In situ chemical reductive growth of platinum nanoparticles on indium tin oxide surfaces and their electrochemical applications

Platinum nanoparticles directly attached to indium tin oxide (PtNP/ITO) were successfully fabricated by using an in situ chemical reductive growth method. In this method, PtNPs could be grown on the ITO surface via the one-step immersion into the growth solution containing PtCl4(2-) and ascorbic acid. The attached and grown PtNPs were spherical having an agglomerated nanostructure composed of small nanoclusters. From the morphological changes depending on the growth time, which were observed with an FE-SEM, PtNPs were found to be grown via the progressive nucleation mechanism. As the characteristics of the PtNP/ITO were those of a working electrode, it was found that the charge transfer resisivity was significantly lowered due to the grown PtNPs. Hence, for a typical redox system of [Fe(CN)6]3-/[Fe(CN)6]4-, the PtNP/ITO electrode exhibited the electrochemical responses similar to those of the bulk Pt electrode. Furthermore, it was clarified that the PtNP/ITO electrode had significant electrocatalytic properties for the oxygen reduction and methanol oxidation. The present PtNPs that had the agglomerated nanostructure may be promising for a new type of electrode material.     

Micropatterning of biomolecules on a glass substrate in fused silica microchannels by using photolabile linker-based surface activation

Platinum nanoparticles were electrodeposited onto a film of dihexadecyl hydrogen phosphate deposited on a glassy carbon electrode (GCE) and modified with dispersed acetylene black. Scanning electron microscopy and electrochemical impedance spectroscopy revealed that this nanocomposite has a uniform nanostructure and a large surface area that enables fast electron-transfer kinetics. The modified GCE showed high electrocatalytic activity for the oxidation of nitric oxide (NO). Under optimal conditions, the oxidation peak current of nitric oxide is linearly related to the concentration of NO in the concentration range between 0.18 and 120?μM, and the detection limit is as low as 50?nM (at an S/N of 3). The modified electrode was successfully applied to sensing of NO as released from rat liver.

A Novel Amperometric Immunosensor for Phytohormone Abscisic Acid Based on In Situ Chemical Reductive Growth of Gold Nanoparticles on Glassy Carbon Electrode

Abstract

An amperometric immunosensor for phytohormone abscisic acid was developed based on in situ chemical reductive growth of gold nanoparticles on glassy carbon electrode. First, an approximate 10 nm gold layer was sputtered uniformly onto the electrode surface, and then gold nanoparticles were grown directly on the gold layer for antibody adsorption by immersing the electrode into the H₂AuCl₄ solution. Determination was based on an enzyme-linked competitive immunoreaction between free and enzyme-labeled abscisic acid to bind on immobilized antibody on electrode. The linear response was from 10 ng/ml to 10 µg/ml with a detection limit of 5 ng/ml.     

Hybrid platinum nanoparticle ensemble for the electrocatalytic oxidation of H2O2: Toward nanostructured biosensor design

This paper reports the electrocatalysis of H₂O₂ oxidation by Langmuir–Blodgett (LB) thin films based on polymer-grafted platinum nanoparticles (PtNPs). 4-mercaptoaniline-functionalized PtNPs have been chemically modified to obtain poly(methacrylic acid)-grafted platinum nanoparticles (PMAA-PtNP) via surface-ATRP. These elementary bricks are used to form mixed LB films consisting of controlled mixtures of PMAA-PtNP and a redox-inactive fatty acid molecule to tune the PtNP surface density. Nanostructures are formed in which the number of layers and the number of particles in each layer may be varied. The nanostructure morphology strongly depends on the amount of PtNP. High Pt content leads to quite large nanoparticle domains whereas low content gives small domains with a finely divided nanostructure. The H₂O₂ oxidation current increases when the PMAA-PtNP surface density decreases. This result is discussed in terms of electrocatalyst accessibility modification related to the nanostructure of the films.     

