Search

Microchip electrophoresis (MCE) is particularly attractive as it provides high sensitivity and selectivity, short analysis time and low sample consumption. An on-line preconcentration strategy combining field-amplified stacking (FASS) and reversed-field stacking (RFS) was developed for efficient and sensitive analysis of neurotransmitters in real urine samples by MCE with laser induced fluorescence (LIF) detection. In this study, the multiple-preconcentration strategy greatly improves the sensitivity enhancement and surpass other conventional analytical methods for neurotransmitters detection. Under optimal conditions, the separation of three neurotransmitters (dopamine, norepinephrine and serotonin), was achieved within 3min with limits of detection (S/N=3) of 1.69, 2.35, and 2.73nM, respectively. The detection sensitivities were improved by 201-, 182-, and 292-fold enhancement, for the three neurotransmitters respectively. Other evaluation parameters such as linear correlation coefficients were considered as satisfactory. A real urine sample was analyzed with recoveries of 101.8-106.4%. The proposed FASS-RFS-MCE method was characterized in terms of precision, linearity, accuracy and successfully applied for rapid and sensitive determination of three neurotransmitters in human urine.

In this work, a recyclable electrochemical sensing platform to detect breast cancer susceptibility gene (BRCA) was constructed by pillararenes based host–guest recognition and homogeneous DNA hybridization. BRCA target DNA (T-DNA) formed sandwich-type DNA via homogeneous hybridization with methylene blue labeled signal DNA and alkylamino modified capture DNA, which could form complexes with pillararenes. Such sandwich-type DNA was captured by a novel trithiocarbonate modified pillar[5]arene (P5A-CTA) which was immobilized on the Au electrode. With the help of enzyme amplification, the electrochemical detection signal of target DNA in sensing platform was apparently amplified. This sensing platform exhibited wide linear range and excellent specificity, and was particularly recyclable after simple washing with hot acetonitrile due to the reversible host–guest complexation between P5A-CTA and alkylamino modified DNA.

A novel label-free electrochemical strategy was designed for multi-sites recognizing the guanine-rich DNA (G-rich DNA) with surface molecular imprinting polymer composite, in which the multi-walled carbon nanotubes (MWNCTs) were regarded as supporting material and the molecularly imprinted polymer (MIP) with guanine sites of DNA was applied as recognition element. Firstly, the vinyl groups were grafted onto the surface of carboxylic acid-functionalized MWNCTs (MWCNTs-COOH) through chemical modification. Then, the composite of MWCNTs-MIP was fabricated by the selective copolymerization of methacrylic acid, ethylene glycol dimethacrylate and guanine on the vinyl group-functionalized MWNTs surface. MWCNTs-MIP was characterized by different techniques, including Fourier transform infrared (FTIR) spectroscopy, scanning electronic microscopy (SEM), cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS), showing that the MWCNTs-MIP composite was successfully prepared. Under the optimized conditions, the imprinting factor was nearly 5.68 according to the comparative slopes obtained on MWCNT-MIP and MWCNTs-non-imprinted polymer (MWCNTs-NIP), indicating that MWCNTs-MIP exhibited high selectivity for G-rich DNA. Moreover, the MWCNTs-MIP composite had a relatively wide linear range over G-rich DNA concentration of 0.05–1 μM and 5–30 μM with a detection limit of 7.52 nM (S/N = 3). Furthermore, the novel electrochemical strategy based on imprinted composite has very excellent performance in real samples of human serum and human urine.

