Chengguo Hu

Simultaneous determination of lead(II) and cadmium(II) at a diacetyldioxime modified carbon paste electrode by differential pulse stripping voltammetry

A simple and effective chemically modified carbon paste electrode (CMCPE) for the simultaneous determination of lead(II) and cadmium(II) was developed in this work. The electrode was prepared by the addition of diacetyldioxime into a carbon paste mixture. Pb(2+) and Cd(2+) were preconcentrated on the surface of the modified electrode by complexing with diacetyldioxime and reduced at a negative potential (-1.10 V). Then the reduced products were oxidized by differential pulse stripping. The fact that two stripping peaks appeared on the voltammograms at the potentials of -0.65 V (Cd(2+)) and -0.91 V (Pb(2+)) demonstrates the possibility of simultaneous determination of Pb(2+) and Cd(2+). Under the optimized working conditions, calibration graphs were linear in the concentration ranges of 1.0x10(-7)-1.5x10(-5) mol l(-1) (Pb(2+)) and 2.5x10(-7)-2.5x10(-5) mol l(-1) (Cd(2+)), respectively. For 5 min preconcentration, detection limits of 1x10(-8) mol l(-1) (Pb(2+)) and 4x10(-8) mol l(-1) (Cd(2+)) were obtained at the signal noise ratio (SNR) of 3. To evaluate the reproducibility of the newly developed electrode, the measurements of 5x10(-7) mol l(-1) Pb(2+) and Cd(2+) were parallel carried out for six times at different electrodes and the relative standard deviations were 2.9% (Pb(2+)) and 3.2% (Cd(2+)), respectively. Interferences by some metals were investigated. Only Ni(2+) and Hg(2+) apparently affected the peak currents of Pb(2+) and Cd(2+). The diacetyldioxime modified carbon paste electrode was applied to the determination of Pb(2+) and Cd(2+) in water samples. The results indicate that this electrode is sensitive and effective for the simultaneous determination of Pb(2+) and Cd(2+).

Inkjet Printing of Nanoporous Gold Electrode Arrays on Cellulose Membranes for High-Sensitive Paper-Like Electrochemical Oxygen Sensors Using Ionic Liquid Electrolytes

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 (O(2)) sensor was therefore developed using an IL electrolyte, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF(6)). The sensor looked like a piece of paper but possessed high sensitivity for O(2) 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.

Ultrasensitive All-Carbon Photoelectrochemical Bioprobes for Zeptomole Immunosensing of Tumor Markers by an Inexpensive Visible Laser Light

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 disposable electrochemical sensor for the determination of indole-3-acetic acid based on poly(safranine T)-reduced graphene oxide nanocomposite

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%.

Surface Design of Carbon Nanotubes for Optimizing the Adsorption and Electrochemical Response of Analytes

Carbon nanotubes (CNTs) from different sources were dissolved in water with high solubility by Congo red (CR) via strong noncovalent pi-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.

Single-chain surfactant monolayer on carbon paste electrode and its application for the studies on the direct electron transfer of hemoglobin

A variety of single-chain surfactants with different charge properties and tail lengths can spontaneously adsorb on the hydrophobic surface of carbon paste electrode and form stable monolayers on the electrode surface. Hemoglobin (Hb) was successfully immobilized on these surfactant monolayers to form stable protein-surfactant composite films regardless of the charge and the tail length of surfactants. The resulting surface-confined Hb exhibited well-defined direct electron-transfer behaviors in all positively, neutrally and negatively charged surfactant films, suggesting the important role of hydrophobic interactions in the adsorption of Hb on surfactant films. When the density of surfactant monolayers was controlled to be the same, Hb was found to possess a better direct electron-transfer behavior on monolayers of cationic surfactants with a longer tail length. This, in combination with the tunneling effect in the direct electron transfer of Hb on surfactant films, demonstrated that the adsorption of Hb on surfactant monolayers may be mainly achieved by the partial intercalation of Hb in the loose structures of surfactant films through hydrophobic interactions between the alkane chains of surfactants and the hydrophobic regions of Hb. The native conformation of Hb adsorbed on these surfactant films was proved to be unchanged, reflected by the unaltered ultraviolet-visible (UV-vis) and reflection-absorption infrared (RAIR) spectra, and by the catalytic activity toward hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) in comparison with the free Hb molecules.

Ultrasensitive Photoelectrochemical Biosensing of Multiple Biomarkers on a Single Electrode by a Light Addressing Strategy

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.

Fully Converting Graphite into Graphene Oxide Hydrogels by Preoxidation with Impure Manganese Dioxide

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 × 10(4) 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 Mn(3+)), 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.

A highly sensitive electrochemical method for the determination of Sudan I at polyvinylpyrrolidone modified acetylene black paste electrode based on enhancement effect of sodium dodecyl sulphate.

A novel electrochemical method for the sensitive determination of trace Sudan I at a polyvinylpyrrolidone (PVP) modified acetylene black carbon paste electrode (PVP/CPE) based on the enhancement effect of sodium dodecyl sulphate (SDS) was reported. Compared with the poor response at a bare acetylene black paste electrode (CPE), a well-defined oxidation peak of Sudan I was observed at the PVP modified CPE. The oxidation peak current of Sudan I was further enhanced with the addition of SDS, which was attributed to the enhancement effect of SDS at PVP/CPE. Under optimal working conditions, the oxidation peak current of Sudan I was proportional to its concentration in the range of 2.0 × 10−7–8.0 × 10−6 mol L−1, with a low detection limit of 1.0 × 10−8 mol L−1. The proposed method was successfully applied to the detection of Sudan I in chilli products.

Development and application of estradiol sensor based on layer-by-layer assembling technique

A simple strategy for the modification of disposable combination graphite-clay electrode, pencil graphite electrode (PGE), by multi-walled carbon nanotube–gold nanoparticle (MWNT–GNP) composite multilayers was proposed as a sensor to determine estradiol. The modification was carried out by the layer-by-layer (LBL) assembling of polyethyleneimine (PEI), decorated GNPs and polyacrylic acid (PAA) functionalised MWNTs via electrostatic interactions on a negatively charged PGE. The resulting MWNT–GNP multilayer modified PGE (MWNT–GNP/PGE) exhibited a sensitive electrochemical response towards the oxidation of estradiol at 0.90 V. Under optimal working conditions, the oxidation current of estradiol at MWNT–GNP/PGE increased linearly with its concentration in the range 7.0 × 10−8–4.2 × 10−5 mol l−1, with a low-detection limit of 1.0 × 10−8 mol l−1 for 200 s accumulation at an open circuit. This sensor was successfully applied to the detection of estradiol in blood serums.