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In this paper, we report a novel and sensitive optical sensing protocol for thrombin detection based on magnetic nanoparticles (MNPs) and thrombin aptamer, employing split HRP-mimicking DNAzyme halves as its sensing element, which can catalyze the H2O2-mediated oxidation of the colorless ABTS into a blue-green product. A single nucleotide containing the recognition element and sensing element is utilized in our protocol. The specific recognition of thrombin and its aptamer leads to the structure deformation of the DNA strands and causes the split of the DNAzyme halves. Therefore, the decrease of absorption spectra can be recorded by the UV–visible Spectrophotometer. DNA-coated MNPs are utilized to separate the interferential materials from the analyst, thus making this assay can be applied in the detection of thrombin in complex samples, such as human plasma. This original, sensitive and cost-effective assay showed favorable recognition for thrombin. The absorbance signals with the concentration of thrombin over a range from 0.5 to 20 nM and the detection limit of thrombin was 0.5 nM. The controlled experiments showed that thrombin signal was not interfered in the presence of other co-existence proteins.

A simple and effective capillary electrophoresis–chemiluminescence (CE–CL) detection system was developed based on an ultra-fast bis(2,4,6-trichlorophenyl)oxalate (TCPO) chemiluminescence (CL) reaction (0.6 s duration) that avoided overlapping peaks and peak tailing. Through a series of static injection experiments, this unusually rapid CL reaction was ascribed to the catalytic effect of imidazole in the tetrahydrofuran solvent, which has been rarely utilized in such investigations. A possible mechanism is given to explain the results. Under the optimized conditions, rhodamine 6 G (R6G) and its hydrolysis product (R6G-COOH) could be efficiently separated through electrophoresis in 7 min, with sensitive CL detection in the proposed CE–CL system. In this way, the alkaline hydrolysis of R6G was monitored, followed by estimation of relative rate constants and activation energy. This finding and application should be helpful in further study for the TCPO CL reaction, and revealed an attractive opportunity for simplifying the CE–CL system, such as in a microchip device. Copyright © 2011 John Wiley & Sons, Ltd.

High yield preparation of silver nanowires (AgNWs) was prepared by polyol method. In this developed polyol process, uniform AgNWs have been successfully synthesized at higher yield by introducing CuCl2·2H2O, when ethylene glycol is used as the solvent and reductant while poly vinyl pyrrolidone (PVP) is used as the capper agent. Then Ag thin films were made by screen printing using silver nanowires and nanoparticles as semitransparent conduction electrodes. The test results indicated that the electrical resistivity could be as low as 0.091 Ω/□, when the transparence rate can reach 45–46%, which shows great promise in the improvement of conductive antireflection coating.

The aggregation and adhesion of bacterial cells is a serious disadvantage for electrophoretic separations of bacteria. In this study, lipid-based liquid crystalline nanoparticles were used as a pseudostationary phase to minimise the bacterial aggregation and adsorption to the inner walls of microchannels. Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus and Lactobacillus rhamnosus were selected as analytes and were separated by microchip electrophoresis (MCE) with laser-induced fluorescence (LIF) detection using 4.5 mM tris(hydroxymethyl) aminomethane (TRIS)–4.5 mM boric acid–0.1 mM ethylenediaminetetraacetate (EDTA) (TBE) containing poly(ethylene oxide) (PEO) and lipid-based nanoparticles as the running buffer. The mechanism of lipid-based nanoparticles affecting bacterial adhesion and aggregation was discussed and supported by zeta potential experiments. Under the optimal conditions, the three species of bacteria were identified with patterned peaks. This proposed MCE method using lipid-based nanoparticles as running buffer additives was also used to analyse a real yogurt sample, and valuable bacterial information was obtained by the electropherograms.

Microchip electrophoresis (MCE) coupled to laser-induced fluorescence detection was applied to the rapid separation of Bifidobacterium, Lactobacillus casei, Lactobacillus acidophilus, and Enterococccus faecalis. All bacteria were quickly separated within 150 s using a running buffer of pH 8.5 containing Tris, borate, EDTA, and poly(ethylene oxide). The latter was crucial to reduce the bacterial adsorption on the walls of the microchannels. The pH of 8.5 warrants that bacteria carry a negative charge at their surface and thus display good electrophoretic performance. The method was used to analyze medical samples containing these probiotics, and the results showed that the identification and detection of bacteria by MCE is advantageous in terms of sample consumption, waste production, time of analysis, and instrumental effort.

The electrochemical monitoring of glucose consumption is relevant for cell biology studies because of its wide detection range, high sensitivity and easy implementation. Whereas the glucose consumption and cell growth rate can be tightly correlated, they should also be cell population density dependent. In this work, we fabricated high sensitive enzyme electrodes for accurate monitoring of glucose consumption of cells in different growth stages. The performance of the fabricated device was firstly evaluated by cyclic voltammetry (CV) with p-benzoquinone (PBQ) as redox mediator, showing a linear response over a wide detection range (0.3–60 mM), a high sensitivity (1.61 ± 0.10 μA mM−1 mm−2 (n = 5)) and a low detection limit (80 μM). Then, daily glucose consumptions of NIH 3T3 cells in 24-well plates were determined for a period of 7 days. The results could be compared to the cell population growth curve, showing a close correlation but different behavior. We found that the increase of the glucose consumption took place prior the cell number increase but the glucose consumption per cell decreases linearly in the exponential growth stage of cells.

