Product citations
NanoSPR product citations
Ag Nanoparticle-Poly(acrylic acid) Composite Film with Dynamic Plasmonic Properties
Published in:
Aust. J. Chem. 2012, 65, 1223–1227
Abstract:
Poly(acrylic acid) (PAA) thin films with embedded Ag nanoparticles (AgNPs) prepared by UV photoreduction exhibitedcyclically changeable optical absorbance properties during variation of ambient aqueous medium. The observedphenomenon is due to conformational changes in the polymer matrix which leads to variation in the 3D configurationof the AgNPs ensemble. Reversible variation of the distance between nanoparticles during swelling and shrinkingprocesses within the PAA matrix changes the optical parameters of these plasmonic metamaterials and can be considered auseful feature for optoelectronic devices and sensors. The finite-difference time-domain method was used for modelling oflight extinction of developed matrix structures in their swollen and shrunken states.
Sensitivity comparison of surface plasmon resonance and plasmon-waveguide resonance biosensors
Published in:
Sensors and Actuators B 156 (2011) 169–175
Abstract:
Plasmon-waveguide resonance (PWR) sensors are particularly useful for the investigation of biomolecular interactions with or within lipid bilayer membranes. Many studies demonstrated their ability to provide unique qualitative information, but the evaluation of their sensitivity as compared to other surface plasmon resonance (SPR) sensors has not been broadly investigated.Wereport here a comprehensive sensitivity comparison of SPR and PWR biosensors for the p-polarized light component. The sensitivity of five different biosensor designs to changes in refractive index, thickness and mass are determined and discussed. Although numerical simulations show an increase of the electric field intensity by 30–35% and the penetration depth by four times in PWR, the waveguide-based method is 0.5–8-fold less sensitive than conventional SPR in all considered analytical parameters. The experimental results also suggest that the increase in the penetration depth in PWR is made at the expense of the surface sensitivity. The physical and structural reasons for PWR sensor limitations are discussed and a general viewpoint for designing more efficient SPR sensors based on dielectric slab waveguides is provided.
Electrochemically Triggered Au Nanoparticles “Sponges” for the Controlled Uptake and Release of a Photoisomerizable Dithienylethene Guest Substrate
Published in:
ACS Nano, 2011, 5 (7), pp 5936–5944
Abstract:
1,2-Di(2-methyl-5-(N-methylpyridinium)-thien-3-yl)-cyclopentene undergoes a reversible photoisomerization between open and closed states. The closed isomer state exhibits electron acceptor properties, whereas its irradiation using visible light (λ > 530 nm) yields the open state that lacks electron acceptor features. The electropolymerization of thioaniline-functionalized Au nanoparticles (NPs) in the presence of the closed photoisomer state yields a molecularly imprinted Au NPs matrix, cross-linked by redox-active bis-aniline π-donor bridges. The closed isomer is stabilized in the imprinted sites of the bis-aniline-bridged Au NPs composite by donor–acceptor interactions. The electrochemical oxidation of the bis-aniline bridging units to the quinoid acceptor state leads to imprinted sites that lack affinity interactions for the binding of the closed state to the matrix, leading to the release of the closed photoisomer to the electrolyte solution. By the cyclic reduction and oxidation of the bridging units to the bis-aniline and quinoid states, the reversible electrochemically controlled uptake and release of the closed photoisomer is demonstrated. The quantitative uptake and release of the closed isomer to and from the imprinted Au NPs composites is followed by application of CdSe/ZnS quantum dots as auxiliary probes. Similarly, by the reversible photochemical isomerization of the closed substrate to the open substrate (λ > 530 nm) and the reversible photoizomerization of the open substrate to the closed state (λ = 302 nm), the cyclic photonic uptake and release of the closed substrate to and from the imprinted Au NPs matrix are demonstrated. Finally, we demonstrate that the electrochemically stimulated uptake and release of the closed substrate to and from the imprinted Au NPs composite controls the wettability of the resulting surface.
Electrified Au nanoparticle sponges with controlled hydrophilic/hydrophobic properties.
Published in:
ACS Nano. 2011 Jan 25;5(1):299-306
Abstract:
Molecularly imprinted Au nanoparticle (NP) composites for the selective binding of the electron acceptors N,N'-dimethyl-4,4'-bipyridinium, MV(2+) (1), or bis-N-methylpyridinium-4,4'-ethylene, BPE(2+) (2), are prepared by the electropolymerization of thioaniline-functionalized Au NPs in the presence of the electron acceptor molecules and the subsequent rinsing off of the imprint substrates. The electrochemical oxidation of the π-donor bisaniline units bridging the Au NPs yields the quinoid electron acceptor bridges, which are re-reduced to the bisaniline state. By the cyclic oxidation and reduction of the bridging units, they are reversibly switched between the π-acceptor and the π-donor states, thus allowing the electrochemically triggered uptake and release of the electron acceptors (1 or 2) to and from the imprinted sites. While the electron acceptors 1 or 2 bind to the imprinted sites via donor-acceptor interactions, these substrates are released from the Au NP matrices upon the oxidation of the bridges to the quinoid state. The electrochemically switched wettability of the imprinted composites is demonstrated upon the reversible uptake, or release, of the substrates to and from the matrices. While the association of 1 or 2 to the respectively imprinted composites generates hydrophilic surfaces (θ = 30 and 41°, respectively), the release of the substrates from the matrices yields surfaces of enhanced hydrophobicity (θ = 60 and 55°, respectively). The electrochemically switched wettability is selective to the imprinted substrates and is amplified in the presence of the imprinted matrices as compared to the non-imprinted composites. The association of MV(2+) or BPE(2+) to the imprinted sites is further electrochemically characterized.
