硫醇分子链长对氧化还原自组装多层膜电化学行为影响的初步研究(英文)

以烷基硫醇和二茂铁衍生物构建的氧化-还原自组装多层膜为模型体系,研究烷基硫醇分子链长对多层膜电化学行为的影响.实验表明,二茂铁基团和电极之间的电子传递反应速率随两者距离的增加呈现指数级下降的趋势;烷基硫醇分子链长对自组装膜电化学行为的影响于不同情况下表现不同.本实验条件下,当多层膜上的电活性基团与电极比较接近时,长链分子自组装膜呈现较强的电化学响应.而当电极与电活性基团之间的距离较远时,短链烷基硫醇分子自组装膜呈现较强的电化学响应.     

Redox cycling amplified electrochemical detection of DNA hybridization: application to pathogen E. coli bacterial RNA

An electrochemical genosensor in which signal amplification is achieved using p-aminophenol (p-AP) redox cycling by nicotinamide adenine dinucleotide (NADH) is presented. An immobilized thiolated capture probe is combined with a sandwich-type hybridization assay, using biotin as a tracer in the detection probe, and streptavidin-alkaline phosphatase as reporter enzyme. The phosphatase liberates the electrochemical mediator p-AP from its electrically inactive phosphate derivative. This generated p-AP is electrooxidized at an Au electrode modified self-assembled monolayer to p-quinone imine (p-QI). In the presence of NADH, p-QI is reduced back to p-AP, which can be re-oxidized on the electrode and produce amplified signal. A detection limit of 1 pM DNA target is offered by this simple one-electrode, one-enzyme format redox cycling strategy. The redox cycling design is applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria, and provides a detection limit of 250 CFU μL⁻¹.     

Electroactive dipyrromethene-Cu(II) self-assembled monolayers: complexation reaction on the surface of gold electrodes

In the work presented, thiol- and COOH-terminated dipyrromethene derivatives have been applied for gold electrode modification. Dipyrromethene deposited onto a solid support, after binding Cu2+, can act as a redox active monolayer. The complexation of Cu(II) ions has been performed on the surface of gold electrodes modified with dipyrromethene. The characterization of dipyrromethene-Cu(II) self-assembled monolayers (SAMs) has been done by cyclic voltammetry (CV), wettability contact angle measurements, and atomic force microscopy (AFM). The new electroactive monolayer could be applied for the immobilization of proteins and ssDNA or for electrochemical anion sensing without redox markers in the solution.     

Electron transfer between ferrocene-modified Au/octadecanethiol/lipid BLM electrode and redox couples in solution

Bilayers incorporated with ferrocene consisting of self-assembled octadecanethiol and lipid monolayer on gold substrates were fabricated. Its electrochemical behaviors in solutions containing different redox couples were investigated by cyclic voltammetry and ac impedance. The transmembrane electron transfer reaction across octadecanethiol self-assembled film and an adsorbed phospholipid layer mediated by ferrocene have been observed in the solution of Fe(CN)6(3-/4-). The formal potential difference between mediator in bilayer lipid membrane (BLM) and redox couple in solution has a great impact on the transmembrane electron transfer behavior. The ferrocene-modified BLM electrodes might be useful for constructing a bilayer-based electrochemical current rectifying device.     

Heterogeneous electron transfer at Au/SAM junctions in a room-temperature ionic liquid under pressure

Proven electrochemical approaches were applied to study heterogeneous electron transfer (ET) between selected redox couples and gold electrodes modified with alkanethiol self-assembled monolayers (SAMs), using the room-temperature ionic liquid (RTIL) [bmim][NTf2] as reaction medium; ferrocene as freely diffusing redox probe in the RTIL was tested for ET through both thin (butanethiol) and thick (dodecanethiol) assemblages at pressures up to 150 MPa; well behaved kinetic patterns and reproducibility of data were demonstrated for ET within the unique Au/SAM/RTIL arrays.     

