•Nano-Au-polymer film was fabricated by eletrodeposition and electropolymerization.•Naphthol isomers were detected simultaneously.•Surfactant improved the sensitivity and selectivity.A polymer film incorporated gold nanoparticle modified electrode was fabricated. The fabricated process involved eletrodeposition of gold nanoparticles and electropolymerization of the 3-methylthiophene (abbreviated 3MT) onto the glassy carbon electrode (GCE). The resulting electrode (P3MT-nano-Au/GCE) was characterized by scanning electron microscopy (SEM), and a simultaneous determination of naphthol isomers at P3MT-nano-Au/GCE was studied using semi-derivative voltammetry. Because of the synergistic effect of gold nanoparticles and poly(3MT), the sensitivity and distinguishability in the simultaneous determination of naphthol isomers were greatly increased. Besides, a further increase in the detecting sensitivity of naphthol isomers could be obtained in the presence of surfactant, cetyl trimethyl ammonium bromide (CTAB). Also, the role of different kinds of surfactants was texted and the action mechanism was discussed in detail. Under the optimal conditions, the linear calibration ranges of the determination of naphthols were 7.0 × 10− 7 to 1.5 × 10− 4 mol/L for 1-naphthol and 1.0 × 10− 6 to 1.5 × 10− 4 mol/L for 2-naphthol with detection limits of 1.0 × 10− 7 and 3.0 × 10− 7 mol/L (S/N = 3), respectively.

Based on silica and nanocomposite prepared from reduced graphene oxide and gold nanoparticles (SiO2/rGO–AuNPs), a novel and sensitive electrochemical sensor for bisphenol A (BPA) was fabricated. The electrochemical behavior of BPA on a SiO2/rGO–AuNP nanocomposite was investigated by cyclic voltammetry. Compared with bare GCE, the SiO2/rGO–AuNPs/GCE electrochemical sensor obviously reduced the oxidation overpotential of BPA and greatly enhanced the peak current. The direct detection of BPA was accomplished by using differential pulse voltammetry (DPV) under optimized conditions. A linear voltammetric response to BPA within the concentration range of 3.0 × 10−8 to 1.0 × 10−5 mol L−1 and 1.0 × 10−5 to 1.2 × 10−4 mol L−1 with a low detection limit of 5.0 × 10−9 mol L−1 (S/N = 3) was obtained. In addition, the fabricated sensor was successfully applied to detect BPA in thermal paper samples, and the results were satisfactory.

•Graphene/nano-Au composite was synthesized by electrochemical co-reduction method in one step.•Glucose oxidase achieves direct electrochemistry on the graphene/nano-Au composite film.•The glucose biosensor shows a high sensitivity of 56.93 μA mM−1 cm−2 toward glucose.•Glucose was detected with a wide linear range and low detection limit.A simple, green and controllable approach was employed for electrochemical synthesize of the graphene/nano-Au composites. The process was that graphene oxide and HAuCl4 was electrochemically co-reduced onto the glassy carbon electrode (GCE) by cyclic voltammetry in one step. The obtained graphene/nano-Au/GCE exhibited high electrocatalytic activity toward H2O2, which resulted in a remarkable decrease in the overpotential of H2O2 electrochemical oxidation compared with bare GCE. Such electrocatalytic behavior of the graphene/nano-Au/GCE permitted effective low-potential amperometric biosensing of glucose via the incorporation of glucose oxidase (GOD) with graphene/nano-Au. An obvious advantage of this enzyme electrode (graphene/nano-Au/GOD/GCE) was that the graphene/nano-Au nanocomposites provided a favorable microenvironment for GOD and facilitated the electron transfer between the active center of GOD and electrode. The immobilized GOD showed a direct, reversible redox reaction. Furthermore, the graphene/nano-Au/GOD/GCE was used as a glucose biosensor, displaying a low detection limit of 17 μM (S/N = 3), a high sensitivity of 56.93 μA mM−1 cm−2, acceptable reproducibility, very good stability, selectivity and anti-interference ability.

