Highly conductive graphene nanoplatelet (GNP) inks for the rapid surface coating of diverse substrates are prepared by a simple ball-milling method. The method which employs direct yellow 50 (DY50) as a modifier is able to prepare a DY50-decorated GNP nanohybrid (GNP-DY50) from graphite with high production yield (∼100%), high conductivity (up to 3.5 × 104 S/m), high dispersion concentration and excellent film formation ability. The unique structure of DY50, i.e., a rigid, planar and conjugated diazo dye bearing four sulfonate groups, and its strong π-π and charge transfer interactions with exfoliated GNPs, are demonstrated responsible for the efficient synthesis of such GNPs. Very interestingly, the dispersion of 20 mg/mL GNP-DY50 in isopropanol produces a stable and viscous ink, which can achieve the formation of smooth, compact and strongly adhesive GNP coatings within several minutes on the surface of a variety of substrates, e.g., glass beads, copper wires, plastic films, porous sponges and plant leaves. The resulting GNP coatings possess good mechanical property, high conductivity, favorable electrochemical behaviors and efficient electrothermal effects, which have potential applications in a wide range of fields including energy storage devices, electrochemical sensors, smart thin-film heaters and functional coatings.Download high-res image (375KB)Download full-size image

•The photoelectrochemical properties of NO was first investigated.•A novel photoelectrochemical sensor of NO was developed.•C60 was functionalized by polyhydroquinone (PH2Q), forming an electron donor–acceptor linked supramolecular system.•An enhanced cathodic photocurrent response of NO was obtained on a PH2Q-C60 modified ITO electrode under visible light radiation.•The main interferent NO2− has no apparent photoelectrochemical response on the NO photoelectrochemical sensor.An electron donor–acceptor linked supramolecular system composed of polyhydroquinone (PH2Q) and fullerene (C60) was prepared and characterized by different techniques like TEM, UV–vis, XRD and photoelectrochemical photocurrent detection techniques. The photoelectrochemical properties of nitric oxide (NO) were first investigated. An enhanced cathodic photocurrent response was obtained on the PH2Q-C60 modified ITO electrode under visible light radiation with NO as electron acceptor. The photoelectrochemical process of NO was discussed and a novel photoelectrochemical sensor of NO was developed. The influence of the main interferents, especially the significant interfering species NO2− was proved to be negligible. The photoelectrochemistry of NO and the new NO sensor may have potential applications in photoelectrochemistry and biological analysis field.

In recent years, graphene-based enzyme biosensors have received considerable attention due to their excellent performance. Enormous efforts have been made to utilize graphene oxide and its derivatives as carriers of enzymes for biosensing. However, the performance of these sensors is limited by the drawbacks of graphene oxide such as slow electron transfer rate, low catalytic area and poor conductivity. Here, we report a new graphene-based enzyme carrier, i.e. a highly conductive 3D nitrogen-doped graphene structure (3D-NG) grown by chemical vapour deposition, for highly effective enzyme-based biosensors. Owing to the high conductivity, large porosity and tunable nitrogen-doping ratio, this kind of graphene framework shows outstanding electrical properties and a large surface area for enzyme loading and biocatalytic reactions. Using glucose oxidase (GOx) as a model enzyme and chitosan (CS) as an efficient molecular binder of the enzyme, our 3D-NG based biosensors show extremely high sensitivity for the sensing of glucose (226.24 μA mM−1 m−2), which is almost an order of magnitude higher than those reported in most of the previous studies. The stable adsorption and outstanding direct electrochemical behaviour of the enzyme on the nanocomposite indicate the promising application of this 3D enzyme carrier in high-performance electrochemical biosensors or biofuel cells.