Molecularly Imprinted Au Nanoparticles Composites on Au Surfaces for the Surface Plasmon Resonance Detection of Pentaerythritol Tetranitrate, Nitroglycerin, and Ethylene Glycol Dinitrate
Published in:
Analytical Chemistry 2011, 83, 3082-3088
Abstract:
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.
Stereoselective and Chiroselective Surface Plasmon Resonance (SPR)Analysis of Amino Acids by Molecularly Imprinted Au-NanoparticleComposites
Published in:
Chem. Eur. J. 2010, 16, 7114 – 7120
Abstract:
Au nanoparticles (NPs) functionalizedwith thioaniline and cysteineare used to assemble bis-anilinebridgedAu-NP composites on Au surfacesusing an electropolymerizationprocess. During the polymerization ofthe functionalized Au NPs in the presenceof different amino acids, for example,l-glutamic acid, l-aspartic acid,l-histidine, and l-phenylalanine, zwitterionicinteractions between theamino acids and the cysteine unitslinked to the particles lead to the formationof molecularly imprinted sitesin the electropolymerized Au-NP composites.Following the elimination ofthe template amino acid molecules, theelectropolymerized matrices reveal selectiverecognition and binding capabilitiestoward the imprinted amino acid.Furthermore, by imprinting of l-glutamicor d-glutamic acids, chiroselectiveimprinted sites are generated in theAu-NP composites. The binding ofamino acids to the imprinted recognitionsites was followed by surface plasmonresonance spectroscopy. The refractiveindex changes occurring uponthe binding of the amino acids to theimprinted sites are amplified by thecoupling between the localized plasmonassociated with the Au NPs andthe surface plasmon wave.
Imprinted Au-Nanoparticle Composites for theUltrasensitive Surface Plasmon Resonance Detection ofHexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)
Published in:
Adv. Mater. 2010, 22, 1387–1391
Abstract:
The analysis of explosives attracts recent research efforts due tohomeland security needs and the broad demand for the clearanceof minefields. While numerous studies have addressed thedevelopment of sensing platforms for nitroaromatic explosives,and specifically trinitrotoluene (TNT), the detection of morehazardous explosives, such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) or pentaerythritol tetranitrate (PETN), is lessdeveloped and needs further efforts, particularly the improvementof the sensitivities associated with the analyses of thesesubstrates.Here, we report on the ultrasensitive SPR detection of RDX bythe composites of bisaniline-crosslinked Au NPs associated with aAu surface (detection limit 12 fM). Specifically, we demonstratethat electropolymerization of the Au NPs in the presence ofKemp’s acid yields an imprinted composite with high bindingaffinities for RDX. This imprinting leads to the selective andsensitive detection of this explosive by SPR.
Selective and enantioselective analysis of mono- and disaccharidesusing surface plasmon resonance spectroscopy and imprinted boronicacid-functionalized Au nanoparticle composites
Published in:
Analyst. 2010 Nov;135(11):2952-9
Abstract:
A method was developed for the synthesis of molecularly imprinted Au nanoparticle (NP) compositeson electrodes by electrochemical means. The resulting composites include specific recognition sites formono- or disaccharides. The method is based on the formation of a boronate complex between therespective saccharide and the boronic acid ligands associated with the Au NPs. Theelectropolymerization of the Au NPs leads, after cleavage of the respective boronate esters, andremoval of the saccharide, to specific recognition sites for the association of the imprintedmonosaccharides or disaccharides. The binding of the saccharides to the imprinted sites is followed bysurface plasmon spectroscopy (SPR). The changes in the refractive index of the Au NP compositesupon the binding of the saccharides to the imprinted sites are amplified by the coupling between thelocalized plasmon associated with the NPs and the surface plasmon wave propagating on the Ausurface. This leads to the highly sensitive stereoselective and chiroselective detection ofmonosaccharides and disaccharides.
Surface Plasmon Resonance Analysis of Antibiotics Using Imprinted Boronic Acid-Functionalized Au Nanoparticle Composites
Published in:
Anal. Chem. 2010, 82, 2512-2519
Abstract:
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.