Controllable immobilization of polyacrylamide onto glass slide: synthesis and characterization

A novel route was introduced to synthesize dense polyacrylamide (PAM) onto the glass slide surface. To investigate the surface chemistry of the PAM on the glass slides, X-ray photoelectron spectroscopy (XPS) was utilized to obtain detailed chemical state information on the PAM layer constituents. The XPS peak data were consistent with the presented model of the PAM on the glass slide surface. Scanning electron microscopy and atomic force microscope data indicated the presence of PAM on the glass slides, which consist of nodules. The results showed that PAM was successfully immobilized onto glass slides with a two-tier structure under aqueous condition and a monolayer structure under anhydrous condition. Compared with those under aqueous condition, the controllability of the molecular layer on glass slides and the reproducibility under anhydrous condition were much better, which makes anhydrous condition an advisable condition for the study of the reaction mechanisms of glass slides modified by PAM.     

Enzyme-functionalized gold nanowires for the fabrication of biosensors

Gold nanowires were prepared by an electrodeposition strategy using nanopore polycarbonate (PC) membrane, with the average diameter of the nanowires about 250 nm and length about 10 microm. The nanowires prepared were dispersed into chitosan (CHIT) solution and stably immobilized onto glassy carbon electrode (GCE) surface. The electrochemical behavior of gold nanowire modified electrode and its application to the electrocatalytic reduction of hydrogen peroxide (H(2)O(2)) were investigated. The modified electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. Moreover, the good biocompatibility of nanometer-sized gold, the vast surface area of the nanowire-structure make it ideal for adsorption of enzymes for the fabrication of biosensors. Glucose oxidase was adsorbed onto the nanowire surface to fabricate glucose biosensor as an application example. The detection of glucose was performed in phosphate buffer (pH 6.98) at -0.2 V. The resulting glucose biosensor exhibited sensitive response, with a short response time (<8 s), a linear range of 10(-5)-2 x 10(-2) M and detection limit of 5 x 10(-6) M.     

Fabrication of Translucid Gold-Nanocellulose Electrodes and their Potential Application as Hydrogen Peroxide Sensor

In this work, we describe the fabrication of a transparent gold electrode based on nanocellulose. The electrode was prepared via electron beam evaporation of gold onto nanocellulose films previously spread over a glass slip. Electrodes with different thickness of Au was fabricated, and the material's optical, morphological and electrical properties were assessed. Finally, as a proof of concept, a possible application of this electrode in hydrogen peroxide sensing was performed. The results show that a thin layer of gold on a nanocellulose translucid film allows obtaining a conductive transparent surface that could be used to design a transparent electrode.     

Functionalization of platinum nanoparticles for electrochemical detection of nitrite

In this work, a novel electrochemical method for nitrite detection by using functionalized platinum nanoparticles (PtNPs) is proposed. Firstly, a gold electrode is immobilized with 4-(2-aminoethyl)benzenamine. Then, PtNPs are modified with 5-[1, 2]dithiolan-3-yl-pentanoic acid [2-(naphthalene-1-ylamino)-ethyl]amide (DPAN). Consequently, in the presence of nitrite ions, Griess reaction occurs between 4-(2-aminoethyl)benzenamine on the electrode and DPAN on PtNPs, thus PtNPs are localized onto the electrode surface. So, PtNPs-electrocatalyzed reduction of H₂O₂ can be achieved to correlate the electrochemical signal with the concentration of nitrite ions. The linear concentration range can be as wide as 10–1,000 μM, while the detection limit is as low as 5 μM. The proposed method has been also successfully applied to the detection of nitrite with the local lake water, and the result is well consistent with that obtained by UV-visible spectrophotometric method. So, this method has potential use for monitoring nitrite in drinking water supplies in the future.     

Fabrication of a gold microelectrode for amperometric detection on a polycarbonate electrophoresis chip by photodirected electroless plating