The long DNA concatemers have been well developed to fabricate various biosensing platforms for the signal amplification. Herein, this signal amplification strategy was firstly used for an ultrasensitive scanning electrochemical microscopy (SECM)-based DNA biosensing platform. This platform was constructed through the hybridization of target DNA (TD) with thiol-tethered DNA capture probes (CP), immobilized on the gold substrate surface, and biotinylated DNA signal probes (SP), which formed then the long DNA concatemers through the continuous self-assembly with alternating DNA auxiliary probes (AP). The streptavidin-horseradish peroxidase (HRP) was linked to the long DNA concatemers through biotin-streptavidin interaction. In the HRP-catalyzed reaction, hydroquinone (H 2 Q) was oxidized to benzoquinone (BQ) with H 2 O 2 at the modified substrate surface where sequence-specific hybridization had occurred, and the BQ generated could be monitored by a SECM tip. This platform exhibited a low detection limit of 0.18 aM estimated by the 3σ rule. Combined with DNA microarrays, four kinds of TDs (100 fM) as the models were detected simultaneously by using this proposed strategy, which also demonstrated sufficient selectivity to distinguish specific DNA sequences and good reproducibility. This method opens a promising direction to improve the SECM sensitivity for high-throughput DNA detection.

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.

A novel Congo red (CR) derivatized silica stationary phase was prepared and packed into a fused silica capillary tube for nano-flow HPLC. A variety of analytes including poly-aromatic hydrocarbons, parabens, acids, sulfonamides, bases, and nucleosides were successfully separated using the CR. In comparison with commercial ODS columns, this new stationary phase has a different separation mechanism (hydrophobically-assisted ion-exchange), which was evident in the separation of benzoic acid derivatives and sulfonamides. The successful application of CR-bonded silica stationary phase in the HILIC and PALC modes demonstrates the effectiveness of this potential chromatographic material in nano flow HPLC.

Probe-lengthening amplification (PLA) is a target-specific nucleic acid amplification method that realizes good selectivity by effectively avoiding nonspecific amplification. Here, we propose a probe-lengthening amplification-assisted microchip electrophoresis (MCE) strategy for sensitive analysis of 16S rRNA genes of five bacteria. In this assay, four specific short probes were designed for a target bacterium to recognize its bacterial 16S rRNA gene, integrated into longer DNA ligation duplexes using Ampligase, and subsequently separated and detected by MCE. Along with the rapid generation of ligation duplexes, this approach provides exponential amplification of nucleic acid signals that are useful for sensitive bacterial quantification. Through tactfully combining PLA and MCE, the detection sensitivity of bacterial genes was significantly improved, and a limit of detection (LOD) of 30 fM was realized for the artificial target DNA. This approach was also applied to detect actual bacterial genomic samples with excellent results, demonstrating the potential application of this methodology in infection diagnosis.

A novel potentiometric aptasensor array based on a 4-channel screen-printed carbon electrode was developed with a dual-internal calibration system for the simultaneous detection of streptomycin and kanamycin. Two channels were used as working channels for assembling the aptamers of the two targets, and the other two channels acted as calibration channels. The calibration channels functioned by immobilizing two all-A sequences were employed to subtract the influence from the background matrix and further improve the detection accuracy. Consequently, under optimal conditions, this aptasensor array showed high sensitivity for the detection of streptomycin and kanamycin with detection limits of 9.66 pM and 5.24 pM, respectively, and corresponding linear response ranges of 10 pM–10 μM and 10 pM–1 μM, respectively. Moreover, it presented high specificity without mutual interference between the two targets or with other antibiotics and also demonstrated good repeatability. This aptasensor array was further applied to the simultaneous detection of streptomycin and kanamycin in real milk samples, and the results were validated by liquid chromatography-mass spectrometry (LC–MS). The results demonstrated satisfactory accuracy and precision and showed the great application potential of the aptasensor array with internal calibration for on-site detection of multiple targets.

