A label-free electrochemical aptasensor was developed for selective detection of saxitoxin (STX). It is taking advantage of target-induced conformational change of an STX-specific aptamer when it binds to the toxin. A monolayer of octadecanethiol was deposited on a gold electrode, and then coated with a film of multiwalled carbon nanotubes (MWCNTs) to which the aptamer was covalently conjugated. Methylene blue (MB) was electrostatically anchored on carboxylated MWCNTs and used as the electrochemical indicator that produced a strong differential pulse voltammetric signal in the absence of target (STX). If, however, STX binds to its aptamer, this triggers a conformational change of the aptamer and results in the establishment of a barrier for heterogeneous electron transfer. The oxidation peak current of MB, acquired at −0.27 V (vs. Ag/AgCl), linearly decreases with increasing concentrations of STX in the 0.9 and 30 nM concentration range. The detection limit is 0.38 nM. Marine toxins that maybe present along with STX do not interfere even if they have a similar chemical structure. The assay was applied to the determination of STX in mussels samples and was found to be acceptably accurate. Hence, the method introduced here provides a rapid and sensitive tool for monitoring red tide pollution.

A simple and green method for the determination of trace bisphenol A (BPA) was established by coupling supported ionic liquid solid-phase extraction to β-cyclodextrin modified ionic liquids carbon paste electrode-based electrochemical detection (SILs-SPE-ED). The synthesized imidazolium ionic liquids modified styrene type macroporous resin was used as adsorbent for SPE of BPA. The experimental parameters that affected the extraction efficiency were investigated and optimized. Dynamic adsorption test showed that the maximum adsorption capacity of BPA on the SILs-SPE cartridge was 10.1 mg g−1, and the enrichment factor was 40. The calibration curve showed a good linearity between the anodic current and the BPA concentration in the range of 1.0 × 10−8−1.0 × 10−6 M. The detection limit was 4.16 nM (equal to 0.95 μg L−1). The SILs-SPE-ED method, with the advantages including high sensitivity and good practicability, was applied to the analysis of real water and plastic samples, and the results agreed well with HPLC method.A simple and green method for the determination of trace bisphenol A was established by coupling supported ionic liquids solid-phase extraction to β-cyclodextrin modified ionic liquid carbon paste electrode-based electrochemical detection. It was successfully applied to the analysis of real samples with the advantages including high sensitivity and good practicability.

•We devise a new impedimetric immunoassay for sensitive detection of low-abundance protein.•HCR-stimulated formation of DNAzyme concatamers on gold nanoparticle are used as molecular tags.•Using the enzymatic biocatalytic precipitation method can reach the aim of signal amplification.A novel signal-amplified impedimetric immunosensing strategy was successfully developed for ultrasensitive detection of low-abundance proteins (carcinoembryonic antigen, CEA, used as a model) based on hybridization chain reaction (HCR)-stimulated formation of DNAzyme concatamers on nanogold particle accompanying enzyme-triggered biocatalytic precipitation. The assay was carried out on capture antibody-modified electrode by using gold nanoparticle heavily functionalized with initiator strand and detection antibody as the signal-transduction tag with a sandwich-type immunosensing format. In the presence of target CEA, the formed immunocomplex underwent an unbiased strand-displacement reaction by the initiator strand on the gold nanoparticle between two auxiliary single-stranded DNA with the hemin aptamer. Upon hemin introduction, numerous DNAzyme molecules were formed on the concatamers and nanogold particle, which could catalyze 4-chloro-1-naphthol to produce an insoluble precipitation on the electrode, thereby resulting in the amplification of impedimetric signal. Under the optimal conditions, the immuno-HCR assay exhibited good impedimetric responses for the detection of target CEA in the working range from 1.0 pg mL−1 to 20 ng mL−1 with a detection limit of 0.42 pg mL−1. In addition, the immuno-HCR assay was validated by measuring six human serum specimens for target CEA, receiving a highly matched correction between the obtained results by the immuno-HCR assay and the commercialized ELC-based immunoassay method.

•A reusable and cost effective analytical platform for bisphenol A (BPA) sensing.•The combination of unique properties of BMIMBF4 ionic liquid and β-CD in carbon paste electrode presents obviously enhanced sensitivity and selectivity toward BPA.•The presence of ionic liquid/aqueous solution interface affects the mechanism of electrode processes.•The sensor can reliably detect BPA in water and food contact materials.A highly effective approach was developed for specific detection of bisphenol A (BPA) in real samples, based on a β-cyclodextrin (β-CD) modified ionic liquid-based carbon paste electrode (β-CD/ILCPE). Voltammetry and electrochemical impedance spectroscopy measurements reveal significantly improvements in the conductivity and compatibility of the sensor, when using an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) as a super conductive binder in the composition of carbon paste. The introduction of β-CD as a modifier as well as a host molecule exhibited obviously enhanced sensitivity and selectivity toward BPA over a wide concentration range of 1.0 × 10−7 to 1.1 × 10−5 mol L−1, with a detection limit (S/N = 3) of 8.3 × 10−8 mol L−1. Compared to classic carbon paste electrodes, the BPA sensor not only possesses the inherent reusability and cost effectiveness, but also shows better sensing performance and stability. This can be attributed to the combination of the high ion conductivity and non-covalently interaction properties of BMIMBF4, and the supramolecular recognition and enrichment capability of β-CD. The mechanism of electrode processes was also presented. The proposed sensor was successfully used in the determination of BPA in real samples with good recovery.

