Various Current Responses of Single Silver Nanoparticle Collisions on a Gold Ultramicroelectrode Depending on the Collision Conditions

Collisions of silver nanoparticles (NPs) with a more electrocatalytic gold or platinum ultramicroelectrode (UME) surface have been observed by using an electrochemical method. Depending on the applied potential to the UME, the current response to the collision of Ag NPs on the UME resulted in various shape changes. A staircase decrease, a blip decrease, and a blip increase of the hydrazine oxidation current were obtained at an applied potential of 0.33, 0.80, and 1.3 V, respectively. Different collision behaviors of Ag NPs on the UME surface were suggested for each shape of current response. Ag NP attachment, which hindered the diffusion flux to the UME, caused a staircase decrease of the electrocatalytic current. Instantaneous blocking of the hydrazine oxidation by Ag NP collision and, following recovery of the current by means of oxidation of Ag NP, caused a blip decrease of the electrocatalytic current. The formation of a higher oxidation state of Ag on the Ag NP and its electrocatalytic hydrazine oxidation resulted in a blip increase of the electrocatalytic current. The analysis of the current response of a single NP collision experiment can be a useful tool to understand the various behaviors of NPs on the electrode surface.     

Silver UPD ultra-thin film modified nanoporous gold electrode with applications in the electrochemical detection of chloride

Nanoporous noble metals are usually expected to exhibit much higher surface areas than smooth ones, making them of particular importance in many electrochemical applications. This paper describes a simple electrochemical method to modify a nanoporous Au (NPG) surface by using an under potentially deposited (UPD) Ag adlayer. The NPG electrode was obtained by the dealloying of Zn from Au_xZn_1−x in a 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl₂-EMIC) ionic liquid. The Ag UPD modified nanoporous gold (NPG/Ag(UPD)) electrode possessed dual properties, including an intrinsic high surface area from the nanoporous structure and the characteristics of the Ag UPD adlayer. The potential utility of using NPG/Ag(UPD) for sensors was demonstrated by its excellent sensitivity and selectivity in the electrochemical determination of chloride ions. An atomic scale metal monolayer obtained in the UPD process was selected as a sensing agent. The long-term storability and operational stability of the electrode were strongly demonstrated. Specifically, two couples of redox waves at ∼552 mV and ∼272 mV, respectively, were observed in the cyclic voltammograms (CVs) of the NPG/Ag(UPD) after the adsorption of chloride ions. The first couple of redox waves was related to the UPD and silver stripping and the second couple of redox waves was induced by the adsorption of Cl⁻. The Cl⁻ adsorption process on the NPG/Ag(UPD) electrode followed the transient Langmuir adsorption kinetic model. The ratio of the integrated charges for these two anodic stripping peaks was selectively used to determine dilute chloride ion levels. The calibration curve was linear in the Cl⁻ concentration range of 0.5-30.0 μM.     

DNA analysis by application of Pt nanoparticle electrochemical amplification with single label response

This study demonstrates a highly sensitive sensing scheme for the detection of low concentrations of DNA, in principle down to the single biomolecule level. The previously developed technique of electrochemical current amplification for detection of single nanoparticle (NP) collisions at an ultramicroelectrode (UME) has been employed to determine DNA. The Pt NP/Au UME/hydrazine oxidation reaction was employed, and individual NP collision events were monitored. The Pt NP was modified with a 20-base oligonucleotide with a C6 spacer thiol (detection probe), and the Au UME was modified with a 16-base oligonucleotide with a C6 spacer thiol (capture probe). The presence of a target oligonucleotide (31 base) that hybridized with both capture and detection probes brought a Pt NP on the electrode surface, where the resulting electrochemical oxidation of hydrazine resulted in a current response.     

