Magnetoswitchable electrochemistry gated by alkyl-chain-functionalized magnetic nanoparticles: control of diffusional and surface-confined electrochemical processes

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter ca. 5 nm) are used to selectively gate diffusional and surface-confined electrochemical reactions. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended undecanoate-capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. Two different phenomena are controlled by attraction of the magnetic nanoparticles to the electrode by means of an external magnet: (i) The attracted magnetic nanoparticles form a hydrophobic layer on the electrode surface resulting in the blocking of diffusional electrochemical processes, while retaining the redox functions of surface-confined electrochemical units. (ii) For certain surface-immobilized redox species (e.g., quinones), the attraction of the magnetic nanoparticles to the electrode surface alters the mechanism of the process from an aqueous-type electrochemistry to a dry organic-phase-type electrochemistry. Also, bioelectrocatalytic and electrocatalytic transformations at the electrode are controlled by means of attraction of the magnetic nanoparticles to the electrode surface. Controlling the catalytic functions of the modified electrode by means of the magnetic nanoparticles attracted to the electrode is exemplified in two different directions: (i) Blocking of the bioelectrocatalyzed oxidation of glucose by glucose oxidase (GOx) using a surface-confined ferrocene monolayer as electron-transfer mediator. (ii) Activation of the microperoxidase-11 electrocatalyzed reduction of cumene hydroperoxide. In the latter system, the hydrophobic magnetic nanoparticles adsorb toluene, and the hydrophobic matrix acts as a carrier for cumene hydroperoxide to the electrode surface modified with the microperoxidase-11 catalyst.     

Controlling chemical reactivity at solid-solution interfaces by means of hydrophobic magnetic nanoparticles

Hydrophobic magnetic nanoparticles are employed to reversibly regulate the hydrophobic/hydrophilic properties of surfaces and to control the electrochemistry and bioelectochemistry at chemically modified electrodes. Selective bioelectrocatalytic transformations at relay-functionalized electrodes are accomplished by the magnetic attractions of the hydrophobic magnetic nanoparticles with coadsorbed hydrophobic redox relays to the electrode. The selective activation of one of two biocatalysts solubilized in the aqueous electrolyte solution in the absence or presence of hydrophobic magnetic nanoparticles results in the specific activation of bioelectrocatalytic processes. The magnetic attraction and retraction of hydrophobic magnetic nanoparticles to and from semiconductor nanoparticle (CdS)-functionalized electrodes enable the control of the photocurrent directions at the electrode from cathodic to anodic directions, respectively. The magnetic attraction of the hydrophobic magnetic nanoparticles to the surfaces is also employed to control biorecognition and biocatalytic transformations at solid supports. The magnetic attraction and retraction of the hydrophobic magnetic nanoparticles to and from the surfaces allow the blockage and activation of DNA hybridization, polymerization, and enzymatic digestion, respectively.     

Magnetoswitchable controlled hydrophilicity/hydrophobicity of electrode surfaces using alkyl-chain-functionalized magnetic particles: application for switchable electrochemistry

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter approximately 4.5 nm; saturated magnetization, M(s), 38.5 emu g(-1)) are used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. The magnetic attraction of the functionalized particles to the electrode by means of an external magnet yields a hydrophobic interface that acts as an insulating layer, prohibiting interfacial electron transfer. The retraction of the magnetic particles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. The electron-transfer resistance and double-layer capacitance of the electrode surface upon the attraction and retraction of the functionalized magnetic particles to and from the electrode, respectively, by means of the external magnet were probed by Faradaic impedance spectroscopy (R(et) = 170 Omega and C(dl) = 40 microF sm(-2) in the hydrophilic state of the electrode and R(et) = 22 k Omega and C(dl) = 0.5 microF sm(-2) in the hydrophobic state of the interface). The magnetoswitchable control of the interface enables magnetic switching of the bioelectrocatalytic oxidation of glucose in the presence of glucose oxidase and ferrocene dicarboxylic acid to "ON" and "OFF" states.     

Magneto-switchable single-electron charging of Au-nanoparticles using hydrophobic magnetic nanoparticles

Reversible magneto-switchable quantum charging of a Au nanoparticle array associated with a Au electrode is observed in the presence of hydrophobic magnetic nanoparticles attracted to the functionalized electrode surface.     

