Enhanced charge transport and incorporation of redox mediators in layer-by-layer films containing PAMAM-encapsulated gold nanoparticles

In this work, we exploit the molecular engineering capability of the layer-by-layer (LbL) method to immobilize layers of gold nanoparticles on indium tin oxide (ITO) substrates, which exhibit enhanced charge transfer and may incorporate mediating redox substances. Polyamidoamine (PAMAM generation 4) dendrimers were used as template/stabilizers for Au nanoparticle growth, with PAMAM-Au nanoparticles serving as cationic polyelectrolytes to produce LbL films with poly(vinylsulfonic acid) (PVS). The cyclic voltammetry (CV) of ITO-PVS/PAMAM-Au electrodes in sulfuric acid presented a redox pair attributed to Au surface oxide formation. The maximum kinetics adsorption is first-order, 95% of the current being achieved after only 5 min of adsorption. Electron hopping can be considered as the charge transport mechanism between the PVS/PAMAM-Au layers within the LbL films. This charge transport was faster than that for nonmodified electrodes, shown by employing hexacyanoferrate(III) as the surface reaction marker. Because the enhanced charge transport may be exploited in biosensors requiring redox mediators, we demonstrate the formation of Prussian blue (PB) around the Au nanoparticles as a proof of principle. PAMAM-Au@PB could be easily prepared by electrodeposition, following the ITO-PVS/ PAMAM-Au LbL film preparation procedure. Furthermore, the coverage of Au nanoparticles by PB may be controlled by monitoring the oxidation current.     

3-Glycidoxypropyltrimethoxysilane mediated in situ synthesis of noble metal nanoparticles: application to hydrogen peroxide sensing

The in situ synthesis is reported of noble metal nanoparticles via 3-glycidoxypropyltrimethoxysilane mediated reduction of 3-aminopropyltrimethoxysilane treated metal salts during sol-gel processing. The method described involves the synthesis of uniform spherical nanoparticles of gold, silver and palladium with controlled size that can be directly utilized for thin film preparation. A detailed study of the synthesis and application of gold nanoparticles to the electrochemical detection of hydrogen peroxide was carried out and reveals that the amplification of hydrogen peroxide sensing is size-dependent. In addition, these nanoparticles exhibit excellent compatibility towards composite preparation. As an example, a nanocomposite with Prussian Blue (PB) is synthesized and found to be useful for the fabrication of chemically modified electrodes (CME). The resulting CME shows dramatic improvement in the electrochemistry of PB with gradual enhancement in electrocatalytic efficiency towards hydrogen peroxide sensing. The nanocomposite is used to study the direct and horseradish peroxidase (HRP)-catalyzed reduction of hydrogen peroxide. The results recorded for hydrogen peroxide analysis show an improvement in sensitivity and limit of detection on decreasing the size of gold nanoparticles in all cases.     

The electroactive multilayer films of polyelectrolytes and Prussian blue nanoparticles and their application for H2O2 sensors

Prussian blue (PB) nanoparticles were immobilized in polyelectrolyte (PE) multilayers of various compositions and thickness. Films containing nanoparticles and poly(allylamine hydrochloride) (PAH) were formed using the layer-by-layer adsorption method. A layer of branched poly(ethyleneimine) (PEI) was used to anchor the multilayer structure at the surface of a gold electrode. The films exhibited electroactive properties, increasing with the number of deposited PB layers. The properties of PEI/(PB/PAH) _n multilayers were then compared with the ones containing additionally the conductive polymer poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS). We found that the addition of the conductive, water-soluble polymer enhances the electroactive properties of the multilayer films. It also increased sensitivity of the multilayer-covered electrodes for electrochemical detection of hydrogen peroxide.     

CYP450 2B4 covalently attached to carbon and gold screen printed electrodes by diazonium salt and thiols monolayers

An easy covalent immobilization method used to develop enzyme biosensors based on carbon and gold screen printed electrodes (SPCEs and gold SPEs) is described. The linkage of biomolecules through 4-nitrobenzenediazonium tetrafluoroborate, mercaptopropionic acid and thioctic acid monolayers has been attempted using bare SPCEs and gold SPEs, as well as gold nanoparticles (AuNPs) modified SPCEs and gold SPEs. Direct covalent attachment of Cytochrome P450 2B4 (CYP450 2B4) to the transducer has been carried out by carbodiimide and hydroxysuccinimide. Experimental variables in the immobilization process and in the chronoamperometric determination of Phenobarbital (PB) have been optimized by the experimental design methodology. Reproducibility of the different biosensors has been checked under the optimum conditions, yielding values lower than 6%. Their performances have been shown by the determination of PB in pharmaceutical drugs.     

