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An all-solid-state ion-selective electrode (ASS-ISE) array that is portable and easily miniaturized can meet the needs of home sensing devices for long-term health monitoring. However, their stability and accuracy are affected by the multistep modification required for ASS-ISE manufacturing and the complex background signal of real samples. In this study, a four-channel ISE array with the integration of a calibration channel has been developed based on polystyrene-Au (PS-Au) ion-sensing nanocomposites (PS-Au ISE array) for the home detection of Na+ and K+. The nanocomposites combine target recognition function and ion-electron transduction function and could be modified on the channel surface by direct drop-casting, thus simplifying the preparation process and then improving the stability. Meanwhile, the integrated calibration channel could automatically deduct complex background signals in real sample analysis and thus improve the accuracy. As a result, the proposed self-calibrated PS-Au ISE array showed a near Nernstian behavior for Na+ and K+ in the range of 1 × 10-2 M-1 × 10-4 M, and the detection limits were 6.8 × 10-5 M and 5.5 × 10-5 M in artificial urine. The linear equations can be obtained according to the slopes and intercepts of Na+ and K+, and thus, the concentration of the target ions can be directly read out by combining this PS-Au ISE array with the smart electronic device. Furthermore, the detection results of Na+ and K+ in human urine agreed well with those obtained by ICP-AES, suggesting that this proposed self-calibrated PS-Au ISE array is very suitable for home smart sensing devices, facilitating the health monitoring.

An all-solid-state potentiometric aptasensor based on signal amplification by polycation has been proposed for the detection of streptomycin. The carboxylated multi-walled carbon nanotubes (CMWCNTs), polyethylenimine (PEI), and the aptamers of streptomycin were assembled successively on the screen-printing carbon electrode surface by Layer-by-Layer (LbL) technique. The streptomycin would specifically bind to the aptamers, leading to the release of aptamers from the modified electrode surface. Thus, the charges of electrode were changed, causing the variation of open circuit potential (OCP). The introduction of polycation – PEI makes the electrode exposing a large amount of positive charges, so it can combine more aptamers to realize signal amplification. Consequently, under the optimal conditions, this aptasensor showed high sensitivity with corresponding linear response ranges of $1.00\times 10^{-11}-1.00\times 10^{-9}$ M, and a detection limit of $3.43\times 10^{-12}$ M. Moreover, this aptasensor presented good selectivity, reproducibility and stability. It could be applied to the detection of milk samples, demonstrating the practicability of this aptasensor.

Here, an Au–Cu dual-electrode tip was designed to monitor the effect of Cu2+ on the membrane permeability of a single living cell in situ using scanning electrochemical microscopy. The probe approach curves (PACs) were obtained using potassium ferricyanide as a redox mediator. Meanwhile, according to the simulation, theoretical PACs could be acquired. Thus, the cell membrane permeability coefficient (Pm) values were obtained by overlapping the experimental PACs with the theoretical values. Cu2+ was directly generated by electrolyzing the Cu electrode of the dual-electrode tip to investigate its effect on the cell membrane permeability in situ. This work has potential value to improve the understanding of the mechanism of acute heavy metal damage on the cell membrane and will also help clarify the role of heavy metal ions in physiological or pathological processes.

Integrating silica with organic nanoparticles can generate unique properties. Here pillar[5]arene/silica hybrid vesicles were constructed based on the amphiphilic and rigid properties of pillararenes, as well as the catalytic hydrolysis of tetraethoxysilane. Such vesicles exhibited the high strength of silica and unique molecular recognition of pillararenes, both of which could tune the pH-triggered release behavior. Furthermore, a rhodamine B derivative with hexyl group (RhB-C6) was synthesized, which can form a complex with the pillar[5]arene. Based on the host-guest interaction and high strength of silica, the hybrid vesicles could load more RhB-C6 and the rhodamine B was released more slowly compared with the organic vesicles.

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.