Combining Electrodeposition and Optical Microscopy for Probing Size‐Dependent Single‐Nanoparticle Electrochemistry

Electrodeposition of nanoparticles (NPs) is a promising route for the preparation of highly electroactive nanostructured electrodes. By taking advantage of progressive electrodeposition, disordered arrays with a wide size distribution of Ag NPs are produced. Combined with surface‐reaction monitoring by using highly sensitive backside absorbing‐layer optical microscopy (BALM), such arrays offer a platform for screening size‐dependent electrochemistry at the single NP level. In particular, this strategy allows rationalizing the electrodeposition dynamics at the single‐NP level (>10 nm), up to the point of quantifying the presence of metal nanoclusters (<2 nm), and probing easier NP oxidation with size decrease, either through electrochemical or galvanic reactions.     

Electrochemical and sem characterization of Ag electrodes roughened by potential sweep and potential step processes in aqueous chloride and chloride + pyridine media

The effect of solution pH and the presence of pyridine on the redox behavior of Ag electrodes in aqueous chloride media is investigated. Scanning electron microscopy is used to evaluate differences in surface morphology of Ag electrodes subjected to electrochemical oxidation and oxidation—reduction processes in 0.1 M KCl and 0.1 M KCl + 0.05 M pyridine media at pH values of 2, 7, and 12. Potential sweep and potential step methods are used to effect the electrochemical oxidation and oxidation—reduction events. Comparisons are made between the resulting surface morphologies on the submicroscopic level for Ag surfaces roughened in these two ways. The redox chemistry of the oxidation and reduction processes is interpreted in terms of the different species capable of interacting with the Ag electrode surface and Ag⁺ species generated during oxidation in each medium. Surface adsorbates proposed to be important include chloride ions and pyridine. The relative importance of these species in terms of their ability to influence the redox chemistry of the Ag electrodes is seen to be a sensitive function of solution pH.     

Co-adsorption of CO onto a Ag-modified Pt(111)--restructuring of a Ag UPD layer monitored by EC-STM

The effect of co-adsorption of CO on an underpotentially deposited (UPD) silver monolayer on a Pt(111) single crystal electrode in 0.05 M sulfuric acid is investigated for the first time by means of electrochemical scanning tunneling microscopy (EC-STM). Pure electrochemical experiments suggest that the co-adsorption of CO onto Pt single crystal electrodes previously modified by a monolayer of Ag, forces Ag atoms of the first UPD monolayer into a second adlayer. The present EC-STM studies reveal the formation of a large-area Ag network after the co-adsorption of CO. The resulting Ag nanostructures formed on wide Pt(111) terraces are approximately 0.5 nm high and 10 nm wide. The desorption of the newly formed second Ag adlayer, the oxidation of CO and the desorption of Ag atoms from the first adlayer are monitored by EC-STM and simultaneously detected in the corresponding CVs in three different oxidation peaks. EC-STM images recorded afterwards show the unchanged Pt surface. The presence of Ag on the surface leads to a downward shift of the onset of oxygen adsorption on the Pt(111) surface.     

Electrochemical determination of nonylphenol based on ionic liquid-functionalized graphene nanosheet modified glassy carbon electrode and its interaction with DNA

Nonylphenol (NP) was determined using electrochemical method based on ionic liquid-functionalized graphene nanosheet modified electrode. The fabricated electrode was characterized by electrochemical impedance spectroscopy. The different influence parameters, such as pH value, scan rate, accumulation potential, and time, were investigated. Under the optimum conditions, the linear relationship between peak current value and concentration of NP was obtained with differential pulse voltammetry in two ranges from 0.5 to 30 μM and 30 to 200 μM with the detection limit of 0.058 μM (S/N?=?3). Moreover, this modified electrode was applied to NP determination in water and soil samples with the recoveries from 94.8 to 104 %, which showed the method could be applied to determine NP in environment. In addition, to explore the damage to DNA, the interaction between NP and DNA was investigated with the association constant (β) of 0.4867 and the Hill coefficient (m) of 3.75?×?10⁵ M^?1, respectively.     