In this work, electrochemiluminescence resonance energy transfer (ECRET) between CdSe/ZnS quantum dot (QD) as the donor and cyanine dye (Cy5) as the acceptor in the conjugates consisting of QD, DNA and Cy5 was studied in detail. When a negative potential was applied to the conjugates immobilized on an Au electrode, QDs emitted a light with a maximum emission (λm) of 590 nm or transfered energy to proximal ground-state Cy5 molecules in 0.1 mol/L phosphate buffer (pH 7.4) containing 0.1 mol/L K2S2O8 and 0.1 mol/L KNO3. The excited state Cy5 molecules relaxed to their ground state by emitting a light with a λm of 675 nm. ECRET between QD and Cy5 in the conjugates could be used to evaluate the interactions between DNAs and to measure the conformational changes of DNAs as well as the distances between groups in DNAs. For the ECRET system, ECRET efficiency was high due to high Cy5-to-QD ratio and low Förster distance.Graphical abstractElectrochemiluminescence resonance energy transfer in the conjugates consisting of CdSe/ZnS QD, DNA and Cy5 dye.Highlights► Electrochemiluminescence resonance energy transfer (ECRET) between QD and Cy5. ► Evaluation of the interactions between DNAs using ECRET between QD and Cy5. ► Measurement of the conformational changes of DNAs using the ECRET system. ► Measurement of distances between groups in DNAs using the ECRET system.

Graphene nanosheets were directly electrodeposited onto a glassy carbon electrode (GCE) from the electrolyte solution containing graphene oxide (GO); the resulting electrode (ED-GO/GCE) was characterized with scanning electron microscopy. A simple and rapid electrochemical method was developed for the determination of theophylline (TP), based on the excellent properties of ED-GO film. The result indicated that ED-GO film-modified GCE exhibited efficient electrocatalytic oxidation for TP with relatively high sensitivity and stability. The electrochemical behavior of TP at ED-GO/GCE was investigated in detail. Under the optimized conditions, the oxidation peak current was proportional to the TP concentration in the range of 8.0 × 10−7 to 6.0 × 10−5 mol L−1 with the detection limit of 1.0 × 10−7 mol L−1 (S/N = 3). The proposed method was successfully applied to green tea samples with satisfactory results.

•A new apatite SPME coating was prepared and used as the working electrode simultaneously.•Fluoride ions could be extracted selectively by the porous apatite coatings.•An indirect voltammetric determination of fluoride ions method was proposed.Electrodeposition was used to prepare a new solid phase microextraction (SPME) coatings. Two apatite SPME coatings, dicalcium phosphate dihydrate (DCPD or brushite) and hydroxyapatite (HAP) were validly and homogeneously one-step electrodeposited on glassy carbon electrode (GCE) under different conditions. The coatings were characterized by XRD, FTIR, SEM, CV and EIS. The apatite SPME coatings showed excellent and selective adsorbability to fluoride ions. A novel indirect voltammetric strategy for sensitive detection of fluoride was proposed using K3Fe(CN)6 as indicating probe. The detection principle of fluoride ions was based on the increment of steric hindrance after fluoride adsorption, which resulting in the decrease of the amperometric signal to Fe(CN)63−. The liner ranges were 0.5–20.0 μmol/L for n-DCPD/GCE with the limit of detection of 0.14 μmol/L and 0.1–50.0 μmol/L for n-HAP/GCE with the limit of detection of 0.069 μmol/L, respectively. The developed method was applied to the analysis of water samples (lake, spring and tap water) and the recovery values were found to be in the range of 90–106%.

A novel method for sensitive determination of chloride anion at multilayer nano-silver modified indium-tin oxide (ITO) electrode has been developed. The multilayer films were fabricated via self-assembly/electrochemical-assembly methods, in which the 3-aminopropyltriethoxysilane (APTS) was used to modify ITO conducting glass, layer-by-layer (LBL) method was applied to prepare the multilayer films and poly (diallyldimethylammonium chloride) (PDDA) was employed as a bridging ligand. The resulting electrode (Ag/{PDDA/Ag}m/APTS/ITO) surface was characterized with SEM and UV–vis. The electrochemical behavior of Cl− at the Ag/{PDDA/Ag}m/APTS/ITO electrode was studied by cyclic voltammetry. The results indicated that the modified electrode exhibited substantial enhancement in electrochemical sensitivity for Cl− due to its large surface area and particular absorbability. The Ag/{PDDA/Ag}m/APTS/ITO electrode detected Cl− by voltammetry based on the oxidation of Ag/Cl− that generated from a specific reaction of chloride ions with nano-silver. After accumulation of 3 min for Cl− at Ag/{PDDA/Ag}m/APTS/ITO electrode, the peak height (Ag/Cl−) increased linearly with the concentrations of Cl− in the range of 1.0 × 10−8–1.0 × 10−6 mol L−1. The detection limit was 5.2 × 10−9 mol L−1 at 3σ level. This modified electrode could be successfully applied in water samples with low cost and high sensitivity.Highlights► The multilayer nano-silver modified ITO electrode was fabricated via self-assembly/electrochemical-assembly methods. ► This modified electrode exhibited substantial enhancement in electrochemical sensitivity for Cl−. ► Compared with the existing reports about determination of Cl−, the proposed method is much more selective. ► This modified electrode could be applied to determine directly chloride anion in real samples.