Potassium permanganate (KMnO4) has been proved to be an efficient oxidant for converting graphite into graphite oxide, but its slow diffusion in the interlayer of graphite seriously restricts the production of graphene oxide (GO). Here, we demonstrate that the preoxidation of graphite by impure manganese dioxide (MnO2) in a mixture of concentrated sulfuric acid (H2SO4) and phosphorus pentoxide (P2O5) can efficiently improve the synthesis of GO when KMnO4 is employed as the oxidant. The prepared honey-like GO hydrogels possess a high yield of single-layer sheets, large sizes (average lateral size up to 20 μm), wide ranges of stable dispersion concentrations (from dilute solutions, viscous hydrogels, to dry films), and good conductivity after reduction (∼2.9 × 104 S/m). The mechanism for the improved synthesis of GO by impure MnO2 was explored. The enhanced exfoliation and oxidation of graphite by oxidative Mn ions (mainly Mn3+), which are synergistically produced by the reaction of impure MnO2 with H2SO4 and P2O5, are found to be responsible for the improved synthesis of such GO hydrogels. Particularly, preoxidized graphite (POG) can be partially dispersed in water with sonication, which allows the facile construction of flexible and highly conductive graphene nanosheet film electrodes with excellent electrochemical sensing properties.Keywords: graphene oxide; hydrogels; ion intercalated exfoliation; manganese dioxide; potassium permanganate

Ultrasensitive multiplexed detection of biomarkers on a single electrode is usually a great challenge for electrochemical sensors. Here, a light addressable photoelectrochemical sensor (LAPECS) for the sensitive detection of multiple DNA biomarkers on a single electrode was reported. The sensor was constructed through four steps: (1) immobilization of capture DNA (C-DNA) of different targets on different areas of a single large-sized gold film electrode, (2) recognition of each target DNA (T-DNA) and the corresponding biotin-labeled probe DNA (P-DNA) through hybridization, (3) reaction of the biotin-labeled probe DNA with a streptavidin-labeled all-carbon PEC bioprobe, and (4) PEC detection of multiple DNA targets one by one via a light addressing strategy. Through this principle, the LAPECS can achieve ultrasensitive detection of three DNA sequences related to hepatitis B (HBV), hepatitis C (HCV) and human immunodeficiency (HIV) viruses with a similar wide calibration range of 1.0 pM ∼ 0.01 μM and a low detection limit of 0.7 pM by using one kind of PEC bioprobe. Moreover, the detection throughput of LAPECS may be conveniently expanded by simply enlarging the size of the substrate electrode or reducing the size of the sensing arrays and the light beam. The present work thus demonstrates the promising applications of LAPECS in developing portable, sensitive, high-throughput, and cost-effective biosensing systems.

•A gold–PET film electrode (GPETFE) was fabricated by a simple electroless method.•GPETFE modified with a carbon photovoltaic material creates a new PEC sensor.•This PEC sensor was applied to the selective detection of AA in food samples.A simple electroless method for fabricating inexpensive and flexible gold film electrodes was reported. The method was established by the spontaneous adsorption of gold nanoparticle (GNP) seeds on polyethylene terephthalate (PET) film substrates and the self-catalytic growth of the adsorbed GNP seeds into conductive gold layers. The resulting gold–PET composite film electrode (GPETFE) not only possessed better flexibility and conductivity as compared with the widely used indium tin oxide (ITO) substrates, but also exhibited apparently higher conversion efficiency for photoelectrochemical (PEC) sensing. As a result, the modification of GPETFE by a hybrid photovoltaic material that comprised carboxylated multiwalled carbon nanotubes, Congo red and fullerene (MWNTCOOH-CR-C60) created a disposable and highly selective thin-film PEC sensor of ascorbic acid (AA), i.e., the PEC response of 1.0 mM AA was hardly influenced by interferents like 100 folds of dopamine (DA) and hydroquinone (H2Q). The produced PEC sensor also showed a sensitive PEC response toward AA with wide calibration ranges from 2.5 μM to 2.5 mM and a low detection limit of 0.5 μM (S/N = 3), which was successfully applied to the detection of AA in real samples like fruits, vegetables and beverages.

This work reported the rapid in situ detection of ultratrace 2,4-dinitrotoluene (DNT) solids on various substrates by a sandwiched paper-like electrochemical sensor. The sensor, prepared by a simple electroless deposition method without using special instruments, possessed a unique thin-film structure of an insulated polyvinylidene fluoride (PVDF) membrane in between two gold (Au) conducting layers. The resulting gold–PVDF sandwich (GPVDFS) array exhibited excellent flexibility, porosity and electrochemical performance as a highly integrated dual-electrode sensor platform. The infiltration of nonvolatile ionic liquid (IL) electrolytes containing ferrocene (Fc) into the GPVDFS array produced a paper-like electrochemical sensor, which can directly detect ultratrace DNT solids on various substrate surfaces (e.g., plant leaves, gloves and metal knives) with detection limit as low as 0.33 ng/mm2. The critical role of Fc in the detection of DNT at this dual-electrode sensor was explored. The compensating electrochemical oxidation of Fc at the counter/reference electrode was found to be essential to the reduction of DNT at the working electrode when IL electrolytes were employed. The present work thus demonstrated the promising applications of paper-based porous electrode arrays in developing IL-based electrochemical sensors for the in situ detection of analyte solids in complicated environments.

