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Biomedical subjects

I Willner

Publications and source records attributed to I Willner.

At least 19 recordsLinked to original sources
PubMed2001

Electrochemical and quartz crystal microbalance detection of the cholera toxin employing horseradish peroxidase and GM1-functionalized liposomes.

An ultrasensitive method for the detection of the cholera toxin (CT) using electrochemical or microgravimetric quartz crystal microbalance transduction means is described. Horseradish peroxidase (HRP) and GM1-functionalized liposomes act as catalytic recognition labels for the amplified detection of the cholera toxin based on highly specific recognition of CT by the ganglioside GM1. The sensing interface consists of monoclonal antibody against the B subunit of CT that is linked to protein G, assembled as a monolayer on an Au electrode or an Au/ quartz crystal. The CT is detected by a "sandwich-type" assay on the electronic transducers, where the toxin is first bound to the anti-CT-Ab and then to the HRP-GM1-ganglioside-functionalized liposome. The enzyme-labeled liposome mediates the oxidation of 4-chloronaphthol (2) in the presence of H2O2 to form the insoluble product 3 on the electrode support or the Au/quartz crystal. The biocatalytic precipitation of 3 provides the amplification route for the detection of the CT. Formation of the insulating film of 3 on the electrode increases the interfacial electron-transfer resistance, Ret, or enhances the electrode resistance, R', parameters that are quantitatively derived by Faradaic impedance measurements and chronopotentiometric analyses, respectively. Similarly, the precipitate 3 formed on the Au/quartz crystal results in a mass increase on the transducer that is reflected by a decrease in the resonance frequency of the crystal. The methods allow the detection of the CT with an unprecedented sensitivity that corresponds to 1.0 x 10(-13) M.

Biosensing Techniques↗
PubMed2001

Imprinting of chiral molecular recognition sites in thin TiO2 films associated with field-effect transistors: novel functionalized devices for chiroselective and chirospecific analyses.

(R)- or (S)-2-Methylferrocene carboxylic acids, (R)-1 or (S)-1, (R)- or (S)-2-phenylbutanoic acid, (R)-2 or (S)-2, and (R)- or (S)-2-propanoic acid, (R)-3 or (S)-3, can be imprinted in thin TiO2 films on the gate surface of ion-sensitive field-effect transistor (ISFET) devices. The imprinting is performed by hydrolyzing the respective carboxylate TiIV butoxide complex on the gate surface, followed by washing off the acid from the resulting TiO2 film. The imprinted sites reveal chiroselectivity only towards the sensing of the imprinted enantiomer. The chiral recognition sites reveal not only chiroselectivity but also chirospecificity and, for example, the (R)-2-imprinted film is active in the sensing of (R)-2, but insensitive towards the sensing of (R)2-phenylpropanoic acid, (R)-3, which exhibits a similar chirality. Similarly, the (R)-3-imprinted film is inactive in the analysis of (R)-2. The chiroselectivity and chirospecificity of the resulting imprinted films are attributed to the need to align and fit the respective substrates in precise molecular contours generated in the cross-linked TiO2 films upon the imprinting process.

Journal Article↗
PubMed2001

Lithium reduction of the bowl-shaped C60 fragment diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene: an interplay between experiment and calculation.

Diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene (DIC) (one of the smallest symmetrical bowl-shaped fragments of C60) and its tetra-tert-butyl derivative are reduced with lithium metal to yield dianions and tetraanions. Due to the high degree of symmetry (C2v) of DIC and its derivative, their NMR spectra cannot be assigned using the standard two-dimensional NMR techniques. A novel carbon-edited NOESY method was used to complete the assignments of the neutral and dianion species, whereas the tetraanions are aided by DFT calculations for their assignment. Experimental charge-distribution patterns were obtained and match those of the calculations. An extension of the empirical approach for estimating the charge distribution from the 13C NMR spectra enables a direct comparison between experimentally derived charge-distribution data and the computed electron density in each of the lowest unoccupied molecular orbitals. The overall picture evolving from the orbital structure of DIC is presented and reflects the surface reactivity of C60.

Journal Article↗
PubMed2001

Electronic transduction of DNA sensing processes on surfaces: amplification of DNA detection and analysis of single-base mismatches by tagged liposomes.

