Deposition of precious metal catalysts onto the surface of various supporting materials to enhance the stability and catalytic activity is highly desired. Although extensive studies have been focused on the supported metal catalysts, their preparations are mainly based on the use of reducing agents which are not environmentally benign. Herein, we report a one-pot and green synthesis of gold nanoparticles (Au NPs) deposited on cellulose nanocrystals (CNs) under hydrothermal conditions using CNs as a reducing agent and stabilizing template. Our experimental results showed that the abundant electron-rich hydroxyl groups on the surface of CNs played a key role in the reduction and immobilization of Au NPs. The obtained nanohybrid catalyst exhibited much better catalytic activity and stability than the unsupported Au NPs and other Au-containing catalysts for the reduction of 4-nitrophenol. These findings pave the way for the green synthesis of bio-supported nanohybrid catalysts and can spur advancements in nanocellulose-based nanohybrids for their application in sensors, antibacterial materials and electronic devices.

Green synthesis and formation mechanism of cellulose nanocrystal-supported gold nanoparticles with enhanced catalytic performance

Synthesis and utilization of carbon nanotubes for fabrication of electrochemical biosensors

A nanocomposite of graphene (Gr) and CoFe2O4 nanoparticles was synthesized with a facile preparation method in order to fabricate a modified carbon paste electrode. The morphology and structure of Gr/CoFe2O4 nanocomposite were investigated by scanning electron microscopy (SEM), and X-ray diffraction (XRD). Also, electrochemical characterization of the nanocomposite was demonstrated with electrochemical impedance spectroscopy. Based on the synergistic effect of Gr and CoFe2O4 nanoparticles, an ultrasensitive electrochemical sensor for acetaminophen (Ac) and codeine (Cod) was successfully fabricated. The linearity ranged from 0.03 to 12.0 μM for both Ac and Cod. Low detection limits of 0.025 μM for Ac and 0.011 μM for Cod were achieved based on three times of the standard deviation of the blank over sensitivity (3 s/m). The proposed method was free from interference effects of glucose, ascorbic acid, caffeine, naproxen, alanine, phenylalanine, glycine, and others. No electrode surface fouling was observed during successive scans. High stability, high sensitivity, and low detection limit made the proposed electrode applicable for the analysis of various real samples. Moreover, its practical applicability was reliable and desirable in biological fluids and pharmaceutical samples analysis.

Facile simultaneous electrochemical determination of codeine and acetaminophen in pharmaceutical samples and biological fluids by graphene–CoFe2O4 nancomposite modified carbon paste electrode

Biomarkers refer to analytes that can be used in the diagnosis of diseases or disorders. In saliva, there are many components that are potential biomarkers, and increasing research has focussed on the development of saliva as a diagnostic fluid. This review summarizes the existing uses of salivary biomarkers and highlights the importance of the choice of saliva collection as well as the storage procedures. A case study on the effect of collection tools on the concentrations of one of the potential biomarkers, glutathione, is highlighted. Moreover, molecular diagnosis requires reliable measurement assays. This review presents electroanalytical methods for the detection of salivary biomarkers. It further reviews approaches that can be taken to improve the selectivity of electroanalytical assays without the use of biologically selective materials, notably without the use of enzymes or antibodies.

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Chemical analysis in saliva and the search for salivary biomarkers – a tutorial review

Many efficient adsorbents and sensors based on graphene and functionalized graphene have been constructed for the removal and detection of environmental pollutants due to its unique physicochemical properties. In this article, recent research achievements are reviewed on the application of graphene-based materials in the environmental protection and detection. For environmental protection, modified graphene can adsorb heavy metal ions in a high efficiency and selectivity, and thus reduces them to metals for recycling. High adsorption capacity of graphene-based materials to kinds of organic pollutants in water was also presented. Several graphene-based sensors with high limit of detection were reported to detect heavy metal ions, toxic gases and organic pollutants in environment. Finally, a perspective on the future challenge of adsorbents and detection devices based on graphene is given.