A novel method of photoresist-free micropatterning coupled with electroless gold plating is described for the fabrication of an integrated gold electrode for electrochemical detection (ED) on a polycarbonate (PC) electrophoresis microchip. The microelectrode layout was photochemically patterned onto the surface of a PC plate by selective exposure of the surface coated without photoresist to 254 nm UV light through a chromium/quartz photomask. Thus, the PC plate was selectively sensitized by formation of reactive chemical moieties in the exposed areas. After a series of wet chemistry reactions, the UV-exposed area was activated with a layer of gold nanoparticles that served as a seed to catalyze the electroless plating. The gold microelectrode was then selectively plated onto the activated area by using an electroless gold plating bath. Nonselective gold deposition on the unwanted areas was eliminated by sonication of the activated PC plate in a KSCN solution before electroless plating, and the adhesion of the plated electrodes to the PC surface was strengthened with thermal annealing. Compared with the previously reported electroless plating technique for fabrication of microelectrodes on a microchip, the present method avoided the use of a membrane stencil with an electrode pattern to restrict the area to be wet-chemically sensitized. The CE with integrated ED (CE-ED) microchip was assembled by thermal bonding an electrode-plated PC cover plate to a microchannel-embossed PC substrate. The novel method allows one to fabricate low-cost, electrode-integrated, complete PC CE-ED chips with no need of a clean room. The fabricated CE-ED microchip was demonstrated for separation and detection of model analytes, including dopamine (DA) and catechol (CA). Detection limits of 0.65 and 1.03 microM were achieved for DA and CA, respectively, and theoretical plate number of 1.4 x 10(4) was obtained for DA. The plated gold electrode can be used for about 4 h, bearing usually more than 100 runs before complete failure.     

Non-enzymatic sensing of hydrogen peroxide using a glassy carbon electrode modified with a composite consisting of chitosan‐encapsulated graphite and platinum nanoparticles

We report on a non-enzymatic hydrogen peroxide (H₂O₂) sensor which makes use of a nanocomposite consisting of platinum nanoparticles (PtNPs) and chitosan-encapsulated graphite (graphite-CS). The composite was prepared by sonication of pristine graphite in chitosan (CS) in 5 % acetic acid. The PtNP decorated graphite-CS (graphite-CS/PtNPs) composite was prepared by electrodeposition of PtNPs on the graphite-CS modified glassy carbon electrode. The graphite-CS/PtNP composite was characterized by scanning electron microscopy, elemental analysis and FTIR spectroscopy. The modified electrode displays an enhanced reduction peak current for H₂O₂ when compared with electrodes modified with graphite/PtNPs and PtNPs. The modified electrode exhibits excellent electrocatalytic activity towards the reduction of H₂O₂, and the amperometric response is linear over the concentration range from 0.25 to 2890 μM. The sensitivity and the detection limit are 0.465 μA?μM￣¹ ? cm￣² and 66 nM, respectively. The sensor shows fast response (3 s) in detecting H₂O₂. It is also highly selective in the presence of potentially interfering compounds, and may therefore be used as a feasible platform for sensing H₂O₂ in real samples.

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Graphical abstract Preparation of graphite-CS/PtNP composite, and its application to electrochemical reduction of H₂O₂.

     

Evaluation of nucleic acid duplex formation on gold over layers in biosensor fabricated using Czochralski-grown single-crystal silicon substrate

With a view to developing an economical and elegant biosensor chip, we compared the efficiencies of biosensors that use gold-coated single-crystal silicon and amorphous glass substrates. The reflectivity of light over a wide range of wavelengths was higher from gold layer coated single-crystal silicon substrates than from glass substrates. Furthermore, the efficiency of reflection from gold layers of two different thicknesses was examined. The thicker gold layer (100 nm) on the single-crystal silicon showed a higher reflectivity than the thinner gold film (10 nm). The formation of a nucleic acid duplex and aptamer–ligand interactions were evaluated on these gold layers, and a crystalline silicon substrate coated with the 100-nm-thick gold layer is proposed as an alternative substrate for studies of interactions of biomolecules.     

Substantial Influence of Temperature on Anchoring of Gold‐Nanoparticle Monolayer for Performance of DNA Biosensors

This paper presents a way of modification of crystalline gold surface with a high quality layer of gold nanoparticles (Au NPs) via self‐assembled dithiol. The application of additional Au NPs monolayer prepared at various temperatures was tested with three types of biosensors previously described in the literature. The examined DNA biosensors differed by the detection method and the way of the immobilization of DNA probe at the modified gold electrode surface. For the immobilization of DNA probe in the sensing layer either the formation of SAM or the affinity binding (biotin – sterptavidin) or covalent attachment were used. The necessary condition of successful preparation of a perfect such monolayer is the preparation temperature of 4 °C. The preparation of Au NPs layers at higher than 4 °C temperatures leads to poor repeatability and unsatisfactory precision of the measurements. The application of the perfect Au monolayer lowers the detection limit (circa by 10 to 100 times) for all tested DNA biosensors.     