Tagged, negatively charged, liposomes are used to amplify DNA sensing processes. The analyses of the target DNA are transduced electrochemically by using Faradaic impedance spectroscopy, or by microgravimetric measurements with Au-quartz crystals. By one method, a probe oligonucleotide (1) is assembled on Au-electrodes or Au-quartz crystals. The formation of the double-stranded assembly with the analyte DNA (2) is amplified by the association of the 3-oligonucleotide-functionalized liposomes to the sensing interface. The target DNA is analyzed by this method with a sensitivity limit that corresponds to 1 x 10(-12) M. A second method to amplify the sensing of the analyte involves the interaction of the 1-functionalized electrode or Au-quartz crystal with the target DNA sample (2) that is pretreated with the biotinylated oligonucleotide (4). The formation of the three-component double-stranded assembly between 1/2/4 is amplified by the association of avidin and biotin-labeled liposomes to the sensing interfaces. By the secondary association of avidin and biotin-tagged liposomes, a dendritic-type amplification of the analysis of the DNA is accomplished. The analyte DNA (2) is sensed by this method with a sensitivity limit corresponding to 1 x 10(-13) M. The biotin-tagged liposomes are also used to probe and amplify single-base mismatches in an analyte DNA. The 6-oligonucleotide-functionalized Au-electrode or Au-quartz crystal was used to differentiate the single-base mismatch (G) in the mutant (5) from the normal A-containing gene (5a). Polymerase-induced coupling of the biotinylated-C-base to the double-stranded assembly generated between 6 and 5 followed by the association of avidin and biotin-tagged liposomes is used to probe the single base mismatch. The functionalized liposomes provide a particulate building unit for the dendritic amplification of DNA sensing.

Base Pair Mismatch↗
PubMed2001

Lanthanide oxide-doped titanium dioxide photocatalysts: novel photocatalysts for the enhanced degradation of p-chlorophenoxyacetic acid.

The photocatalytic degradation of p-chlorophenoxyacetic acid has been investigated in oxygenated aqueous suspensions of lanthanide oxide-doped TiO2 photocatalysts. Complete mineralization was achieved. The enhanced degradation is attributed to the formation of Lewis acid-base complex between the lanthanide ion and the substrate.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2001

Tailored chemosensors for chloroaromatic acids using molecular imprinted TiO2 thin films on ion-sensitive field-effect transistors.

The SiO2 gate of an ion-sensitive field-effect transistor, (ISFET), is functionalized with a TiO2 film that includes imprinted molecular sites for 4-chlorophenoxy acetic acid, (1), or 2,4-dichlorophenoxy acetic acid, (2). The functionalized devices that include the imprinted interfaces reveal an impressive selectivity in the sensing of the imprinted substrates Na+ -1 or Na+ -2. The detection limit for Na+ -1 is (5+/-2) x 10(-4) M, which corresponds to 38 mV x dec(-1) in the concentration range of 0.5 to 6 mM. The detection limit for the analysis of Na+ -2 is (1.0+/-0.2) x 10(-5) M, which corresponds to 28 mV dec(-1) in the concentration range 0.1-9.0 mM. The equilibration time of the devices is ca. 5 min.

Letter↗
PubMed2001

Liposomes labeled with biotin and horseradish peroxidase: a probe for the enhanced amplification of antigen--antibody or oligonucleotide--DNA sensing processes by the precipitation of an insoluble product on electrodes.

Liposomes labeled with biotin and the enzyme horseradish peroxidase (HRP) are used as a probe to amplify the sensing of antigen-antibody interactions or oligonucleotide-DNA binding. The HRP-biocatalyzed oxidation of 4-chloro-1-naphthol (1) in the presence of H2O2, and the precipitation of the insoluble product 2 on electrode supports, are used as an amplification route for the sensing processes. The anti-dinitrophenyl antibody (DNP-Ab) is sensed by a dinitrophenyl-L-cysteine antigen monolayer associated with an Au electrode. A biotinylated anti-IgG-antibody (Fc-specific) is linked to the antigen-DNP-Ab complex, and the biotin-labeled HRP-liposomes associate with the assembly through an avidin bridge. The biocatalyzed precipitation of 2 on the electrode increases the electron-transfer resistances at the electrode-solution interface or the electrode resistance itself. The binding events of the different proteins on the electrode and the biocatalyzed precipitation of 2 on the conductive support are followed by Faradaic impedance spectroscopy or constant-current chronopotentiometry. DNP-Ab concentrations as low as 1 x 10(-11) g x mL(-1) can be detected by this method. The labeled liposomes were also used for the amplified detection of DNA 3. The oligonucleotide 4, complementary to a part of the target DNA 3 that is a model nucleic acid sequence for the Tay-Sachs genetic disorder, is assembled on an Au electrode. Hybridization of the analyte 3 followed by the association of the biotin-tagged oligonucleotide 5 yields a three-component double-stranded assembly. Sensing of the analyte 3 is amplified by the association of avidin, the labeled liposomes, and the subsequent biocatalyzed precipitation of 2 on the electrodes. The DNA 3 is detected with a sensitivity that corresponds to 6.5 x 10(-13) M. Faradaic impedance spectroscopy and chronopotentiometry were employed to follow the stepwise assembly of the systems and the electronic transduction of the detection of the analyte DNA 3.

