biocatalyzed transformation of (4) to (5) and the formation of a precipitate on the electrode or the Au-quartz crystal. As numerous precipitate molecules are formed as a result of the formation of a single telomere, the methods represent routes for the amplified detection of telomerase activity. The formation of the precipitate on the respective transducers is probed by following the changes in the electrode resistance using chronopotentiometry, or by following the frequency changes of the piezoelectric quartz crystals. The amount of precipitate generated on the electrodes is controlled by the concentration of the HeLa cancer cells. The methods enable the detection of telomerase activity that is extracted from 1000 HeLa cancer cells.

Biomarkers, Tumor↗
PubMed2004

Magnetoswitchable controlled hydrophilicity/hydrophobicity of electrode surfaces using alkyl-chain-functionalized magnetic particles: application for switchable electrochemistry.

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter approximately 4.5 nm; saturated magnetization, M(s), 38.5 emu g(-1)) are used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. The magnetic attraction of the functionalized particles to the electrode by means of an external magnet yields a hydrophobic interface that acts as an insulating layer, prohibiting interfacial electron transfer. The retraction of the magnetic particles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. The electron-transfer resistance and double-layer capacitance of the electrode surface upon the attraction and retraction of the functionalized magnetic particles to and from the electrode, respectively, by means of the external magnet were probed by Faradaic impedance spectroscopy (R(et) = 170 Omega and C(dl) = 40 microF sm(-2) in the hydrophilic state of the electrode and R(et) = 22 k Omega and C(dl) = 0.5 microF sm(-2) in the hydrophobic state of the interface). The magnetoswitchable control of the interface enables magnetic switching of the bioelectrocatalytic oxidation of glucose in the presence of glucose oxidase and ferrocene dicarboxylic acid to "ON" and "OFF" states.

Journal Article↗
PubMed2004

Actin-based metallic nanowires as bio-nanotransporters.

The synthesis of conductive nanowires or patterned conductive nanoelements is a challenging goal for the future fabrication of nanoscale circuitry. Similarly, the realization of nanoscale mechanics might introduce a new facet to the area of nanobiotechnology. Here we report on the design of conductive and patterned actin-based gold nanowires, and on the ATP-driven motility of the nano-objects. The polymerization of G-actin labelled with Au nanoparticles, followed by the catalytic enlargement of the nanoparticles, yields gold wires (1-4 microm long and 80-200 nm high) exhibiting high electrical conductivity. The polymerization of the Au nanoparticle/G-actin monomer followed by the polymerization of free G-actin, or alternatively the polymerization of the Au-nanoparticle-labelled G-actin on polymerized F-actin followed by the catalytic enlargement of the particles, yields patterned actin-Au wire-actin or Au wire-actin-Au wire nanostructures, respectively. We demonstrate the ATP-fuelled motility of the actin-Au wire-actin filaments on a myosin interface. These actin-based metallic wires and their nanotransporting funcionality introduce new concepts for developing biological/inorganic hybrid devices.

Actins↗
PubMed2004

Magnetic field effects on cytochrome c-mediated bioelectrocatalytic transformations.

Constant magnetic fields affect many biological transformations, but we lack mechanistic understanding of the processes. The magnetohydrodynamic effect may account for the enhancement of bioelectrocatalytic transformations at interfaces. This is exemplified by the bioelectrocatalyzed cytochrome c-mediated reduction of oxygen and oxidation of lactate in the presence of cytochrome oxidase and lactate dehydrogenase, respectively. We observe significant magnetic field effects on the rates of bioelectrochemical transformations (ca. 3-fold increase) at the functionalized interfaces at field strengths, B, up to 1 T. We show that the limiting current is proportional to the B(1/3)C*(4/3), where C is the concentration of electroactive species. The results may have important implications on the understanding of the magnetic field effects on natural biocatalytic processes at membranes and on the enhancement of biotransformations in biotechnology.

Animals↗
PubMed2004

Biomolecule-functionalized carbon nanotubes: applications in nanobioelectronics.

Carbon nanotubes (CNTs) revealing metallic or semiconductive properties depending on the folding modes of the nanotube walls represent a novel class of nanowires. Different methods to separate semiconductive CNTs from conductive CNTs have been developed, and synthetic strategies to chemically modify the side walls or tube ends by molecular or biomolecular components have been reported. Tailoring hybrid systems consisting of CNTs and biomolecules (proteins and DNA) has rapidly expanded and attracted substantial research effort. The integration of biomaterials with CNTs enables the use of the hybrid systems as active field-effect transistors or biosensor devices (enzyme electrodes, immunosensors, or DNA sensors). Also, the integration of CNTs with biomolecules has allowed the generation of complex nanostructures and nanocircuitry of controlled properties and functions. The rapid progress in this interdisciplinary field of CNT-based nanobioelectronics and nanobiotechnology is reviewed by summarizing the present scientific accomplishments, and addressing the future goals and perspectives of the area.

Biosensing Techniques↗
PubMed2004

Amplified telomerase analysis by using rotating magnetic particles: the rapid and sensitive detection of cancer cells.

A highly sensitive telomerase detection method that involves amplified telomerase analysis and the use of rotating magnetic particles has been developed. Magnetic particles, functionalized with a primer (1) that is recognized by telomerase, are mixed with a nucleotide mixture that includes biotinylated-dUTP, and telomerase-induced elongation of the primers proceeds with simultaneous biotin incorporation. Avidin-Horseradish peroxidase conjugate, coupled to biotin labels, yields the biocatalytic functional particles. Mixing the resulting particles with naphthoquinone-modified magnetic particles enables the optoelectronic detection of telomerase. Attraction of the magnetic particles to an electrode, followed by rotation of the particles, causes the electrocatalytic reduction of O(2) to H(2)O(2) and HRP-catalyzed oxidation of luminol (3); this results in chemilumunescence. The intensity of the emitted light depends on the telomerase content of the sample and the rotation speed of the particles. A minimum number of 10 cancer cells could be detected.

Adenocarcinoma↗
PubMed2004

Electronic transduction of HIV-1 drug resistance in AIDS patients.

A drug composition consisting of nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), and protease inhibitors (PIs) is commonly used in AIDS therapy. A major difficulty encountered with the therapeutic composite involves the emergence of drug-resistant viruses, especially to the PIs, regarded as the most effective drugs in the composition. We present a novel bioelectronic means to detect the appearance of mutated HIV-1 exhibiting drug resistance to the PI saquinavir. The method is based on the translation of viral RNA, the association of cleaved or uncleaved Gag polyproteins at an electrode surface functionalized with the respective antibodies, and the bioelectronic detection of the Gag polyproteins associated with the surface. The bioelectronic process includes the association of anti-MA or anti-CA antibodies, the secondary binding of an antibody-horseradish peroxidase (HRP) conjugate, and the biocatalyzed precipitation of an insoluble product on the electronic transducers. Faradaic impedance measurements and quartz crystal microbalance analyses are employed to follow the autoprocessing of the Gag polyproteins. The method was applied to determine drug resistance in infected cultured cells and also in blood samples of consenting AIDS patients. The method described here is also applicable to the determination of drug effectiveness in AIDS patients and to screening of the efficiency of newly developed drugs.

Anti-HIV Agents↗
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↗