Electrochemical growth of two-dimensional gold nanostructures on a thin polypyrrole film modified ITO electrode

Two-dimensional gold nanostructures have been fabricated by electrochemical deposition of gold nanoparticles onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. By controlling the electrodeposition conditions, gold nanoparticles with dendritic rod, sheet, flower-like (consisting of staggered nanosheets), and pinecone-like structures were generated. The flower-like gold nanoparticles showed high catalytic activity on electrochemical reduction of oxygen, and its activity was measured to be approximately 25 times that of gold pinecones and 10(4) times that of gold nanosheets in terms of gold weight. The pinecone-like nanoparticles can form a compact film with nano-/microscale binary structure like a lotus leaf surface. After modification with n-dodecanethiol, the surface showed superhydrophobic properties with a water contact angle of 153.4 degrees and a tilt angle of 4.4 degrees (5 microL droplet).     

Laser-induced formation of Au/Pt nanorods with peroxidase mimicking and SERS enhancement properties for application to the colorimetric determination of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

Platinum nanoparticles (PtNPs) were uniformly grown on the surface of gold nanorods (AuNRs) by a laser irradiation procedure. Transmission electron microscopy confirmed that the PtNPs are uniformly grown on the surface of the AuNRs. The formation of PtNPs on the AuNRs leads to a red-shift of the absorption maximum from 734 nm to 766 nm. In addition, the efficiency of surface enhanced Raman scattering (SERS) is increased, but the photothermal conversion efficiency is decreased compared to pure AuNRs. The result indicates that electron transfer occurs between gold and platinum. The peroxidase mimicking effect of PtNPs, AuNRs and Au/Pt NRs by catalyzing the oxidation of colorless 3,3’,5,5’-tetramethylbenzidine (TMB) to blue oxidized 3,3’,5,5’-tetramethylbenzidine (oxTMB; a quinone) in the presence of H₂O₂. The catalytic activity of Au/Pt NRs is higher than that of sole AuNRs or PtNPs by factors of 4.2 and 2.1, respectively. Thus, Au/Pt NRs have been used for the detection of peroxide and the limit of detection is 0.04 μM. This work provides an approach to integrate the peroxidase mimicking effect with SERS enhancement for potential application in detection.

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Graphical abstract A schematic diagram for the laser-induced growth of Au/Pt NRs and the colorimetric determination of hydrogen peroxide concentration with their peroxidase mimicking properties. The limit of detection is 0.04 μM based on the use of Au/Pt NRs as a catalyst.

     

Modification of composites of block copolymers–gold nanoparticles with enzymes and their characterization by electrochemical techniques

In this work, the poly(styrene-vynil pyridine) block copolymer was used as a porous pattern to study the electrodeposition of gold inside the pores, as a new method to obtain gold nanoparticles. The porous pattern left by the copolymer film onto a conductive glass surface was characterized by atomic force microscopy (AFM), evidencing pores of 30 nm diameter. After the electrodeposition, 30 nm diameter gold nanoparticles were obtained and they were characterized by cyclic voltammetry (CV) and AFM, and then used to study the adsorption of glucose oxidase enzyme. The adsorption process of glucose oxidase on gold nanowires was investigated by CV and electrochemical impedance spectroscopy. The morphological and capacitance results indicate that the block copolymer–gold nanoparticle composite seems to be a good candidate to design biosensors and immunosensors.     

Electrochemical activities of platinum-decorated multi-wall carbon nanotube/chitosan composites for the oxidations of alcohols

Electrooxidation of alcohols including methanol, ethanol, and isopropanol is studied on the modified solid glassy carbon electrodes with various amounts of platinum nanoparticles (PtNPs) immobilized on a composite of functionalized multi-walled carbon nanotubes (MWCNTs) and chitosan in an acidic solution. Here the chitosan is available as a binder to tightly anchor Pt nanoparticles onto the MWCNTs surfaces. MWCNTs/chitosan composite support can significantly improve the activity of the catalyst for alcohol oxidation and reduce the Pt catalyst loading. The calculated electrochemical active surface area is 379.2 m²/g Pt for PtNP–MWCNT/chitosan. Cyclic voltammetry and chronoamperometry techniques are employed for catalytic activity evaluation. The effects of operational parameters including platinum loading, concentration of the corresponding alcohol, concentration of the acid solution, scanning rate, and the final limit of anodic potential on the performance of the electrodes are also investigated.     