Unobstructed electron transfer on porous polyelectrolyte nanostructures and its characterization by electrochemical surface plasmon resonance
Published in:
Electrochimica Acta 55 (2010) 4468-4474
Abstract:
Thin organic films with desirable redox properties have long been sought in biosensor research. We report here the development of a polymer thin film interface with well-defined hierarchical nanostructure and electrochemical behavior, and its characterization by electrochemical surface plasmon resonance (ESPR) spectroscopy. The nano-architecture build-up is monitored in real time with SPR, while the redox response is characterized by cyclic voltammetry in the same flow cell. The multilayer assembly is built on a self-assembled monolayer (SAM) of 1:1 (molar ratio) 11-ferrocenyl-1-undecanethiolate (FUT) and mercaptoundecanoic acid (MUA), and constructed using a layer-by-layer deposition of cationic poly(allylamine hydrochloride) (PAH) and anionic poly(sodium 4-styrenesulfonate) (PSS).Electron transfer (ET) on the mixed surface and the effect of the layer structures on ET are systematically studied. Under careful control, multiple layers can be deposited onto the 1:1 FUT/MUA SAM that presents unobstructed redox chemistry, indicating a highly ordered, extensively porous structure obtained under this condition.The use of SPR to trace the minute change during the electrochemical process offers neat characterization of local environment at the interface, in particular double layer region, allowing for better control over the redox functionality of the multilayers. The 1:1 SAM has a surface coverage of 4.1±0.3×10-10 molcm-2 for ferrocene molecules and demonstrates unperturbed electrochemistry activity even in the presence of a 13 nmpolymer film adhered to the electrode surface. This thin layer possesses some desirable properties similar to those on a SAM while presenting ~15nm exceedingly porous structure for high loading capacity. The high porosity allows perchlorate to freely partition into the film, leading to high current density that is useful for sensitive electrochemical measurements.
Grading the commercial optical biosensor literature - Class of 2008: 'The Mighty Binders'
Published in:
J. Mol. Recognit. 2010; 23: 1-64
Abstract:
Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.
Surface plasmon resonance immunosensor for bacteria detection
Published in:
Talanta 82 (2010) 810-814
Abstract:
Thisworkdescribes an approach for the development oftwobacteria biosensors basedonsurface plasmon resonance (SPR) technique. The first biosensor was based on functionalized gold substrate and the second one on immobilized gold nanoparticles. For the first biosensor, the gold substrate was functionalized with acid-thiol using the self-assembled monolayer technique, while the second one was functionalized with gold nanoparticles immobilized on modified gold substrate. A polyclonal anti-Escherichia coli antibody was immobilized for specific (E. coli) and non-specific (Lactobacillus) bacteria detection. Detection limit with a good reproducibility of 104 and 103 cfu mL-1 of E. coli bacteria has been obtained for the first biosensor and for the second one respectively. A refractive index variation below 5×10-3 due to bacteria adsorption is able to be detected. The refractive index of the multilayer structure and of the E. coli bacteria layer was estimated with a modeling software.
Electrochemical, Photoelectrochemical, and Surface Plasmon Resonance Detection of Cocaine Using Supramolecular Aptamer Complexes and Metallic or Semiconductor Nanoparticles
Published in:
Anal. Chem., 2009, 81 (22), pp 9291–9298
Abstract:
Metallic or semiconductor nanoparticles (NPs) are used as labels for the electrochemical, photoelectrochemical, or surface plasmon resonance (SPR) detection of cocaine using a common aptasensor configuration. The aptasensors are based on the use of two anticocaine aptamer subunits, where one subunit is assembled on a Au support, acting as an electrode or a SPR-active surface, and the second aptamer subunit is labeled with Pt-NPs, CdS-NPs, or Au-NPs. In the different aptasensor configurations, the addition of cocaine results in the formation of supramolecular complexes between the NPs-labeled aptamer subunits and cocaine on the metallic surface, allowing the quantitative analysis of cocaine. The supramolecular Pt-NPs-aptamer subunits-cocaine complex allows the detection of cocaine by the electrocatalyzed reduction of H2O2. The photocurrents generated by the CdS-NPs-labeled aptamer subunits-cocaine complex, in the presence of triethanol amine as a hole scavenger, allows the photoelectrochemical detection of cocaine. The supramolecular Au-NPs-aptamer subunits-cocaine complex generated on the Au support allows the SPR detection of cocaine through the reflectance changes stimulated by the electronic coupling between the localized plasmon of the Au-NPs and the surface plasmon wave. All aptasensor configurations enable the analysis of cocaine with a detection limit in the range of 10−6 to 10−5 M. The major advantage of the sensing platform is the lack of background interfering signals.
Ultrasensitive Surface Plasmon Resonance Detection of Trinitrotoluene by a Bis-aniline-Cross-Linked Au Nanoparticles Composite
Published in:
J. AM. CHEM. SOC. 2009, 131, 7368-7378
Abstract:
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 π-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 ~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, Kass I . for the association of TNT to the imprinted sites, 6.4 × 12 M-1, followed by a less sensitive detection of TNT by the nonimprinted π-donor bis-aniline sites (Kass.NI ) 3.9 × 109 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 π-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.