Amyloid-β oligomers (AβOs) are highly toxic species involved in Alzheimer's disease (AD). Hence, a reliable detection method for AβOs, which are promising potential therapeutic targets and biomarkers for AD, is of great significance for improving the diagnosis of AD. Herein, a novel sandwich assay electrochemical biosensor was developed for highly sensitive and selective detection of AβO, using molecularly imprinted polymers (MIPs) and aptamer as the recognition element. Instead of using an antibody to recognize the AβO target molecules, the AβO in the samples were captured by the film of MIPs and the AβO-specific aptamer, forming a MIPs/target/aptamer sandwich assay for the highly selective detection of AβO. The AβO-specific aptamer was immobilized on the surface of core-shell nanoparticles that combined silver nanoparticles with silica nanoparticles (SiO2@Ag NPs). The highly sensitive electrochemical signal from the sandwich assay was generated by using a small amount of AβO to trigger a large number of electrochemically active Ag NPs. Under the optimized conditions, the developed biosensor showed good linearity in the concentration range of 5 pg mL−1 to 10 ng mL−1 with a limit of detection of 1.22 pg mL−1. The biosensor also showed excellent specificity, reproducibility and stability. In addition, the feasibility of detecting AβO in human serum was successfully verified, demonstrating the promising potential of this approach for clinical research and the early diagnosis of AD.

Exosomes (30–150 nm) secreted by cells play an important role in intercellular communication. Herein, a novel double imprinting-based electrochemical method has been developed for analyzing the particle size distribution (PSD) of mimetic exosomes – a mixture of SiO2@HRP with the diameters in 50 nm, 100 nm and 150 nm at a ratio similar to the exosomes. Double imprinting polymers (DIP) were synthesized with SiO2@HRP at different sizes as template, providing the both recognition of size and morphology. With the capture of the target and the binding of the signal amplification tag – SiO2@Ag/MPBA on the DIP film, a sandwich structure was constructed on Au NPs-GO modified glassy carbon electrode. Under the optimal conditions, the DIP film exhibits the linear correlations between the current intensity and the logarithmic concentration of SiO2@HRP as ΔI50 = −1.52 + 0.50 × lgc50 (2.89 × 104–2.89 × 109 particles/mL), ΔI100 = −1.61 + 0.48 × lgc100 (2.89 × 104–2.89 × 109 particles/mL) and ΔI150 = −1.54 + 0.49 × lgc150 (5.75 × 104–5.75 × 109 particles/mL) with the limit of detection of 1.44 × 103 particles/mL, 5.68 × 102 particles/mL and 7.70 × 102 particles/mL, respectively. Furthermore, the DIP film was applied to the PSD analysis of mimetic exosomes – SiO2@HRP at mixed sizes with a ratio of 50 nm:100 nm:150 nm = 5.0%:42.5%:52.5% detected by nanoparticle tracking analysis (NTA), obtaining a similar result of 50 nm:100 nm:150 nm = 3.6%:43.0%:53.4% with small relative concentration errors. It also exhibited excellent reproducibility and stability. This double imprinting-based method shows high potential in the separation and detection of complex biosamples.

The specific and sensitive detection of multiple pathogens is critical for the prevention and identification of health- and safety-related problems. A microchip electrophoresis/LED-induced fluorescence (MCE-LIF) method, combining an aptamer-based probe and a novel universal primer-duplex polymerase chain reaction (PCR) process (UP-DPCR), was designed to simultaneously detect two kinds of bacteria. The probe consists of a recognition unit (aptamer) for specifically capturing bacterial cells and eventually releasing complementary DNAs (C1 and C2). The two released DNA strands (C1 and C2) can be simultaneously amplified by a pair of universal primers, because of the identical sequences designed at both ends of the two DNA strands. The UP-DPCR products of C1 and C2 can be separated and detected by MCE-LIF, and the heights of the two peaks are correlated with the concentrations of the corresponding bacteria. Here, Salmonella enterica serovar Typhimurium (S. Typhimurium) and Pseudomonas aeruginosa (P. aeruginosa) were detected as a proof of concept. Under optimal conditions, the limits of detection (S/N = 3) were 15 CFU mL−1 for S. Typhimurium and 5 CFU mL−1 for P. aeruginosa. This approach was also applied for detecting these two types of bacteria in defatted milk, indicating its potential application in the analysis of real samples. This method can not only simultaneously detect two kinds of bacteria without lysing the bacterial cells, but also simplify duplex PCR with the use of universal primers.