A novel enzyme-free and all-carbon photoelectrochemical (PEC) bioprobe, based on carboxylated multiwalled carbon nanotube–Congo red–fullerene nanohybrids (MWNTCOOH–CR–C60), for the ultrasensitive immunosensing of carcinoembryonic antigen (CEA) was reported. The MWNTCOOH–CR–C60 nanohybrids, prepared by mechanically grinding a mixture of MWNTCOOH, C60, and CR at a certain mass ratio, had good water dispersibility and high PEC conversion efficiency in visible light ranges. Covalent binding of the detection antibody of CEA on the MWNTCOOH–CR–C60 nanohybrids produced a sensitive PEC bioprobe for detection of CEA by sandwich immunosensing. The corresponding immunosensor, employing an inexpensive and portable green laser light, possessed a wide calibration range of 1.0 pg/mL∼100.0 ng/mL and a low detection limit of 0.1 pg/mL (calculated 5 zmol for a 10.0 μL sample solution) (S/N = 3), which was successfully applied to the detection of CEA in serum samples from both healthy people and cancer patients. The present work thus demonstrated the promising application of fullerene-based nanocomposites in developing highly sensitive, environmentally friendly, and cost-effective PEC biosensors.

A simple approach to the mass production of nanoporous gold electrode arrays on cellulose membranes for electrochemical sensing of oxygen using ionic liquid (IL) electrolytes was established. The approach, combining the inkjet printing of gold nanoparticle (GNP) patterns with the self-catalytic growth of these patterns into conducting layers, can fabricate hundreds of self-designed gold arrays on cellulose membranes within several hours using an inexpensive inkjet printer. The resulting paper-based gold electrode arrays (PGEAs) had several unique properties as thin-film sensor platforms, including good conductivity, excellent flexibility, high integration, and low cost. The porous nature of PGEAs also allowed the addition of electrolytes from the back cellulose membrane side and controllably produced large three-phase electrolyte/electrode/gas interfaces at the front electrode side. A novel paper-based solid-state electrochemical oxygen (O2) sensor was therefore developed using an IL electrolyte, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6). The sensor looked like a piece of paper but possessed high sensitivity for O2 in a linear range from 0.054 to 0.177 v/v %, along with a low detection limit of 0.0075% and a short response time of less than 10 s, foreseeing its promising applications in developing cost-effective and environment-friendly paper-based electrochemical gas sensors.

cis-Jasmone is a plant activator in terms of production of defence-related volatile semiochemicals. The redox and quantitative analysis of cis-jasmone are practically significant for the investigation of physiological processes in plants. In this work, the electrochemical characteristics of cis-jasmone in different acid media were investigated at a multi-wall carbon nanotube/Nafion composite film modified glassy carbon electrode (MWNT/Nafion/GCE) by cyclic voltammetry, chronocoulometry and infrared spectroscopy. The redox mechanism of cis-jasmone in strong acid media, i.e., a remarkable catalytic oxidation process for the reduction product of cis-jasmone at MWNT/Nafion/GCE, was demonstrated to be completely different from the cases in weakly acidic or neutral solution. The standard rate constant k0, the diffusion coefficient D and the surface coverage Γ were calculated and discussed. The sensitive anodic stripping voltammetric response of cis-jasmone was employed to determine its content in the extract of rice spikelet. The electrochemical redox and quantitative analysis of cis-jasmone are therefore of great significance for studying not only the physiological processes of cis-jasmone in plants but also the electrochemical redox mechanism of other α,β-unsaturated ketones.Highlights► The electrochemical characteristics of cis-jasmone in strong acid media were different from those in weakly acidic or neutral solution. ► A remarkable catalytic redox process for cis-jasmone was demonstrated at MWNT/Nafion/GCE. ► The redox mechanism of cis-jasmone in strong acid media has been proposed.