Carbon nanofiber vs. carbon microparticles as modifiers of glassy carbon and gold electrodes applied in electrochemical sensing of NADH

Carbon materials (CMs), such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon microparticles (CMPs) are used as doping materials for electrochemical sensors. The efficiency of these materials (either before or after acidic treatments) while being used as electrocatalysts in electrochemical sensors is discussed for β-nicotinamide adenine dinucleotide (NADH) detection using cyclic voltammetry (CV). The sensitivity of the electrodes (glassy carbon (GC) and gold (Au)) modified with both treated and untreated materials have been deeply studied. The response efficiencies of the GC and Au electrodes modified with CNF and CMP, using dimethylformamide (DMF) as dispersing agent are significantly different due to the peculiar physical and chemical characteristics of each doping material. Several differences between the electrocatalytic activities of CMs modified electrodes upon NADH oxidation have been observed. The CNF film promotes better the electron transfer of NADH minimizing the oxidation potential at +0.352 V. Moreover higher currents for the NADH oxidation peak have been observed for these electrodes. The shown differences in the electrochemical reactivities of CNF and CMP modified electrodes should be with interest for future applications in biosensors.     

Surface modification of GC and HOPG with diazonium, amine, azide, and olefin derivatives

Surface modification of glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG) was carried out with diazonium, amine, azide, and olefin derivatives bearing ferrocene as an electroactive moiety. Features of the modified surfaces were evaluated by surface concentrations of immobilized molecule, blocking effect of the modified surface against redox reaction, and surface observation using cyclic voltammetry and electrochemical scanning tunneling microscope (EC-STM). The measurement of surface concentrations of immobilized molecule revealed the following three aspects: (i) Diazonium and olefin derivatives could modify substrates with the dense-monolayer concentration. (ii) The surface concentration of immobilized amine derivative did not reach to the dense-monolayer concentration reflecting their low reactivity. (iii) The surface modification with the dense-monolayer concentration was also possible with azide derivative, but the modified surface contained some oligomers produced by the photoreaction of azides. Besides, the blocking effect against redox reaction was observed for GC modified with diazonium derivative and for HOPG modified with diazonium and azide derivatives, suggesting fabrication of a densely modified surface. Finally, the surface observation for HOPG modified with diazonium derivative by EC-STM showed a typical monolayer structure, in which the ferrocene moieties were packed densely at random. On the basis of those results, it was demonstrated that surface modification of carbon substrates with diazonium could afford a dense monolayer similar to the self-assembled monolayer (SAM) formation.     

Facilitated electrochemical oxidation of NADH and its model compound at gold electrode modified with terminally substituted electroinactive self-assembled monolayers

The electrochemical oxidation of NADH and its model compound, N-benzyl-1,4-dihydronicotinamide (DHN), has been studied at gold electrode modified with self-assembled monolayer of terminally substituted thiols/disulfide, i.e., cystamine (CYST), mercaptopropionic acid (MPA) and mercaptoethanol (ME). A substantial decrease in the overpotential (approximately 250 mV) when compared to the bare electrode has been observed for the oxidation of NADH at the monolayer-modified electrodes, containing no so-called redox mediator. The bare electrode shows an ill-defined voltammetric peak for the oxidation of DHN, whereas the monolayer-modified electrodes showed a well-defined voltammetric peak. The monolayer assembly on the gold electrode prevents the fouling of electrode surface by the oxidation products, which favors the oxidation at the less positive potential. The square-wave voltammograms showed a sharp voltammetric signal for the oxidation of NADH at all the monolayer-modified electrodes. All the monolayer-modified electrodes showed a linear current response to change in the NADH concentration in its range of 25-300 microM and their sensitivities were found to be 0.005+/-0.0003, 0.0063+/-0.0002 and 0.0052+/-0.0003 microA/microM for CYST-Au, ME-Au and MPA-Au electrodes, respectively. The hydrodynamic voltammograms obtained at the rotating CYST-Au electrode for the oxidation of NADH and DHN were used to estimate the diffusion coefficient of DHN, and the number of electrons involved in the oxidation process of NADH.     