A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4‐Nitrophenol Using Multiwall Carbon Nanotubes

The electrochemical detection of the hazardous pollutant 4‐nitrophenol (4‐NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4‐NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4‐NP on the GC/MWNCT surface) in a potential region which is approximately 700 mV less positive than that needed to oxidize 4‐NP, thus minimizing the interference of matrix components. The limit of detection for 4‐NP obtained using square‐wave voltammetry (0.12 μmol L^?1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4‐NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4‐NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV‐vis detection.     

Single Oil Drop Electrochemistry on a Screen‐Printed Electrode Surface

The use of a contaminated single oil drop on a screen‐printed carbon electrode is described for the first time here. The simple methodology developed herein opens the possibility of conducting such measurements. R‐(+)‐limonene oil, some samples of which were contaminated with 4‐nitrophenol (4‐NP), was used as the oil phase, and Britton? Robinson (BR) buffer was used as the aqueous phase. An oxidation peak at approximately 0.8 V vs. Ag was obtained when the system comprised an oil/water interface. The charge transfer resistance decreased by a factor of approximately 7.1 when an interfacial system composed of two immiscible liquids was used as an electrochemical tool.     

集成化金膜阵列电极的制作研究

以聚乙烯不干胶掩膜版法结合金属溅射沉积技术在FR-4玻璃纤维版上制作了由6个金膜工作电极(1 mm×2 mm)、1个大面积金膜对电极(2 mm×13 mm)和1个厚膜Ag/AgCl参比电极构成的集成化金膜阵列电极系统,并利用电化学手段对阵列电极系统进行了考察。研究结果表明,K3Fe(CN)6在厚膜Ag/AgCl/1.0 mol/L NaCl参比电极上的式电位与商业Ag/AgCl/3.0 mol/L NaCl参比电极相差0.067 V;参比电极放置1个月后,测量电位未发生明显变化。利用扫描电化学显微镜对工作电极表面平整度进行考察,结果表明工作电极表面具有较好的平整度。通过测量H2SO4还原峰面积评价了工作电极电化学面积的批内、批间一致性;通过K3Fe(CN)6在电极上的Ipa/Ipc比值评价了工作电极电化学特性的批内、批间一致性。结果表明,阵列电极面积和电化学特性具有良好的批内和批间一致性。对集成化金膜阵列电极系统的研究结果表明,聚乙烯不干胶掩膜版法结合金属溅射沉积技术制作的阵列电极能够满足电化学电极的要求,可作为电化学生物传感器的基础电极。     

Optical microscopy to study single nanoparticles electrochemistry: From reaction to motion

Nanoparticles (NPs)-based electrochemical devices are generating a growing interest and optical microscopy has recently proven to be a powerful tool to apprehend their electrochemical behavior. Through several striking examples, this review demonstrates how label-free optical imaging coupled to an electrochemical actuation can be used to probe operando the physical and electrochemical properties of single NPs, with high resolution and sensitivity and without additional emitters. Such an approach can be particularly relevant to establish clear structure-motion/reactivity relationships required to optimize NPs exploited as electrode materials.     

4-Mercaptophenylboronic acid-induced in situ formation of silver nanoparticle aggregates as labels on an electrode surface

This work presented a general way for in situ formation of citrate-capped silver nanoparticle (AgNP) aggregates as labels on an electrode surface. When the electrode surface was functionalised with a member of the o-diphenol family, 4-mercaptophenylboronic acid (MPBA) was anchored onto the electrode surface via a boronate ester covalent bond. The anchored MPBA captured AgNPs through AgS interaction. The resulting surface-tethered AgNPs could recruit more MPBA molecules and AgNPs through the formation of an AgS bond and the covalent interaction between the α-hydroxycarboxylate of the citrate and the boronate of the MPBA. This led to in situ formation of a network of AgNPs. The complexes formed between MBPA and citrate acid, as well as dopamine (a member of the o-diphenol family), were characterized by mass spectrometry. The MBPA-induced aggregation of citrate-capped AgNPs in solution was confirmed by UV–Vis spectrophotometry and transmission electron microscopy. The network of AgNPs formed on the diphenol-covered electrode surface was characterized by scanning electron microscopy. The electrochemical signal was measured based on the solid-state Ag/AgCl reaction of the AgNPs. To demonstrate the applications and analytical merits of our design, tyrosinase and protease (thrombin) were measured as model analytes. The proposed strategy is likely to lead to the development of sensors for the detection of other biomolecules.     