Direct electrochemiluminescence (ECL) from peroxydisulfate (S2O82-), a common ECL co-reactants, can be efficiently enhanced by nanocomposite of electrochemically reduced graphene oxide (abbreviated ERGO) and gold nanoparticles, which provided a novel sensing strategy for bio-molecules. The nano-Au–ERGO composites were electrochemically prepared by a two-step reduction method, in which graphene oxide (GO) was firstly reduced to graphene at the electrode surface, and then followed by electrochemical reduction of HAuCl4. As 15 times enhanced ECL intensity of (S2O82-) was observed with the formation of nanocomposite at glassy carbon electrode (GCE) and immunoreaction occurred at electrode surface can suppress corresponding ECL emissions, a new immunoassay strategy was developed with Human IgG (HIgG) as model molecule. A leaner response from 0.02 to 100 ng mL−1 was obtained between the concentration of the target molecular and ECL intensity with a detection limit of 1.3 pg mL−1 (S/N = 3). The proposed ECL sensor showed high sensitivity, stability and satisfactory reproducibility and opened a new avenue to apply ECL in more biological assays. Besides, this method is economical, efficient, and potentially attractive for clinical immunoassays.Graphical abstractHighlights► A sensitive immunosensor based on the enhanced ECL of peroxydisulfate was developed. ► Nano-Au–ERGO composite was prepared through a two-step electroreduction. ► Nano-Au–ERGO composite was first applied to enhance the peroxydisulfate ECL intensity. ► Provide an ECL immunosensing platform for ultrasensitive protein detection.

A solution-based approach of chemical co-reduction of Au (III) and graphene oxide (GO) was used to prepare graphene/Au (GR/Au) nanocomposites. The gold nanoparticles (nano-Au) integrated in GR acted as spacers for inhibiting the aggregation of GR sheets. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) results revealed that nano-Au particles were dispersed uniformly on the GR sheets. The obtained GR/Au nanocomposites modified glassy carbon electrode (GR/Au/GCE) exhibited high sensitivity in the detection of epinephrine (EP). It has been found that oxidation of EP at this modified electrode occurred at less positive potentials than on bare GCE. The anodic peak current observed were directly proportional to EP concentration between the range of 5.0 × 10−8 and 8.0 × 10−6 mol L−1 (L.O.D. = 7.0 × 10−9 mol L−1). In addition, the oxidation peaks of EP and ascorbic acid (AA) were separated from each other by approximately 180 mV. Therefore the GR/Au nanocomposites modified electrode successfully differentiates the signals of the two analytes. At the same time, this electrode also showed favorable electrocatalytic activity toward some other small biomolecules (such as dopamine, β-nicotinamide adenine dinucleotide, and uric acid), suggesting the potential applications of GR/Au nanocomposites for constructing biosensors.Highlights► A water-soluble GR/Au nanocomposites was synthesized by a chemical co-reduction method. ► A novel electrochemical sensor for epinephrine was fabricated based on the GR/Au nanocomposites. ► This sensor showed high sensitivity in the detection of epinephrine. ► The sensor in real sample analysis was examined in pharmacal injection.

A solution-based approach of chemical co-reduction of graphene oxide (GO) and HAuCl4 was used to prepare graphene/Au nanocomposite (GR/Au). The resulting hybrid material was characterized by scanning electron microscope and transmission electron microscope, which demonstrated that Au nanoparticles could been uniformly deposited on the GR sheets. Then, nanocomposite (GR/Au/ILs) of ionic liquids (ILs), GR and Au nanoparticles (NPs) were successfully prepared. Such a nanostructured composite greatly facilitated electron-transfer process and the sensing behavior for PQ detection, leading to remarkably improved sensitivity. The GR/Au/ILs modified glassy carbon electrode showed a broad linear range from 2.0 × 10−9 mol L−1 to 1.0 × 10−7 mol L−1, with a detection limit of 7.3 × 10−10 mol L−1 (S/N = 3) for PQ, along with good reproducibility and stability. At the same time, this sensor could be applied to the determination of PQ in real samples with satisfactory results.