Deposition of functionalized polymer layers in surface plasmon resonance immunosensors by in-situ polymerization in the evanescent wave field
Published in:
Biosensors and Bioelectronics 24 (2009) 1270-1275
Abstract:
Traditionally, the integration of sensing gel layers in surface plasmon resonance (SPR) is achieved via 'bulk' methods, such as precipitation, spin-coating or in-situ polymerization onto the total surface of the sensor chip, combined with covalent attachment of the antibody or receptor to the gel surface. This is wasteful in terms of materials as the sensing only occurs at the point of resonance interrogated by the laser. By isolating the sensing materials (antibodies, enzymes, aptamers, polymers, MIPs, etc.) to this exact spot a more efficient use of these recognition elements will be achieved. Here we present a method for the in-situ formation of polymers, using the energy of the evanescent wave field on the surface of an SPR device, specifically localized at the point of interrogation. Using the photo-initiator couple of methylene blue (sensitizing dye) and sodium p-toluenesulfinate (reducing agent) we polymerized a mixture of N,Nmethylene- bis-acrylamide and methacrylic acid in water at the focal point of SPR. No polymerization was seen in solution or at any other sites on the sensor surface. Varying parameters such as monomer concentration and exposure time allowed precise control over the polymer thickness (from 20-200 nm). Standard coupling with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide andN-hydroxysuccinimidewas used for the immobilization of protein G which was used to bind IgG in a typical biosensor format. This model system demonstrated the characteristic performance for this type of immunosensor, validating our deposition method.
Electrochemical, Photoelectrochemical, and Surface Plasmon Resonance Detection of Cocaine Using Supramolecular Aptamer Complexes and Metallic or Semiconductor Nanoparticles
Published in:
Anal. Chem. 2009, 81, 9291-9298
Abstract:
Metallic or semiconductor nanoparticles (NPs) are used as labels for the electrochemical, photoelectrochemical, or surface plasmon resonance (SPR) detection of cocaine using a common aptasensor configuration. The aptasensors are based on the use of two anticocaine aptamer subunits, where one subunit is assembled on a Au support, acting as an electrode or a SPR-active surface, and the second aptamer subunit is labeled with Pt-NPs, CdS-NPs, or Au-NPs. In the different aptasensor configurations, the addition of cocaine results in the formation of supramolecular complexes between the NPs-labeled aptamer subunits and cocaine on the metallic surface, allowing the quantitative analysis of cocaine. The supramolecular Pt-NPs-aptamer subunits-cocaine complex allows the detection of cocaine by the electrocatalyzed reduction of H2O2. The photocurrents generated by the CdS-NPs-labeled aptamer subunits-cocaine complex, in the presence of triethanol amine as a hole scavenger, allows the photoelectrochemical detection of cocaine. The supramolecular Au-NPs-aptamer subunits-cocaine complex generated on the Au support allows the SPR detection of cocaine through the reflectance changes stimulated by the electronic coupling between the localized plasmon of the Au-NPs and the surface plasmon wave. All aptasensor configurations enable the analysis of cocaine with a detection limit in the range of 10-6 to 10-5 M. The major advantage of the sensing platform is the lack of background interfering signals.
Conformational Dynamics of Poly(acrylic acid)-Bovine Serum Albumin Polycomplexes at Different pH Conditions
Published in:
Macromol. Symp. 2008, 269, 138-144
Abstract:
This work presents the real time surface plasmon resonance (SPR) and fluorescence spectroscopy observation of cooperative interactions between aggregate- forming bovine serum albumin (BSA) and oppositely charged linear macromolecule poly(acrylic) acid (PAA). Interactions between protein and polymer result in formation of polyelectrolyte-protein polycomplexes, which exhibit expressed conformational transformations, especially at low pH. The rate constants of observed kinetic transformations were calculated and found to vary in the range from 0.8 × 10-3 to 6.7 × 10-3 for different pH values. The processes of aggregation, sedimentation and conformation of BSA-PAA complex are discussed.
Stimulation of human olfactory receptor 17-40 with odorants probed by surface plasmon resonance
Published in:
Eur Biophys J (2008) 37:807-814
Abstract:
We report here the results of human olfactory receptor (OR) 17-40 stimulation with some odorants probed by means of the double-channel surface plasmon resonance platform NanoSPR-6. OR 17-40 tagged with Nterminal cmyc sequence was heterologously co-expressed with Gαolf protein in yeast, and receptor-carrying nanosomes were prepared from yeast membrane fraction. Then, receptors were speciWcally captured via anti-cmyc antibody attached to the gold-coated substrate in orientated or random way. Measurement of odorants eVects were carried out in the presence of GTP-γ-S in diVerential mode in order to compensate bulk changes of refractive index. For the Wrst time, biosensing eYciency of olfactory Wlms was discussed in terms of their thickness and Gαolf accessibility to GTP-γ-S. Bell-shaped response proWle with two maxima (near 1 nM and near 1 μM) was established for helional, which is documented as highly speciWc agonist of OR 17-40. Unrelated odorant heptanal used as control, did not evoke signiWcant variations of diVerential signal.