A novel electrochemical system for the sensitive determination of cis-jasmone on an electrodeposited Nafion film modified glassy carbon electrode (e-Nafion/GCE) in the presence of cetyltrimethylammonium bromide (CTAB) was described. The redox mechanism of cis-jasmone on e-Nafion/GCE was studied by voltammetry, chronocoulometry and infrared spectroscopy. The property and interface behavior of the e-Nafion film were characterized by electrochemical impedance spectrometry. The standard rate constant k0, the diffusion coefficient D and the surface coverage Γ were calculated and discussed. Under optimal working conditions, the anodic stripping peak current of cis-jasmone linearly increased with its concentration in the range of 6.0 × 10−7 to 1.0 × 10−4 mol/L, with a detection limit of 4.0 × 10−7 mol/L. The proposed method was applied to the determination of cis-jasmone in spikelet samples of rice and the good recoveries showed that it may have potentially valuable applications.Highlights► Electrochemical redox mechanism of cis-jasmone. ► Electrodeposited Nafion film modified glassy carbon electrode (e-Nafion/GCE). ► Enhancement effect of cetyltrimethylammonium bromide. ► Sensitive determination of cis-jasmone by anodic stripping voltammetry.

A disposable electrochemical sensor for the determination of indole-3-acetic acid (IAA) based on nanocomposites of reduced graphene oxide (rGO) and poly(safranine T) (PST) was reported. The sensor was prepared by coating a rGO film on a pre-anodized graphite electrode (AGE) through dipping–drying and electrodepositing a uniform PST layer on the rGO film. Scanning electron microscopic (SEM) and infrared spectroscopic (IR) characterizations indicated that PST–rGO formed a rough and crumpled composite film on AGE, which exhibited high sensitive response for the oxidation of IAA with 147–fold enhancement of the current signal compared with bare AGE. The voltammetric current has a good linear relationship with IAA concentration in the range 1.0 × 10−7–7.0 × 10−6 M, with a low detection limit of 5.0 × 10−8 M. This sensor has been applied to the determination of IAA in the extract samples of several plant leaves and the recoveries varied in the range of 97.71–103.43%.

In this work, Au–Ag alloy nanoparticles were biosynthesized by yeast cells and applied to fabricate a sensitive electrochemical vanillin sensor. Fluorescence microscopic and transmission electron microscopic characterizations indicated that the Au–Ag alloy nanoparticles were mainly synthesized via an extracellular approach and generally existed in the form of irregular polygonal nanoparticles. Electrochemical investigations revealed that the vanillin sensor based on Au–Ag alloy nanoparticles modified glassy carbon electrode was able to enhance the electrochemical response of vanillin for at least five times. Under optimal working conditions, the oxidation peak current of vanillin at the sensor linearly increased with its concentration in the range of 0.2–50 μM with a low detection limit of 40 nM. This vanillin sensor was successfully applied to the determination of vanillin from vanilla bean and vanilla tea sample, suggesting that it may have practical applications in vanillin monitoring system.

We report a simple method for the stable dispersion of multi-walled carbon nanotubes (MWNTs) in water by vanillin and controllable surface addition onto carbon fiber microelectrodes (CFE) via electropolymerization. We have characterized these polyvanillin-carbon nanotube (PVN-MWNT) composite films with techniques including scanning electron microscopy (SEM), infrared spectroscopy (IR) and voltammetry. These investigations showed that the films have a uniform porous nanostructure with a large surface area. This PVN-MWNT composite-modified CFE (PVN-MWNT/CFE) exhibited a sensitive response to the electrochemical oxidation of nitrite. Under optimal working conditions, the oxidation peak current of nitrite linearly increased with its concentration in the range of 0.2 μM–3.1 mM, with the system exhibiting a lower detection limit of 50 nM (S/N = 3). We successfully applied the PVN-MWNT/CFE system to the determination of nitrite from lake water. The efficient recovery of nitrite indicated that this electrode was able to detect nitrite in real samples.