Special fractal dendrite Cu nanostructures have been synthesized through a simple hydrothermal method, and the effects of the volume ratio between glycerol and water and the concentration of H{sub 3}PO{sub 3} on the morphologies of dendrite Cu have been studied in detail. The Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used to characterize these Cu products. The results indicate that rhombic diamond and different morphologies of fractal dendrite were prepared because of the accumulation of Cu nuclei based on the diffusion-limited aggregation (DLA) and the nucleation-limited aggregation (NLA) model. Fortunately, symmetrical leaf-like dendrite Cu nanostructures different from Cu dendrites reported before have been obtained. Additionally, an explanation for the growth of fractal dendrite Cu has been discussed carefully. - Graphical abstract: Uniform dendritic Cu are grown through controlling V{sub glycerol/water} in range of 0.6-1.2 and the concentration of H{sub 3}PO{sub 3} in range of 0.06-0.3 M. The rhombic cluster Cu are obtained by decreasing the amount of glycerol. Highlights: > Volume ratio of glycerol/water and concentration of H{sub 3}PO{sub 3} were varied, respectively. > Morphologies of dendritic Cu have some changes. > Leaf-like and rhombic cluster Cu were obtained. > Themore » concentration changes affect the aggregation of Cu crystallites. > The aggregation and crystallographic orientation cause leaf-like Cu nanostructures.« less

One solid-state electrochemiluminescence (ECL) protein biosensor based on the competing reaction and substitute reaction between protein-to-DNA aptamer and DNA-to-DNA aptamer was proposed. Additionally, the biosensor was based on ECL photo-quenching effect of ferrocene (Fc) to tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+). It was built up by modification of Au nanoparticles (AuNPs) and Ru(bpy)32+ on one Au electrode firstly, and then self-assembly of one special double-stranded DNA (dsDNA) onto the electrode. This dsDNA was prepared by hybridization of one Fc labeled molecular beacon single-stranded DNA(ssDNA) and one anti-thrombin aptamer ssDNA. Without the target protein, this Fc-dsDNA/Ru(bpy)32+-AuNPs/Au electrode trigged strong ECL signal, so we called it ECL “signal on” state. When thrombin was present in the sensing solution, the protein reacted with its aptamer from the Fc-dsDNA/Ru(bpy)32+-AuNPs/Au electrode. Then the left molecular beacon ssDNA on the electrode recovered to its normal stem-loop structure and consequently its Fc labeler was close enough to the electrode surface to quench the ECL signal from Ru(bpy)32+. It was in ECL “signal off” state. We measured the decrease in ECL intensity to sense the target protein. This was one endeavour to sense protein by using un-labeling target or probe strategy, which gave higher sensitivity and selectivity due to the better combination efficiency of protein and the un-labeled aptamer. 6.25 fmol/L thrombin was detected out.

A colorimetric nanoprobe-mercury-specific DNA-functionalized gold nanoparticles (Au-MSD) was developed for sensing Hg(2+). The new mercury-sensing concept relies on measuring changes in the inhibition of "non-crosslinking" aggregation of Au-MSD-induced by the folding of mercury-specific DNA strand through the thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination. In the absence of Hg(2+), a high concentration of MgCl(2) (50 mM) results in a rapid aggregation of Au-MSD because of the removal of charge repulsion. When Hg(2+) is present, the particles remain stable due to the folding of MSD functionalized on the particle surface. The assay enables the colorimetric detection of Hg(2+) in the concentration range of 0.1-10 μM Hg(2+) ions with a detection limit of 60 nM, and allows for the selective discrimination of Hg(2+) ions from the other competitive metal ions. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg(2+) in fish tissue samples.

A label-free ECL aptamer biosensor based on CdS QDs/ACNTs electrode for the sensitive detection of thrombin was fabricated. CdS QDs and Chitosan (CTS) complex films were coated and filled the tubes of ACNTs by carrying out electrodeposition reaction of CTS-CdS QDs on ACNTs electrode, the resulting electrode showed high ECL intensity and good biocompatibility. After aptamer was bound to the film via glutaric dialdehyde, the modified electrode could be used as an ECL aptamer sensor for the thrombin detection. The specific reaction between thrombin and aptamer resulted in the decrease in ECL intensity. The change of the ECL intensity was found to be linear with the logarithm of thrombin concentration in the range from 1.0×10−13 M to 1.0×10−9 M. The ECL aptamer sensor had the advantages of speed, high sensitivity, specificity and stability, which could be a promising technique for protein detection.

A novel G-quadruplex-based DNAzymes aptasensor for the amplified electrochemical detection of thrombin has been described. The aptasensor utilized a combination of hemin and guanine-rich thrombin-binding aptamer (TBA) to form horseradish peroxidase (HRP)-mimicking DNAzymes with peroxidase catalytic activity. In the presence of thrombin, the enzyme activity could be extensively promoted, thereby providing the amplified electrochemical readout signals for detecting thrombin. This aptasensor exhibited high sensitivity and selectivity for thrombin determination, which enabled the analysis of thrombin with a detection limit of 6×10–11 M. On the basis of results, this method could have broad applications in the detection of proteins and other biomolecules.