Breast cancer is a heterogeneous disease, and it lacks special tumor markers. Exosomes, new noninvasive biomarkers, with the proteins on the exosome surface show potential for the diagnosis and prognosis of a tumor. However, assessing the variations of exosomal proteins still faces significant challenges. Herein, a magneto-mediated electrochemical sensor based on host-guest recognition has been developed for simultaneous analysis of breast cancer exosomal proteins. Magnetic beads (MB) modified with CD63 aptamer was first employed to capture exosomes. Silica nanoparticles (SiO2 NPs) was modified with MUC1, HER2, EpCAM, and CEA aptamers for specific exosomal proteins identification, respectively, and functionalized with N-(2-((2-aminoethyl)disulfanyl)ethyl) ferrocene carboxamide (FcNHSSNH2) as the signal molecule. The sandwich structure (MB-exosomes-SiO2 NPs probe) was separated by a magnet, and N-(2-mercaptoethyl) ferrocene carboxamide (FcNHSH) was released to the supernatant by the addition of reductants (dithiothreitol, DTT) that break the disulfide bond of FcNHSSNH2. FcNHSH and the graphene oxide-cucurbit [7](GO-CB[7]) modified screen-printed carbon electrode (SPCE) was employed to monitor the oxidation current signals. In this way, four tumor markers on different breast cancer cells (MCF-7, SK-BR-3, MDA-MB-231, and BT474) derived exosomes were sensitively detected. Furthermore, the present assay enabled accurate analysis of exosomes from breast cancer patients, suggesting the potential of exosome analysis in clinic diagnosis.

A PEDOT-modified Pt microelectrode was used in SECM for DNA biosensing and combined with long self-assembled DNA concatemers to realize dual signal amplification. The approach curve could also be plotted for tip location using this modified microelectrode with no impact on the catalytic effect so that both signal amplification and tip locating were achieved in one single tip. The detection limit of this method reached 0.076 fM, providing an ultra-sensitive DNA biosensing platform. Furthermore, this strategy could be applied in scanning a DNA chip, showing great potential in high-throughput bioanalysis with high sensitivity.

Abnormal glycosylation of exosomal proteins is related to many diseases. However, there is still a lack of convenient and easy methods for the determination of exosomal glycoproteins. In this work, a ratiometric electrochemical sensor based on the recognition of glycoproteins by boronic acid and core-shell nanoparticles of silica-silver (SiO2@Ag) amplified signals was developed for the highly sensitive detection of exosomal glycoproteins. The CD63 aptamer-SiO2-N-(2-((2-aminoethyl)disulfanyl)ethyl) ferrocene carboxamide (FcNHSSNH2) probe was first connected to graphene oxide-cucurbit [7] (GO-CB [7]) modified GCE through host-guest recognition. The CD63 aptamer was employed for the specific capture of exosomes, and the FcNHSSNH2 molecule was used as the internal reference signal of the sensor. The mercaptophenylboronic acid (MPBA) of MPBA-SiO2@Ag probe was used for the identification of exosomes surface glycoproteins. SiO2 nanoparticle has a large specific surface area, which can load a large amount of silver nanoparticles (AgNPs) for electrochemical signal amplification. The results were expressed as the current ratio of AgNPs and FcNHSSNH2. The introduction of the internal reference molecule FcNHSSNH2 could effectively reduce the measurement error caused by the different DNA density of the substrate, and further improve the sensitivity and accuracy of the detection. Under the optimal experimental conditions, this sensor allowed the sensitive detection of exosomal glycoproteins in the range of 4.2 × 102 to 4.2 × 108 particles/μL with a limit of detection (LOD) of 368 particles/μL. Furthermore, the ratiometric electrochemical sensor could be employed for the detection of exosomal glycoproteins in human serum samples, which has a good clinical application prospect.