An ultrathin film of gold was grafted on human hair by a chemical liquid deposition method under ambient conditions. The method consisted of the assembling of gold nanoparticles (GNPs) on the adsorptive sites of human hair as seeds and the growth of isolated GNP seeds into a continuous gold layer. The resulting gold film coated hair possessed good conductivity and flexibility, and can be used as a novel gold hair microelectrode (GHME). This electrode inherited some merits of both hair and gold nanoparticles, for instance, good mechanical property, excellent biocompatibility and high surface area. GHME was also proven to exhibit sensitive electrochemical responses toward dopamine and nitric oxide, foreseeing its promising applications in the fields of biomedical analysis.

Multi-walled carbon nanotube multilayers were modified onto a newly proposed gold hair microelectrode via a simple layer-by-layer assembling method. The resulting electrode showed a sensitive oxidation response to estradiol with detection limit as low as 1.0 × 10−8 mol/L, foreseeing a promising approach to the fabrication of high-sensitive microsensors.

A new noncovalent approach for the dissolution of MWNTs in water by azocarmine B (ACB) is reported. Through a simple electro-polymerization procedure, a novel electrochemical NO sensor based on water-soluble MWNTs and polyazocarmine B (PACB) nanofilm electrode was prepared, which showed excellent electrocatalytic activity towards the oxidation of nitric oxide (NO). The oxidation current linearly increased with the nitric oxide concentration in the range of 2.2 × 10−7–1.2 × 10−4 mol L−1 with a low detection limit of 2.8 × 10−8 mol L−1. The sensor has the merit of good stability, reproducibility, high sensitivity and selectivity, and it can be used to monitor NO released from rat liver cells effectively.

Carbon nanotubes (CNTs) from different sources were dissolved in water with high solubility by Congo red (CR) via strong noncovalent π-stacking interactions. The resulting CNTs were capable of forming uniform, compact, stable films on various substrates. This provided a chance to explore the relationship between the surface property of CNTs and the adsorptive behavior of analytes on CNTs without considering the influence of film structures or free additives. Electrochemical behaviors of several small biomolecules and glucose oxidase (GOD) on various CR-functionalized CNT films were examined. The results showed that both the hydrophobic structural defect sites and the hydrophilic oxygen-containing groups were the electroactive sites of CNTs, which was further proven by UV−vis and FTIR spectra. Moreover, the surface properties of CNTs could be conveniently designed by simple pretreatments for optimizing the adsorption and the electrochemical response of analytes. For instance, the hydrophobic defect sites created during the growth or the workup of CNTs were favorable to the adsorption and the electrochemical response of hydrophobic analytes, whereas the hydrophilic oxygen-containing groups produced by acid treatment facilitated the stable adsorption and the direct electrochemistry of redox proteins.

•A simple deposition method for producing uniform Bi2S3 films was established.•A label-free and light-addressable PEC sensor was constructed on the Bi2S3 films.•The sensor can achieve sensitive multiplexed detection on a single electrode.•The sensor possesses properties of high throughput and self-calibration ability.The sensitive and label-free detection of multiple biomarkers on a single electrode by photoelectrochemical (PEC) sensors based on light addressing strategies is very attractive for developing portable and high-throughput biosensing systems. The essential prerequisite of this proposal is the employment of uniform photovoltaic material modified electrodes with high conversion efficiency. Herein, a novel two-step constant potential deposition method for the rapid fabrication of bismuth sulfide film modified ITO electrodes (Bi2S3/ITO) was established. The produced Bi2S3/ITO, with excellent uniformity and high conversion efficiency in visible light ranges, was further modified with gold nanoparticles (AuNPs) and then divided into separated identical sensing zones by insulative paints. The adsorption-based immobilization of antibodies of three tumor markers, i.e., a-fetoprotein (AFP), carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA19-9), onto different sensing zones of the electrode and the further blocking with BSA established a label-free and light-addressable PEC sensor (LF-LAPECS), which can achieve the rapid and sensitive detection of these biomarkers with wide linear ranges, low detection limits and self-calibration ability. Moreover, the detection throughput can be conveniently improved by enlarging the size of the substrate electrode and increasing the number of separated sensing zones. The present work thus demonstrates the promising applications of PEC techniques for developing sensitive, time-saving, cost-effective and high-throughput biosensing methods.