3D-quantification of biomolecular covers using surface plasmon-polariton resonance experiment
Published in:
Sensors and Actuators B 134 (2008) 66-71
Abstract:
The concentration of surface molecules Ns and components of molecular susceptibility χjlω can both be determined from surface plasmon-polariton resonance (SPPR) experiments, instead of effective layer thickness and index of refraction, which are usually determined. The theoretical consideration of a molecular layer as monolayer of separated 3D-oscillators provides a newperspective for investigating molecules during SPPR experiment. It is shown that SPPR response and the form of the reflective curve depend on the form of a biomolecule and its orientation relative to the surface of the metal-carrier of plasmon oscillations. The experimental data for immunological reaction for the calculation of surface molecular concentration and mass of biomolecular covering are presented.
Microfluidic fabrication of addressable tethered lipid bilayer arrays and optimization using SPR with silane-derivatized nanoglassy substrates
Published in:
Lab Chip, 2007, 7, 927-930
Abstract:
We report the microfluidic fabrication of robust and fluid tethered bilayer arrays within a poly(dimethylsiloxane) (PDMS) chip, and demonstrate its addressability and biosensing by incorporating the GM1 receptor into the bilayer framework for detection of cholera toxin. Rapid optimization of the experimental conditions is achieved by using nanoglassified surfaces in combination with surface plasmon resonance. The ultrathin glassy film on gold mimics glass surfaces employed in microfluidics, allowing real-time monitoring of multiple assembly steps and therefore permitting rapid prototyping of microfluidic arrays. The tethered bilayer array utilizes a covalently immobilized biotinylated protein for generation of well-defined capture zones where a streptavidin link is employed for the immobilization of biotinylated vesicles. Fusion of captured vesicles is accomplished using a concentrated PEG solution, and the lateral diffusion of the tethered bilayer membrane is characterized by fluorescence recovery after photobleaching methods. The tethered membrane arrays demonstrate marked stability and high mobility, which provide an ideal host environment for membrane-associated proteins and open new avenues for high-throughput analysis of these proteins.
Cyclic Control of the Surface Properties of a Monolayer-Functionalized Electrode by the Electrochemical Generation of Hg Nanoclusters
Published in:
Chem. Eur. J. 2006, 12, 8549 - 8557
Abstract:
Hg2+ ions are bound to a 1,4-benzenedimethanethiol (BDMT) monolayer assembled on a Au electrode. Electrochemical reduction of the Hg2+-BDMT monolayer to Hg+-BDMT (at E degrees =0.48 V) and subsequently to Hg0-BDMT (at E degrees =0.2 V) proceeds with electron-transfer rate constants of 8 and 11 s(-1), respectively. The Hg0 atoms cluster into aggregates that exhibit dimensions of 30 nm to 2 microm, within a time interval of minutes. Electrochemical oxidation of the nanoclusters to Hg+ and further oxidation to Hg2+ ions proceeds with electron-transfer rate constants corresponding to 9 and 43 s-1, respectively, and the redistribution of Hg2+ on the thiolated monolayer occurs within approximately 15 s. The reduction of the Hg2+ ions to the Hg0 nanoclusters and their reverse electrochemical oxidation proceed without the dissolution of mercury species to the electrolyte, implying high affinities of Hg2+, Hg+, and Hg0 to the thiolated monolayer. The electrochemical transformation of the Hg2+-thiolated monolayer to the Hg0-nanocluster-functionalized monolayer is characterized by electrochemical means, surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact-angle measurements. The Hg0-nanocluster-modified surface reveals enhanced hydrophobicity (contact angle 76 degrees ) as compared to the Hg2+-thiolated monolayer (contact angle 57 degrees ). The hydrophobic properties of the Hg0-nanocluster-modified electrode are further supported by force measurements employing a hydrophobically modified AFM tip.
Nanoscale glassification of gold substrates for surface plasmon resonance analysis of protein toxins with supported lipid membranes.