Because foodborne pathogenic bacteria are in a great variety and may cause many infectious diseases even at low concentrations, a highly sensitive and selective method has long-been desired for bacteria detection. In this study, a microchip electrophoretic method for biosensing E. coli O157:H7 was developed by using E. coli O157:H7 aptamer (apt-E) for specific bacteria recognition together with aptamer-induced catalysed hairpin assembly (CHA) for significantly improving the sensitivity of bacteria detection. Briefly, three nucleic acid strands (apt-E, hairpin H1, and H2) were used in the CHA amplification. Because different quantities of H1/H2 complexes were formed due to the circle amplification induced with different amounts of apt-E and the correlation between the concentrations of apt-E and E. coli O157:H7, E. coli O157:H7 thus could be quantified by the detection of H1/H2 complexes with microchip electrophoresis (MCE). Under the optimal conditions, the limit of detection was 75 CFU mL−1. This method was also applied to detect E. coli O157:H7 in defatted milk with a satisfying recovery rate. The proposed strategy for E. coli O157:H7 detection is label-free, enzyme-free, ultra-sensitive, and cost-effective. It is also practical and could be applied to detect other bacteria in food samples.

The release of cytochrome C (Cyt C) plays an important role in apoptosis. In this study, selective and sensitive detection of Cyt C based on an aptamer strategy coupled with MCE was developed. Following the binding of a specific aptamer to Cyt C, the aptamer exhibited an irregular state, reducing the binding affinity of a fluorescent probe, and thus preventing the aptamer-Cyt C complexes from detection within the MCE. The height of the detection peak of the residual aptamer linearly decreased, and therefore, the difference in peak height of residual aptamer compared to that of the initial aptamer was used to quantify the captured protein concentration. Experimental conditions such as incubation time, pH, temperature, and ionic strength were optimized. A measurement of Cyt C concentration by MCE was achieved within 135 s, with a limit of detection as low as 0.4 nM. The proposed method has high selectivity and good stability for the detection of Cyt C. The experimental results demonstrate that this method is quick, consumes only a small quantity of sample, is highly selectivity and exhibits high sensitivity.

Foodborne bacteria are some of the most important human pathogens and can cause many diseases. In this study, multiplex PCR amplification combined with microchip electrophoresis (MCE) was studied to simultaneously and sensitively detect Staphylococcus aureus, Proteus mirabilis, and Enterobacter sakazakii. In order to simultaneously and accurately detect the aim bacteria, three pairs of primers were specially designed for the multiplex PCR amplification of the target genes of three bacteria, which were the specific genes corresponding to these bacteria respectively. After the DNA fragments of three bacteria were simultaneously extracted, the multiplex PCR amplification was performed by adding the three pairs of specific primers in the mixed DNA fragments solution. The multiplex PCR products of the three food-borne pathogens were analyzed by MCE and the limits of detection of target DNA fragments were 1.2-2.2ngμL-1, (S/N=3). The limits of detection of the aim bacteria were calculated as 53CFUmL-1 for Enterobacter sakazakii, 32CFUmL-1 for Proteus mirabilis, 28CFUmL-1 for Staphylococcus aureus, respectively. Satisfactory results were obtained when this method was applied to detect the three foodborne bacteria in milk samples. The experimental results show that this method has the advantages of quickness, less sample consumption, high selectivity and high sensitivity.

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.

