Electrified Selective "Sponges" Made of Au Nanoparticles

Imprinted Au nanoparticle (NP) composites are assembled on Au surfaces by the electropolymerization of thioaniline-functionalized Au NPs in the presence of the imprint molecules, picric acid (1), N,N'-dimethyl-4,4'-bipyridinium (2), and N,N'-dimethylbipyridinium-4,4'-ethylene dichloride (3). The existence of pi-donor acceptor complexes between the substrates (1-3) and the pi-donor thioaniline units associated with the Au NPs or the pi-donor bis-aniline bridges cross-linking the Au NPs on the electrode surfaces led to the formation of the imprinted sites. Upon elimination of the electron acceptors (1-3) from the Au NP matrices, molecular contours for the selective binding of the respective substrates are generated. The bis-aniline bridges linking the Au NPs in the composite exhibit quasireversible redox properties. At E 0.12 V vs Ag ORE, the bridging units exist in the quinoid, pi-acceptor state. As a result, the potential-induced uptake and release of any of the pi-acceptor substrates 1 3 is accomplished. While at E 0.12 V, the bound substrates are released from the matrices, due to transformation of the bridging units to the quinoid pi-acceptor state, which lacks binding affinity for the substrates. The binding and release of the substrates 1-3 to and from the Au NP composites are followed by surface plasmon resonance (SPR) spectroscopy, and the quantitative assay of the uptake and release is monitored by the extent of fluorescence quenching of the solution-soluble fluorescent labels, meso-tetramethyl pyridinium porphyrin (TMPyP(4+)) or Zn(II)-meso-tetraphenylsulfonatoporphyrin (Zn-TPPS(4-)). The electrostimulated functions of the Au NP "sponges" are controlled by several means: (i) Imprinting of the molecular contours for 1-3 in the Au NP composites generates high-affinity binding sites for the imprinted substrates. This leads to higher contents of the bound substrates at the Au NP sponges, as compared to the nonimprinted Au NP composites, and to an impressive selectivity in the association of the imprinted substrates. (ii) The binding capacity of the Au NP composites is substantially improved by the electrosynthesis of the matrices on a rough Pt black support bound to the base Au electrode

Electrochemically Stimulated pH Changes: A Route To Control Chemical Reactivity

A bis-aniline-cross-linked Au nanoparticle (NP) composite is electrochemically prepared on a rough Pt film supported on a Au electrode The electrochemical oxidation of the bis-aniline units to the quinoid state releases protons to the electrolyte solution, while the reduction of the quinoid bridges results in the uptake of protons from the electrolyte. By the cyclic oxidation of the bridging units (E = 0.25 V vs SCE), and their reduction (E = -0 05 V vs SCE), the pH of the solution could be reversibly switched between the values 5 8 and 7 2, respectively The extent of the pH change is controlled by the number of electropolymerization cycles applied to synthesize the Au NP composite, demonstrating a ca 1 5 pH units change by a matrix synthesized using 100 electropolymerization cycles The pH changes are used to reversibly activate and deactivate a C-quadruplex (i-motif)-bridged Mg(2+)-dependent DNAzyme

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

Metal Nanoparticle-Loaded Mesoporous Carbon Nanoparticles: Electrical Contacting of Redox Proteins and Electrochemical Sensing Applications

A new method to incorporate metal nanoparticles, NPs, into pores of mesoporous carbon nanoparticles, MPC NPs, is presented. MPC NPs loaded with metal ion solutions are capped with protein units. The electrochemical reduction of the pore-entrapped ions, followed by digestion of the protein caps, yields metal NPs-loaded MPC NPs electrodes. Pt NPs/MPC NPs electrodes are used for the electrocatalyzed reduction of O2 or H2O2. Furthermore, the metal NPs electrically contact enzymes with the bulk electrodes, as demonstrated for glucose oxidase-capped Pt NPs/MPC NPs electrodes that electrocatalyze glucose oxidation, and for horseradish peroxidase-capped Au NPs/MPC NPs electrodes, which electrocatalyze H2O2 reduction

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 H2O2. The modified electrode is then implemented to follow the activity of the enzyme by the electrochemical monitoring of the generated H2O2. The effect of the composition of the Pt NPs/GOx crosslinked nanostructures and the optimal conditions for the preparation of the electrodes are discussed

Stereoselective and Chiroselective Surface Plasmon Resonance (SPR) Analysis of Amino Acids by Molecularly Imprinted Au-Nanoparticle Composites

Au nanoparticles (NPs) functionalized with thioaniline and cysteine are used to assemble bis-aniline-bridged Au-NP composites on Au surfaces using an electropolymerization process. During the polymerization of the functionalized Au NPs in the presence of different amino acids, for example, L-glutamic acid, L-aspartic acid, L-histidine, and L-phenylalanine, zwitterionic interactions between the amino acids and the cysteine units linked to the particles lead to the formation of molecularly imprinted sites in the electropolymerized Au-NP composites. Following the elimination of the template amino acid molecules, the electropolymerized matrices reveal selective recognition and binding capabilities toward the imprinted amino acid. Furthermore, by imprinting of L-glutamic or D-glutamic acids, chiroselective imprinted sites are generated in the Au-NP composites. The binding of amino acids to the imprinted recognition sites was followed by surface plasmon resonance spectroscopy. The refractive index changes occurring upon the binding of the amino acids to the imprinted sites are amplified by the coupling between the localized plasmon associated with the Au NPs and the surface plasmon wave

Optoelectronic Properties of Natural Cyanin Dyes

An integrated theoretical/experimental study of the natural cyanin dye is presented in terms of its structural and optoelectronic properties for different gas-phase and prototypical device configurations. Our microscopic analysis reveals the impact of hydration and hydroxylation reactions, as well as of the attached sugar, on ground and optically excited states, and it illustrates the visible-light harvesting capability of the dye. Our optical experiments at different and controlled pH concentrations allow for a direct comparison with theoretical results. We analyze the many different contributions to photocurrent of the various portions of a prototypical device and, as a proof of principle, we propose the addition of specific ligands to control the increase of the photocurrent yield in the cyanin-based electrochemical device

Optoelectronic properties of natural cyanin dyes

An integrated theoretical/experimental study of the natural cyanin dye is presented in terms of its structural and optoelectronic properties for different gas-phase and prototypical device configurations. Our microscopic analysis reveals the impact of hydration and hydroxylation reactions, as well as of the attached sugar, on ground and optically excited states, and it illustrates the visible-light harvesting capability of the dye. Our optical experiments at different and controlled pH concentrations allow for a direct comparison with theoretical results. We analyze the many different contributions to photocurrent of the various portions of a prototypical device and, as a proof of principle, we propose the addition of specific ligands to control the increase of the photocurrent yield in the cyanin-based electrochemical device. © 2009 American Chemical Society