A competitor-switched electrochemical sensor based on a generic displacement strategy was designed for DNA detection. In this strategy, an unmodified single-stranded DNA (cDNA) completely complementary to the target DNA served as the molecular recognition element, while a hairpin DNA (hDNA) labeled with a ferrocene (Fc) and a thiol group at its terminals served as both the competitor element and the probe. This electrochemical sensor was fabricated by self-assembling a dsDNA onto a gold electrode surface. The dsDNA was pre-formed through the hybridization of Fc-labeled hDNA and cDNA with their part complementary sequences. Initially, the labeled ferrocene in the dsDNA was far from surface of the electrode, the electrochemical sensor exhibited a "switch-off" mode due to unfavorable electron transfer of Fc label. However, in the presence of target DNA, cDNA was released from hDNA by target DNA, the hairpin-open hDNA restored its original hairpin structure and the ferrocene approached onto the electrode surface, thus the electrochemical sensor exhibited a "switch-on" mode accompanying with a change in the current response. The experimental results showed that as low as 4.4×10−10 mol/L target DNA could be distinguishingly detected, and this method had obvious advantages such as facile operation, low cost and reagentless procedure.

A novel β-cyclodextrin (β-CD) derivative containing mono-phenylamino (MPA-β-CD) was newly synthesized by classical Mitsunobu reaction in good yield, and its structure has been confirmed by 1 H NMR, 13 C NMR and electrospray ionization mass spectra. The compound MPA-β-CD was immobilized onto glassy carbon electrode (GCE) by diazotization, and with this modified electrode the binding behavior of MPA-β-CD for ferrocene (Fc) was investigated qualitatively, and the comparison of differential pulse voltammetry before and after immersion in ferrocene solution indicated that the MPA-β-CD immobilized GCE exhibited the molecular recognition behavior between β-CD and ferrocene.

The dye-doped silica nanoparticles can be used as nanobiosensors that are able to recognize and detect specific DNA sequence. In his paper, spherical nanosized luminol/SiO2 composite particles have been synthesized with reverse micells via hydrolysis of tetraethyl orthosilicate (TEOS) in the microemulsion. The nanoparticles were modified with chitosan and used to label DNA, forming the DNA probe which was used to hybridize with target DNA immobilized on a PPy modified Pt electrode. The hybridization events were evaluated by electro generated chemiluminescence's (ECL) measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of luminol molecules inside silica nanoparticles, the assay allows detection at levels as low as 2.0×10−12 mol/L of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 5.0×10−12-1.0×10−9 mol/L.

The composition of laminarin was firstly determined by analyzing its hydrolysis monosaccharides with capillary zone electrophoresis-amperometric detection (CZE-AD). Under the selected optimum conditions, fucose, galactose, glucose, mannose and xylose, which are hydrolysis products of laminarin, could be perfectly separated within 20 min and showed significant current responses at copper electrodes. The linear ranges of fucose, galactose and glucose were from 1.0 ± 10–6 to 2.0 ± 10–4 mol ± L−1, those of mannose and xylose were from 5.0 ± 10–6 to 2.0 ± 10–4 mol ± L−1, and their detection limits were at 10–7mol ± L−1 level (S/N = 3). The molar ratio of fucose, galactose, glucose, mannose and xylose in laminarin was 10.5: 2.8:1.0:7.3: 3.4 and the purity of this polysaccharide leached by the introduced leaching method was 95.7%. Compared to usual UV-vis and other spectrometric methods, analyzing polysaccharide by this method has some merits of quickness, low-volume sampling, simple instrumentation, high sensitivity and high reproducibility.

A new electrochemical aptamer molecular beacon (MB) was designed by the carminic acid (CA) covalently linking at the each end of a special single-stranded stem-loop shaped oligonucleotide and named as CAs-MB. CA is an electrochemically active molecule and two CA molecules at the ends of molecular beacon stem were closed enough to associate each other to be as CA dimer. The dimer was electrochemically inactive. It separated into two CA monomers and produced the electrochemical signal while CAs-MB combined with target. In this protocol, the detection strategy of CAs-MB for thrombin is based on electrochemical active–inactive switching between monomer and dimer forms of CA. In order to enhance the electrochemical signal, magnetic nanobeads (MNB) was applied by connecting CAs-MB with MNB through a duplex of DNA. With the magnetic enrichment, the detection limit for thrombin reached to 42.4 pM. The experiment results showed that this type of electrochemical active–inactive switching aptamer molecular beacon allowed the direct detection of target proteins in the solution with no requirement of removing uncombined CAs-MB. Besides, CAs-MB/MNB can be easily regenerated by using 2 M NaCl solution to cleave the thrombin from the aptasensor.

We herein constructed a sensor that converts target DNA hybridization-induced conformational transformation of the probe DNA to electrochemical response based on host-guest recognition and nanoparticle label. In the sensor, the hairpin DNA terminal-labeled with 4-((4-(dimethylamino)phenyl)azo)benzoic acid (dabcyl) and thiol group was immobilized on Au electrode surface as the probe DNA by Au-S bond, and the CdS nanoparticles surface-modified with β-cyclodextrins (CdS-CDs) were employed as electrochemical signal provider and host-guest recognition element. Initially, the probe DNA immobilized on electrode kept the stem-loop configuration, which shielded dabcyl from docking with the CdS-CDs in solution due to the steric effect. After target hybridization, the probe DNA underwent a significant conformational change, which forced dabcyl away from the electrode. As a result, formerly-shielded dabcyl became accessible to host-guest recognition between β-cyclodextrin (β-CD) and dabcyl, thus the target hybridization event could be sensitively transduced to electrochemical signal provided by CdS-CDs. This host-guest recognition-based electrochemical sensor has been able to detect as low as picomolar DNA target with excellent differentiation ability for even single mismatch.