Published in:
Anal Chem. 2006 Jan 15;78(2):596-603
Abstract:
Surface plasmon resonance (SPR) spectroscopy, a powerful tool for biosensing and protein interaction analysis, is currently confined to gold substrates and the relevant surface chemistries involving dextran and functional thiols. Drawbacks of using self-assembled monolayers (SAMs) for SPR-related surface modification include limited stability, pinhole defects, bioincompatibility, and nonspecific protein adsorption. Here we report the development of stable nanometer-scale glass (silicate) layers on gold substrates for SPR analysis of protein toxins. The nanoscale silicate layers were built up with layer-by-layer deposition of poly(allylamine hydrochloride) and sodium silicate, followed by calcination at high temperature. The resulting silicate films have a thickness ranging from 2 to 15 nm and demonstrate outstanding stability in flow cell conditions. The use of these surfaces as a platform to construct supported bilayer membranes (SBMs) is demonstrated, and improved performance against protein adsorption on SBM-coated surfaces is quantified by SPR measurements. SBMs can be formed reproducibly on the silicate surface via vesicle fusion and quantitatively removed using injection of 5% Triton X-100 solution, generating a fresh surface for each test. Membrane properties such as lateral diffusion of the SBMs on the silicate films are characterized with photobleaching methods. Studies of protein binding with biotin/avidin and ganglioside/cholera toxin systems show detection limits lower than 1 microg/mL (i.e., nanomolar range), and the response reproducibility is better than 7% RSD. The method reported here allows many assay techniques developed for glass surfaces to be transferred to label-free SPR analysis without the need for adaptation of protocols and time-consuming synthetic development of thiol-based materials and opens new avenues for developing novel bioanalytical technologies for protein analysis.
Switchable Surface Properties through the Electrochemical or Biocatalytic Generation of Ag0 Nanoclusters on Monolayer-Functionalized Electrodes
Published in:
J. AM. CHEM. SOC. 2006, 128, 1253-1260
Abstract:
The electroswitchable and the biocatalytic/electrochemical switchable interfacial properties of a Ag+-biphenyldithiol (BPDT) monolayer associated with a Au surface are described. Upon the application of a potential corresponding to -0.2 V the Ag+-BPDT is reduced to the Ag0-BPDT interface, and silver nanoclusters are generated on the interface. The application of a potential that corresponds to 0.2 V reoxidizes the monolayer to the Ag+-BPDT monolayer. The reversible electrochemical transformation of the Ag+-BPDT monolayer and of the Ag0-BPDT surface was followed by electrochemical means and surface plasmon resonance spectroscopy (SPR). The SPR experiments enabled us to follow the kinetics of nanoclustering of Ag0 on the surface. The hydrophobic/hydrophilic properties of the surface are controlled by the electrochemically induced transformation of the interface between the Ag+-BPDT and Ag0-BPDT states. The Ag0-BPDT monolayer reveals enhanced hydrophilicity. The hydrophobic/hydrophilic properties of the interface were probed by contact angle measurements and force interactions with a hydrophobicallyfunctionalized AFM tip. The Ag0-BPDT interface was also biocatalytically generated using alkaline phosphatase, AlkPh, and ρ-aminophenyl phosphate as substrate. The biocatalytically generated paminophenol reduces Ag+ ions associated with the surface to Ag0 nanoclusters. This enables the cyclic biocatalytic/electrochemical control of the surface properties of the modified electrode.
Direct observation of UV-B radiation effect on antigen-antibody coupling using surface plasmon resonance
Published in:
Sensors and Actuators B xxx (2004) xxx-xxx
Abstract:
We studied the effect of UV irradiation on (non)specific bounding of bovine serum albumin (BSA) and mouse antiBSA immunoglobulin (IgG) using a surface plasmon resonance (SPR) apparatus NanoSPR-2 and special photodetectors. It was found that specific bounding of AG-AB complex is broken under UV irradiation. Contrary to this, UV irradiation of BSA layer before its contact with IgG did not demonstrate any peculiarities. On the basis of quantitative determination of kinetics of specific bounding and washing and precise measurement of photon flux, the product γσ of quantum yield γ and active centre cross-section σ was evaluated to be about 10-20 cm2. As the dimension of amino acid residues tryptophan and tyrosine is about 1 nm, we have concluded that the quantum yield of reaction is very small (about 0.001). This indicates at presence of a barrier for direct photochemical reaction between the interacting substances.
Enzyme-Catalyzed Bio-Pumping of Electrons into Au-Nanoparticles: A Surface Plasmon Resonance and Electrochemical Study
Published in:
AM. CHEM. SOC. 2004, 126, 7133-7143
Abstract:
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, θP , in the surface plasmon resonance (SPR) spectra. As the biocatalytic charging phenomenon is controlled by the concentration of glucose, the changes in the θP 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.
Detection of plant viruses using a surface plasmon resonance via complexing with specific antibodies
Published in:
Journal of Virological Methods xxx (2004) xxx-xxx
Abstract:
The use of instrumental systems based on the surface plasmon resonance (SPR) for rapid diagnosis of intact plant viruses (in particular, tobacco mosaic virus (TMV)) is considered. A new approach using detection of viral antigen and antibody (IgG) complexes formed during the preincubation step (instead of their consecutive application in classical approach) is discussed. A comparison between signal level registered from the mixture of virus and specific serum and that from the sample without virus (samples deposited onto the sensor surface treated with thiocyanate and protein A Staphylococcus aureus) allows unambiguous detection of viral particles in the material studied. The performance capabilities of the method are discussed and illustrated by quantitative detection of virus in the actual samples (cells homogenate) at high concentration.
