Ran Tel-Vered

Imprinting of Molecular Recognition Sites through Electropolymerization of Functionalized Au Nanoparticles: Development of an Electrochemical TNT Sensor Based on π-Donor−Acceptor Interactions

Electrochemical sensors for the analysis of TNT with enhanced sensitivities are described. The enhanced sensitivities are achieved by tailoring pi-donor-acceptor interactions between TNT and pi-donor-modified electrodes or pi-donor-cross-linked Au nanoparticles linked to the electrode. In one configuration a p-aminothiophenolate monolayer-modified electrode leads to the analysis of TNT with a sensitivity corresponding to 17 ppb (74 nM). In the second configuration, the cross-linking of Au NPs by oligothioaniline bridges to the electrode yields a functionalized electrode that detects TNT with a sensitivity that corresponds to 460 ppt (2 nM). Most impressively, the imprinting of molecular TNT recognition sites into the pi-donor oligoaniline-cross-linked Au nanoparticles yields a functionalized electrode with a sensitivity that corresponds to 46 ppt (200 pM). The electrode reveals high selectivity, reusability, and stability.

Amplified Biosensing Using the Horseradish Peroxidase-Mimicking DNAzyme as an Electrocatalyst

The hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme is assembled on Au electrodes. It reveals bioelectrocatalytic properties and electrocatalyzes the reduction of H(2)O(2). The bioelectrocatalytic functions of the hemin/G-quadruplex DNAzyme are used to develop electrochemical sensors that follow the activity of glucose oxidase and biosensors for the detection of DNA or low-molecular-weight substrates (adenosine monophosphate, AMP). Hairpin nucleic structures that include the G-quadruplex sequence in a caged configuration and the nucleic acid sequence complementary to the analyte DNA, or the aptamer sequence for AMP, are immobilized on Au-electrode surfaces. In the presence of the DNA analyte, or AMP, the hairpin structures are opened, and the hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme structures are generated on the electrode surfaces. The bioelectrocatalytic cathodic currents generated by the functionalized electrodes, upon the electrochemical reduction of H(2)O(2), provide a quantitative measure for the detection of the target analytes. The DNA target was analyzed with a detection limit of 1 x 10(-12) M, while the detection limit for analyzing AMP was 1 x 10(-6) M. Methods to regenerate the sensing surfaces are presented.

Ultrasensitive Surface Plasmon Resonance Detection of Trinitrotoluene by a Bis-aniline-Cross-Linked Au Nanoparticles Composite

A bis-aniline-cross-linked Au nanoparticles (NPs) composite is electropolymerized on Au surfaces. The association of trinitrotoluene, TNT, to the bis-aniline bridging units via pi-donor-acceptor interactions allows the amplified detection of TNT by following the surface plasmon resonance (SPR) reflectance changes as a result of the coupling between the localized plasmon of the AuNPs and the surface plasmon wave associated with the gold surface. The detection limit for analyzing TNT by this method is approximately 10 pM. The electropolymerization of the bis-aniline-cross-linked AuNPs composite in the presence of picric acid results in a molecular-imprinted matrix for the enhanced binding of TNT. The imprinted AuNPs composite enabled the sensing of TNT with a detection limit that corresponded to 10 fM. Analysis of the SPR reflectance changes in the presence of different concentrations of TNT revealed a two-step calibration curve that included the ultrasensitive detection of TNT by the imprinted sites in the composite, KassI. for the association of TNT to the imprinted sites, 6.4 x 10(12) M-1, followed by a less sensitive detection of TNT by the nonimprinted pi-donor bis-aniline sites (KNIass. = 3.9 x 10(9) M-1). The imprinted AuNPs composite reveals impressive selectivity. The structural and functional features of the bis-aniline-cross-linked AuNPs composites were characterized by different methods including ellipsometry, AFM, and electrochemical means. The dielectric properties of the AuNPs composite in the presence of different concentrations of TNT were evaluated by the theoretical fitting of the respective experimental SPR curves. The ultrasensitive detection of the TNT by the AuNPs composite was attributed to the changes of the dielectric properties of the composite, as a result of the formation of the pi-donor-acceptor complexes between TNT and the bis-aniline units. These changes in the dielectric properties lead to a change in the conductivity of the AuNPs matrix.

Surface Plasmon Resonance Analysis of Antibiotics Using Imprinted Boronic Acid-Functionalized Au Nanoparticle Composites

Au nanoparticles (NPs) are functionalized with thioaniline electropolymerizable groups and (mercaptophenyl)boronic acid. The antibiotic substrates neomycin (NE), kanamycin (KA), and streptomycin (ST) include vicinal diol functionalities and, thus, bind to the boronic acid ligands. The electropolymerization of the functionalized Au NPs in the presence of NE, KA, or ST onto Au surfaces yields bisaniline-cross-linked Au NP composites that, after removal of the ligated antibiotics, provide molecularly imprinted matrixes which reveal high sensitivities toward the sensing of the imprinted antibiotic analytes (detection limits for analyzing NE, KA, and ST correspond to 2.00 +/- 0.21 pM, 1.00 +/- 0.10 pM, and 200 +/- 30 fM, respectively). The antibiotics are sensed by surface plasmon resonance (SPR) spectroscopy, where the coupling between the localized plasmon of the NPs and the surface plasmon wave associated with the Au surface is implemented to amplify the SPR responses. The imprinted Au NP composites are, then, used to analyze the antibiotics in milk samples.