Sodium hydroxide as pretreatment and fluorosurfactant-capped gold nanoparticles as sensor for the highly selective detection of cysteine

A sensor for detecting cysteine (Cys) in a solution of fluorosurfactant (FSN)-capped gold nanoparticles (AuNPs) has been developed. Under acidic conditions, FSN-capped AuNPs are aggregated in the presence of homocysteine (HCys) and Cys but not in the presence of cysteinylglycine, glutathione, and gamma-glutamycysteine. When adding NaOH to a solution of HCys, the five-membered ring transition state is formed through intramolecular hydrogen abstraction. By contrast, it is difficult for Cys to form a four-membered ring transition state after Cys has been pretreated with NaOH. As a result, the HCys-induced aggregation of the FSN-capped AuNPs is suppressed because the five-membered ring transition state exhibits relatively larger steric hindrance and has stronger interaction with the FSN molecules. Thus, we can discriminate between Cys and HCys on the basis of different aggregation kinetics. Under the optimum condition, the selectivity of the probe for Cys in aqueous solutions is remarkably high over the other aminthiols. Note that HCys and Cys have very similar structure and pK(a) value. We have validated the applicability of our method through the analyses of Cys in urine samples. It is believed that this approach has great potential for the detection of Cys in biological samples.     

Commercial Screen‐Printed Gold Electrodes for the Detection and Quantification of Aminothiols in Human Plasma by Liquid Chromatography with Electrochemical Detection

In order to show the possibilities of screen‐printed electrodes in HPLC detection, a method is presented for routine quantification of aminothiols in human plasma. It uses commercial gold screen‐printed electrodes and provides a rapid, simple and economical procedure with a disposable detector and without any additional electrode. By working at 98 : 2 (0.05 % trifluoroacetic acid: methanol) and 0.9 V, it allows us to determine cysteine (Cys), cysteinyl‐glycine (Cys‐Gly), and homocysteine (HCys) at μmol/L levels. The method was validated, and linearity range, detection and quantification limits, precision and accuracy were evaluated by external calibration and by using N‐acetylcysteine as internal standard, which exhibited better precision.     

Synthesis and characterization of copper hexacyanoferrate nanoparticles for building up long-term stability electrochromic electrodes

Nanoparticles of a Prussian blue (PB) analogue, copper hexacyanoferrate, were synthesized by using ultrasonic radiation and characterized by spectroscopic and electrochemical techniques. The nanoparticles (ca. 10 nm diameter) were immobilized onto transparent indium tin oxide electrodes by electrostatic layer-by-layer deposition. These modified electrodes showed interesting electrochromic properties, changing the coloration during the redox process from brown to orange when oxidized. The nanostructured electrode presented high stability, in contrast to that observed for PB nanoparticles; this fact must be related to the maintenance of the electrostatic assembly because the oxidized compound, CuII/FeIII(CN)6, still possesses a negative excess of charge due to the high number of cyanide groups that link the nanoparticles with the polycation, assuring the integrity of the whole electrostatic assembled film.     

Nonionic surfactant‐capped gold nanoparticles for selective enrichment of aminothiols prior to CE with UV absorption detection

In this study, we describe the use of Tween 20‐capped gold nanoparticles (AuNPs) as selective probes for the extraction of aminothiols from an aqueous solution. Tween 20 molecules noncovalently attached to the surface of AuNPs to form Tween 20–AuNPs were used for the selective extraction of aminothiols through the formation of Au–S bonds. After extraction and centrifugation, the aminothiols were detached from the surface of the AuNPs by adding DTT in a high concentration. We used this probe in combination with CE and UV absorption detection. On‐line concentration and separation of the released aminothiols were performed by using 1.6% v/v poly(diallyldimethylammonium chloride) as an additive in CE. Under optimal extraction and stacking conditions, the LOD at a S/N of 3 were 28, 554, and 456 nM for glutathione (GSH), cysteine (Cys), and homocysteine (HCys), respectively. In comparison with the normal injection without the extraction procedure, approximately 2280‐, 998‐, and 904‐fold improvements in the sensitivity were observed for GSH, Cys, and HCys, respectively. We have validated the application of our method on the basis of the analysis of GSH and HCys in human urine samples. It is believed that this approach has significant potential to be extended to clinical diagnosis.     