Coiled carbon nanostructure (CNS) is prepared by a catalytic chemical vapor deposition (CVD) process on copper/chromium films deposited by radio frequency (RF) sputtering. Uniform CNS with coiled structure is fabricated by changing the size of the catalyst particles. The effects of Cu catalyst size and RF sputtering power, on the growth of the coiled CNS are discussed, and the results importantly conclude that Cu-catalyzed CVD offers a preferable control of coiled CNS to optimize the field emission property for application.

This communication reports on a new electrochemical method to detect the hybridization specificity by using host–guest recognition technique. A hairpin DNA with dabcyl-labeled at its 3′ and NH2 group at 5′ terminal was combined with CdS nanoparticle to construct a double-labeled probe (DLP), which could selectively hybridize with its target DNA in homogeneous solution. A β-CD modified Poly(N-acetylaniline) glassy carbon electrode was used for capturing the dabcyl label in DLP. When without binding with target DNA, the DLP kept its stem-loop structure which shielded the dabcyl molecule due to the loop of the hairpin DNA and CdS nanoparticle blocking dabcyl enter into the cavity of these β-CD molecules on the electrode. However, in present of complementary sequence, the target-binding DLP was incorporated into double stranded DNA, causing the DLP’s loop-stem structure opened and then the dabcyl was easily captured by the β-CD modified electrode. During electrochemical measurement, the signal from the dissolved Cd2+ was used for target DNA quantitative analysis. Keywords: DNA, Electrochemical, Homogeneous, Cyclodextrins, Double-labeled probe

With a view of simultaneous determination of physio-active ingredients in oolong tea infusion: sugars, amino acids, epigallocatechin gallate and ascorbic acid, a novel CZE with amperometric detection method was studied. Operated in a wall-jet configuration, 100 mmol/L NaOH was used in detecting cell to lead the electrocatalysis oxidation behaviors of the analytes on a 300 mum diameter copper-disc electrode (working electrode), while in separating capillary, a mild alkaline running buffer consisting in a mixture of 30 mmol/L borate and 40 mmol/L phosphates charged and carried analytes to detecting end. The methodology research was performed for system stability and suitability. Under the optimal CE conditions, analytes could be separated within moderate time period. Good linearity between peak area and concentration existed over three orders of magnitude; lower RSD and LOD were achieved. The oolong tea infusion was assayed and result was satisfactory.

A composite electrode was fabricated from Cu2O powder, carboxyl-functionalized multi-wall carbon nanotubes (MWCNT-COOH), and paraffin oil in the proportions 51:17:32 (w/w). This composite electrode was used for amperometric detection (CZE–AD) in simultaneous capillary zone electrophoretic analysis of chlorogenic acid, rutin, sucrose, glucose, mannose, and fructose in tobacco samples. Under the optimum conditions, the six analytes could be separated in 100 mmol L−1 NaOH buffer within 30 min. Good linearity was achieved in the range 1 × 10−7–1 × 10−4 mol L−1 for the two polyphenols and 5 × 10−6–1 × 10−3 mol L−1 for the four sugars. The detection limits (S/N = 3) for the polyphenols and sugars were as low as 10−8 mol L−1 and 10−6 mol L−1, respectively.

Polythymine oligonucleotide (PTO)-modified gold electrode (PTO/Au) was developed for selective and sensitive Hg2+ detection in aqueous solutions. This modified electrode was prepared by self-assembly of thiolated polythymine oligonucleotide (5′-SH-T15-3′) on the gold electrode via AuS bonds, and then the surface was passivated with 1-mercaptohexanol solution. The proposed electrode utilizes the specific binding interactions between Hg2+ and thymine to selectively capture Hg2+, thereby reducing the interference from coexistent ions. After exchanging the medium, electrochemical reduction at −0.2 V for 60 s, voltammetric determination was performed by differential pulse voltammetry using 10 mM HEPES; pH 7.2, 1 M NaClO4 as supporting electrolyte. This electrode showed increasing voltammetric response in the range of 0.21 nM Hg2+, with a relative standard deviation of 5.32% and a practical detection limit of 60 pM. Compared with the conventional stripping approach, the modified electrode exhibits good sensitivity and selectivity, and is expected to be a new type of green electrode.

Thionine molecules have been electropolymerized onto different types of carbon nanotubes (CNT) using a cyclic voltammetry scanning technology, including multi-walled carbon nanotubes, single-walled carbon nanotubes and aligned carbon nanotubes. Results indicate that such prepared nanocomposites have combined the intrinsic faradic capacitance of polythionine with the double layer capacitance of polythionine-CNT, and thus the polythionine modification obviously enhanced the CNT capacitance. Especially the carboxyl group modified multi-walled carbon nanotubes, which have made their nanotube tips opened, allowed much more electropolymerization cycles and then obtained a most significant increment in capacitance than the other three ones.

In the paper, a new kind of vitamin B 12 (acquo-cobalamine) chemically modified electrode was fabricated and applied in capillary zone electrophoresis coupled with amperometric detection (CZE-AD) for simultaneous determination of six antioxidants in fruits and vegetables. The catalytic electrochemical properties of the chemically modified electrode could obviously enhance oxidation peak heights responses by about five times to glutathione, ascorbic acid, vanillic acid, chlorogenic acid, salicylic acid, and caffeic acid compared with common carbon disk electrode. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Under the optimum conditions, the six analytes could be completely separated and detected in a borate–phosphate buffer (pH 8.4) within 15 min. Their linear ranges were from 2.5 × 10 −7 to 1.0 × 10 −4 mol L −1 and the detection limits were as low as 10 −8 mol L −1 magnitude ( S / N = 3). The proposed method has been successfully employed to monitor the six analytes in practical samples with recoveries in the range 96.0–106.0% and RSDs less than 5.0%. Above results demonstrate that capillary zone electrophoresis coupled with electrochemical detection using vitamin B 12 modified electrode as detector is of convenient preparation, high sensitivity, good repeatability, and could be used in the rapid determination of practical samples.