Electrochemical solid-state phase transformations of silver nanoparticles

Adenosine triphosphate (ATP)-capped silver nanoparticles (ATP-Ag NPs) were synthesized by reduction of AgNO(3) with borohydride in water with ATP as a capping ligand. The NPs obtained were characterized using transmission electron microscopy (TEM), UV-vis absorption spectroscopy, X-ray diffraction, and energy-dispersive X-ray analysis. A typical preparation produced ATP-Ag NPs with diameters of 4.5 ± 1.1 nm containing ~2800 Ag atoms and capped with 250 ATP capping ligands. The negatively charged ATP caps allow NP incorporation into layer-by-layer (LbL) films with poly(diallyldimethylammonium) chloride at thiol-modified Au electrode surfaces. Cyclic voltammetry in a single-layer LbL film of NPs showed a chemically reversible oxidation of Ag NPs to silver halide NPs in aqueous halide solutions and to Ag(2)O NPs in aqueous hydroxide solutions. TEM confirmed that this takes place via a redox-driven solid-state phase transformation. The charge for these nontopotactic phase transformations corresponded to a one-electron redox process per Ag atom in the NP, indicating complete oxidation and reduction of all Ag atoms in each NP during the electrochemical phase transformation.     

Formation of a perylenetetracarboxylic diimide network film by post electrochemical treatment

Perylenetetracarboxylic diimide (PDI) derivatives bearing two or four peripheral pyrrole pendants (PDI-nPy, n=2 or 4) are cross-linkable materials by electro/phototreatment. In this paper, we introduce a new posttreatment technique to produce an insoluble film. Unlike the common solution-phase electrochemical deposition, we first spin-coated PDI-nPy on an electrode and then electrotreated the coated surface in a monomer-free electrolyte solution. This method gives the film a smooth surface with no granules, while the common method induces a rough film with a lot of granules. The post electrochemical treatment also provides a merit of higher resolution in a patterning process on a specific metal electrode. As one of the applications, we carried out an electrochromic study on the posttreated PDI-4Py film. It turned purple (lambdamax=590 nm) and sky blue (lambdamax=797 nm) at 0 and -1.9 V vs Ag/Ag+, respectively. We believe this method will broaden the patterning concept with the desired film morphology and resolution using PDI on a specific electrode.     

Electrochemical studies of copper fatty amides complex in organic medium

The electrochemical behavior of complexes of fatty amides, synthesized from vegetable oil, with Cu(II) has been investigated. In this study, a platinum electrode was used in presence of DMSO as a medium. Reduction of Cu(II)/fatty amides complex was found with quasi-reversible reaction. The peak potential of voltammetric behavior of fatty amides is about ?0.77 V at a scan rate v = 0.1 V s^?1 versus Ag|Ag⁺ electrode. This study shows that Cu(II)-fatty amides complex is poorly adsorbed on the electrode surface. Additionally, the copper complex form of fatty amides has a more stable structure than pure fatty amides to form the electrochemical reduction of the complex.     

Electrochemical reduction of nitroprusside on a glassy carbon electrode modified by poly-l-lysine films

The present work describes the preparation and characterization of polyelectrolyte coatings of poly-l-lysine (PLL) to modify a glassy carbon electrode and its application to the pre-accumulation of nitroprusside (NP). The effects of the coating on the electrochemical reduction of NP were investigated. The performance of the modified electrode indicates that the drug can be immobilized by electrostatic interaction and the voltammetric signal monitored at all pH values in the range of 2–12. The strong interaction between NP and PLL stabilizes the complex on the electrode surface and minimizes the chemical reaction of lost CN⁻ ions as a subsequent reaction of electron transfer, which could improve the action mechanism of NP.     