A novel and sensitive electrogenerated chemiluminescence (ECL) sensor for formaldehyde was developed with the amine-functionalized Ru(bpy)32+-doped silica nanoparticles (Ru-DSNPs) as ECL emitter. Ru(bpy)32+ doped on the silica nanoparticle can maintain its electrochemical activities, which made silica nano-beads a excellent carrier of Ru(bpy)32+ species. The uniform Ru-DSNPs (about 75 nm) were conjugated with Au electrode using mercaptoacetic acid as the intermediate to fabricate an ECL sensor for formaldehyde. The ECL analytical performances of this ECL sensor for formaldehyde based on its enhancement ECL emission of Ru(bpy)32+ were investigated in details. Under the optimum condition, the ECL intensity was linear with the formaldehyde concentration in the range of 1.0 × 10− 8 mol/L to 1.0 × 10− 6 mol/L. The detection limit was 6.0 × 10− 9 mol/L (S/N = 3). This approach offered obvious advantages of being simpler, faster, and more stable compared with other sensors, and possessed great potential for formaldehyde detection which could be applied to determine directly the formaldehyde in real samples without pre-separation.Graphical abstractHighlights► A new electrogenerated chemiluminescence sensor was built to detecte formaldehyde. ► The ECL signal was enhanced by using silica nano-beads as the carrier of Ru(bpy)32+ species. ► This sensor could be applied to determine formaldehyde directly in real samples.

We report on the first label-free electrochemiluminescence (ECL) immunosensor for α-fetoprotein (AFP). It is based on the use of CdSe quantum dots that were electrodeposited directly on a gold electrode from an electrolyte (containing cadmium sulfate, EDTA and selenium dioxide) by cycling the potential between 0 and -1.2 V (vs. SCE) for 60 s. The electrodeposited dots were characterized by scanning electron microscopy and energy dispersive spectroscopy. Under optimal conditions, the specific immunoreaction between AFP and anti-AFP resulted in a decrease of the ECL signal because of the steric hindrance and the transfer inhibition by peroxodisulfate. The quenching effect of the immunoreaction on the intensity of the ECL was used to establish a calibration plot which is linear in the range from 0.05 to 200 ng mL−1. The detection limit is 2 pg mL−1. The assay is highly sensitive and satisfactorily reproducible. In our opinion it opens new avenues to apply ECL in label-free biological assays.

We developed an ultrasensitive electrochemiluminescence (ECL) method for DNA determination using magnetic submicrobeads (SMBs) as the carrier of Ru(bpy)32+ (bpy = 2,2′-bipyridy) and carbon nanotubes (CNTs) as accessorial electrode material. The SMBs with Ru(bpy)32+ were wrapped with CNTs and then immobilized on an Au electrode. In the presence of tri-n-propylamine, ECL of the Ru(bpy)32+ on the SMBs was detected. Since one target DNA (t-DNA) molecule corresponded to one SMB with a large number of Ru(bpy)32+, the ECL signal was amplified. In addition, the Ru(bpy)32+-loaded SMBs were wrapped with CNTs that contacted the electrode. The ECL of Ru(bpy)32+ was greatly increased. Using this method, t-DNA of 3 × 10−16 mol/L could be detected. The method could be used to quantify mRNA in cells.Highlights► Electrochemiluminescence (ECL) of Ru(bpy)32+-coated submicrobeads wrapped with carbon nanotubes is measured. ► Ultrasensitive ECL method for determination of 3 × 10−16 mol/L DNA is investigated. ► The ECL method is used to quantify mRNA in cells.

An electrochemiluminescence-based immunoassay using quantum dots (QDs) as labels for the carcinoembryonic antigen (CEA) was developed using an electrode modified with leafs of nanoporous gold. CEA was initially immobilized on the electrode via a sandwich immunoreaction, and then CdTe quantum dots capped with thioglycolic acid were used to label the second antibody. The intensity of the ECL of the QDs reflects the quantity of CEA immobilized on the electrode. Thus, in the presence of dithiopersulfate as the coreactant, the ECL serves as the signal for the determination of CEA. The intensity of the electroluminescence (ECL) of the electrode was about 5.5-fold higher than that obtained with a bare gold electrode. The relation between ECL intensity and CEA concentration is linear in the range from 0.05 to 200 ng.mL-1, and the detection limit is 0.01 ng.mL-1. The method has the advantages of high sensitivity, good reproducibility and long-term stability, and paves a new avenue for applying quantum dots in ECL-based bioassays.