A rapid and sensitive PCR based strategy in combination with microchip capillary electrophoresis (MCE) was employed to simultaneously detect three foodborne pathogenic bacteria. Three pairs of primers were specially designed for the amplification of target genes from Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Salmonella enterica serovar Typhimurium (S. Typhimurium). The PCR products along with standard DNA fragments were employed to optimize the separation conditions in MCE. Under optimal conditions, detectable separation of the PCR products (1.6–3.5 ng μL−1) from the three foodborne pathogenic bacteria was achieved within 135 s. The limits of detection of the three bacteria were concluded to be as low as 45 CFU mL−1 for E. coli, 62 CFU mL−1 for S. aureus and 42 CFU mL−1 for S. Typhimurium. The RSD of migration time was in the range of 0.5–0.8%. We conclude that MCE along with PCR holds real potential for rapid analysis and detection of nucleic acids from routine foodborne pathogenic bacteria.

Porous solids composed of shape-persistent organic cage molecules have attracted considerable attention due to their important applications such as molecular separation, heterogeneous catalysis, and gas storage. In this study, an imine-linked porous organic cage (POC) CC10 diluted with a polysiloxane OV-1701 was explored as a novel stationary phase for high-resolution gas chromatography (GC). A wide variety of enantiomers belonging to different classes of organic compounds have been resolved on the coated capillary column, including chiral alcohols, esters, ketones, ethers, halohydrocarbons, epoxides, and organic acids. The fabricated column complements to commercial β-DEX 120 column and our recently reported CC3-R column for separating enantiomers, which indicates that the excellent chiral recognition ability of CC10 is not only interesting academically, but also has potential for practical application. In addition, CC10 also exhibits good selectivity for the separation of n-alkanes, n-alcohols, Grob mixture, and positional isomers. This work also indicates that this type of chiral POCs will become a new class of chiral selector in the near future.

A simple and sensitive method for glucose determination was described based on the host-guest inclusive complex of cucurbit[7]uril and ferrocenemonocarboxylic acid. In this work, the mixture of cucurbit[7]uril and graphene oxide, ferrocenemonocarboxylic acid as electron transfer mediator and glucose oxidase as catalytic material were modified successively on the electrode. Under the optimized conditions, a linear response between current intensity and glucose concentrations over a range of 0.1–10 mM was obtained with a relatively low detection limit (27 µM, S/N=3). Meanwhile, this method exhibited high selectivity in the interference investigation, and the reliability and applicability in human serum samples analysis.

Here, polydopamine derivative monolayer was generated by electro-polymerization of thiol dopamine derivatives modified on gold electrode, and the adhesion of polydopamine made it being a platform for secondary reaction. The influence of pH on formation of polydopamine derivative was investigated. Horseradish peroxidase (HRP) was adhered on the polydopamine derivative monolayer electrode catalyzing the oxidation of H2O2. Cyclic voltammetry (CV) was used to detect the polydopamine monolayer as well as electrochemical catalysis of H2O2. Besides, electrochemical impedance spectroscopy (EIS) and atomic force microscope (AFM) were also employed to characterize the polymeric monolayer.

Data analysis for nanopore experiments remains a fundamental and technological challenge because of the large data volume, the presence of unavoidable noise, and the filtering effect. Here, we present an accurate and robust data process that recognizes the current blockades and enables evaluation of the dwell time and current amplitude through a novel second-order-differential-based calibration method and an integration method, respectively. We applied the developed data process to analyze both generated blockages and experimental data. Compared to the results obtained using the conventional method, those obtained using the new method provided a significant increase in the accuracy of nanopore measurements.

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.

Chiral nematic mesoporous silica (CNMS) is a novel inorganic mesoporous material that has properties of both mesoporous and liquid crystal materials. In this work, we report CNMS as a stationary phase for high-performance liquid chromatographic (HPLC) separation of positional isomers. High-resolution separation of aminophenol, dihydroxybenzene, nitroaniline, nitrophenol, chloroaniline, bromoaniline, iodoaniline, dinitrobenzene, nitrochlorobenzene and nitrobromobenzene isomers on CNMS columns was performed. Slurry-packed CNMS columns had better selectivity than commercial β-cyclodextrin HPLC columns for separating these positional isomers. The effects of mobile phase composition, injected analyte mass and column temperature on separation were investigated. The relative standard deviations for five replicate separations of positional isomers were 0.10–0.43% for the retention time and 0.5–3.9% for the peak area. Therefore, CNMS columns are promising for separating positional isomers based on their good reproducibility, high resolution and excellent selectivity. In addition, the column also exhibits recognition ability toward racemates.