Functionalized mesoporous silica films as a matrix for anchoring electrochemically active guests

Mesoporous silica thin films were shown to be an appropriate matrix for immobilization of discrete electroactive moieties, yielding uniform transparent thin film electrodes with defined texture and enhanced electrochemical activity. The mesoporous silica films prepared on conducting FTO-coated glass substrate were postsynthetically functionalized. Alkoxysilanes were used as precursors for subsequent grafting via ionic or covalent bonds of representative electroactive species, such as polyoxometalate PMo12O(40)3-, hexacyanoferrate(III), and ferrocene. The electrochemically active concentration within the silica-based composite electrodes achieves 90, 260, and 60 micromol cm(-3) for polyoxometalate, hexacyanoferrate(III), and ferrocene, respectively. The amount of molecules involved in the charge-transfer sequence is proportional to the film thickness and comparable to the total amount of embedded guests. Thus, eventually the whole bulk volume of the modified silica films is electrochemically accessible. Immobilization in the chemically modified silica matrix alters the redox potential of the electroactive molecules. Electron exchange between the adjacent redox centers (electron hopping) is proposed as a possible charge propagation pathway through the insulating silica matrix, which is supported by the fact that the high charge uptake is observed also for the hybrid electrodes with the covalently anchored redox guests.     

灿烂甲酚蓝在DNA修饰金电极上的电化学行为

利用自组装技术将巯基乙醇固定在金电极表面形成巯基乙醇自组装膜修饰金电极, 用乙基-(3-二甲基氨丙基)碳二亚胺盐酸盐(EDC)和N-羟基琥珀酰亚胺(NHS)为偶联试剂, 分别将鲱鱼精单链DNA(ssDNA)和双链DNA(dsDNA)固定于金电极表面形成ssDNA和dsDNA 修饰电极. 考察了灿烂甲酚蓝(BCB)在不同DNA 修饰电极上的电化学行为,结果表明, BCB 在ssDNA 和dsDNA 修饰电极上的吸附常数分别为1.67×10^4和3.22×10^4 L·mol-1, BCB 与ssDNA 主要以静电作用结合, 而与dsDNA作用存在静电和嵌插两种模式. dsDNA 对BCB 具有更高的亲和力, 使BCB 可以作为一种有效的电化学杂交指示剂.     

Electrochemically controlled assembly and logic gates operations of gold nanoparticle arrays

The reversible assembly of β-cyclodextrin-functionalized gold NPs (β-CD Au NPs) is studied on mixed self-assembled monolayer (SAM), formed by coadsorption of redox-active ferrocenylalkylthiols and n-alkanethiols on gold surfaces. The surface coverage and spatial distribution of the β-CD Au NPs monolayer on the gold substrate are tuned by the self-assembled monolayer composition. The binding and release of β-CD Au NPs to and from the SAMs modified surface are followed by surface plasmon resonance (SPR) spectroscopy. The redox state of the tethered ferrocene in binary SAMs controls the formation of the supramolecular interaction between ferrocene moieties and β-CD-capped Au NPs. As a result, the potential-induced uptake and release of β-CD Au NPs to and from the surface is accomplished. The competitive binding of β-CD Au NPs with guest molecules in solution shifted the equilibrium of the complexation-decomplexation process involving the supramolecular interaction with the Fc-functionalized surface. The dual controlled assembly of β-CD Au NPs on the surface enabled to use two stimuli as inputs for logic gate activation; the coupling between the localized surface plasmon, associated with the Au NP, and the surface plasmon wave, associated with the thin metal surface, is implemented as readout signal for "AND" logic gate operations.     