Nano-engineered Flavin-Dependent Glucose Dehydrogenase/Gold Nanoparticle-Modified Electrodes for Glucose Sensing and Biofuel Cell Applications

A three-dimensional composite consisting of the oxygen-insensitive flavin-dependent glucose dehydrogenase, GDH, and Au nanoparticles (NPs) is assembled on a Au surface using an electropolymerization process. The bis-aniline-cross-linked GDH/Au NPs composite reveals effective electrical contact with the electrode (ket=1100 s(-1)), and the effective bioelectrocatalyzed oxidation is driven by the enzyme/NPs matrix. The GDH/Au NPs-functionalized electrode is implemented as an amperometric glucose sensor, and it reveals superior functions when compared to an analogous glucose oxidase/Au NPs system. The O2-insensitive GDH/Au NPs composite electrode was further used as an anode in a membraneless glucose/O2 biofuel cell. The cathode in this system was composed of bilirubin oxidase cross-linked onto a carbon nanotube-modified glassy carbon electrode. The power output of the cell was 32 μW cm(-2).

Integrated photosystem II-based photo-bioelectrochemical cells

Photosynthesis is a sustainable process that converts light energy into chemical energy. Substantial research efforts are directed towards the application of the photosynthetic reaction centres, photosystems I and II, as active components for the light-induced generation of electrical power or fuel products. Nonetheless, no integrated photo-bioelectrochemical device that produces electrical power, upon irradiation of an aqueous solution that includes two inter-connected electrodes is known. Here we report the assembly of photobiofuel cells that generate electricity upon irradiation of biomaterial-functionalized electrodes in aqueous solutions. The cells are composed of electrically contacted photosystem II-functionalized photoanodes and an electrically wired bilirubin oxidase/carbon nanotubes-modified cathode. Illumination of the photoanodes yields the oxidation of water to O(2) and the transfer of electrons through the external circuit to the cathode, where O(2) is re-reduced to water.

Imprinted Au‐Nanoparticle Composites for the Ultrasensitive Surface Plasmon Resonance Detection of Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX)

Adv. Mater. 2010, 22, 1387–1391 2010 WILEY-VCH Verlag G The analysis of explosives attracts recent research efforts due to homeland security needs and the broad demand for the clearance of minefields. While numerous studies have addressed the development of sensing platforms for nitroaromatic explosives, and specifically trinitrotoluene (TNT), the detection of more hazardous explosives, such as hexahydro-1,3,5-trinitro-1,3,5triazine (RDX) or pentaerythritol tetranitrate (PETN), is less developed and needs further efforts, particularly the improvement of the sensitivities associated with the analyses of these substrates. Different optical, electrochemical, or microgravimetric sensors or biosensors for TNTwere reported. Fluorescent organic polymers, which are quenched by nitroaromatic explosives, luminescent polysilole nanoparticles (NPs), or fluorescent silicon NPs quenched by nitroaromatic vapors enabled the development of optical sensors. The electrochemical activity of the nitro groups of TNT provided the basis for developing voltammetric sensors for this explosive, and recently, a composite of Au NPs linked to electrodes enabled a sensitive electrochemical detection of TNT. Also, different sensing matrices, such as cyclodextrin polymers, carbowax, or silicon polymers, were used for TNT analysis by surface acoustic wave devices, and the aggregation of functionalized Au NPs in the presence of TNTwas used to develop an optical sensor for the explosive. Similarly, antibody-based optical or microgravimetric quartz-crystal-microbalance biosensors for TNT were developed. Different optical or voltammetric sensors for RDX were also reported. These included the fluorescence detection of RDX with an acridinium dye, or the application of NADH-functionalized quantum dots. Also, a competitive fluorescence immunoassay for the detection of RDX was reported. The sensitivities accomplished by these methods are, however, unsatisfactory for analyzing trace amounts of the RDX explosive. Surface plasmon resonance (SPR) is a versatile method for probing changes in the refractive index occurring on thin metal films as a result of recognition events or chemical reactions. Numerous SPR sensors and biosensors were developed, and metal NPs were implemented to enhance the SPR response and to amplify SPR-based sensors. The electronic coupling between the localized plasmon of the metallic NPs (e.g., Au NPs) and the surface plasmon wave enhances the SPR response and, thus, the labeling of recognition complexes with metallic NPs amplifies the sensing events. Different biosensing processes, such as DNA hybridization, formation of immunocomplexes, and the probing of biocatalytic transformations, used Au NPs as labels for amplified SPR analyses. Recently, composites of bisaniline-crosslinked Au NPs were electropolymerized on Au electrodes, and the resulting matrices were used for the ultrasensitive SPR detection of TNT. The formation of p-donor–acceptor complexes between TNT and the p-donor bisaniline bridging units altered the dielectric properties of the Au-NP composites. This affected the coupling between the localized plasmon of the NPs and the surface plasmon wave, resulting in a shift in the surface resonance spectrum (reflectance changes), that enabled the optical readout for analyzing TNT. Theoretical modeling of the SPR shifts indicated that the charge-transfer complexes between TNT and the bisaniline bridging units altered the dielectric functions of the Au-NP composite, and this enabled the highly sensitive detection of TNT. Here, we report on the ultrasensitive SPR detection of RDX by the composites of bisaniline-crosslinked AuNPs associated with a Au surface (detection limit 12 fM). Specifically, we demonstrate that electropolymerization of the Au NPs in the presence of Kemp’s acid yields an imprinted composite with high binding affinities for RDX. This imprinting leads to the selective and sensitive detection of this explosive by SPR. Au NPs, 3.5 nm, were functionalized with a capping mixed monolayer consisting of thioaniline electropolymerizable units and mercaptoethane sulfonic acid to enhance the solubility of the NPs in an aqueous medium. The functionalized Au NPs were electropolymerized onto a thioaniline-monolayer-modified Au electrode, to yield the matrix of bisaniline-crosslinked Au NPs (Fig. 1A). Ellipsometry and coulometric analyses of the matrix of bisaniline-crosslinked Au NPs, generated by the application of ten electropolymerization cycles, indicated that the thickness of the matrix corresponded to ca. 10 nm and that ca. 4 10 bisaniline units cm 2 were electropolymerized on the electrode. Knowing the size of the Au NPs and the thickness of the composite, we estimate that approximately three random densely packed Au-NP layers compose the matrix. Complementary AFM measurements indicated that the height of the Au-NP composite is ca. 12 1 nm. The p-donor bisaniline units bridging the Au NPs could, then, associate RDX (that includes p-acceptor nitro groups), via