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.

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

Porous organic cages composed of discrete cage molecules have attracted considerable recent attention as gas adsorption materials and separation media. In this study, we report a homochiral porous organic cage CC5 with a large cavity and pore windows as a novel stationary phase for high-resolution gas chromatographic separations. The capillary column was prepared by a static coating method. A large number of racemic compounds have been resolved on the coated capillary column, including derivatized amino acids, alcohols, alcohol amines, esters, ethers, ketones, and epoxides. It is interesting that the CC5-coated capillary column exhibits significant chiral recognition complementarity to a commercial β-DEX 120 column and a previously reported homochiral porous organic cage CC3-R-coated column, which could expand the range of the analytes amenable to separation on porous organic cage-based capillary columns. Moreover, the fabricated column also shows excellent selectivity for the separation of positional isomers, including the challenging ethylbenzene and xylene isomers. Experimental results demonstrate an excellent separation performance and stability of the CC5-coated column, making it promising for gas chromatography applications.

In this paper, polydopamine/gold nanoparticles (PDA/Au NPs) were used to construct a functional film on a glass microfluidic channel surface in microchip electrophoresis (MCE) for the separation of reduced glutathione (GSH) and oxidized glutathione (GSSH). The formation of the PDA/Au NPs was characterized by scanning electron microscopy, transmission electron microscope, UV–Vis spectra and ATR-FTIR. An online pre-concentration strategy involving field-amplified sample stacking was used to determine the sensitivity of the assay for measuring GSH and GSSH in bacteria (Escherichia coli, Staphylococcus aureus and Salmonella enterica serovar Typhimurium) and HaCaT cells samples by MCE with laser-induced fluorescence detection. The influences of the separation voltage, the concentration of the running buffer and the pH value of running buffer, were carefully investigated. Using this studied method, GSH and GSSH could be simultaneously pre-concentrated and separated within 70 s. The limits of detection of GSH and GSSH were as low as 0.81 and 0.91 nM, respectively (S/N = 3), which corresponded to approximately 180–301-fold improvements in peak height. Moreover, this method was successfully applied to the analysis of bacteria (E. coli, S. aureus and S. typhimurium) and HaCaT cell samples with a satisfactory recovery rate.

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%.

An ultrasensitive and signal-on electrochemiluminescence (ECL) aptasensor to detect target protein (thrombin or lysozyme) was developed using the host-guest recognition between a metallocyclodextrin complex and single-stranded DNA (ss-DNA). The aptasensor uses both the photoactive properties of the metallocyclodextrins named multi-tris(bipyridine)ruthenium(II)-β-cyclodextrin complexes and their specific recognition with ss-DNA, which amplified the ECL signal without luminophore labeling. After investigating the ECL performance of different multi-tris(bipyridine)ruthenium(II)-β-cyclodextrin (multi-Ru-β-CD) complexes, tris-tris(bipyridine)-ruthenium(II)-β-cyclodextrin (tris(bpyRu)-β-CD) was selected as a suitable host molecule to construct an atasensor. First, double-stranded DNA (ds-DNA) formed by hybridization of the aptamer and its target DNA was attached to a glassy carbon electrode via coupling interaction, which showed low ECL intensity with 2-(dibutylamino) ethanol (DBAE) as coreactant, because of the weak recognition between ds-DNA and tris(bpyRu)-β-CD. Upon addition of the corresponding protein, the ECL intensity increased when target ss-DNA was released because of the higher stability of the aptamer-protein complex than the aptamer-DNA one. A linear relationship was observed in the range of 0.01 pmol/L to 100 pmol/L between ECL intensity and the logarithm of thrombin concentrations with a limited detection of 8.5 fmol/L (S/N=3). Meanwhile, the measured concentration of lysozyme was from 0.05 pmol/L to 500 pmol/L and the detection limit was 33 fmol/L (S/N=3). The investigations of proteins in human serum samples were also performed to demonstrate the validity of detection in real clinical samples. The simplicity, high sensitivity and specificity of this aptasensor show great promise for practical applications in protein monitoring and disease diagnosis.

