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Simultaneous detection of various intracellular biomarkers is promising for early diagnosis and treatment of cancer. Herein, a split primer ligation-triggered catalyzed hairpin assembly-based on dual-signal electrochemical biosensor was constructed for the determination of two pairs of cancer mRNAs: TK1 and c-myc, survivin and GalNAc-T by using ferrocene molecular beacon and hemin molecular beacon as detection signal sources. Each pair of targets exists simultaneously, can release the split primers and ligated as the integral primers, hybridization occurred between the integral primers and part of MBs, causing a double-stranded DNA formed. The probes hybridized with the unfolded MBs and displaced integral primers. Finally, the displaced integral primers again hybridized with the MBs and initiated cycle amplification. Under the optimal conditions, the detection limit of TK1 and c-myc mRNA is as low as 0.022 nM, and that of survivin and GalNAc-T mRNA is 0.029 nM. In addition, two pairs of cancer mRNAs could act as outputs to activate an AND logic gate.

Herein, a novel and convenient electrochemically active-inactive switching molecular beacon based on hemin (Hs-MB) has been designed for easy discrimination of single nucleotide polymorphisms (SNPs) and sensitive detection of insulin. The electrochemically active changing capability of Hs-MB is based on two identical hemin groups labeled at both ends of MB sequence in dimer or monomer forms depending on the conformation of MB which is in stem-loop structure or line shaped structure. The Hs-MB assay permits discrimination of SNPs and the highly sensitive and specific detection of insulin with detection limit successively as low as 0.5 pmol/L. Even at a very low target concentration, the Hs-MB assay also shows a good specificity in the presence of other potentially interfering components. The experimental results also show that Hs-MB can also be used for the accurate and rapid monitoring of insulin secretion by glucose-stimulated from MIN6 cells at different time periods, demonstrating that Hs-MB has potential in monitoring of biomarker variation in vivo.

This paper reports the development of an ultra-sensitive colorimetric method for the detection of trace mercury ions involving DNAzymes, Au nanoparticle aggregation, magnetic nanoparticles and an endonuclease. DNAzyme-sensing elements are conjugated to the surface of Au nanoparticle-2, which can crosslink with the T-rich strands coated on Au nanoparticle-1 to form Au nanoparticle aggregation. Other T-rich stands are immobilized on the surface of MNPs. The specific hybridization of these two T-rich strands depends on the presence of Hg(2+), resulting in the formation of a T-Hg(2+)-T structure. Added endonuclease then digests the hybridized strands, and DNAzyme-modified Au NP aggregation is released, catalysing the conversion of the colourless ABTS into a blue-green product by H2O2-mediated oxidation. The increase in the adsorption spectrum of ABTS(+) at 421 nm is related to the concentration of Hg(2+). This assay was validated by detecting mercury ion concentrations in river water. The colorimetric responses were not significantly altered in the presence of 100-fold excesses of other metal ions such as Zn(2+), Pb(2+), Cd(2+), Mn(2+), Ca(2+) and Ni(2+). The inclusion of both Au NP aggregation and an endonuclease enables the assay to eliminate interference from the magnetic nanoparticles with colorimetric detection, decrease the background and improve the detection sensitivity. The calibration curve of the assay was linear over the range of Hg(2+) concentrations from 1 to 30 nM, and the detection limit was 0.8 nM, which is far lower than the 10 nM US EPA limit for drinking water.

In this work, an on-line preconcentration method of field-enhanced sample injection (FESI) was implemented in the determination of four β2-agoinsts terbutaline (TER), procaterol (PRO), formoterol (FOR) and bambuterol (BAM) by capillary electrophoresis coupled with capacitively coupled contactless conductivity detection (CE-C4D). Under optimized conditions the background electrolyte (BGE) was 5mM Tris(hydroxymethyl)aminomethane (Tris) and 10mM citric acid (Cit) at a pH of 3.2 while the sample dilution solution was obtained by methanol. The detection limits (defined as S/N=3) of this method were 0.02mg/L for TER, PRO, FOR, BAM, which were much lower than that of the conventional CE-C4D method without preconcentration procedure, the enhancement factors were greatly improved to be 30-40-fold. The linearity ranges of four β2-agoinsts were 0.1-15mg/L, with good linear correlation coefficients (r2>0.9900). In order to evaluate the application potential of the developed method, real sample from pig feed was analyzed with recoveries of 91.4-106.2%.

A three-dimensional glassy carbon electrode (GCE) was fabricated from one-dimensional multiwalled carbon nanotubes (MWCNTs) and two-dimensional graphene (GR), using 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) ionic liquid to improve its dispersibility and stability. This GR/MWCNTs/BMIMPF6 modified GCE was found to be a highly sensitive electrochemical sensor for the simultaneous determination of hydroquinone (1,4-dihydroxybenzene, HQ) and catechol (1,2-dihydroxybenzene, CT). The GR was characterized using a transmission electron microscope. The electrochemical behaviours of HQ and CT at the GR/MWCNTs/BMIMPF6/GCE were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The chemically modified electrode exhibited excellent electrochemical catalytic activities towards HQ and CT. Linear relationships between the oxidation peak current and concentration of HQ/CT were obtained in the ranges 0.5 μM to 2.9 mM and 0.2 μM to 0.66 mM with detection limits (S/N = 3) of 0.1 μM and 0.06 μM, respectively. This GR/MWCNTs/BMIMPF6/GCE showed many advantages in terms of dispersibility, stability, sensitivity, facility and economy.

In this study, a novel and ultrasensitive biosensor strategy based on gold nanoparticles and aptamer segments was designed to detect two biomolecule targets: DNA and thrombin. Two DNA probes were designed that included aptamer segments and nucleic acids. The aptamer segments assembled into a G-quadruplex structure in the presence of thrombin, and the nucleic acids formed a double helix structure with the target DNA. The two gold nanoparticle-labeled DNA probes were effectively aggregated by specific recognition of the target molecules. Methylene blue, a redox-active indicator of single-stranded DNA, was incorporated in the unrecognized segment of the probe on the gold nanoparticle aggregation. Furthermore, the gold nanoparticle aggregation not only provided an excellent conductive matrix for methylene blue, but also abundantly enriched the methylene blue molecule. Using this method, DNA and thrombin were detected in low concentration ranges with both probes. These gold nanoparticle aggregation-based elect...

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis–chemiluminescence (CE-CL) detection method for phenols using a hemin–luminol–hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br− and F− could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE-CL detection system because of the self-polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin–luminol afforded a stable CE-CL baseline. The indirect CE-CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10−8 mol/L (o-sec-butylphenol), 4.9 × 10−8 mol/L (o-cresol), 5.4 × 10−8 mol/L (m-cresol), 5.3 × 10−8 mol/L (2,4-dichlorophenol) and 7.1 × 10−8 mol/L (phenol). Copyright © 2013 John Wiley & Sons, Ltd.

Qualitative and quantitative detection of DNA was achieved by a "sandwich" DNA sensor through SG/TC (substrate generation and tip collection) mode of scanning electrochemical microscopy (SECM). The "sandwich" DNA structure was formed by the hybridization of thiol-tethered oligodeoxynucleotide probes (capture probe), assembled on the gold substrate surface, with target DNA and biotinylated indicator probe. HRP (horseradish peroxidase)-wrapped SiO2 nanoparticles were linked to the sandwich structure through biotin-streptavidin interaction. Hydroquinone (H2Q) was oxidized to benzoquinone (BQ) at the modified substrate surface where sequence-specific hybridization had occurred through the HRP-catalyzed reaction in the presence of H2O2. The detection was based on the reduction of BQ generated on the modified substrate by SECM tip. For SECM imaging experiment, we structured the microsensor platform through localized desorption of 1-dodecanethiol monolayer. Approach curves were employed for quantitative detection of DNA concentration. The detection limit of complementary DNA was as low as 0.8pM. This technique is promising for the application on electrochemical DNA chip.

A novel magnetic ordered mesoporous carbon composite was prepared. Electrochemical measurements showed that the ordered mesoporous carbon composite provided an excellent matrix for the co-adsorption of horseradish peroxidase (HRP). HRP could be separated and collected by the application of a magnetic field and its direct electron-transfer could be achieved in the solution, not on the electrode thereby preventing the degradation of the enzyme. The cyclic voltammetric experimental results of HRP indicated that HRP displayed a pair of stable peaks with a formal potential of −0.306 V in PBS. The resulting biosensor exhibited fast amperometric response to hydrogen peroxide.

A highly sensitive electrochemical sensor for the simultaneous determination of SO32− and NO2− based on a glassy carbon electrode (GCE) modified with graphene (GR)-chitosan (CS) and gold nanoparticles (AuNPs) was developed. The GR and GR-CS/AuNPs GCEs were characterized using a transmission electron microscope (TEM). The electrochemical behaviours of SO32−and NO2− at the GR-CS/AuNPs GCE were investigated using cyclic voltammetry (CV). The chemically modified electrode displayed excellent electrochemical catalytic activities towards sulphite and nitrite. Linear relationships between the values of the oxidation peak current and the concentration of SO32−and NO2− were obtained in the ranges of 5 μM to 0.41 mM (R = 0.9986) and 1 μM to 0.38 mM (R = 0.9940) with detection limits (S/N = 3) of 1 μM and 0.25 μM, respectively. This GR-CS/AuNPs GCE showed many advantages in terms of stability, sensitivity, facility and economy. The proposed method was employed to example real samples with recoveries of 97.2% to 102.6%.

Electrochemical DNA biosensor with high sensitivity of homogenous hybridization was fabricated on the basis of host-guest recognition between β-cyclodextrin (β-CD) and m -toluic acid (mTA). β-CD, as the host molecule, was electropolymerized on the poly( N -acetylaniline)-modified glassy carbon electrode, and mTA, was labeled on the probe DNA as the guest through acid-amine condensation reaction. Two intercalators were used as electrochemical indicators to detect DNA hybridization:methylene blue (MB) and daunorubicin (DNM). The electrochemical signals of MB were linear in the range of complementary DNA from 2.0 × 10 −12 M to 2.0 × 10 −10 M with a detection limit of 7.6 × 10 −13 M. The electrochemical response of DNM was linear with the concentrations of complementary from 1 × 10 −12 M to 1 × 10 −9 M with a detection limit of 6.0 × 10 −13 M. This DNA biosensing technique exhibited excellent reproducibility and stability.

A palladium nanoparticle/graphene/chitosan/glassy carbon electrode (PdNPs/GR/CS GCE) was prepared and characterized in this paper. This chemical modified electrode displayed excellent eletrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) compared with bare GCE, PdNPs/GCE and GR/CS GCE by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). All oxidation potentials of AA, DA and UA at the PdNPs/GR/CS GCE shifted negatively and the peak currents were much larger than other electrodes. DPV was used for simultaneous determination of AA, DA and UA in their mixture, and the peak potential separations between AA and DA, DA and UA, AA and UA were 252 mV, 144 mV and 396 mV, respectively. The limits of detection ( S / N = 3) for AA, DA and UA were 20 μM, 0.1 μM and 0.17 μM, respectively. This PdNPs/GR/CS GCE showed many merits in stability, sensitivity, facility and economy.

Little is known about human polyol metabolism, but recent studies indicate that abnormal polyol concentrations in body fluids are related to several diseases. In this study, a rapid and sensitive method for the determination of seven major polyols in urine including two groups of polyol isomers, C5-polyols (Rib+Arb+Xyl) and C6-polyols (Sor+Gal+Man), was developed using capillary zone electrophoresis coupled with amperometric detection (CZE-AD). The effects of the working electrode potential, pH, running buffer components and concentrations, separation voltage and injection times were investigated. Under the optimised conditions, seven types of polyols could be perfectly separated via the formation of anionic polyol-borate complexes in a borate buffer solution. Highly linear current responses to the polyol concentrations were obtained with good correlation (0.9984

The human neuroblastoma SH-SY5Y cell line has been used as a model to study mechanisms of neurotransmitter release. In order to study the mechanism of SH-SY5Y single cell exocytosis stimulated by different stimulants, including high K+ , 3-(1-nitroso-2-pyrrolidinyl) pyridine and nicotine, a type of indium tin oxide (ITO) micro-pore electrode was used to obtain the corresponding amperometric response time. When the cell is stimulated by 0.1 M K+ , almost immediate exocytosis could be detected, due to the rapid depolarization of cell membrane. However, the stimulations with 1 mM nicotine and 3-(1-nitroso-2-pyrrolidinyl) pyridine result in a short delay between stimulation and exocytosis, which can be correlated with the time needed for binding of the stimulant to the nicotinic acetylcholine (ACh) receptor and the induction of post-binding phenomena. Thus, the response time of SH-SY5Y single cell exocytosis is significantly affected by the exocytosis mechanisms.

In this work, a simple and sensitive electrochemical method was developed to determine Sudan I by cyclic voltammetry and differential pulse voltammetry using a glassy carbon electrode modified with a chitosan/carbon nanotube composite. In cyclic voltammetry, Sudan I exhibited a well-defined oxidation peak located at 0.72 V at the multi-walled carbon nanotube (MWCNT)/chitosan-modified GCE. The determination conditions, including pH, scan rate, and chitosan: MWCNT mass ratio at the modified electrode, were optimized. Under the optimum experimental conditions, Sudan I could be linearly detected by differential pulse voltammetry with a detection limit of 3.0 × 10-8 mol?L-1.

A quantitative determination of six neuroactive amino acids (NAAs) was performed by capillary zone electrophoresis with amperometric detection (CZE-AD). This CZE-AD method utilized two electrolytes: the borate solution flowing in a capillary has the NAAs-separation effects, and the sodium hydroxide (NaOH) solution filled in the detection reservoir for the amperometric analysis of NAAs. The following experimental parameters were optimized: the working electrode potential, the pH value, the component, and the concentration of running buffer, the separation voltage, and the injection time on CZE-AD. Then, under the optimum conditions, the six NAAs could be completely separated in 30 min and had well-shaped AD responses at 0.75 V (versus SCE) on a copper electrode. The linear calibration range of NAAs was from 5 × 10−4 to 5 × 10−6 mol L−1 with the limits of detection (LODs) ranging from 10−6 to 10−7 mol L−1 (signal-to-noise ratio = 3), and the relative standard deviations (RSDs) of the migration time and peak area were 0.45–0.55 and 3.8–6.3 %, respectively. Moreover, this method has succeeded in human serum analysis, and the determined contents of the six NAAs in human serum were in an average recovery range of 85.3–117.9 %, which confirmed the validity and practicability of this method.

A simple and sensitive method for determination of free amino acids in milk by microchip electrophoresis (MCE) coupled with laser-induced fluorescence (LIF) detection was developed. Seven kinds of standard amino acids were derivated with sulfoindocyanine succinimidyl ester (Cy5) and then perfectly measured by MCE-LIF within 150 s. The parameters of MCE separation were carefully investigated to obtain the optimal conditions: 100 mmol·L−1 sodium borate solution (pH 10.0) as running buffer solution, 0.8 kV as injection voltage, 2.2 kV as separation voltage etc. The linear range of the detection of amino acids was from 0.01 µmol·L−1 to 1.0 µmol·L−1 and the detection limit was as low as about 1.0 nmol·L−1. This MCE-LIF method was applied to the measurements of free amino acids in actual milk samples and satisfactory experimental results were achieved.

A sensitive electrochemical aptasensor for thrombin detection is presented based on the host-guest recognition technique. In this sensing protocol, a 15 based thrombin aptamer (ab. TBA) was dually labeled with a thiol at its 3′ end and a 4-((4-(dimethylamino)phenyl)azo) benzoic acid (dabcyl) at its 5′ end, respectively, which was previously immobilized on one Au electrode surface by Au S bond and used as the thrombin probe during the protein sensing procedure. One special electrochemical marker was prepared by modifying CdS nanoparticle with β-cyclodextrins (ab. CdS-CDs), which employed as electrochemical signal provider and would conjunct with the thrombin probe modified electrode through the host–guest recognition of CDs to dabcyl. In the absence of thrombin, the probe adopted linear structure to conjunct with CdS-CDs. In present of thrombin, the TBA bond with thrombin and transformed into its special G-quarter structure, which forced CdS-CDs into the solution. Therefore, the target-TBA binding event can be sensitively transduced via detecting the electrochemical oxidation current signal of Cd of CdS nanoparticles in the solution. Using this method, as low as 4.6 pM thrombin had been detected.

Analysis of the neutral sugars of Asparagus officinalis Linn. polysaccharide by different methods has yielded inconsistent results. In the work discussed in this paper, capillary zone electrophoresis with amperometric detection (CZE–AD) was used for analysis of neutral sugars in A. officinalis Linn. polysaccharide. The configuration of the wall-jet and the diameter of the copper disk electrode were investigated to achieve optimized detection sensitivity. The separation electrolyte, separation voltage, and injection time were studied for their effects on CZE separation. Under the optimum CZE–AD conditions, seven monosaccharides were separated to baseline by using 120 mM NaOH as separation electrolyte. Linear response was excellent and repeatability was satisfactory. It was found that Asparagus polysaccharide was composed of fucose, galactose, glucose, rhamnose, arabinose, fructose, and xylose at a mole ratio of 0.2:16.2:5.0:1.0:15.5:0.6:18.8. Compared with other methods, analysis of the composition of Asparagus polysaccharide by CZE–AD had the merits of rapidness, accuracy, and lower sampling volume.

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.

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.

Zero-valent iron particles were prepared by wet reduction chemistry assisted with ultrasonic treatment. Such prepared particles have uniform size, exhibit crystalline structure and show strong pararnagnetic property. Their surface modification by coating poly（N-vinyl-2-pyrrolidone） （PVP） was investigated. The resulting Fe（0）-PVP particles were monodispersed and possessed enhancing magnetization saturation. Those synthesis conditions to control the particle size and distribution were exploited.

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.

An on-line two-dimension microflow liquid chromatography was developed for better separation and analysis of the highly complex ingredients of medicinal preparation of traditional Chinese medicine Coptis Chinensis Franch. A two-valve switching system was utilized for two-dimension chromatography with strong cation exchange and reverse-phase capillary columns separation. The components were separated well by this system and yielded over 420 peaks. Under the optimal condition, 4 compounds were detected quantitatively. A good linear relationship was obtained from 0.2 µg mL−1 to 24 µg mL−1with detection limits (S/N = 3) ranging from 0.05 µg mL−1 to 0.2 µg mL−1for the compounds. We demonstrated that the method can be successfully applied to the analysis of a natural complex sample, with satisfactory results.

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.

Cholesterol oxidase biosensor has been constructed by using bovine serum albumin and glutaraldehyde as cross linker to immobilize cholesterol oxidase and cholesterol esterase on a glassy carbon electrode modified with Nafion and methyl viologen. The biosensor has been used to determine total cholesterol in blood. The linear range of the determination is 2.5×10−7 to 1.0×10−4 mol/L. The detection limit is about 5.0×10−8 mol/L. The response time is 12 s. This biosensor has the advantage of high selectivity, sensitivity and short response time.

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 form of single-strand DNA-conformation polymorphism analysis (SSCP) employing nondenaturing slab gel electrophoresis is applicable to the genetic diagnosis of mutations at exons 7, 8 and 9 of the p53 gene. Recently, microchip electrophoresis (ME) systems have been used in SSCP analysis instead of conventional slab gel electrophoresis in terms of speed, sensitivity and automation. The aim of the present study was to investigate the application of SSCP and ME analysis as a rapid and effective method to the detection of mutations for exons 7, 8 and 9 of the p53 gene. It was found that using the electric field strength 260 V/cm and the sieving matrix of 4 mg/mL poly(ethylene oxide) was very useful to achieve better resolution and fast detection of mutations at exons 7, 8 and 9 of p53 gene. Under the optimized conditions, mutations at exons 7–9 of p53 gene were analyzed within 60 s and the relative standard deviation values of the migration times were less than 5.81% (n=5). The detection limit can be as low as 1 ng·L−1.

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.

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.