Analysis of NAD(P)+ and NAD(P)H cofactors by means of imprinted polymers associated with Au surfaces: A surface plasmon resonance study
Published in:
Analytica Chimica Acta 504 (2004) 101-111
Abstract:
Crosslinked films consisting of the acrylamide-acrylamidophenylboronic acid copolymer that are imprinted with recognition sites for β-nicotinamide adenine dinucleotide (NAD+), β-nicotinamide adenine dinucleotide phosphate NADP+, and their reduced forms (NAD(P)H), are assembled on Au-coated glass supports. The binding of the oxidized cofactors NAD+ or NADP+ or the reduced cofactors NADH or NADPH to the respective imprinted sites results in the swelling of the polymer films through the uptake of water. Surface plasmon resonance (SPR) spectroscopy is employed to follow the binding of the different cofactors to the respective imprinted sites. The imprinted recognition sites reveal selectivity towards the association of the imprinted cofactors. The method enables the analysis of the NAD(P)+ and NAD(P)H cofactors in the concentration range of 1×10-6 to 1×10-3 M. The cofactor-imprinted films associated with the Au-coated glass supports act as active interfaces for the characterization of biocatalyzed transformations that involve the cofactor-dependent enzymes. This is exemplified with the characterization of the biocatalyzed oxidation of lactate to pyruvate in the presence of NAD+ and lactate dehydrogenase using the NADH-imprinted polymer film. c 2003 Elsevier B.V. All rights reserved.
Self-assembled multilayer superstructures as immobilization support for bioreceptors
Published in:
Sensors and Actuators B 95 (2003) 336-343
Abstract:
A new strategy for the preparation of layer-by-layer inorganic assemblies are discussed which allows simple fabrication of multifunctional thin film on various substrates. The procedure involves alternating layers of the cyanoferrate derivatives with layers of copper ions. A film growth was investigated in situ by surface plasmon resonance (SPR) and characterized by atomic force microscopy (AFM). It was shown that the topography of the surface strongly depends on a number of layers. In particular, the change-over to the formation of 3D aggregates after 12-15 cycles of deposition was observed. It was demonstrated that biological captors, immunoglobulins, can easily be immobilized onto these films in closely packed oriented monolayer, and stable theoretically predicted response was obtained in SPR geometry. This suggests that the functional multilayer built using this approach will have useful application owing to their controllable chemical reactivity. © 2003 Elsevier B.V. All rights reserved.
Au Nanoparticle-Enhanced Surface Plasmon Resonance Sensing of Biocatalytic Transformations
Published in:
Chem. Eur. J. 2003, 9, 6108 + 6114
Abstract:
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 (MPAV2+-Au nanoparticles). In situ electrochemical surface plasmon resonance (SPR) measurements are used to followthe 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 MPAV2+-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 1×10-4m to 2×10-3m. Similarly, the diaphorase-mediated formation of the bipyridinium radical cation film on the Au-coated glass surface by the reduction of the MPAV2+-functionalized Au nanoparticles by NADH is used for the amplified SPR detection of NADH in the concentration range of 1×10-4m to 1×10-3m.
Probing Photoelectrochemical Processes in Au-CdS Nanoparticle Arrays by Surface Plasmon Resonance:Application for the Detection of Acetylcholine Esterase Inhibitors
Published in:
J. AM. CHEM. SOC. 2003, 125, 16006-16014
Abstract:
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.
Electrical contacting of glucose dehydrogenase by the reconstitution of a pyrroloquinoline quinone-functionalized polyaniline film associated with an Au-electrode: an in situ electrochemical SPR study
Published in:
CHEM. COMMUN., 2002, 1936-1937
Abstract:
The studied system based on the electrically contacted GDH allows simultaneous electrochemical and optical transduction of the biocatalytic oxidation of glucose.
Redox-Switching of Electrorefractive, Electrochromic, and Conductivity Functions of Cu2+/Polyacrylic Acid Films Associated with Electrodes
Published in:
Advanced Materials, 2002, 14, No. 21, November 4, p. 1549-1553
Abstract:
The present study has revealed a new redox-switchable functional polymer consisting of a CU2+/polyacrylic acid film associated with an electrode support. By redox transformation of the polymer between the Cu2+/PA A and Cu0/PAA states the electrorefractive, electrochromic, and conductivity properties of the film could be reversibly switched. These electroswitchable properties of the polymer matrix may be used to assemble new types of optical filters, optical modulators, optoelectronic devices, smart windows, and interfaces of controlled conductivity. Preliminary studies indicate that other metal-ion/PAA films such as Pb2+/PAA or ZN2+/PAA show similar redox-switchable optoelectronic properties. The features of these systems will be the subject of a forthcoming report.