Synthesis of Au–ZnS hybrid nanostructures and their application for electrochemical biosensor

Au–ZnS core–shell nanostructures were grown onto the transparent indium tin oxide (ITO) thin film-coated glass surface by successive electrodeposition of Au and ZnS in cyclic voltammetry. The resulting hybrid nanostructures were characterized using scanning electron microscopy, X-ray diffraction, UV–vis spectroscopy, and electrochemical impedance spectroscopy. The glucose oxidase (GOD) was immobilized onto the surface of the Au–ZnS hybrid nanostructures in silica sol–gel network. Furthermore, the Au–ZnS nanostructures demonstrate an enhanced direct electron transfer between GOD and the electrode due to their unique chemical and electrocatalytic properties and their synergy effect. The analytical performance of the GOD-based electrode was improved greatly compared with that of ITO substrate modified by Au or ZnS nanostructures alone. The proposed enzyme electrode based on Au–ZnS hybrid nanomaterials displays high sensitivity and wide linear range in the determination of glucose. The Au–ZnS hybrid nanostructures have potential for “green chemistry” application in the fabrication of enzyme-based electrochemical biosensors.     

Recyclable hydrophilic-hydrophobic micropatterns on glass for microarray applications

A novel method for fabricating recyclable hydrophilic-hydrophobic micropatterns on glass chips is presented. TiOx patterns (100-2000 microm) were sputtered on glass chips via a through-hole mask. The patterned chips were then vapor-coated with fluoroalkylsilane, for example, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FTES) to form a hydrophobic coating layer. The fluoroalkyl chain of FTES film on TiOx patterns was photocleaved under UV irradiation, exposing the fresh hydrophilic TiOx patterns. The resulting chip could be used multiple times by repeating the coating and photocleaving processes with negligible deterioration of the hydrophobic FTES film coated on glass. If desired, bare glass patterns could also be generated by removing the TiOx patterns with KOH. The patterned glass chips have been successfully used for microarray fabrication.     

基于柔性衬底的ZnO葡萄糖酶电极制备及特性

通过水热法在长有ZnO籽晶层的柔性聚酰亚胺(PI)衬底上生长了整齐的ZnO纳米棒,ZnO纳米棒的晶体结构和表面形貌通过X射线衍射(XRD)、扫描电子显微镜(SEM)等进行表征.通过静电吸附方式,将葡萄糖氧化酶(GOx)固定在其表面.分别对GOx及修饰前后的ZnO纳米棒进行了紫外-可见光谱表征,发现修饰后存在ZnO的吸收峰和GOx的特征吸收峰,表明GOx固定在ZnO表面.通过对修饰样品进行傅里叶变换红外(FTIR)光谱测试发现了与GOx相关的吸收峰,这进一步表明GOx仍保持生物活性.最后在循环伏安曲线的测试中,这种在柔性衬底上制备的生物酶电极表现出非常灵敏的电流响应,为制备柔性葡萄糖生物传感器奠定了实验基础.     

Electrochemical Properties of Lanthanum Hexacyanoferrate Particles Immobilized onto Electrode Surface by Au‐Codeposition Method

Lanthanum hexacyanoferrate (LaHCF) was immobilized onto a substrate surface as an electroactive material by Au‐codeposition method. The LaHCF particles were attached to the electrode surface as the result of occlusion within the gold film deposited. This deposition method was first introduced for the preparation of hexacyanoferrate‐based modified electrodes. It was demonstrated that this deposition method provides a higher stability of the electroactive film in comparison with available methods for the mechanical attachment of electroactive films. On the other hand, electrochemical properties of the LaHCF film modified electrode were studied for the first time. The results showed that LaHCF film has excellent electrochemical activity as well as other analogues of Prussian blue. The modified electrode was successfully used as an electrocatalyst for the oxidation of ascorbic acid.