Electrochemical DNA biosensors based on platinum nanoparticles combined carbon nanotubes

Platinum nanoparticles were used in combination with multi-walled carbon nanotubes (MWCNTs) for fabricating sensitivity-enhanced electrochemical DNA biosensor. Multi-walled carbon nanotubes and platinum nanoparticles were dispersed in Nafion, which were used to fabricate the modification of the glassy carbon electrode (GCE) surface. Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement of the intercalated daunomycin. Due to the ability of carbon nanotubes to promote electron-transfer reactions, the high catalytic activities of platinum nanoparticles for chemical reactions, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.0 × 10⁻¹¹ mol l⁻¹.     

应用纳米磁性球电化学检测特定序列DNA

采用分散聚合法制备纳米磁性羧基球,利用化学偶联法将末端修饰氨基的寡聚核苷酸固定在纳米磁性球表面,制成新型核酸探针,该探针可特异性结合目标单链寡聚核苷酸.在磁场作用下,将纳米磁珠与本体溶液分离并富集在电极表面,以中性红为嵌合指示剂,用示差脉冲伏安法测定杂交结果.经过条件优化,本法测定DNA的浓度线性范围为1.0×10^-6～5.0×10^-9mol/L,检出限为8.6×10^-10mol/L.     

An electrochemical DNA sensor based on a layers-film construction modified electrode

This work developed a relatively inexpensive and layers-film construction electrochemical sensor for DNA recognition and its performance was investigated. The Fe(3)O(4) magnetic nanoparticles-cysteine were immobilized on the carbon paste electrode (CPE) surface using magnetic force. Multiwalled carbon nanotubes (MWCNTs), gold nanoparticles (GNPs), and chitosan (Chi) were used successively to coat on the electrode surface. The thiolated capture probe was assembled and competitively hybridized with the target nucleic acid and biotinylated response probe. The electrochemical behavior was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. In addition, the sensor performance was also analyzed by introducing the notion of detection efficiency. The experimental results showed that although the electron transfer capability of the CPE is less strong than that of a metal electrode used in the DNA sensor, the materials modified on the CPE could significantly improve the performance. A detection limit of 1 nM of target DNA and a sensitivity of 2.707 × 10(3) mA M(-1) cm(-2) were obtained. Although the resulting detection limit was not remarkable, further experiments could improve it.     

Quartz crystal microbalance detection of DNA single-base mutation based on monobase-coded cadmium tellurium nanoprobe

A new method for the detection of point mutation in DNA based on the monobase-coded cadmium tellurium nanoprobes and the quartz crystal microbalance (QCM) technique was reported. A point mutation (single-base, adenine, thymine, cytosine, and guanine, namely, A, T, C and G, mutation in DNA strand, respectively) DNA QCM sensor was fabricated by immobilizing single-base mutation DNA modified magnetic beads onto the electrode surface with an external magnetic field near the electrode. The DNA-modified magnetic beads were obtained from the biotin-avidin affinity reaction of biotinylated DNA and streptavidin-functionalized core/shell Fe(3)O(4)/Au magnetic nanoparticles, followed by a DNA hybridization reaction. Single-base coded CdTe nanoprobes (A-CdTe, T-CdTe, C-CdTe and G-CdTe, respectively) were used as the detection probes. The mutation site in DNA was distinguished by detecting the decreases of the resonance frequency of the piezoelectric quartz crystal when the coded nanoprobe was added to the test system. This proposed detection strategy for point mutation in DNA is proved to be sensitive, simple, repeatable and low-cost, consequently, it has a great potential for single nucleotide polymorphism (SNP) detection.     