A new analytical method, pressurized capillary electrochromatography with indirect amperometric detection, has been developed for the determination of some non-electroactive organophosphorus pesticides (OPPs). When 0.1 mmol L−1 of 3,4-dihydroxybenzylamine (DHBA) was added to the mobile phase containing 50% v/v of ACN and 50% v/v of MES buffer (10 mmol L−1, pH 5.5), and +0.9 V (vs. Ag/AgCl) of working potential were used, maximal signal levels of analytes could be achieved. A separation voltage of +10 kV, a column pressure of 7.0 MPa and a pump flow rate of 0.05 mL min−1 were selected as the other optimal conditions for separation of six OPPs, namely, dimethoate, methyl parathion, ethyl parathion, chlorpyrifos, chlorpyrifos-methyl, trichlorfon. The OPPs could be separated within 15 min and determined with the detection limits ranging from 0.008 to 0.2 mg/kg. Combining with a solid phase extraction procedure, mean recoveries between 78.9 and 87.2% for vegetable samples and from 81.4 to 98.6% for fruit samples were obtained.

A sensitive pressurized capillary electrochromatography-laser induced fluorescence detection (pCEC-LIF) method has been developed for the simultaneous analysis of five structurally related free bile acids including cholic acid (CA) and lithocholic acid (LCA), as well as the stereoisomers of chenodeoxycholic acid (CDCA), deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA). 4-nitro-7-N-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was used for the precolumn derivatization of non-chromogenic free bile acids to form strongly fluorescent adducts. Efficient separation of these derivatization products was performed within 17 min by isocratic elution pCEC on an octadecyl silica (ODS) packed capillary column, using a mobile phase consisting of acetonitrile and 10 mM CAPS buffer (pH 8.0) (60:40 v/v), 20 kV of applied voltage and 10.8 MPa of supplementary pressure. The derivatized bile acids could be determined by a LIF detector at an excitation wavelength of 473 nm and an emission wavelength of 530 nm, with detection limits (signal/noise = 3) down to 2 nmol L−1. Applicability of this pCEC-LIF method to the analysis of human serum samples was demonstrated. Accepted recoveries ranging between 94.8% and 109.7% for all analytes in spiked human serum samples were achieved. This method has potential for the trace analysis of physiologically important acidic analogs.

A highly performing ECL glucose biosensor was developed by immobilizing glucose oxidase (GOD) onto a membrane modified glassy carbon electrode, which was prepared by using poly(diallyldimethylammonium chloride) (PDDA) doped with chitosan. In order to obtain the optimal performance of the ECL biosensor, the composition of modified membranes and a series of measurement conditions were investigated. Under the optimal conditions, this ECL biosensor was able to detect glucose in the range of 0.5–4.0 × 104 nM with a detection limit of 0.1 nM (defined as the concentration that could be detected at the signal-to-noise ratio of 3). The relative standard deviation was 0.99% for 5 × 10−8 mol/L glucose in repetitive measurements in the primary 12 potential cycles. This ECL biosensor offered the effectively improved stability of the electron transfer mediator and exhibited excellent properties for the ultrasensitive and selective determination of glucose with good reproducibility and stability. The present biosensor has also been used to determine the glucose concentrations in real serum samples. The recovery value for the assay of glucose ranged from 96.2 to 107% in the serum samples. The present biosensor displayed both specificity for glucose and retention of signal response even in a complex environment. Therefore, it provided an approach to the sensitive determination of glucose.

A sensitive pressurized capillary electrochromatography-laser induced fluorescence detection (pCEC-LIF) method has been developed for the simultaneous analysis of five structurally related free bile acids including cholic acid (CA) and lithocholic acid (LCA), as well as the stereoisomers of chenodeoxycholic acid (CDCA), deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA). 4-nitro-7-N-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was used for the precolumn derivatization of non-chromogenic free bile acids to form strongly fluorescent adducts. Efficient separation of these derivatization products was performed within 17 min by isocratic elution pCEC on an octadecyl silica (ODS) packed capillary column, using a mobile phase consisting of acetonitrile and 10 mM CAPS buffer (pH 8.0) (60:40 v/v), 20 kV of applied voltage and 10.8 MPa of supplementary pressure. The derivatized bile acids could be determined by a LIF detector at an excitation wavelength of 473 nm and an emission wavelength of 530 nm, with detection limits (signal/noise = 3) down to 2 nmol L−1. Applicability of this pCEC-LIF method to the analysis of human serum samples was demonstrated. Accepted recoveries ranging between 94.8% and 109.7% for all analytes in spiked human serum samples were achieved. This method has potential for the trace analysis of physiologically important acidic analogs.