In this work, we demonstrate the applicability of an electrochemical supramolecular platform to detect Hepatitis B virus (HBV) sequences. A DNA molecular beacon was designed as the probe, and immobilized onto the electrodes through the biotin at the 3′-end, while the 5′-end of the probe was labeled with 4-(4-dimethyl aminophenylazo) benzoic acid (dabcyl). The β-cyclodextrins functionalized Au nanoparticles (Au-CDs) were employed as electrochemical signal provider. The probe DNA immobilized on the electrode kept the stem-loop configuration, which shielded dabcyl from docking with Au-CDs in solution due to the steric effect. While in the presence of the target DNA, the probe conformation was changed and a double-stranded DNA (dsDNA) molecule was formed through the hybridization. Consequently, Au-CDs were linked to dsDNA 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. The designed sensor favored discrimination between the healthy and single-nucleotide polymorphisms (SNP)-containing sequences. Under optimized detection conditions, the proposed method showed high sensitivity and specificity with a detection limit of 3.00 × 10 −13 M for HBV DNA sequence.

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.

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.

We describe herein the synthesis of supramolecular metallocyclodextrins containing multiruthenium centers. These compounds exhibit especially strong fluorescence and electrochemiluminescence (ECL), as well as excellent quenching efficiency because of their ability to perform host–guest recognition.

Bacterial lipopolysaccharides (LPS) are endotoxins, which can cause fever, inflammation, cell and tissue damage, irreversible septic shock and death in mammals as well as other organisms. Herein, a highly sensitive and selective strategy was proposed for detecting LPS using microchip electrophoresis (MCE) based on aptamer-modified magnetic beads and polymerase chain amplification. In this strategy, the biotinylated aptamer for the LPS (LBA) was hybridized partially with the complementary DNA (cDNA), then the double-stranded DNA obtained was immobilized onto the magnetic beads. In the presence of target LPS, the target-aptamer complex was formed and the cDNA would be freed. After a magnetic separation, the cDNA was released into the supernatant and subsequently triggered the polymerase chain amplification. This process eventually generated a large number of output DNA, which could be quantitatively detected by MCE. With the polymerase chain amplification, this designed protocol provided an ultrasensitive detection of LPS down to the 1.1 × 10−14 g/mL with a linear range of 5 orders of magnitude. The proposed method also exhibited a high specificity toward LPS in the presence of other common interfering substances. Moreover, the assay showed a good practical application for LPS determination in serum samples.

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.

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...

Aptamers are single-stranded nucleic acid molecules that can be used for protein recognition, detection, and inhibition. Over the past decades, two thrombin-binding aptamers (15apt and 27apt) were reported by systemic evolution of ligands by exponential enrichment technique. Though many studies have been reported about the interactions between the aptamers and thrombin by atomic force microscopy, the thrombins in those studies were all immobilized by chemical agents. Recently, we developed a new method using atomic force microscopy to directly investigate the specific interactions between thrombin and its two aptamers without immobilizing the thrombin. Furthermore, the unbinding dynamics and dissociation energy landscapes of aptamer/thrombin were discussed. The results indicate that the underlying interaction mechanisms of thrombin with its two aptamers will be similar despite that the structures of 15apt and 27apt are different in buffer solution.

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 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

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.