Nanocatalyst-based assay using DNA-conjugated Au nanoparticles for electrochemical DNA detection

Compared to enzymes, Au nanocatalysts show better long-term stability and are more easily prepared. Au nanoparticles (AuNPs) are used as catalytic labels to achieve ultrasensitive DNA detection via fast catalytic reactions. In addition, magnetic beads (MBs) are employed to permit low nonspecific binding of DNA-conjugated AuNPs and to minimize the electrocatalytic current of AuNPs as well as to take advantage of easy magnetic separation. In a sandwich-type electrochemical sensor, capture-probe-conjugated MBs and an indium-tin oxide electrode modified with a partially ferrocene-modified dendrimer act as the target-binding surface and the signal-generating surface, respectively. A thiolated detection-probe-conjugated AuNP exhibits a high level of unblocked active sites and permits the easy access of p-nitrophenol and NaBH 4 to these sites. Electroactive p-aminophenol is generated at these sites and is then electrooxidized to p-quinoneimine at the electrode. The p-aminophenol redox cycling by NaBH 4 offers large signal amplification. The nonspecific binding of detection-probe-conjugated AuNPs is lowered by washing DNA-linked MB-AuNP assemblies with a formamide-containing solution, and the electrocatalytic oxidation of NaBH 4 by AuNPs is minimized because long-range electron transfer between the electrode and the AuNPs bound to MBs is not feasible. The high signal amplification and low background current enable the detection of 1 fM target DNA.     

DNA Hybridization at Magnetic Nanoparticles with Electrochemical Stripping Detection

A simple and practical method for electrochemical DNA hybridization assay has been developed to take advantage of magnetic nanoparticles for ssDNA immobilization and zinc sulfide nanoparticle as oligonucleotide label. Magnetic nanoparticles were prepared by coprecipitation of Fe²⁺ and Fe³⁺ with NH₄OH, and then amino silane was coated onto the surface of magnetite nanoparticles. The magnetic nanoparticles have the advantages of easy preparation, easy surface modification and low cost. The target ssDNA with the phosphate group at the 5′ end was then covalently immobilized to the amino group of magnetite nanoparticles by forming a phosphoramidate bond in the presence of 1‐ethyl‐3‐(3‐dimeth‐ylaminopropyl)carbodiimide (EDAC). The zinc sulfide (ZnS) nanoparticle‐labeled oligonucleotides probe was used to identify the target ssDNA immobilized on the magnetic nanoparticles based on a specific hybridization reaction. The hybridization events were assessed by the dissolution of the zinc sulfide nanoparticles anchored on the hybrids and the indirect determination of the dissolved zinc ions by anodic stripping voltammetry (ASV) at a mercury film glassy carbon electrode (GCE). The proposed method couples the high sensitivity of anodic stripping analysis for zinc ions with effective magnetic separation for eliminating nonspecific adsorption effects and offers great promise for DNA hybridization analysis.     

A Novel Photo‐Induced Electrochemical Biosensing Method Based on Fluorescent Labeled Molecular Beacon

A novel photo‐induced electrochemical biosensing method has been developed based on fluorescence quenching effect and electrochemical method. In this sensing strategy, the molecular beacon probes labeled with methylene blue were immobilized on the gold nanoparticles modified gold electrode surface firstly; then dopamine was assembled on the electrode surface through electrostatic interaction with gold nanoparticles. Under the continuous illumination, the fluorescence of the methylene blue was quenched by the gold nanoparticles before hybridization; after hybridization with the complementary DNA, methylene blue was far away from the gold nanoparticles and the fluorescence recovered, and then singlet oxygen was generated in the photosensitive reaction of methylene blue in the presence of dissolved oxygen. Singlet oxygen reacted with dopamine, which resulted in the reduction of concentration of the dopamine on the electrode surface. The current of the dopamine on the electrode was used for the sensing of the conformational change of molecular beacon and hence for the detection of target DNA.     

A Universal Approach for the Reversible Phase Transfer of Hydrophilic Nanoparticles

The ability to engineer the surface properties of magnetic nanoparticles is important for their various applications, as numerous physical and chemical properties of nanoscale materials are seriously affected by the chemical constitution of their surfaces. For some specific applications, nanoparticles need to be transferred from a polar to a nonpolar environment (or vice versa) after synthesis. In this work we have developed a universal method for the phase transfer of magnetic nanoparticles that preserves their shape and size. Octadecyltrimethoxysilane was used to cap the surfaces of the aqueous magnetic nanoparticles, thereby allowing their transfer into nonpolar solution. The resulting hydrophobic magnetic nanoparticles were transferred back into aqueous solution by subsequently covering them with an egg‐PC lipid monolayer. The superparamagnetic properties of the particles were retained after the phase transfer. The maximum transfer yields are dependent on their particle size with a maximum value of 93.16±4.75 % for magnetic nanoparticles with a diameter of 100 nm. The lipid‐modified magnetic particles were stable over 1 week, and thus they have potential applications in the field of biomedicine. This work also provides a facile strategy for the controllable engineering of the surface properties of nanoparticles.     