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Applications of graphene-based materials in environmental protection and detection

A new voltammetric sensor based on poly(L-arginine)/graphene–Nafion composite film modified electrode for sensitive determination of Terbutaline sulfate

A new electrochemical sensor for codeine was fabricated based on composite graphene and Nafion film modified glassy carbon electrode. It was found that the electrochemical response of this sensor was greatly improved and displayed excellent analytical performance for codeine detection, which could be attributed to the high codeine loading capacity on the electrode surface and the outstanding electric conductivity of graphene. Under the optimized conditions at pH 4.0, the peak currents were linear relationship with codeine concentrations in the range of 5 × 10−8 to 9 × 10−6 mol L−1 and 9 × 10−6 to 3 × 10−5 mol L−1, using square wave voltammetry with a detection limit of 1.5 × 10−8 mol L−1. The proposed method was successfully applied to the determination of codeine in both urine samples and cough syrup.

Electrochemical behavior of codeine and its sensitive determination on graphene-based modified electrode

A voltammetric sensor for Sunset Yellow was fabricated by polymerizing L-cysteine on the surface of a glassy carbon electrode. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical behavior and kinetic parameters of Sunset Yellow in phosphate buffer solution (pH 6.6) were investigated by cyclic voltammetry and chronocoulometry using the proposed sensor, and results showed that the electrochemical response of Sunset Yellow was significantly improved. The peak current (differential pulse voltammetry) of Sunset Yellow linearly increased with the concentrations in the range of 8.0 × 10−9–7.0 × 10−7 mol L−1, and the minimum detectable concentration of Sunset Yellow was estimated to be 4.0 × 10−9 mol L−1. Moreover, the linear relationship between the peak current and the concentration of Sunset Yellow in the presence of Lemon Yellow was 1.0 × 10−8–5.0 × 10−7 mol L−1, with a minimum detectable concentration of 6.0 × 10−9 mol L−1. The reported electrochemical sensor was excellent for the determination of Sunset Yellow because of merits such as extreme simplicity, low cost, high sensitivity, good stability and reproducibility.

Highly sensitive determination of Sunset Yellow in drink using a poly (L-cysteine) modified glassy carbon electrode

An ultrasensitive voltammetric sensor, a simply coated graphene-Na?on suspension on a glass carbon electrode surface, was fabricated and used to investigate the electrochemical behavior of theophylline as described in the present paper. The results indicated that this voltammetric sensor exhibited a special recognition capacity to determine theophylline as well as having high sensitivity due to the excellent characteristics of graphene and the adsorption action of Nafion for theophylline. Under the selected condition using differential pulse voltammetry, the response peak currents had a linear relationship with the theophylline concentrations in two ranges from 1.0 × 10(-8) - 1.0 × 10(-6) and 2.0 × 10(-6) - 3.0 × 10(-5) mol L(-1) with a low detection limit of 6.0 × 10(-9) mol L(-1). Moreover, according to the results obtained in the analysis of theophylline in two standard samples, it demonstrated the applicability of present method into real sample determination.

Electrochemical behavior and voltammetric determination of theophylline at a glassy carbon electrode modified with graphene/nafion.

A new voltammetric sensor was designed by covering a layer of gold nanoparticles (AuNPs) on a carbon paste electrode that was pre-mixed in some multi-walled carbon nanotubes (MWCNT). This sensor exhibited super sensitive detection of the electroactive flavonoid rutin due to the large surface area and good conductivity of MWCNT and AuNPs. Cyclic voltammetry curves at various scan rates and pH were recorded to investigate the redox properties of rutin. Further experiments demonstrated that the oxidative peaks increased linearly with rutin concentrations in the ranges of 4.0 × 10−10 to 1.0 × 10−8 mol L−1 and 2.0 × 10−8 to 1.0 × 10−6 mol L−1 with a limit of detection of 4.0 × 10−11 mol L−1. The method was successfully applied to detect rutin in medicine tablets with satisfactory results.

Kai Zhang

Papers

A new voltammetric sensor based on poly(L-arginine)/graphene–Nafion composite film modified electrode for sensitive determination of Terbutaline sulfate

Electrochemical behavior of codeine and its sensitive determination on graphene-based modified electrode

Highly sensitive determination of Sunset Yellow in drink using a poly (L-cysteine) modified glassy carbon electrode

Electrochemical behavior and voltammetric determination of theophylline at a glassy carbon electrode modified with graphene/nafion.

A supersensitive sensor for rutin detection based on multi-walled carbon nanotubes and gold nanoparticles modified carbon paste electrodes