致密二茂铁硫醇自组装膜的电化学行为

合成了11-二茂铁基十一烷基-1-硫醇(HS-(CH₂)₁₁-Fc)，利用自组装膜的特点，通过分子设计将二茂铁基团引入到自组装膜中。在金电极表面构筑有序单分子膜，制备出具有电化学活性的修饰层，研究其电化学行为，作为考察复杂电化学动力学的理想模型。进一步探究其电子传递的特点与自组装膜表面覆盖度之间的联系，提出了一种新的电子传递模型，研究电子转移与膜结构的对应关系，为更深层次的分子设计和功能组装提供理论指导。     

Electroactive gold nanoparticles protected by 4-ferrocene thiophenol monolayer

Numerous reports have focused on ferrocene-terminated electroactive self-assembled monolayers (SAMs) on a flat Au surface but only a few on ferrocene SAMs on Au colloid. In this paper, we employ 4-ferrocene thiophenol as a novel capping agent to produce electroactive gold nanoparticles in consideration of the peculiar pi-conjugated structure. Transmission electron microscopy shows the narrow-dispersed gold core with an average core diameter of ca. 2.5 nm. UV/vis spectra examine the pi-conjugated structure of 4-ferrocene thiophenol and surface plasmon absorbance of the indicated gold nanoparticles. X-ray photoelectron spectroscopy reveals electronic properties of the Au core and thiol ligands. Electrochemical measurement shows that the oxidation peak current is proportional to the scan rate, indicating the electrode process is controlled by adsorbed layer reaction. The formal potential of the Fc-MPCs is compared with that of free ferrocene in MeCN solution and the Fc-SAMs. The shifts are attributed to the phenyl moiety in the 4-ferrocene thiophenol and dielectric constant of the solvation environment.     

Preparation,Characterization, and Electrocatalytic Properties of Cobalt Oxide and Cobalt Hexacyanoferrate Hybrid Films

Polynuclear mixed‐valent films of cobalt oxide and cobalt hexacyanoferrate (CoOCoHCF) have been deposited on electrode surfaces from a solution of Co²⁺ and Fe(CN)₆^3? ions by repetitive potential cycling method. Simultaneous cyclic voltammetry and electrochemical quartz crystal microbalance measurements demonstrate the steady growth of modified film. The effect of type of monovalent cations as well as acidity of the supporting electrolyte on film growth and redox behavior of resulting film was investigated. In pure supporting electrolyte, electrochemical responses of modified electrode resemble with that of a surface immobilized redox couple. The hybrid film electrodes showed electrocatalytic activity toward oxidation of NADH, hydrazine and hydroxylamine. The feasibility of using our modified electrodes for analytical application was also explored.     

Measurement of Ibuprofen Binding to Mixed Monolayers Containing β-Cyclodextrin Active Sites

A molecular imprinting method involving a three-step sequential self-assembly procedure was applied to prepare gold electrodes responsive towards ibuprofen. The electrode modified with the cyclodextrin derivative binds ferrocene to form an electroactive complex with the ferrocene oxidation current decreasing in the presence of ibuprofen in the solution. The competition of ferrocene and ibuprofen for the cyclodextrin cavities in the monolayer provided a means for the determination of the binding constants of ibuprofen with two derivatives of lipoylamide β-cyclodextrin of different hydrophobicity.     

Direct electrochemistry of cytochrome c immobilized on a novel macroporous gold film coated with a self-assembled 11-mercaptoundecanoic acid monolayer

We have successfully constructed a novel gold film with open interconnected macroporous walls of nanoparticles by combining the hydrogen bubble dynamic template synthesis with galvanic replacement reaction. After modified by a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (MUA), the three-dimensionally (3D) interconnected macroporous Au film has been used as a biocompatible substrate for the immobilization of cytochrome c. The morphology, structure and electrochemical features of the modified and unmodified macroporous Au films were characterized by field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results reveal that the resultant films had a large electroactive surface area for high protein loading, enhanced electron transfer of cytochrome c, retained electrochemical activity, good stability and repeatability. And the excellent electrochemical behaviors could be attributed to the hierarchical structure of the macroporous Au film constructed by nanoparticles.     