Antigen-Antibody Reactions↗
PubMed2001

An N,N'-dialkyl-4,4'-bipyridinium-modified titanium-dioxide photocatalyst for water remediation--observation and application of supramolecular effects in photocatalytic degradation of pi-donor organic compounds.

The photocatalytic activity of TiO2 (Degussa P-25) modified with a 4,4'-bipyridinium monolayer (V2+-TiO2) has been compared with that of conventional TiO2-P-25 by investigating the efficiency of degradation of a series of four organic model compounds with increasing pi-donor capacity (2,4-xylidine, 2,4-dimethylphenol, hydroquinone, and dimethylhydroquinone). As far as the mechanism of the first oxidation reaction is concerned, evidence for the formation of supramolecular donor-acceptor complexes with the bipyridinium units at the semiconductor surface was obtained by comparison of the Langmuir-adsorption characteristics and the efficiencies of photodegradation of the different substrates. Furthermore, the main intermediates of the photocatalytic degradation of 2,4-xylidine were identified, and the presence of 2,4-dimethylphenol indicates that the main pathway of substrate oxidation proceeds via electron transfer from the adsorbed organic substrate to the "holes" within the valence band of the photoexcited semiconductors V2+-TiO2 and TiO2. The efficiencies of photocatalytic degradation by both V2+-TiO2 and TiO2 were limited by the trapping efficiency of the conduction band electrons by molecular oxygen.

Journal Article↗
PubMed2001

Biomaterials integrated with electronic elements: en route to bioelectronics.

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.

Antigen-Antibody Reactions↗
PubMed2001

Chronopotentiometry and Faradaic impedance spectroscopy as signal transduction methods for the biocatalytic precipitation of an insoluble product on electrode supports: routes for enzyme sensors, immunosensors and DNA sensors.

The biocatalyzed precipitation of an insoluble product produced on electrode supports is used as an amplification path for biosensing. Enzyme-based electrodes, immunosensors and DNA sensors are developed using this biocatalytic precipitation route. Faradaic impedance spectroscopy and chronopotentiometry are used as transduction methods to follow the precipitation processes. While Faradaic impedance spectroscopy leads to the characterization of the electron-transfer resistance at the electrode, chronopotentiometry provides the total resistance at the interfaces of the modified electrodes. A horseradish peroxidase, HRP, monolayer-functionalized electrode is used to sense H(2)O(2) by the biocatalyzed oxidation of 4-chloro-1-naphthol (1), to the insoluble product benzo-4-chlorohexadienone (2). An antigen monolayer electrode is used to sense the dinitrophenyl antibody, DNP-Ab, applying an anti-antibody-HRP conjugate as a biocatalyst for the oxidative precipitation of 1 by H(2)O(2) to yield the insoluble product 2. An oligonucleotide (3) functionalized monolayer electrode is used to sense the DNA-analyte (4), that is one of the Tay-Sachs genetic disorder mutants. Association of a biotin-labeled oligonucleotide to the sensing interface, followed by the association of the avidin-HRP conjugate and the biocatalyzed precipitation of 2 leads to the amplified sensing of 4. The amount of the precipitate accumulated on the conductive support is controlled by the concentration of the respective analytes and the time intervals employed for the biocatalytic precipitation of 2. The electron-transfer resistances of the electrodes covered by the insoluble product (2) are derived from Faradaic impedance measurements, whereas the total electrode resistances are extracted from chronopotentiometric experiments. A good correlation between the total electrode resistances and the electron-transfer resistances at the conducting supports are found. Chronopotentiometry is suggested as a rapid transduction means (a few seconds). The precautions needed to apply chronopotentiometry in biosensors are discussed.

Animals↗
PubMed2001

Electronically transduced molecular mechanical and information functions on surfaces.

Supramolecular chemistry and nanotechnology, along with their use in the construction of functional assemblies and devices, have merged into a challenging field of study. The development of methodologies for the integration and interfacing of molecular building blocks with solid supports and electronic transducers is essential for this research. We address recent applications of molecular, macromolecular, and biomolecular substances in the organization of signal-activated, electronically transduced molecular architectures on electrode surfaces. Photonic, electronic, magnetic, and chemical stimuli are used to trigger the switchable functions of these systems, which demonstrate either mechanical (e.g., translocation) or computational (e.g., memory) functions and provide enlightening insight and directions for the future evolution of the field.

Electrodes↗
PubMed2001

Detection of single-base DNA mutations by enzyme-amplified electronic transduction.