Kaempferol, apigenin, rutin, quercetin, luteolin and ferulic acid are separated and detected in Chinese herbal tea using capillary zone electrophoresis coupled to amperometric detection. The phosphate running buffer also contains s-cyclodextrin (s-CD), which assists in separation and gives excellent separations within 20 min and detection limits as low as 10 ng mL−1 (S/N = 3). The effects of working electrode potential, pH and concentration of running buffer, concentration of s-CD, separation voltage and injection time were investigated. The method was applied to analyze tea samples with recoveries in the range of 90.0 to 107.0%. The method offers high separation efficiency, short analysis time, small sample consumption, and good repeatability.

In general capillary zone electrophoresis (CZE) separation models, o-, m-, and p-phenylenediamine isomers can be separated in a weak acidic running buffer for their pK(a) values being 4.52, 5.64, 6.04, respectively, while o-, m-, and p-dihydroxybenzene isomers can be separated in a weak basic buffer for their pK(a) values being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE-AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10(-7) mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pK(a) and had some advantages of high sensitivity, good repeatability and small sample requirement.

An effective method for selective immobilization of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+ ) onto one target electrode surface based on the electrodeposition of RuDS NPs (Ru(bpy) 3 2+ doped silica nanoparticles)/chitosan composite film is presented in this paper. Ru(bpy) 3 2+ was selectively deposited onto four individual electrodes in an Au electrode array. The results demonstrate the possibility of selective immobilization of Ru(bpy) 3 2+ onto array electrodes and selective immobilization of different ECL composite. Therefore have potential applications in bioanalysis, capillary electrophoresis and drug screening. RuDS NPs and the resulting composite film were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM) and Field emission-scanning electron microscope (FE-SEM). The electrochemiluminescence (ECL) sensor based on the composite film modified electrode exhibited excellent reproducibility, stability and sensitivity for the detection of tri-n-propylamine (TPA). The linear range was from 1 × 10 −10 to 1 × 10 −6 M ( R 2 = 0.9954) with the detection limit of 5 × 10 −11 M.

A simple and efficient electrochemical method is utilized to functionalize aligned carbon nanotubes (ACNTs) by the electrochemical reduction of 4-carboxyphenyl diazonium salt. Thus hemoglobin (Hb) molecules were covalently immobilized on the diazonium-ACNTs surface via carbodiimide chemistry. Direct electrochemistry and bioelectrocatalytic activity of the immobilized Hb were then investigated by cyclic voltammetry (CV) and amperometry techniques. It is showed that the Hb film on the diazonium-ACNTs electrode had well-defined redox peaks with a formal potential (E°) at −312 mV (vs. Ag/AgCl), and the Hb-ACNTs electrode displayed good electrocatalytic activity to H2O2 reduction. Owing to the high Hb covering on the ACNTs surface (Γ*=2.7×10−9 mol cm−2), the catalytic current were significantly improved when compared to the current measured at an Hb-tangled carbon nanotubes electrode. The Hb-ACNTs electrode exhibited high sensitivity, long-term stability and wide concentration range from 40 μM to 3 mM for the amperometric detection of H2O2. The heterogeneous reaction rate constant (ks) was 0.95±0.05 s−1 and the apparent Michaelis–Menten constant (K was 0.15 mM.

In this protocol, a fluorescent aptasensor based on magnetic separation for simultaneous detection thrombin and lysozyme was proposed. Firstly, one of the anti-thrombin aptamer and the anti-lysozyme aptamer were individually immobilized onto magnetic nanoparticles, acting as the protein captor. The other anti-thrombin aptamer was labeled with rhodamine B and the anti-lysozyme aptamer was labeled with fluorescein, employing as the protein report. By applying the sandwich detection strategy, the fluorescence response at 515 nm and 578 nm were respectively corresponding to lysozyme and thrombin with high selectivity and sensitivities. The fluorescence intensity was individually linear with the concentration of thrombin and lysozyme in the range of 0.13–4 nM and 0.56–12.3 nM, and the detection limits were 0.06 nM of thrombin and 0.2 nM of lysozyme, respectively. The preliminary study on simultaneous detection of thrombin and lysozyme in real plasma samples was also performed. It shows that the proposed approach has the good character for simultaneous multiple protein detection.

A solid-state electrochemiluminescence (ECL) biosensing switch system based on special ferrocene-labeled molecular beacon aptamer (Fc-MBA) has been developed successfully for thrombin detections. Such special switch system includes two main parts, an ECL substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Au nanoparticle and Ruthenium (II) tris-(bipyridine) (Ru(bpy)(3)(2+)-AuNPs) onto Au electrode. A molecular beacon aptamer labeled by ferrocene acted as the ECL intensity switch. The loop bases of the ECL intensity switch are designed with special anti-thrombin aptamer sequence which could be combined with its target protein via the reaction between aptamer and thrombin. During the reactions, the molecular beacon aptamer opened its stem-loop, and the labeled Fc was consequently kept away from the ECL substrate. Such structural change resulted in an obvious ECL intensity increment due to the decreased quenching effect of Fc to the ECL substrate. The analytic results are sensitive and specific.