Selective enrichment of aminothiols using polysorbate 20-capped gold nanoparticles followed by capillary electrophoresis with laser-induced fluorescence

In this article, we report a simple method for selective enrichment of aminothiols using Tween 20-capped gold nanoparticles (AuNPs) prior to capillary electrophoresis coupled with laser-induced fluorescence (CE-LIF). Compared to citrate-capped AuNPs, Tween 20-capped AuNPs exhibit the ability to disperse in a highly saline solution and selectively extract aminothiols through the formation of Au–S bonds. After extraction and centrifugation, 1 mM thioglycollic acid (TGA) was utilized to remove aminothiols that attached to the NP surfaces. After a solution of 8.0 mL aminothiols were extracted using 2× AuNPs (200 μL), the extracted aminothiols derivatized with o-phthalaldehyde at pH 12.0 were detected by CE-LIF. As a result, the limits of detection at a signal-to-noise ratio of 3 for homocysteine (HCys), glutathione (GSH), and γ-glutamycysteine (Glu-cys) are 4013.2, 79.8, and 382.8 pM, respectively. The use of this probe provided approximately 11-, 282-, and 21-fold sensitivity improvements for HCys, GSH, and Glu-cys, respectively. A practical analysis of HCys, GSH, and Glu-cys in human urine sample has been accomplished by this present method.     

Preparation, characterization, and electrocatalytic activity of surface anchored, Prussian Blue containing starburst PAMAM dendrimers on gold electrodes

Gold bead electrodes were modified with submonolayers of 3-mercaptopropionic acid or 2-aminoethanethiol and further reacted with poly(amidoamine) (PAMAM) dendrimers (generation 4.0 and 3.5, respectively) to obtain films on which Prussian Blue (PB) was later absorbed to afford mixed and stable electrocatalytic layers. Experiments carried out with these novel materials not only showed an improved surface coverage of PB on the dendrimer modified electrodes as compared to PB modified gold electrodes prepared under acidic conditions, but also showed an increased stability at neutral pH values for one of the dendrimer containing substrates where the PB film on a bare gold electrode is simply not formed. The dendrimer modified electrodes were also tested as electrocatalytic substrates for the electroxidation of L(+)-ascorbic acid (AA), and it was found that their sensitivity as well as the corresponding detection limits were improved as compared to the voltammetric response of a Au-PB modified electrode. On the basis of UV-visible (UV-vis) spectroscopy and electrochemical experiments, it is suggested that the PB molecules are located within the dendritic structure of the surface attached PAMAM dendrimers.     

甲醛电化学传感器多孔气体扩散电极不同催化层结构与响应性能研究

多孔气体扩散电极的制备是制备甲醛电化学传感器的关键所在, 其中催化层的结构直接影响到传感器的响应性能. 通过柠檬酸三钠还原法合成了纳米金-活性炭、纳米金-碳纳米管催化剂, 制备了甲醛电化学传感器多孔气体扩散电极, 并对电极进行SEM(扫描电子显微镜)物理表征. 在甲醛气体浓度为0.24和0.63 mg/m³时, 电极C具有较好的响应, 在0.1到0.84 mg/m³浓度范围内, 线性方程为y＝10.515x＋4.4049 (R²＝0.9917), 响应时间约80 s. 分析了不同催化剂的气体扩散电极结构与甲醛响应性的关系, 为研制开发性能优良的甲醛电化学传感器奠定了基础.     

A Novel Electrochemical Method for the Analysis of Hydrogen Peroxide with the Use of a Glassy Carbon Electrode Modified by a Prussian Blue/Copper‐Gold Bimetallic Nanoparticles Hybrid Film

A novel Prussian blue/copper‐gold bimetallic nanoparticles hybrid film modified electrode was prepared by electrochemical deposition on a glassy carbon electrode (PB/Cu‐AuNPs/GCE). Morphology and electrochemistry of this electrode were studied by UV‐vis spectroscopy, scanning electron microscopy, X‐ray diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. The sensor showed significantly better electrocatalytic activity for the reduction of hydrogen peroxide in comparison with the single PB/GCE and PB/AuNPs/GCE. This was attributed to the synergistic effect of PB and Cu‐Au bimetallic nanoparticles. Also, the sensor demonstrated an overall high level of performance for the analysis of H₂O₂ in the concentration range from 0.002 to 0.84 mM.     