Electrochemical Studies of Nanoparticle Self-Assembled Monolayers

Electrochemical studies of the self-assembled monolayers of gold nanoparticles were reported. The particle surface assemblies were constructed by using surface-active particle molecules where multiple copies of peripheral thiol groups were introduced via exchange reactions with alkanedithiols^[1,2]. Excessive dithiol and displaced thiol ligands were removed from the cluster exchange solution by liquid extraction using a hexane-methanol system. The resulting particle adlayers exhibited discrete electron-transfer features that were ascribed to the quantized capacitance charging to the particle double layers. The electrode double-layer capacitance, evaluated from impedance measurements, also showed a modulation with electrode potentials. Consistent electron-transfer rate constants were obtained from the Laviron evaluation as well as from the impedance measurements^[1].In particular, in aqueous solutions, in the presence of certain hydrophobic electrolyte ions, the discrete charging was rectified depending on the electrode^[2].     

表面羧基化Fe3O4磁性纳米粒子的快捷制备及表征

亲水性磁性纳米颗粒在生物科学领域有着广泛应用,本研究提出了一种快速对磁性纳米粒子表面进行羧基化的方法. 首先使用氯化铁和氯化亚铁为原料, 以油酸为表面活性剂, 通过共沉淀法制得油酸包覆的亲油性磁性纳米粒子, 然后用高锰酸钾进行原位氧化, 将覆盖在粒子表面的油酸中的C＝C键氧化成-COOH, 从而得到单层羧基功能化的亲水性磁性纳米粒子. 利用透射电镜(TEM)、X射线衍射(XRD)、傅利叶红外光谱仪(FT-IR)、热重分析仪(TGA)、振动样品磁强计(VSM)、Zeta电位分析仪等对其进行表征. 结果表明磁性纳米粒子表面被成功羧基化,粒子的平均直径约为9 nm,饱和磁化值为64.5 emu/g,剩磁和矫顽力近似为零,具有典型的超顺磁性. 羧基化磁性纳米粒子可在pH7-10的水溶液中形成稳定分散的磁流体,保存6周无沉淀出现.     

亲水金和憎水二氧化硅纳米颗粒对葡萄糖生物传感器响应灵敏度的增强作用

用亲水金、憎水二氧化硅纳米颗粒固定葡萄糖氧化酶(GOD),采用聚乙烯醇缩丁醛(PVB)为辅助固酶膜基质来制备葡萄糖生物传感器,并考察了亲水金、憎水二氧化硅纳米颗粒对酶电极电流响应的影响.实验表明,引入纳米粒子可显著增强电极响应灵敏度.并对两种不同性质纳米颗粒所起作用的可能机理进行讨论,从理论和实验上证明了纳米颗粒对固定酶的作用.为制备有实用价值的葡萄糖生物传感器提供了可供参考的实验和理论依据.     

Sonochemical formation of iron oxide nanoparticles in ionic liquids for magnetic liquid marble

Ionic liquids (ILs)-stabilized iron oxide (Fe(2)O(3)) nanoparticles were synthesized by the ultrasonic decomposition of iron carbonyl precursors in [EMIm][BF(4)] without any stabilizing or capping agents. The Fe(2)O(3) nanoparticles were isolated and characterized by X-ray powder diffraction, transmission electron microscopy and susceptibility measurements. The physicochemical properties of ILs containing magnetic Fe(2)O(3) nanoparticles (denoted as Fe(2)O(3)@[EMIm][BF(4)]), including surface properties, density, viscosity and stability, were investigated in detail and compared with that of [EMIm][BF(4)]. The Fe(2)O(3)@[EMIm][BF(4)] can be directly used as magnetic ionic liquid marble by coating with hydrophobic and unreactive polytetrafluoroethylene (PTFE), for which the effective surface tension was determined by the puddle height method. The resulting magnetic ionic liquid marble can be transported under external magnetic actuation, without detachment of magnetic particles from the marble surface that is usually observed in water marble.     