The detection of Staphylococcus aureus specific gene in combination with the mecA gene is vitally important for accurate identification of methicillin-resistant Staphylococcus aureus (MRSA). A homogeneous electrochemical DNA sensor was fabricated for simultaneous detection of mecA and nuc gene in MRSA. Metal-organic framework (type UiO-66-NH2) was applied as nanocarrier. Two electroactive dyes, methylene blue (MB) and epirubicin (EP), were encapsulated in UiO-66-NH2, respectively, and were locked by the hybrid double-stranded DNA. Based on the target-response electroactive dye release strategy, once target DNA exists, it completely hybridizes with displacement DNA (DEP and DMB). So DEP and DMB is displaced from the MOF surface, causing the release of electroactive dyes. Co-Zn bimetallic zeolitic imidazolate framework-derived N-doped porous carbon serves for electrode modification to improve electrocatalytic performance and sensitivity. The differential pulse voltammetry peak currents of MB and EP were accurately detected at − 0.14 V and − 0.53 V versus the Ag/AgCl reference electrode, respectively. Under the optimal conditions, the detection limits of mecA gene and nuc gene were 3.7 fM and 1.6 fM, respectively. Combining the effective application of MOFs and the homogeneous detection strategy, the sensor exhibited satisfactory performance for MRSA identification in real samples. The recovery was 92.6–103%, and the relative standard deviation was less than 5%. Besides, MRSA and SA can also be distinguished. This sensor has great potential in practical applications.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main pathogens involved in hospital and community infection. To rapidly and sensitively detect the mecA gene, which is relevant to methicillin-resistant strains, microchip electrophoresis (MCE) integrated with isothermal strand-displacement polymerase reaction (ISDPR) was developed. In the ISDPR signal recycle amplification, the target DNA opened the DNA hairpin structure by specifically binding with the hairpin probe (HP), and then the primer hybridized with the probe and released the target DNA in the presence of Klenow Fragment exo− (KF exo−) polymerase. The released target DNA hybridized with the next HP and then was displaced by the primer again, consequently achieving target recycling and amplification. The amplified products of the HP-cDNA duplex were separated rapidly from other DNAs by MCE. Under optimal conditions, the limit of detection of the target DNA was as low as 12.3 pM (S/N = 3). The proposed ISDPR with MCE method was also successfully applied to detect methicillin-resistant S. aureus, and the experimental results showed that it had some advantages such as being label free, ultrasensitive, rapid and well separated.

In this study, a mixed mode stationary phase for capillary liquid chromatography (cLC) was prepared by chemical modification of glycol diglycidyl ether (EGDE) and γ-aminobutyric acid (GABA) bonded to the silica, named as Sil–EGDE–GABA. The Sil–EGDE–GABA was characterized by Fourier transform infrared spectroscopy and elemental analysis. The retention of nucleotide bases at different acetonitrile levels in the mobile phase indicated that the stationary phase possessed both hydrophilic chromatography (HILIC) and reversed-phase chromatography (RPLC) characteristics. Positional isomers, aniline compounds and a mixture of polar–nonpolar analytes were separated in RPLC mode. The stationary phase exhibited different separation mechanisms in the separation of positional isomers, compared with a commercial ODS column. Sulfonamides and biogenic amines were successfully separated in HILIC mode. These results demonstrated the application possibilities of the prepared Sil–EGDE–GABA as packing materials in cLC.

The detection of Staphylococcus aureus (S. aureus) is very important as it is responsible for bacterial infectious diseases and food poisoning. In this paper we explored the application of fluorescently labelled vancomycin to specifically bind and detect S. aureus. In view of the specificity of vancomycin towards bacterial cell surfaces, we utilized Cy5 to label vancomycin (Cy5-Van) for the identification of S. aureus. Our experiments were designed to examine in greater detail the specificity of the reaction between Cy5-Van and S. aureus. Detection parameters such as the derivatization conditions, concentrations of buffer, pH value, response performance of Cy5-Van to bacterial surface, injection time and reversed-polarity time have been investigated and optimized. To develop a simple and quick assay for the detection of S. aureus at low concentrations, we propose to use the Cy5-Van for labeling the S. aureus coupled with an on-line multiple-concentration in microchip electrophoresis. Under the optimized conditions, the detection of S. aureus was achieved within 150 s with limit of detection (S/N = 3) of 981 CFU/mL, and 350-fold enhancement was obtained for S. aureus as compared to using the no concentration step. It is self-evident that this approach has great potential in the future for the analysis of S. aureus.