基于纳米金的分子印迹传感器检测果蔬中的氧化乐果和乐果

以甲基丙烯酸为功能单体,氧化乐果为印迹分子,构建了一种可用于检测果蔬中氧化乐果和乐果的分子印迹传感器.在金电极上电沉积金纳米粒子,然后将修饰电极浸入10 mL含有氧化乐果和甲基丙烯酸的聚合物溶液中进行9次循环电聚合(-0.3～0.3 V),无水甲醇/乙酸洗涤除去模板分子.循环伏安法和电化学阻抗谱表征传感器,差分脉冲伏安...     

Amperometric Determination of Glucose at Conventional vs. Nanostructured Gold Electrodes in Neutral Solutions

The conventional gold electrodes were compared with recently published electrodes based on gold nanoparticles and gold nanostructured films as amperometric sensors for glucose in pH 7.40 phosphate buffer solutions. The conventional electrodes provided similar electroanalytical benefits while required much simpler and shorter preparation. It is recommended that the future reports on the development of electrochemical sensors based on metal nanoparticles/nanostructures include also the analytical figures of merit obtained at relevant conventional metal electrodes. The voltammetric studies indicated that, in contrast to phosphate buffers, the Tris buffers were not suitable for activation of gold surface toward the direct oxidation of glucose.     

Fabrication, characterisation and voltammetric studies of gold amalgam nanoparticle modified electrodes.

The tabrication, characterisation, and electroanalytical application of gold and gold amalgam nanoparticles on glassy carbon electrodes is examined. Once the deposition parameters for gold nanoparticle electrodes were optimised, the analytical utility of the electrodes was examined in CrIII electroanalysis. It was found that gold nanoparticle modified (Au-NM) electrodes possess higher sensitivity than gold macroelectrodes. In addition, gold amalgam nanoparticle modified (AuHg-NM) electrodes were fabricated and characterised. The response of those electrodes was recorded in the presence of important environmental analytes (heavy metal cations). It was found AuHg-NM electrodes demonstrate a unique voltammetric behaviour and can be applied for electroanalysis when enhanced sensitivity is crucial.     

Prussian Blue Modified Submicron Structured Gold Electrodes for Amperometric Hydrogen Peroxide Sensing

In this work, we present a simple and effective approach for fabricating sub‐micron structured gold (SM−Au) electrodes by chemically etching the magnetron co‐sputtered gold film in KI solution for certain time. Such electrodes with a large surface area to volume ratio were used as the matrix for electrochemical deposition of Prussian blue (PB) to develop an electrochemical hydrogen peroxide sensor. Experimental characterization using scanning electron microscope and atomic force microscope shows that the thickness of PB layer on SM−Au electrode is around 140 nm, and is composited with cubic PB nanocrystals. The electrochemical performance of the designed sensor, studied using cyclic voltammograms and chronoamperometry methods, suggests that the sensor based on SM−Au/PB electrode presents the direct electron transfer of PB particle towards SM−Au film, and exhibits fast response, wide linearity, low detection limit and high stability. Under the optimized conditions, the sensitivity of the developed sensor for the detection of H₂O₂ reaches the value of 512 mA cm⁻² M⁻¹ with a linear range from 1 μM to 4.5 mM.     

Comparative studies on electrogenerated chemiluminescence of luminol on gold nanoparticle modified electrodes

Comparative studies on the electrogenerated chemiluminescence (ECL) behavior of luminol on various electrodes modified with gold nanoparticles of different size were carried out in neutral solution by conventional cyclic voltammetry (CV). The results demonstrated that the gold nanoparticle modified electrodes could generate strong luminol ECL in neutral pH conditions. The catalytic performance of gold nanoparticle modified electrodes on luminol ECL depended not only on the gold nanoparticles but also on the substrate. Gold electrode and glassy carbon electrode were the most suitable substrates for the self-assembly of gold nanoparticles. Moreover, the gold nanoparticle modified gold and glassy carbon electrode had satisfying stability and reproducibility and did not need tedious pretreatment of electrode surface before each measurement. It was also found that luminol ECL behavior depended on the size of gold nanoparticles. The most intense ECL signals were obtained on a 16-nm-diameter gold nanoparticle modified electrode. The modified electrode prepared by the self-assembly method exhibited much better catalytic effect on luminol ECL than that prepared by the electrically deposited method. The ECL behavior of luminol on a gold nanoparticle self-assembled gold electrode was also investigated by other transient-state electrochemical techniques, such as chronoamperometry, differential pulse voltammetry, normal pulse voltammetry, and square wave voltammetry. The strongest ECL intensity was obtained under square wave voltammetric condition.     