The combinatorial chemical synthesis offers in vitro aptamer generation with limitless aptamer selection for various analytes. Additionally, aptamer has quite many outstanding properties as the biomolecular recognition elements, thus competing with traditional affinity ligands (enzyme, antibodies, lectins etc.) in biological and medicine employments. This article reviews the advancements in electrochemical aptasensors for biomolecule monitoring, emphasizing the efficient detection strategies of sandwich structure formation using two recognition elements to capture and label target respectively, EIS measuring the electronic transfer resistance change, the aptamer conformation change triggering the electrochemical signal on/off and target molecules displacing electroactive markers.

A versatile method for preparing nanoporous polypyrrole (PPy) film using electrogenerated nanobubbles as templates on highly oriented pyrolytic graphite (HOPG) is presented using in situ electrochemical atomic force microscopy (EC-AFM). Keywords: Polypyrrole, Nanobubbles, Highly oriented pyrolytic graphite, Electrochemical atomic force microscopy

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+ ) has been successfully immobilized onto electrode through the electrodeposition of Ru(bpy) 3 2+ /AuNPs/chitosan composite film. In the experiments, chitosan solution was first mixed with Au nanoparticles (AuNPs) and Ru(bpy) 3 2+ . Then, during chronopotentiometry experiments in this mixed solution, a porous 3D network structured film containing Ru(bpy) 3 2+ , AuNPs and chitosan has been electrodeposited onto cathode due to the deposition of chitosan when pH value is over its p K a (6.3). The applied current density is crucial to the film thickness and the amount of the entrapped Ru(bpy) 3 2+ . Additionally, these doping Ru(bpy) 3 2+ in the composite film maintained their intrinsic electrochemical and electrochemiluminescence activities. Consequently, this Ru(bpy) 3 2+ /AuNPs/chitosan modified electrode has been used in ECL to detect tripropylamine, and the detection limit was 5 × 10 −10 M.

We report a new kind of electrochemical molecular beacon, termed “electrochemically active–inactive switching molecular beacon”, for direct detection of DNA in homogenous solution. The electrochemical molecular beacon consists of a stable stem-loop oligonucleotide carrying two carminic acid moieties (acting as electrochemical reporter) attached at its termini. In a close form, the electrochemical signal is quenched because two carminic acid moieties are close enough to associate into dimer. In the presence of the complementary DNA target, the electrochemical molecular beacon undergoes a conformational transformation from closed (hairpin) to open (linear) structure, which is associated with an increase in electrochemical signal. We found that the electrochemical molecular beacon is as effective as conventional molecular beacon in signaling the presence of complementary target and discriminating targets that differ by a single nucleotide. The proposed electrochemical molecular beacon has a great potential for investigating the interactions of DNA-protein and developing electrochemical real-time polymerase chain reaction. Keywords: DNA, Electrochemical molecular beacon, Molecular recognition, Nucleotides, Probe

Aligned carbon nanotubes (ACNTs) electrode has been developed for the direct protein electrochemistry and enzyme-biosensor study involving two types of nanoparticles. Pt nanoparticles (Ptnano) were electro-modified on the ACNTs’ each tube, greatly increasing the electrode surface area for locating protein and also its electronic transfer ability. Glucose oxidase (GOD) with chitosan (CS) and CdS nanoparticles electrochemically coated on each tube of ACNTs–Ptnano by the electrodeposition reaction of CS when pH value passing its pKa. The CdS nanoparticles between ACNTs electrode and GOD have stimulated the GOD’s direct electron transfer during its redox reaction of FAD/FADH2. The CS–GOD–CdS/ACNTs–Ptnano electrode also offer sensitive response to the substrate of glucose with detection limit of 46.8 μM (S/N = 3) and apparent Michaelis–Menten constant of 11.86 mM. Keywords: Aligned carbon nanotubes, Glucose oxidase, Chitosan, Direct electron transfer, Biosensor

A sensitive electrochemical aptasensor for detection of thrombin based on target protein-induced strand displacement is presented. For this proposed aptasensor, dsDNA which was prepared by the hybridization reaction of the immobilized probe ssDNA (IP) containing thiol group and thrombin aptamer base sequence was initially immobilized on the Au electrode by self-assembling via AuS bind, and a single DNA labeled with CdS nanoparticles (DP-CdS) was used as a detection probe. When the so prepared dsDNA modified Au electrode was immersed into a solution containing target protein and DP-CdS, the aptamer in the dsDNA preferred to form G-quarter structure with the present target protein resulting that the dsDNA sequence released one single strand and returned to IP strand which consequently hybridized with DP-CdS. After dissolving the captured CdS particles from the electrode, a mercury-film electrode was used for electrochemical detection of these Cd2+ ions which offered sensitive electrochemical signal transduction. The peak current of Cd2+ ions had a good linear relationship with the thrombin concentration in the range of 2.3×10−9–2.3×10−12 mol/L and the detection limit was 4.3×10−13 mol/L of thrombin. The detection was also specific for thrombin without being affected by the coexistence of other proteins, such as BSA and lysozyme.

A carbon paste electrode modified with multiwall carbon nanotubes and copper(I) oxide (MWCNT–Cu2O CPME) was fabricated, and the electrochemical behaviors of 19 kinds of natural amino acids at this modified electrode were studied. The experimental results showed that the various kinds of amino acids without any derivatization displayed obvious oxidation current responses at the modified electrode. It was also found that the current response values of amino acids were dependent mainly on pH values of buffer solutions. The phenomenon could be explained by the fact that the amino acids suffered complexation or electrocatalytic oxidation processes under different pH values. Six kinds of amino acids (arginine, tryptophan, histidine, threonine, serine, and tyrosine), which performed high-oxidation current responses in alkaline buffers, were selected to be detected simultaneously by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). These amino acids could be perfectly separated within 20 min, and their detection limits were as low as 10−7 or 10−8 mol L−1 magnitude (signal/noise ratio = 3). The above results demonstrated that MWCNT–Cu2O CPME could be successfully employed as an electrochemical sensor for amino acids with some advantages of convenient preparation, high sensitivity, and good repeatability.