Surface functionalization with redox active molecule-based imidazolium via click chemistry

In this study, the redox active molecule N-ferrocenylmethyl-N-propargylimidazolium bromide was immobilized onto the surface of an electrode. The surface modification was performed by coupling the electrochemical reduction of the 4-azidophenyldiazonium generated in situ with a copper(I) catalyzed click chemistry reaction. Surface and electrochemical investigations suggest the attachment of a monolayer of redox active molecules containing an ionic liquid framework onto the electrode surface. Furthermore, scanning electrochemical microscopy studies revealed the conductive behavior of the attached ferrocenyl moieties on the ITO surface.     

银纳米颗粒的合成及用于抗癌药氟他胺的电化学检测（英文）

Ag nanoparticles were synthesized on the surface of a glassy carbon electrode modified with p‐tert‐butylcalix[4]arene and p‐tert‐butylcalix[6]arene by the deposition of Ag+ at an open circuit potential followed by the electrochemical reduction of the Ag+.The presence of the calixarene layer on the electrode surface controlled the particle size and prevented agglomeration.Cyclic voltam‐metry showed that the Ag nanoparticles on the modified glassy carbon electrode had good catalytic ability for the reduction of flutamide.The effects of calixarene concentration,potential applied for the reduction of Ag+,number of calixarene layers,and p H value on the electrocatalytic activity of the Ag nanoparticles were investigated.The modified electrode had a linear range in differential pulse voltammetry of 10-1000 μmol/L with a detection limit of 9.33 μmol/L for flutamide at an S/N = 3.The method was applied to the detection of flutamide in practical samples.     

基于纳米银-石墨烯复合材料的增强效应电化学测定对乙酰氨基酚

利用氧化还原反应制备纳米银-石墨烯复合纳米材料(Ag NPs-GN),将其修饰在玻碳电极表面制备了纳米银-石墨烯修饰玻碳电极(Ag NPs-GN/GCE)。在p H 4.78的Britton-Robinson(B-R)缓冲溶液中,用循环伏安法(CV)和方波伏安法(SWV)研究了对乙酰氨基酚在Ag NPs-GN/GCE和GN/GCE上的电化学行为。结果表明,二者对对乙酰氨基酚的氧化还原反应均有电催化作用,而且复合纳米材料Ag NPs-GN具有较单一GN更好的催化效果。用方波伏安法测得对乙酰氨基酚的还原峰电流与其浓度在1.0×10-7~5.0×10-4mol/L范围内呈线性关系,检出限(S/N=3)为3.0×10-8mol/L。建立了片剂中对乙酰氨基酚含量测定的新方法,修饰电极具有较好的重现性和稳定性。     

An introduction to bismuth film electrode for use in cathodic electrochemical detection

A new electrode surface design, the bismuth film electrode (BiFE), is presented as a promising alternative to mercury and other solid electrodes for direct cathodic electrochemical detection of organic compounds. The preparation of the BiFE, involving an ex situ electroplating of metallic bismuth onto a glassy carbon (GC) substrate electrode, was optimised. The useful negative potential windows of the BiFE in the pH range 1 (−0.2 to −0.8 V vs Ag/AgCl) to 10 (−0.2 to −1.5 V) were determined. The reproducibility of measuring 2-nitrophenol as a model compound (relative standard deviation, r.s.d., n=10) was found to be 0.5% at the same BiFE, and 1.0% at successive newly prepared BiFEs. No polishing or any other pre-treatment of the substrate GC surface was required prior to re-plating of a new Bi film. The BiFE showed similar or even favourable voltammetric behaviour when compared to mercury and bare GC electrodes, and was successfully tested for amperometric detection under hydrodynamic conditions. The results revealed that BiFE is an attractive new non-mercury metallic electrode particularly suitable for cathodic electrochemical detection in flow analytical systems.