Physicochemical Characteristics of Polypyrrole/(Glucose oxidase)/(Prussian Blue)‐based Biosensor Modified with Ni‐ and Co‐Hexacyanoferrates

In this work, three types of electrodes suitable for amperometric glucose biosensors were designed. One type of electrode was based on bio‐selective layer of polypyrrole/(glucose oxidase)/(Prussian Blue) (Ppy/GOx/PB) and it was used as a control electrode regarding to which electrochemical properties of two other types of electrodes were compared. During the formation of Prussian blue layers graphite electrodes were additionally modified by Ni‐hexacyanoferrate (NiHCF) and by Co‐hexacyanoferrate (CoHCF) in order to design Ppy/GOx/PB‐NiHCF and Ppy/GOx/PB‐CoHCF electrodes, respectively. Some physicochemical characteristics of all three types of electrodes were evaluated and compared. The Ppy/GOx/PB‐NiHCF electrode showed wider linear range of the calibration curve than Ppy/GOx/PB and Ppy/GOx/PB‐CoHCF electrodes. The effect of temperature on analytical performance of the Ppy/GOx/PB‐NiHCF based biosensor has been evaluated and activation energy of enzyme catalysed reaction has been calculated within the temperature range of 15 °C to 30 °C.     

Gold nanoparticle/alkanedithiol conductive films self-assembled onto gold electrode: Electrochemistry and electroanalytical application for voltammetric determination of trace amount of catechol

This paper describes novel electrochemical properties of gold nanoparticles/alkanedithiol conductive films and their electroanalytical applications for voltammetric determination of trace amount of one kind of environmental pollutants, catechol. The conductive films are prepared by closely packing 12-nm diameter gold nanoparticles (Au-NPs) onto Au electrodes modified with the self-assembled monolayers (SAMs) of alkanedithiols (i.e., HS(CH₂)_nSH, n = 3, 6, 9). The assembly of the Au-NPs onto the SAM-modified electrodes essentially restores the heterogeneous electron transfer between Au substrate and redox species in solution phase that is almost totally blocked by the SAMs and, as a result, the prepared Au-NP/SAM-modified electrodes possess a good electrode reactivity without a remarkable barrier toward the heterogeneous electron transfer. Moreover, the prepared Au-NP/SAM-modified electrodes are found to exhibit a largely reduced interfacial capacitance, compared with bare Au electrode. These electrochemical properties of the Au-NP/SAM-modified electrodes essentially make them very useful for electroanalytical applications, which is illustrated by voltammetric determination of trace amount detection of environmental pollutant, catechol.     

巯基化改性壳聚糖在电化学生物传感器制备中的应用

以壳聚糖、N-乙酰-L-半胱氨酸(NAC)为原料,以1-羟基苯并三唑(HOBt)和1-乙基-3-(3-二甲基胺丙基)碳化二亚胺盐酸盐(EDAC)为缩合剂,合成功能化壳聚糖衍生物巯基壳聚糖(CHS-NAC).用红外光谱(FTIR)、核磁共振(1H-NMR)及X射线衍射(XRD)对其结构进行表征,用Ellman’s试剂通过标准曲线法测得巯基含量.利用CHS-NAC的黏附性,通过层层吸附的方法将CHS-NAC、纳米金及细胞色素c分别修饰到玻碳电极(GC)上,通过扫描电子显微镜(SEM)对修饰电极表面的形貌进行了观察,采用循环伏安和电化学阻抗研究了不同修饰膜电极的电化学行为,及扫描速率对细胞色素c修饰电极的影响,并开展了对过氧化氢的电催化分析.实验结果表明,CHS-NAC能高效地将纳米金及细胞色素c固定在电极表面,并能有效发挥纳米金辅助转移电子及细胞色素c对过氧化氢催化的能力.