A biocompatible nanocomposite film was fabricated for hemoglobin (Hb) molecules immobilization. This film consists of multiwalled carbon nanotubes (MWNTs), 1-pyrenebutanoic acid, succinimidyl ester (PASE), hemoglobin (Hb) and Au nanoparticles (AuNPs). Herein, PASE molecules physically adsorbed onto MWNTs, and its groups then covalently bond with Hb. AuNPs were then linked with Hb/PASE/MWNTs via electrostatic adsorption force. UV-visible adsorption spectra, Fourier transform infrared spectra, scanning electron microscope and electrochemical impedance spectroscopy have characterized the film. Cyclic voltammetry (CV) scans showed that in the film Hb has well-defined redox reaction, with the formal potential (E°) at about −0.27 V (vs. Ag/AgCl). Herein, differential pulse voltammetry (DPV) was employed to electrochemically detect the Hb in the film with a detection limit of 9.3×10−8 M. The proposed method was also succeeded for Hb detection in clinical blood samples. Furthermore, the Hb in the film showed good electrocatalytic activities to the reduction of H2O2, TCA, NaNO2 and O2.

Despite the separation efficiency of capillary electrophoresis (CE) is much higher than other chromatographic methods, it is sometimes difficult to perfectly separate the complex ingredients in biological samples. One possible and simple way to develop the separation effect in CE is to add some modifiers in the running buffer. In this paper, the suitable running buffer modifiers were explored to simultaneously separate and detect six typical flavonoids (apigenin, luteolin, kaempferol, quercetin, (+)-catechin and (-)-epicatechin) which are the main active ingredients in chrysanthemum by capillary zone electrophoresis with amperometric detection (CZE-AD). It was found that when beta-cyclodextrin (beta-CD) and the mixture of methanol and ethanol were used as running buffer modifiers, a baseline separation of the six analytes could be accomplished in less than 20 min and the detection limits were as low as 10(-7) or 10(-8)gm l(-1). Other factors affecting the CZE separation, such as working potential, pH value and ionic strength of running buffer, separation voltage and sample injection time were extensively investigated. Under the optimum conditions, a successful practical application on the determination of chrysanthemum samples confirmed the validity and practicability of this method.

A novel Au nanoparticles (Au-NPs)-based protocol for DNA hybridization detection based on assembly of alternating DNA and poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by layer-by-layer (LBL) electrostatic adsorption has been studied. Electrochemical impedance spectroscopy (EIS) and UV–vis absorbance measurements were used to study the film assembly. All the results indicate that the uniform multilayer can be obtained on the polypyrrole (PPy) coated electrode surface and the hybridization reaction can be amplified by the layer-by-layer progress. The hybridization was detected by the reductive signal of Au-NPs and nonspecific adsorption was greatly eliminated by an unrelated DNA sequence to the target DNA. Under optimum conditions, a significant sensitivity enhancement had been obtained, and the detection limit was down to 3.20 × 10 −14 M when 6 layers assembled. The DNA biosensor has good stability and reproducibility.

Palladium nanoparticles, in combination with multi-walled carbon nanotubes (MWCNTs), were used to fabricate a sensitivity-enhanced electrochemical DNA biosensor. MWCNTs and palladium nanoparticles were dispersed in Nafion, which were used to modify a glassy carbon electrode (GCE). 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 using methylene blue (MB) as an indicator. Due to the ability of carbon nanotubes to promote electron-transfer and the high catalytic activities of palladium nanoparticles for electrochemical reaction of MB, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.2×10−13 M.

In this paper, a nano-NiO modified carbon paste electrode in capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the determination of carbohydrates. Effects of several important factors such as detection potential, the concentration of running buffer, separation voltage and injection time were investigated to acquire the optimum conditions. Under the selected optimum conditions, three carbohydrates: glucose, sucrose and fructose could be perfectly separated within 20 min. The relationships between peak current and concentration of three carbohydrates were linear over about 3 orders of magnitude with detection limits (S/N = 3) ranging from 3.0 × 10 −7 to 6.0 × 10 −7 mol L −1 . The electrode was stable, and can be used for at least one week. The proposed method has been successfully applied to monitor carbohydrates in the real samples with satisfactory assay results.

A simple preparation scheme is described for the quantitative analysis of a magnesium niobate sample using slurry introduction axially viewed inductively coupled plasma optical emission spectrometry. Relationships between the stability of slurries and the conditions, such as particle size, pH, dispersant and amount of dispersant, were investigated experimentally. The MgNb(2)O(6) slurry sample was prepared by adding the dispersant sodium polyacrylate and agitation in an ultrasonic bath to ensure good dispersion. Under optimization of pH and amount of dispersant, an analysis of minor and trace impurities (Ba, Ca, Cr, Cu, Fe, Mn, Ni, Pb) in magnesium niobate was accomplished. Applying a paired t test, we showed that the results were in agreement at a 95% confidence level with the reference values obtained by a fusion method for a magnesium niobate sample, which verified that the calibration curves could be established by aqueous standards. Analytical results demonstrate that the factors that affected the accuracy of determination for MgNb(2)O(6) are mainly the particle size of the sample and the stability of slurry.