A novel method for simultaneous determination of nitrophenol isomers at nano-gold modified glassy carbon electrode has been developed. The gold nanoparticles were directly electrodeposited onto the glassy carbon electrode via a constant potential −0.2 V (vs. SCE) for 60 s from 0.1 mol L−1 KNO3 containing 0.4 g L−1 HAuCl4. The resulting electrode (nano-Au/GCE) was characterized with scanning electron microscopy (SEM). The electrochemistry response of nitrophenol isomers at the nano-Au/GCE was studied. The result indicated that o-, m-, and p- nitrophenol are separated entirely at nano-Au/GCE, and a semi-derivative voltammetric technology was adopted to enhance the determination sensitivity. This modified electrode could be applied to direct simultaneous voltammetric determination of nitrophenol isomers in water samples without preseparation with higher sensitivity.

The electrochemistry of mercaptopropionic acid capped CdTe quantum dots (QDs) was studied by differential pulse voltammetry, three processes were obtained at 0.36 (A1), 0.68 (A2) and 0.84 V (A3), respectively. A1 process could be selectively suppressed by magnesium ion, an electrochemical sensor for magnesium ion was developed with a linear response from 4 × 10−5 to 1 × 10−2 mol/L and good reproducibility. This electrochemical sensing application of QDs may provide a new strategy for QDs-based detection.

AbstractBlack carbon (BC) can strongly adsorb hydrophobic organic compounds (HOCs). The HOC sorption to coated BC could be attenuated in soil and sediment compared with that of the parent BC. To study the potential causes of the sorption attenuation, humic acid (HA) and BC were isolated. Phenanthrene (PHE) was selected as the representative of HOCs. BC was coated with the precipitated HA. The PHE sorption to the HA-coated BC was determined. The HA coatings on BC could result in the significant sorption attenuation of PHE to BC. The attenuation varied in different HA origin and was positively correlated to the aromaticity of HA. The attenuation could be explained by the direct competition between HA and PHE for the available sorption sites on BC and the reduction of the available sorption sites as a result of the pore blockage of BC caused by the HA coatings. Therefore, the HA coatings on BC was one potential cause of the attenuation of HOC sorption to BC in soil and sediment.

A solution-based approach of chemical co-reduction of graphene oxide (GO) and HAuCl4 was used to prepare graphene/Au nanocomposite (GR/Au). The resulting hybrid material was characterized by scanning electron microscope and transmission electron microscope, which demonstrated that Au nanoparticles could been uniformly deposited on the GR sheets. Then, nanocomposite (GR/Au/ILs) of ionic liquids (ILs), GR and Au nanoparticles (NPs) were successfully prepared. Such a nanostructured composite greatly facilitated electron-transfer process and the sensing behavior for PQ detection, leading to remarkably improved sensitivity. The GR/Au/ILs modified glassy carbon electrode showed a broad linear range from 2.0 × 10−9 mol L−1 to 1.0 × 10−7 mol L−1, with a detection limit of 7.3 × 10−10 mol L−1 (S/N = 3) for PQ, along with good reproducibility and stability. At the same time, this sensor could be applied to the determination of PQ in real samples with satisfactory results.

Based on silica and nanocomposite prepared from reduced graphene oxide and gold nanoparticles (SiO2/rGO–AuNPs), a novel and sensitive electrochemical sensor for bisphenol A (BPA) was fabricated. The electrochemical behavior of BPA on a SiO2/rGO–AuNP nanocomposite was investigated by cyclic voltammetry. Compared with bare GCE, the SiO2/rGO–AuNPs/GCE electrochemical sensor obviously reduced the oxidation overpotential of BPA and greatly enhanced the peak current. The direct detection of BPA was accomplished by using differential pulse voltammetry (DPV) under optimized conditions. A linear voltammetric response to BPA within the concentration range of 3.0 × 10−8 to 1.0 × 10−5 mol L−1 and 1.0 × 10−5 to 1.2 × 10−4 mol L−1 with a low detection limit of 5.0 × 10−9 mol L−1 (S/N = 3) was obtained. In addition, the fabricated sensor was successfully applied to detect BPA in thermal paper samples, and the results were satisfactory.