Nanoengineered electrically contacted enzymes on DNA scaffolds: functional assemblies for the selective analysis of Hg2+ ions.

A DNA construct consisting of a nucleic acid template, (1), on which a nucleic acid-modified glucose oxidase (GOx), (3), was hybridized by cooperative bridging of the T-Hg(2+)-T units, and a nucleic acid-functionalized ferrocene, (5), was directly hybridized on a Au electrode. The resulting nanostructure revealed bioelectrocatalytic activities, where the ferrocene units mediated electron transfer between the redox center of the enzyme and the electrode. The bioelectrocatalytic functions of the system are regulated by the concentration of Hg(2+) ions, which controls the content of the enzyme associated with the DNA template by means of the T-Hg(2+)-T bridging units. This phenomenon allowed the amperometric detection of Hg(2+) ions at a detection limit 1 x 10(-10) M with impressive selectivity.

Following the Biocatalytic Activities of Glucose Oxidase by Electrochemically Cross-Linked Enzyme−Pt Nanoparticles Composite Electrodes

An integrated platinum nanoparticles (NPs)/glucose oxidase (GOx) composite film associated with a Au electrode is used to follow the biocatalytic activities of the enzyme. The film is assembled on a Au electrode by the electropolymerization of thioaniline-functionalized Pt NPs and thioaniline-modified GOx. The resulting enzyme/Pt NPs-functionalized electrode stimulates the O 2 oxidation of glucose to gluconic acid and H 2O 2. The modified electrode is then implemented to follow the activity of the enzyme by the electrochemical monitoring of the generated H 2O 2. The effect of the composition of the Pt NPs/GOx cross-linked nanostructures and the optimal conditions for the preparation of the electrodes are discussed.

Molecularly Imprinted Au Nanoparticles Composites on Au Surfaces for the Surface Plasmon Resonance Detection of Pentaerythritol Tetranitrate, Nitroglycerin, and Ethylene Glycol Dinitrate

Molecularly imprinted Au nanoparticles (NPs) composites are generated on Au-coated glass surfaces. The imprinting process involves the electropolymerization of thioaniline-functionalized Au NPs (3.5 nm) on a thioaniline monolayer-modified Au surface in the presence of a carboxylic acid, acting as a template analogue for the respective explosive. The exclusion of the imprinting template from the Au NPs matrix yields the respective imprinted composites. The binding of the analyte explosives to the Au NPs matrixes is probed by surface plasmon resonance spectroscopy, SPR, where the electronic coupling between the localized plasmon of the Au NPs and the surface plasmon wave leads to the amplification of the SPR responses originating from the dielectric changes of the matrixes upon binding of the different explosive materials. The resulting imprinted matrixes reveal high affinities and selectivity toward the imprinted explosives. Using citric acid as an imprinting template, Au NPs matrixes for the specific analysis of pentaerythritol tetranitrate (PETN) or of nitroglycerin (NG) were prepared, leading to detection limits of 200 fM and 20 pM, respectively. Similarly, using maleic acid or fumaric acid as imprinting templates, high-affinity sensing composites for ethylene glycol dinitrate (EGDN) were synthesized, leading to a detection limit of 400 fM for both matrixes.