Integration of Polyaniline/Poly(acrylic acid) Films and Redox Enzymes on Electrode Supports: An in Situ Electrochemical/ Surface Plasmon Resonance Study of the Bioelectrocatalyzed Oxidation of Glucose or Lactate in the Integrated Bioelectrocatalytic Systems
Published in:
J. AM. CHEM. SOC. 2002, 124, 6487-6496
Abstract:
Electropolymerization of aniline in the presence of poly(acrylic acid) on Au electrodes yields a polyaniline/poly(acrylic acid) composite film, exhibiting reversible redox functions in aqueous solutions at pH = 7.0. In situ electrochemical-SPR measurements are used to identify the dynamics of swelling and shrinking of the polymer film upon the oxidation of the polyaniline (PAn) to its oxidized state (PAn2+) and the reduction of the oxidized polymer (PAn2+) back to its reduced state (PAn), respectively. Covalent attachment of N6-(2-aminoethyl)-flavin adenin dinucleotide (amino-FAD, 1) to the carboxylic groups of the composite polyaniline/poly(acrylic acid) film followed by the reconstitution of apoglucose oxidase on the functional polymer yields an electrically contacted glucose oxidase of unprecedented electrical communication efficiency with the electrode: electron-transfer turnover rate ~1000 s-1 at 30°C. In situ electrochemical- SPR analyses are used to characterize the bioelectrocatalytic functions of the biomaterial-polymer interface. The current responses of the bioelectrocatalytic system increase as the glucose concentrations are elevated. Similarly, the SPR spectra of the system are controlled by the concentration of glucose. The glucose concentration controls the steady-state concentration ratio of PAn/PAn2+ in the film composition. Therefore, the SPR spectrum of the film measured upon its electrochemical oxidation is shifted from the spectrum typical for the oxidized PAn2+ at low glucose concentration to the spectrum characteristic of the reduced PAn at high glucose concentration. Similarly, the polyaniline/poly(acrylic acid) film acts as an electrocatalyst for the oxidation of NADH. Accordingly, an integrated bioelectrocatalytic assembly was constructed on the electrode by the covalent attachment of N6-(2-aminoethyl)-β-nicotinamide adenine dinucleotide (amino-NAD+, 2) to the polymer film, and the two-dimensional cross-linking of an affinity complex formed between lactate dehydrogenase and the NAD+-cofactor units associated with the polymer using glutaric dialdehyde as a cross-linker. In situ electrochemical-SPR measurements are used to characterize the bioelectrocatalytic functions of the system. The amperometric responses of the system increase as the concentrations of lactate are elevated, and an electron-transfer turnover rate of 350 s-1 between the biocatalyst and the electrode is estimated. As the PAn2+ oxidizes the NADH units generated by the biocatalyzed oxidation of lactate, the PAn/PAn2+ steady-state ratio in the film is controlled by the concentration of lactate. Accordingly, the SPR spectrum measured upon electrochemical oxidation of the film is similar to the spectrum of PAn2+ at low lactate concentration, whereas the SPR spectrum resembles that of PAn at high concentrations of lactate.
Simple method for plant virus detection: effect of antibody immobilization technique
Published in:
Journal of Virological Methods 105 (2002) 141-146
Abstract:
The possibility has been demonstrated for applying a surface plasmon resonance for detecting plant viruses in real samples. An optimal mode for antiviral immunoglobulin immobilization on sensor surfaces is described. Out of three proposed techniques for sensor surface treatment, namely, unmodified gold surface, gold surface treated with (a) thiocyanate and (b) thiocyanate and protein A (Staphylococcus aureus), the latter was chosen as most suited for retention of the formed native immunoglobulin layer. © 2002 Elsevier Science B.V. All rights reserved.
Probing Antigen-Antibody Binding Processes by Impedance Measurements on Ion-Sensitive Field-Effect Transistor Devices and Complementary Surface Plasmon Resonance Analyses: Development of Cholera Toxin Sensors
Published in:
Anal. Chem.2002, 74,4763-4773
Abstract:
Impedance measurements on ISFET devices are employed to develop new immunosensors. The analysis of the transconductance curves recorded at variable frequencies, upon the formation of antigen-antibody complexes on the ISFET devices, allows determination of the biomaterial film thicknesses. Complementary surface plasmon resonance measurements of analogous biosensor systems, using Au-coated glass slides as support, reveal similar film thicknesses of the biomaterials and comparable detection limits. A dinitrophenyl antigen layer is immobilized on the ISFET gate as a sensing interface for the anti-dinitrophenyl antibody (anti-DNP-Ab). The anti-DNP-Ab is analyzed with a sensitivity that corresponds to 0.1 μg mL-1. The assembly of the biotinylated anti-anti-DNP-Ab and avidin layers on the base anti-DNPAb layer is characterized by impedance measurements. The development of an ISFET-based sensor for the cholera toxin is described. The anti-cholera toxin antibody is immobilized on the ISFET device. The association of the cholera toxin (CT) to the antibody is monitored by the impedance measurements. The detection limit for analyzing CT is 1.0 × 10-11 M.
A novel aldehyde dextran sulfonate matrix for affinity biosensors
Published in:
Biochem. Biophys. Methods 50 2002 201-216
Abstract: