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The accurate, simple and sensitive detection of bacterial infections at the early stage is highly valuable in preventing the spread of disease. Recently, CRISPR-Cas12a enzyme-derived nucleic acid detection methods have emerged along with the discovery of the indiscriminate single-stranded DNA (ssDNA) cleavage activity of Cas12a. These nucleic acid detection methods are made effective and sensitive by combining them with isothermal amplification technologies. However, most of the proposed CRISPR-Cas12a strategies involve Cas-crRNA complexes in the preassembled mode, which result in inevitable nonspecific background signals. Besides, the signal ssDNA used in these strategies needs tedious pre-labeling of the signal molecules. Herein, a post-assembly CRISPR-Cas12a method has been proposed based on target-induced transcription amplification and real-time crRNA generation for bacterial 16S rDNA biosensing. This strategy is label-free through the combination of microchip electrophoresis (MCE) detection. In addition, this method eliminates the need for a protospacer adjacent motif (PAM) on the target sequences, and has the potential to be an effective and simple method for nucleic acid detection and infectious disease diagnosis.

Extracellular pH can indicate the variation in organelle function and cell state. It is important to measure extracellular pH (pHe) with a controllable distance. In this work, a potentiometric SECM dual-microelectrode was developed to monitor the pHe of MCF-7 cells under electrical stimulation. The distance between the dual-microelectrode and the cells was determined first with a gold microelectrode by recording the approaching curve, and the pH was determined using an open-circuit potential (OCP) technique with a polyaniline-modified Pt microelectrode. The pH microelectrode showed a response slope of 53.0 ± 0.4 mV/pH and good reversibility from pH 4 to pH 8, fast response within 10 s, and a potential drift of 1.13% for 3 h, and thus was employed to monitor the pHe of stimulated cells. The value of pHe decreased with the decrease in the distance to cells, likely due to the release of H+. With an increase in the stimulation potential or time, the pHe value decreased, as the cell membrane became more permeable, which was verified by fluorescence staining of calcein-AM/PI (propidium iodide). Based on these results, this method can be widely applied for determining the species released by biosystems at a controllable position.

A programmable multitarget-response electrochemical imaging technique was presented using scanning electrochemical microscopy (SECM) combined with a self-designed waveform. The potential waveform applied to the tip decreased the charging current caused by the potential switch, enhancing the signal-to-noise ratio. This programmable SECM (P-SECM) method was used to scan a metal strip for verifying its feasibility in feedback mode. Since it could achieve simultaneous multitarget imaging during one single imaging process, PC12 cells status was imaged and identified through three different molecules (FcMeOH, Ru(NH

A novel electrochemical DNA (E-DNA) biosensing strategy was designed and used for the detection of breast cancer susceptibility gene (BRCA-1). The biosensor was based on gold nanoparticles-reduced graphene oxide (AuNPs-GO) modified glass carbon electrode (GCE) covered with the layer of molecularly imprinted polymers (MIPs) synthesized with rhodamine B (RhB) as template, methacrylic acid (MAA) as the monomer, and Nafion as additive. The signal amplification tracing tag SiO2@Ag NPs were prepared by covering AgNPs on the surface of SiO2 nanoparticles in situ, and then DNA probes were modified on AgNPs by Ag-S bond, forming the composites SiO2@Ag/DNA. In presence of target DNA (T-DNA), homogeneous hybridization was performed with SiO2@Ag/DNA and RhB labeled DNA, and the resulting SiO2@Ag/dsDNA/RhB was specifically recognized by MIPs via the interaction between imprinting cavities and RhB. Under optimal conditions, the proposed biosensor exhibited wide linear range from 10 fM to 100 nM, low detection limit of 2.53 fM (S/N = 3), excellent selectivity, reproducibility, stability, and feasibility in serum analysis. Overall, these findings suggest the promising prospects of the proposed biosensing strategy in clinical diagnostics.

A simple, economical, and sensitive capillary electrophoresis (CE) method integrated with capacitively coupled contactless conductivity detection was developed for the determination of metal ions such as K+, Na+, Mg2+, Sr2+, Ca2+ in drinking water. 18-Crown-6 ether and Hexadecyltrimethylammonium Bromide (CTAB) were employed as complexing reagents. The effects of electrolyte additives, citric acid buffer solution, and other separation conditions of CE were comprehensively investigated and carefully optimized. The best results were obtained in a running buffer solution composed of citric acid (12 mM), 18-crown-6 ether (0.2 mM), and CTAB (0.015 mM) at pH 3.5. Under these conditions, a complete separation of five metal ions was successfully achieved in less than 12 min. The limits of detection for the optimal procedure were determined to be in the range of 0.02 - 0.2 mg·L-1. The repeatability with respect to migration times and peak areas, expressed as relative standard deviations, was better than 2.3% and 5.1%, respectively. Evaluation of the efficiency of the methodology indicated that it was reliable for the determination of metal ions in six different brands of drinking water samples.

Rapid, sensitive, and accurate DNA detection is of great significance to meet the growing demand of disease diagnostics. Herein, an ultrasensitive and highly specific electrochemical sensing strategy for detection of hepatitis B virus (HBV) DNA hybridization in homogeneous solution was presented. In this sensing protocol, magnetic nanoparticles (MNPs) were prepared and modified with β-CD. MNPs/β-CD were then used for host–guest recognition, separation and detection. In the experiment, a stem-loop structured DNA was designed as the probe to indicate the occurrence of hybridization. It was labeled with dabcyl at the 5′-end as a guest molecule and Au nanoparticles at the 3′-end as an electrochemical tag. Initially, the DNA probe retained the stem-loop configuration, which shielded dabcyl from docking with β-CD/MNP in solution due to the steric effect. While in the presence of the complementary target DNA, the stem-loop structure of the probe was dissociated and the double-stranded DNA (dsDNA) was formed as a result of the hybridization. Consequently, dsDNA was linked to β-CD/MNP owing to the host–guest recognition between β-CD and dabcyl. Thus, the hybridization events could be sensitively transduced to electrochemical signals provided by Au nanoparticles. Au nanoparticles were then captured by the electrode through an external magnetic field. The designed sensor favored discrimination between the healthy and single-nucleotide polymorphism (SNP)-containing sequences. Under the optimized detection conditions, the sensing strategy showed high sensitivity and the detection limit was down to 9.930 × 10−13 M for a complementary HBV DNA sequence.

Plasmonic nanoparticles have been widely applied in cell imaging, disease diagnosis, and photothermal therapy owing to their unique scattering and absorption spectra based on localized surface plasmon resonance (LSPR) property. Recently, it is still a big challenge to study the detailed scattering properties of single plasmonic nanoparticles in living cells and tissues, which have dynamic and complicated environment. The conventional approach for measuring the scattering light is based on a spectrograph coupled to dark-field microscopy (DFM), which is time-consuming and limited by the small sample capacity. Alternatively, RGB-based method is promising in high-throughput analysis of single plasmonic nanoparticles in dark-field images, but the limitation in recognition of nanoparticles hinders its application for intracellular analysis. In this paper, we developed an automatic and robust method for recognizing the plasmonic nanoparticles in dark-field image for RGB-based analysis. The method involves a bias-modified fuzzy C-means algorithm, through which biased illumination in the image could be eliminated. Thus, nearly all of the gold nanoparticles in the recorded image were recognized both on glass slide and in living cells. As confirmed, the distribution of peak wavelength obtained by our method is well agreed to the result measured by conventional method. Furthermore, we demonstrated that our method is profound in cell imaging studies, where its advantages in fast and high-throughput analysis of the plasmonic nanoparticles could be applied to confirm the presence and location of important biological molecules and provide efficiency information for cancer drug selection.

A novel electrochemical DNA (E-DNA) biosensing strategy was designed and used for the detection of breast cancer susceptibility gene (BRCA-1). The biosensor was based on gold nanoparticles-reduced graphene oxide (AuNPs-GO) modified glass carbon electrode (GCE) covered with the layer of molecularly imprinted polymers (MIPs) synthesized with rhodamine B (RhB) as template, methacrylic acid (MAA) as the monomer, and Nafion as additive. The signal amplification tracing tag SiO

Direct current glow discharge mass spectrometry (dc-GD-MS) was applied for the determination of doping elements in synthetic crystals. To get stable discharge, the surface coating method and tantalum carrier method were used to support the sputtering and ionization of samples respectively. For the analysis of BaF2, Y3Al5O12 (YAG), Bi4Si3O12 (BSO), La3Ga5SiO14 (LGS), CsI and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), the stable discharge current and the matrix signals were investigated by using these two methods. While for the analysis of CaF2 and γ-Al2O3, the tantalum carrier method could sustain much stable discharge to achieve fine intensity of matrix elements compared to the surface coating method. Furthermore, two Y3Al5O12 (YAG) samples were also studied by inductively coupled plasma optical emission spectrometer (ICP-AES) to validate the precision, accuracy and reproducibility of these two methods. The results suggested that the dc-GD-MS would be a good choice to determine the doping elements in synthetic crystals by these two methods.

Exosomes, lipid bilayer membrane vesicles, can guide various pathological and physiological processes. However, reliable, convenient and sensitive methods for exosome determination for early cancer diagnosis are still technically challenging. Herein, an electrochemical aptasensor based on click chemistry and the DNA hybridization chain reaction (HCR) for signal amplification has been developed for the ultrasensitive detection of tumor exosomes. CD63 aptamer was first immobilized on a glassy carbon electrode for capturing exosomes, and 4-oxo-2-nonenal alkyne (alkynyl-4-ONE) molecules, functionalized lipid electrophiles, were conjugated to the exosomes via the reaction of amino and aldehyde groups. Azide-labeled DNA probe as an anchor was then connected to the exosomes by copper (I)-catalyzed click chemistry. Signal amplification was achieved by HCR, and the numerous linked horseradish peroxidase (HRP) molecules could catalyze the reaction of o-phenylenediamine (OPD) and H2O2. The concentration of exosomes could be quantified by monitoring the electrochemical reduction current of 2,3-diaminophenazine (DAP). Under the optimal conditions, this method allowed the sensitive detection of exosomes in the range of 1.12 × 102 to 1.12 × 108 particles/μL with a limit of detection (LOD) of 96 particles/μL. Furthermore, the present assay enabled sensitive and accurate quantification of exosomes in human serum, and it has high potential for exosome analysis in clinical samples.

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.

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 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.

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

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.

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

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.

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

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 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 thionine modified aligned carbon nanotubes (ACNTs) electrode was fabricated and was used to electrochemically determine nitrite. The thionine modified ACNTs electrode exhibited enhanced electrocatalytic behavior to the oxidation of nitrite. The electrochemical mechanism of the thionine/ACNTs electrode towards the oxidation of nitrite was discussed. The thionine modified ACNTs electrode exhibited fast response towards nitrite with a detection limit of 1.12 × 10−6 mol L−1 and a linear range of 3 × 10−6 – 5 × 10−4 mol L−1. The proposed method was successfully applied in the detection of nitrite in real samples. Keywords: Thionine, Aligned carbon nanotubes, Nitrite, Modified electrode, Electrocatalytic oxidation

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L(-1) phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L(-1)) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4 x 10(-2) to 2.2 microg mL(-1) for LDME, 2.9 x 10(-1) to 49.5 microg mL(-1) for L-DOPA, and 1.4 x 10(-2) to 1.5 microg mL(-1) for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL(-1), respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.

The electrochemical reduction mechanism of ethidium bromide was first studied by spectroelectrochemistry. This reduction was proved to be a two-step process by cyclic voltammetry, differential pulse voltammetry and spectroelectrochemistry, in which each step was proved to be a one-electron transfer process by a spectropotentiostatic fluorescence technique. Hydroethidine was confirmed to be the final product by comparing the spectrum of the product of the electrochemical reduction to that of the product of the chemical reduction of ethidium bromide, and a carbon-centered radical was concluded to be a reasonable intermediate product during the electrochemical reduction of ethidium bromide.

A magnetic metal organic framework (MOF) composite was prepared. The composite was fabricated by incorporation of Fe3O4 nanoparticals with MOF. It was characterized and expected to offer a promising template for molecular immobilization and sensor fabrication because of its ordered structure and satisfying large specific surface area. The resulting composite was used to detect methyl parathion. Electrochemical measurements showed that the multifunctional composite of MOF provided an excellent matrix for the co-adsorption of methyl parathion. Owing to the ordered structure, the large surface area, excellent compatibility and magnetic property of the material, methyl parathion could be separated, accumulated and directly detected in the solution with high sensitivity. The differential pulse voltammetry (DPV) response was proportional to the concentration range from 5.00 × 10(-6) to 5.00 × 10(-3) g L(-1) with the detection limit of 3.02 × 10(-6) g L(-1). The experimental results can lead to a widespread use of electrochemical sensors to detect organophosphorous pesticides contaminates and other substances.

A family of metallocyclodextrins bearing one, two, three or six β-cyclodextrin binding sites on their ligands have been synthesised, and their structures were confirmed by 1H NMR, 13C NMR, MALDI-TOF MS, UV–vis spectroscopy and elemental analysis. Comparative investigation of the luminescent properties of these metallocyclodextrins found that 6CD-Ru showed the strongest fluorescence intensity. The fluorescence quantum yield results show that 6CD-Ru exhibits the highest emission efficiency, as we expected. To gain insight into the binding properties of the most promising metallocyclodextrin 6CD-Ru, two guest compounds 4-dimethylaminoazobenzene-4′-carboxylic acid (Dab) and methylene blue (MB) were used as analytes. 6CD-Ru exhibited remarkable emission quenching compared with the reference compound CD-Ru. Furthermore, calculated binding constants demonstrated that 6CD-Ru has enhanced binding capacity due to the presence of multiple β-cyclodextrin binding sites. These prominent characteristics of 6CD-Ru suggest that it may be used to detect the two guests Dab and MB, and their analogues, with greater sensitivity, and the relevant research with these metallocyclodextrins is in progress in our group.

An ultrasensitive label-free electrochemiluminescence (ECL) aptasensor for the detection of thrombin was developed based on the specific recognition between tris(bipyridine)ruthenium(II)-β-cyclodextrin (tris(bpyRu)-β-CD) and the anti-thrombin aptamer (aptamer). The NH2-aptamer was first immobilized on the activated glassy carbon electrode (GCE) by coupling interaction. By use of the specific recognition between tris(bpyRu)-β-CD and aptamer, tris(bpyRu)-β-CD was then attached on the surface of GCE. Resulting from the outstanding photoactive properties of tris(bpyRu)-β-CD, the fabricated GCE performed strong ECL signal with the coreactant of 2-(dibutylamino)ethanol (DBAE). However, in the presence of thrombin, aptamer-thrombin bioaffinity complexes were formed, which restricted the recognition activities between aptamer and tris(bpyRu)-β-CD. Thus, fewer tris(bpyRu)-β-CD could be attached on the surface of GCE and led to an obvious decrease of ECL signal. Fortunately, the difference of ECL intensity before and after combination with thrombin was logarithmically linear with the concentration of thrombin in a wide range of 10 nM-1 pM. Meantime, a detection limit of 0.1 pM without any other signal labeling or amplifying procedures indicated that the biosensor performed excellent sensitivity, operability and simplicity.

An enzyme-based solid-state electrochemiluminescence (ECL) sensing platform for sensitive detection of a single point mutation is developed successfully using p53 tumor suppressor gene as a model analyte. A composite of multiwalled carbon nanotubes and Ruthenium (II) tris-(bipyridine) (MWNTs–Ru(bpy)32+) was prepared and coated on an electrode surface, which was covered by polypyrrole (PPy) to immobilize ssDNA. Then, the ssDNA recognized the gold nanoparticle (AuNP)-labeled p53 tumor suppressor gene, and produced AuNP-dsDNA electrode with AuNP layer. The surface adsorbed the glucose-dehydrogenase (GDH) molecules for producing ECL signal. This system combined enzyme reaction with ECL detection, and it can recognize sequence-specific wild type p53 sequence (wtp53) and muted type p53 sequence (mtp53) with discrimination of up to 56.3%. The analytic results were sensitive and specific. It holds promise for the diagnosis and management of cancer.

In this paper, we report a new strategy for electrochemical DNA detection in homogeneous solution based on the host-guest molecule recognition technique. In this sensing protocol, a novel dually labeled DNA probe (DLP) in a stem-loop structure was employed, which was designed with dabcyl labeled at one end as a guest molecule, and with Au nanoparticle labeled at the other end as electrochemical tag to indicate the hybridization occurrence. One α-CD/MCNTs/GCE was used for capturing the DNA hybridization and electrochemical signal transduction. Before the hybridization, the DLP remained in the stem-loop structure, which forced the dabcyl molecular to be closed to the Au nanoparticle. Due to the steric effect of the Au nanoparticle, the dabcyl was prevented from conjugating with the α-CD on the electrode and resulting in that the DLP could not be captured by the electrode. After hybridized with the target DNA, the target-binding DLP caused the DLP's loop-stem structure opened and then the dabcyl molecule was easily entering the cavity of the α-CD modified electrode and resulting in that the DLP could be captured by the α-CD modified electrode and the capture efficiency was proportion with the concentration of the target DNA. Therefore, the target hybridization event can be sensitively transduced via detecting the electrochemical reduction current signal of AuCl(4)(-) of Au nanoparticles labeled at the DLP. Using this strategy, as low as 2.6×10(-10) M DNA target had been detected with excellent differentiation ability for even single mismatch.

A new method has been developed for the simultaneous determination of diflubenzuron and triflumuron residues in greasy wool by reversed-phase high performance liquid chromatography (HPLC). The pesticides were extracted by hexane-ether from greasy wool and cleaned up with gel permeation chromatography (GPC) and solid phase extraction (SPE). The pesticides were analyzed by HPLC-diode array detector (DAD) and quantified by external standard method. The linear ranges of diflubenzuron and triflumuron were 0.41 -41 mg/L and 0.38 - 38 mg/L, and the correlation coefficients were 0.999 6 and 0.999 9, respectively. The limits of detection were 0.22 mg/kg for diflubenzuron and 0.18 mg/kg for triflumuron; the limits of quantification were 0.73 mg/kg for diflubenzuron and 0.60 mg/kg for triflumuron. The average recoveries of pesticides spiked levels from 0.76 to 10.25 mg/kg in greasy wool samples were in the range of 86.3% - 96.7%, and the relative standard deviations were 4.2% - 8.7%. The method developed shows little interferences, good recovery and repeatability. It is suitable for the simultaneous determination of diflubenzuron and triflumuron in greasy wool samples.

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE-AD). 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 five analytes could be perfectly separated in 0.30 mol L(-1) borate-0.40 mol L(-1) phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10(-6) to 1.0 × 10(-4) mol L(-1) and the detection limits were as low as 10(-7) mol L(-1) (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0-108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples.

A simple and rapid capillary electrophoresis (CE) with electrcochemical detection (ED) method has been established for the simultaneous determination of seven active ingredients in the stems and roots of Gaultheria leucocarpa var. yunnanensis and its medicinal preparation, including (+)-catechin, rutin, gentisic acid, vallinic acid, salicylic acid, quercetin, and protocatechuic acid. The effects of working potential, pH, and concentration of running buffer, separation voltage, and injection time on CE‐ED are systematically investigated. Under the optimum conditions, the seven analytes could be completely separated within 23 min in a borax running buffer (pH 8.7). A good linear relationship is obtained over three orders of magnitude with detection limits (signal-to-noise ratio = 3) ranging from 5 ◊ 10 ‐8 g/mL to 3 ◊ 10‐7 g/mL for the analytes. The proposed method is successfully used in the analysis of real samples after a relatively simple extraction procedure, and the assay results are satisfactory.

An ultrasensitive and highly specific electrochemical aptasensor for detection of thrombin based on gold nanoparticles and thiocyanuric acid is presented. For this proposed aptasensor, aptamerI was immobilized on the magnetic nanoparticles, aptamerII was labeled with gold nanoparticles. The magnetic nanoparticle was used for separation and collection, and gold nanoparticle offered excellent electrochemical signal transduction. Through the specific recognition for thrombin, a sandwich format of magnetic nanoparticle/thrombin/gold nanoparticle was fabricated, and the signal amplification was further implemented by forming network-like thiocyanuric acid/gold nanoparticles. A significant sensitivity enhancement had been obtained, and the detection limit was down to 7.82 aM. The presence of other proteins such as BSA and lysozyme did not affect the detection of thrombin, which indicates a high specificity of thrombin detection could be achieved. This electrochemical aptasensor is expected to have wide applications in protein monitoring and disease diagnosis.

Synthesis of the novel Cu@Au alloy nanoparticle and its application in an electrochemical DNA hybridization detection assay is described in this article. We report a low-temperature method for generating core-shell particles consisting of a core of Cu and a thin layer of Au shell that can be readily functionalized with oligonucleotides. Core-shell Cu@Au particles were successfully labeled to a 5′-alkanethiol capped oligonucleotides probe that is related to the colitoxin gene. The DNA genetic sensing assay relies on the electrostatic adsorption of target oligonucleotides onto conducting polypyrrole (PPy) surface at the glassy carbon electrode (GCE), and its hybridization to the alloy particle–oligonucleotides DNA probe. Hybridization events between probe and target were monitored by the release of the copper metal atoms anchored on the hybrids by oxidative metal dissolution and the indirectly determination of the solubilized Cu 2+ ions by sensitive anodic stripping voltammetry (ASV). The detection limit is 5.0 pmol l −1 of target oligonucleotides. The Cu@Au core-shell nanoparticles combining the surface modification properties of Au with the good electrochemical activity of Cu core shows their perspective application in the electrochemical DNA hybridization analysis assay.

A novel and sensitive electrochemical DNA biosensor based on multi-walled carbon nanotubes functionalized with a carboxylic acid group (MWNTs-COOH) for covalent DNA immobilization and enhanced hybridization detection is described. The MWNTs-COOH-modified glassy carbon electrode (GCE) was fabricated and oligonucleotides with the 5'-amino group were covalently bonded to the carboxyl group of carbon nanotubes. The hybridization reaction on the electrode was monitored by differential pulse voltammetry (DPV) analysis using an electroactive intercalator daunomycin as an indicator. Compared with previous DNA sensors with oligonucleotides directly incorporated on carbon electrodes, this carbon nanotube-based assay with its large surface area and good charge-transport characteristics dramatically increased DNA attachment quantity and complementary DNA detection sensitivity. This is the first application of carbon nanotubes to the fabrication of an electrochemical DNA biosensor with a favorable performance for the rapid detection of specific hybridization.

Aligned carbon nanotubes (ACNTs) were modified with polypyrrole (PPy) via electropolymerization. Because of the large specific surface area and excellent electrical conductivity of ACNTs, continuous electropolymerization was able to be carried out, forming a thick PPy coating on the ACNTs. The resulting nanocomposite possessed a core-shell structure with ACNTs as the core, PPy as the shell, and nanoparticles of PPy on the top, and displayed high performance supercapacitance properties.