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.

The detection of Salmonella enterica serovar Typhimurium (S. Typhimurium) is very important for the prevention of food poisoning and other infectious diseases. Here we reported a simple and sensitive strategy to test S. Typhimurium by microchip capillary electrophoresis couple with laser-induced fluorescence (MCE-LIF) based on the specific reaction between the bacterium and corresponding aptamers. Based on the differences in charge to mass ratio between bacteria-aptamer complexes and free aptamers, a separation of the complexes and free aptamers could be obtained by MCE. The optimal parameters of the specific reaction including fluorescent dye concentration, Mg2+ concentration, incubation time, and pH of incubation solution were carefully investigated. Meanwhile, a non-specific DNA was exploited as a contrast for the detection of S. Typhimurium. Under the optimal conditions, a rapid separation of the bacteria-aptamer complex and free aptamers was achieved within 135 s with a limit of detection (S/N = 3) of 3.37 × 102 CFU mL−1. This method was applied for the detection of S. Typhimurium in fresh milk samples and a recovery rate of 95.8% was obtained. The experimental results indicated that the specific aptamers are of enough biostability and the established method could be used to analyze S. Typhimurium in foods.

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

Herein we show that by appending bulky β-cyclodextrin (CD) groups onto sheet-forming peptoids, we obtain cylindrical micelles that further assembly into membranes and intertwined ribbons on substrates in aqueous solution, depending on the choice of solution and substrate conditions. In situ atomic force microscopy (AFM) shows that micelle assembly occurs in two steps, starting with "precursor" particles that transform into worm-like micelles, which extend and coalesce to form the higher order structures with a rate and a degree of cooperativity dependent on pH and Ca2+ concentration. After co-assembly with hydrophobic 4-(2-hydroxyethylamino)-7-nitro-2,1,3-benzoxadiazole (NBD) donors that occupy the hydrophobic core, followed by exposure to hydrophilic Rhodamine B as acceptors that insert into cyclodextrin, the micelles exhibit highly efficient Forster resonance energy transfer efficiency in aqueous solution, thereby mimicking natural light harvesting systems.

Different cells respond differently to environmental stimulation, resulting in different extracellular pH values. Therefore, the pH of the extracellular microenvironment (pHe) is an important manifestation of cell response to the environment. In this study, a pH-selective dual-microelectrode tip was used as the probe tip of a scanning electrochemical microscopy (SECM) instrument to in situ monitor the pHe changes of different cells after being electrically stimulated by the SECM potential method. pHe is the pH at a certain distance from the cells, and the distance is determined by substituting the current measured by the approach curve into a theoretical calculation. A gold microelectrode was used to determine the distance between the dual-microelectrode tip and the cell, and a pH-selective microelectrode was used to measure the pHe. It was found that the pHe value was related to the distance between the pH-measuring electrode and the cell, and different types of cells had different pHe changes after electrical stimulation. Through fluorescent staining with calcein-AM and propidium iodide, it was verified that this phenomenon was caused by changes in the permeability of the cell membrane due to electrical stimulation. In situ monitoring the pHe changes of different cells will be helpful for exploring the response of cells to environmental stimulation and the mechanism of these different responses.