A sensitive and selective aptasensor using tri(2,2'-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)3(2+)-doped SNPs) as DNA tags for detection of thrombin is developed based on the target protein-induced strand displacement of the DNA probe. For the proposed aptasensor, the aptamer was assembled on the surface of the Au electrode through Au-S binding. The hybridization event between the DNA probe labeled by the Ru(bpy)3(2+)-doped SNPs and the aptamer was evaluated by electrogenerated chemiluminescence (ECL) measurements. Then, the DNA probe was displaced by thrombin and the binding event between the thrombin and the aptamer was monitored by ECL measurements again. The difference of ECL intensity (deltaI(ECL)) of the two events could be used to quantify the thrombin. Other proteins, such as bovine serum albumin and bovine hemoglobin, had almost negligible deltaI(ECL). Under the optimal conditions, the deltaI(ECL) was linearly related to the concentration of the thrombin in the range of 10 fM to 10 pM and the detection limit was down to 1.0 fM since SNPs containing a large number of Ru(bpy)3(2+) molecules were labeled on the DNA probe.

A new glucose biosensor design based on glucose oxidase (GOD) immobilized by polypyrrole has been described in this paper. The polymerization of pyrrole was initiated by a hexachloroplatinate which itself was reduced into Pt nanoparticles and thus served as a catalyst for the H2O2 oxidation. Properties of the produced GOD modified electrode were examined and the activity of the entrapped enzyme was determined by basic application on the amperometric detection of glucose. Much better results were found comparatively with the enzyme electrode for which the enzyme was entrapped by the electrochemically polymerized polypyrrole. This kind of technique for Pt nanoparticles deposition can be generalized to many cases where polypyrrole is used.

A series of the multicomponent heteropolysilicates with the same structure has been synthesised by a controllable method. Studies on the correlation between the redox properties and composition of the polyoxometalates indicate that the character of the addenda ion has the highest influence on the oxidising ability of the heteropolyanions for a given structure, and by comparison, the effects of the number of the addenda ions and the charge of the whole heteropolyanions were not completely prominent in mixed-addenda tungstomolybdosilicate heteropolyanions. For transition metal-substituted heteropolyanions, however, the effect of the number of the addenda ions is an important factor and stronger than that of the character of the addenda ion (transition metal ion) in some cases. On the other hand, incorporation of a transition metal ion can lead to a decrease of the reversibility of redox for heteropolyanions.

This paper presents a high specific, sensitive electrochemical biosensor for recognition of protein such as thrombin based on aptamers and nano particles. Two different aptamers were chosen to construct a sandwich manner for detecting thrombin. Aptamer I was immobilized on nano magnetic particle for capturing thrombin, and aptamer II labled with nano gold was used for detection. The electrical current generated from gold after the formation of the complex of magnetic particle, thrombin and nano gold, and then an electrochemical cell designed by ourselves was used for separating, gathering, and electrochemical detecting. Through magnetic separation, high specific and sensitive detection of the target protein, thrombin, was achieved. Linear response was observed over the range 5.6×10−12−1.12×10−9 mol/L, with a detection limit of 1.42×10−12 mol/L. The presence of other protein as BSA did not affect the detection, which indicates that high selective recognition of thrombin can be achieved in complex biological samples such as human plasma.

A sensitive amperometric glucose biosensor based on platinum nanoparticles (PtNPs) combined aligned carbon nanotubes (ACNTs) electrode was investigated. PtNPs which can enhance the electrocatalytic activity of the electrode for electrooxidating hydrogen peroxide by enzymatic reaction were electrocrystallized on 4-aminobenzene monolayer-grafted ACNTs electrode by potential-step method. These PtNPs combined ACNTs8 (PtNPs/ACNTs) surfaces were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The highly dispersed PtNPs on ACNTs can be obtained. The enzyme electrode exhibits excellent response performance to glucose with linear range from 1 � 10 � 5 –7 � 10 � 3 mol L � 1 and fast response time within 5 s. Furthermore, this glucose biosensor also has good reproducibility. It is demonstrated that the PtNPs/ACNTs electrode with high electrocatalytic activity is a suitable basic electrode for preparing enzyme electrodes.

In this paper, a polyamide-modified carbon paste electrode in capillary zone electrophoresis with amperometric detection (CZE–AD) was firstly applied to the determination of four carbamate pesticides: fenobucarb, isoprocarb, metolcarb and carbaryl. The four carbamates were hydrolyzed in alkalescent aqueous solutions, resulting in the formation of 2-sec-butylphenol, 2-isopropylphenol, m-cresol and α-naphthol, which could be determined by amperometry after capillary electrophoretic separation. Under the selected optimum conditions, the four analytes could be perfectly separated within 23 min. The linear ranges of 2-sec-butylphenol, 2-isopropylphenol and m-cresol were from 1.0 × 10 −7 to 2.0 × 10 −5 mol L −1 and that of α-naphthol was from 2.0 × 10 −7 to 2.0 × 10 −5 mol L −1 and their detection limits were 3.0 × 10 −8 , 3.0 × 10 −8 , 3.0 × 10 −8 and 6.0 × 10 −8 mol L −1 , respectively ( S / N = 3). Fenobucarb, isoprocarb, metolcarb and carbaryl can be indirectly determined by this CZE–AD method with recovery of 105, 104, 110 and 98% and R.S.D. of 4, 3, 4 and 3%, respectively. Above results demonstrated that this method was of high sensitivity, good repeatability and could be used in the rapid determination of the pesticide residues.