Synthesis, surface modifications, and size-sorting of mixed nickel-zinc ferrite colloidal magnetic nanoparticles

We report on the spontaneous covalent growth of monomolecular adlayers on mixed nickel-zinc nanoferrite colloidal suspensions (ferrofluids). Synthesized nanoparticles were subjected to surface modification by means of acid chloride chemistry, leading to the formation of covalent bonds between the hydroxy groups at the nanoparticle surface and the acid chloride molecules. This procedure can be easily tailored to allow for the formation of adlayers containing both hydrophobic and hydrophilic regions stacked at predetermined distances from the magnetic core, and also providing the nanoferrites with functional carboxy groups capable of further modifications with, for example, drug molecules. Here, fluorophore aminopyrene molecules were bound to such modified nanoferrites through amide bonds. We also used the same chemistry to modify the surface with covalently bound long-chain palmitoyl moieties, and for comparison we also modified the nanoferrite surface by simple adsorption of oleic acid. Both procedures made the surface highly hydrophobic. These hydrophobic colloids were subsequently spread on an aqueous surface to form Langmuir monolayers with different characteristics. Moreover, since uniformity of size is crucial in a number of applications, we propose an efficient way of sorting the magnetic nanoparticles by size in their colloidal suspension. The suspension is centrifuged at increasing rotational speed and the fractions are collected after each run. The mean size of nanoferrite in each fraction was measured by the powder X-ray diffraction (PXRD) technique.     

空壳纳米金修饰的新型DNA传感器

利用新型材料金纳米空球, 通过层层修饰的技术, 分别将壳聚糖、空壳纳米金、L-半胱氨酸、细胞色素c以及ssDNA探针修饰到玻碳电极表面, 制备了一种新型的DNA生物传感器. 以紫外及透射电子显微镜(TEM)表征了空壳纳米金, 以循环伏安法、阻抗谱图等电化学方法研究了传感器的特性, 通过原子力显微镜方法观察了该DNA生物传感器不同层之间的形态差异. 结果表明, 该修饰电极所吸附的ssDNA探针为1.672×10^―10 mol•cm^－2. 在指示剂柔红霉素的帮助下, DNA探针可与互补的DNA进行杂交, 借此以微分脉冲伏安法测定DNA.     

Highly sensitive hybridization assay using the electrochemiluminescence of an ITO electrode, CdTe quantum dots functionalized with hierarchical nanoporous PtFe nanoparticles, and magnetic graphene nanosheets

We report on a disposable microdevice suitable for sandwich-type electrochemiluminescence (ECL) detection of DNA. The method is making use of CdTe quantum dots functionalized with hierarchical nanoporous PtFe (CdTe@PtFe) nanoparticles and with magnetic graphene nanosheets. The latter were selected as carriers for the capture DNA due to their excellent biomagnetic separation capability and electrical properties. The CdTe@PtFe nanoparticles were used to label the signal DNA which resulted in distinctly enhanced ECL owing to the large specific surface area and good electrical conductivity of the PtFe alloy. A DNA sensor was constructed on a disk-shaped indium tin oxide electrode that was fabricated via etching. Under optimal conditions, the biosensor responds linearly to DNA in the 0.02 fM to 5000 fM concentration range, with a detection limit as low as 15 aM. The electrode is regenerable. The method displays excellent specificity, extremely good sensitivity, and is highly reproducible.

Direct electrochemical detection of individual collisions between magnetic microbead/silver nanoparticle conjugates and a magnetized ultramicroelectrode

Here, we report on the electrochemical detection of individual collisions between a conjugate consisting of silver nanoparticles (AgNPs) linked to conductive magnetic microbeads (cMμBs) via DNA hybridization and a magnetized electrode. The important result is that the presence of the magnetic field increases the flux of the conjugate to the electrode surface, and this in turn increases the collision frequency and improves the limit of detection (20 aM). In addition, the magnitude of the charge associated with the collisions is greatly enhanced in the presence of the magnetic field. The integration of DNA into the detection protocol potentially provides a means for using electrochemical collisions for applications in biological and chemical sensing.