Here we describe a method for the sensitive detection of a single-base mutation in DNA. We assembled a primer thiolated oligonucleotide, complementary to the target DNA as far as one base before the mutation site, on an electrode or a gold-quartz piezoelectric crystal. After hybridizing the target DNA, normal or mutant, with the sensing oligonucleotide, the resulting assembly is reacted with the biotinylated nucleotide, complementary to the mutation site, in the presence of polymerase. The labeled nucleotide is coupled only to the double-stranded assembly that includes the mutant site. Subsequent binding of avidin-alkaline phosphatase to the assembly, and the biocatalyzed precipitation of an insoluble product on the transducer, provides a means to confirm and amplify detection of the mutant. Faradaic impedance spectroscopy and microgravimetric quartz-crystal microbalance analyses were employed for electronic detection of single-base mutants. The lower limit of sensitivity for the detection of the mutant DNA is 1 x 10-14 mol/ml. We applied the method for the analysis of polymorphic blood samples that include the Tay-Sachs genetic disorder. The sensitivity of the method enables the quantitative analysis of the mutant with no PCR pre-amplification.

Alkaline Phosphatase↗
PubMed2001

An integrated relay/nitrate reductase field-effect transistor for the sensing of nitrate (NO3-).

An integrated enzyme-functionalized field-effect transistor (ENFET) device for the sensing of nitrate ions is described. An aminosiloxane-functionalized gate interface is modified with N-methyl-N'-(carboxyalkyl)-4,4'-bipyridinium relay units. The complex formed between nitrate reductase and the bipyridinium units on the gate surface is crosslinked with glutaric dialdehyde to yield a stable relay-enzyme layer on the gate interface. In the presence of sodium dithionite as electron donor, the biocatalyzed reduction of nitrate to nitrite ion is stimulated. The ratio between the oxidized and reduced states of the bipyridinium sites regulates the gate potential, and is controlled by the concentration of NO3- ions in the system. The effect of the chain length tethering the N-methyl-N'-(carboxyalkyl)-4,4'-bipyridinium units to the gate surface on the biocatalyzed reduction of NO3- ions, and on the NO3- FET sensor performance is discussed. The devices that include the bipyridinium units tethered to the gate interface with methylene chain length, -(CH2)n, where n > or = 7, reveal a detection limit of 7 x 10(-5) M for nitrate and a sensitivity of 52 +/- 2 mV dec-1. The response time of the device is as low as 50 s, and the operational time of the system is ca. 85 s. We estimate the surface coverage of nitrate reductase on the gate surface to be ca. 1.2 x 10(-12) mol cm-2.

Journal Article↗
PubMed2001

Amplified detection of DNA and analysis of single-base mismatches by the catalyzed deposition of gold on Au-nanoparticles.

A novel amplification route for DNA detection based on the deposition of gold on a 10 nm Au-colloid/avidin conjugate label acting as a 'seeding' catalyst, is described. Microgravimetric quartz-crystal-microbalance measurements are employed to transduce the catalyzed deposition of gold on the piezoelectric crystals. Three different DNA detection schemes are described: (i) analysis of a 27-base nucleic acid fragment; (ii) analysis of the entire M13phi DNA (7229 bases); and (iii) detection of a single-base mismatch in a DNA. Ultrasensitive detection of DNA is accomplished by the catalyzed deposition of gold, detection limit approximately 1 x 10(-15) M.

Base Pair Mismatch↗
PubMed2001

The decision-making value of magnetic resonance cholangiopancreatography in patients seen in a referral center for suspected biliary and pancreatic disease.

OBJECTIVE: To assess the ability of MRCP to alter the differential diagnosis and to prevent diagnostic and/or therapeutic ERCP. The diagnostic accuracy of magnetic resonance cholangiopancreatography (MRCP) for biliary and pancreatic disease is well documented. Some believe MRCP may prevent diagnostic ERCP or add useful information, however there are no reports of its impact on clinical management. METHODS: Consecutive patients referred for ERCP underwent clinic evaluation, then MRCP, and then ERCP. In Phase 1, the number of differential diagnoses and the perceived need for diagnostic ERCP were evaluated after each step by the endoscopist who performed the ERCP. In Phase 2, the process was repeated after presenting clinical information and MRCP results to different individual physicians: another endoscopist, a hepatologist, a radiologist, and a surgeon (all were blinded to ERCP results). RESULTS: Forty patients were enrolled. Clinical contexts were jaundice (19.7%), abnormal liver enzymes (42.6%), abdominal pain (11.5%), recurrent acute pancreatitis (11.5%), and suspected complications of chronic pancreatitis (14.7%). In Phase 1, adding MRCP information to diagnostic ERCP information did not change the mean number of differential diagnoses significantly and prevented no therapeutic ERCP. In Phase 2, adding MRCP to clinical information only (without ERCP) reduced the differential diagnosis significantly for the radiologist and the surgeon only and would have prevented < or =3% of diagnostic and therapeutic ERCP for all physicians. CONCLUSION: The value of MRCP information may be limited if patient selection is inappropriate and may differ in physicians depending on their speciality.

Biliary Tract Diseases↗