A new method of capillary electrophoresis (CE) using laser induced fluorescence (LIF) detection via online pre-concentration techniques including transient trapping combined with the dynamic pH junction mode was developed for the sensitive determination of glutathione in biological samples. The mechanism together with the important parameters governing the pre-concentration and separation were investigated in order to obtain maximum resolution and sensitivity. The analytes were compressed into a narrow zone due to the effect of the dynamic pH junction mode, and then transiently trapped by SDS micelles at the interface of the sample and micellar areas. Under the optimal conditions, the limits of detection for reduced glutathione, glycine, oxidized glutathione, cysteine, and glutamic acid were 0.01, 0.01, 0.5, 0.7, and 0.1 nM (S/N = 3), respectively. The enhancement factors obtained when using the transient trapping combined with the dynamic pH junction mode as a pre-concentration process were enhanced from 87 to 430 when compared to the results obtained by the classical capillary zone electrophoresis (CZE) mode. Moreover, this optimized method was successfully applied to bacteria (Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus) and HaCaT cell samples for the determination of reduced glutathione with satisfactory recoveries.

Recently, many strategies have been developed to trace the breast cancer susceptibility gene (BRCA), which is closely related to the occurrence of breast cancer. In this work, a novel recyclable electrochemical sensing platform was constructed to detect BRCA DNA based on the homogeneous hybridization of this target sequence with ferrocene-labeled DNA/Au nanospheres (FcNS) and horseradish peroxidase-labeled DNA/Au nanospheres (HRPNS) concatamers, and the host-guest interaction between cucurbit [7]uril (CB [7]) adsorbed on the electrode and Fc on the hybridization complex. With the optimization of experimental conditions, the fabricated sensing platform showed improved sensitivity with a low detection limit of 25 pM (S/N = 3), contributed by the dual amplification of signal using FcNS and HRPNS concatamers, and high specificity for BRCA DNA. The captured complex was dissociated from CB [7]-modified electrode with the rise of pH value to recycle the sensing platform. Furthermore, this detection strategy displayed the reliability and applicability in the analysis of human serum samples, indicating great potential for applications in early diagnosis of breast cancer.

A capillary column was prepared by continuously packing ostadecylsilane (ODS) and taurine derivatized silica (TDS) in one column without interface. This continuously packing chromatography (CPC) column is easy to operate, has good stability and shows simultaneously separation of both polar and non-polar compounds. The simultaneous separation of a series of complex samples with highly hydrophobic components (benzene, toluene, ethylbenzene, and PAHs) and highly hydrophilic components (biogenic amines, bases and nucleosides) using this CPC method was investigated. The relative parameters such as the volume fraction of acetonitrile and length of the ODS and the TDS phases were investigated and optimized. The experimental results show that this column combines the advantages of both ODS and TDS stationary phases, and exhibits a reversed phase liquid chromatography (RPLC) mode followed by a hydrophilic interaction liquid chromatography (HILIC) mode when 80% of acetonitrile was used in the mobile phase. The satisfactory results indicate that the CPC method provides an easy way to simultaneously separate polar and non-polar compounds.

Due to their unique physical and chemical properties, 2D materials have attracted intense interest for applications in filtration, sensing, nanoelectronics, and biomedical devices. Peptoids are a class of biomimetic sequence-defined polymers for which certain amphiphillic sequences self-assemble into 2D crystalline materials with properties that mimic those of cell membranes. In this study the ability of these membrane-like materials to self-repair following damage on a range of substrates is explored. In situ atomic force microscopy (AFM) is used to both create damage and image the subsequent repair process. Damage is induced by using the AFM to scribe peptoid-free patterns within a preassembled membrane. The results show here that, upon introduction of a peptoid-containing solution, for a suitable range of pH conditions, the damage is eliminated through assembly of the peptoids at the newly created edges, regardless of whether the substrates are negatively or positively charged and even in the absence of an underlying surface. The rate of the advancing edge depends on the edge orientation, the pH, and the composition of the substrate. Moreover, if the solution contains a second peptoid having an identical sequence in the hydrophobic block, repair of the defects results in nanoscale patterns of the new peptoid, even if the hydrophilic regions are distinct. Consequently, this ability to self-repair can be exploited to create nm-sized patterns of distinct functional groups within a single coherent membrane.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.