Modification of Escherichia coli single-stranded DNA binding protein with gold nanoparticles for electrochemical detection of DNA hybridization

The unique binding event between Escherichia coli single-stranded DNA binding protein (SSB) and single-stranded oligonucleotides conjugated to gold (Au) nanoparticles is utilized for the electrochemical detection of DNA hybridization. SSB was attached onto a self-assembled monolayer (SAM) of single-stranded oligonucleotide modified Au nanoparticle, and the resulting Au-tagged SSB was used as the hybridization label. Changes in the Au oxidation signal was monitored upon binding of Au tagged SSB to probe and hybrid on the electrode surface. The amplified oxidation signal of Au nanoparticles provided a detection limit of 2.17 pM target DNA, which can be applied to genetic diagnosis applications. This work presented here has important implications with regard to combining a biological binding event between a protein and DNA with a solid transducer and metal nanoparticles.     

Electrochemical characteristics of ferrocenecarboxylate-coupled aminoundecylthiol self-assembled monolayers

The electrochemical characteristics of the modified electrodes with ferrocenecarboxylate-coupled aminoundecylthiol monolayers prepared in two sequential steps were studied. The self-assembled monolayer (SAM) was prepared through the covalent attachment of ferrocenecarboxylate in an activation solution containing N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide coupling agent to aminoundecylthiol SAMs formed on a substrate. In the ferrocenecarboxylate-coupled aminoundecylthiol monolayers, the ferrocene moieties were expected to be packed regularly with enhanced ordering compared with those in the FcCOO(CH2)11SH monolayer. As the ferrocene coverage increases, the formal potential for the ferrocene-ferricenium (Fc/Fc+) couple shifts to the positive potential and the full width at half-maximum (deltaE(fwhm)) increases also. The maximum coverage is found to be about 3 x 10(-10) mol cm(-2), which is considered to be a value obtained from a well-ordered ferrocene-tethered SAM. As for the mass change, the increase in ferrocene coverage caused the enhancement in ion association between the ferricenium cations and perchlorate anions resulting in a mass increase upon oxidation; however, the mass change per mole electron decreases. The results obtained from the ferrocenecarboxylate-coupled aminoundecylthiol monolayers were explained to be due to the well-ordered packing with regular spacing compared with those of the FcCOO(CH2)11SH monolayer.     

Studies of the electrochemical behavior of epinephrine at a homocysteine self-assembled electrode

The self-assembled electrode with the homocysteine monolayer (Hcy/Au) has been characterized by infrared spectroscopy and ac impedance spectroscopy in electrolyte. The Hcy/Au electrode is demonstrated to promote the electrochemical response of epinephrine (E) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k_s) is 2.1×10⁻² cm s⁻¹ at the self-assembled electrode. The reduction peak of E can be used to determine the concentration of E in presence of ascorbic acid (AA) owing to the Hcy/Au also promoting the electrochemical oxidation of AA.     

Electroactive self-assembled biferrocenyl alkanethiol monolayers on Au(111) surface and on gold nanoclusters

The spectroscopic and electrochemical characterizations of electrochemically stable biferrocene-modified Au clusters and chemisorbed biferrocenylalkanethiols on Au(111) surface were studied. The characterizations of biferrocene-modified Au cluster using TEM, UV-vis, and NMR techniques are also reported. Two successive reversible one-electron redox waves were observed for the biferrocenylalkanethiol Au nanoclusters and biferrocenylalkanethiol monolayers on Au(111) surface in the cyclic voltammetry. Furthermore, the positive and negative current peaks for each redox wave occur at almost the same potential, and the peak current increases almost linearly with the sweep rate. Repeat scanning does not change the voltammograms, demonstrating that these monolayers are stable to electrochemical cycling. The coverages of electroactive biferrocene in the monolayers were calculated from the cyclic voltammograms. The standard electron-transfer rate constant was calculated from the splitting between the oxidation and reduction peaks.