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This paper demonstrates, for the first time, the use of paper-based electrochemical devices coupled to external solid working electrodes. The paper-based electrochemical cells were fabricated using inexpensive and largely available office paper, according to a simple protocol that consists on the creation of hydrophobic barriers using paraffinized paper and preheated metal stamp. The counter and reference electrodes were integrated to the paper platform through the deposition of carbon and silver inks, respectively. The electrochemical paper analytical device (ePAD) was coupled to external glassy carbon rod electrode modified with reduced graphene oxide doped with Cu nanoparticles through meniscus configuration. The analytical usefulness of this electrochemical approach was demonstrated through the simultaneous determination of paracetamol and caffeine in biological samples. The analytes were successfully quantified in real urine samples and limits of detection of 24.6 nM (paracetamol) and 36.1 nM (caffeine) were obtained. The paper platform showed good stability (RSD of 1.07 % for the peak currents and 1.43 % for the peak potentials) and satisfactory performance. The use of solid electrodes coupled to paper electrochemical devices, firstly demonstrated here, opens new possibilities for the utilization of ePADs in electrochemistry and electroanalytical chemistry and offers advantages such as the extremely reduced consumption of reagents and the minimal generation of wastes. [ABSTRACT FROM AUTHOR]

The nanoporous graphene papers (NGPs) was prepared by the hard-template method. The Pt−Pd modified NGPs hybrid was prepared by the self-assembly method. Then a glassy carbon electrode (GCE) modified with Pt−Pd bimetallic nanoparticles-functionalized nanoporous graphene composite has been prepared for the electrochemical determination of Xanthine (XA). The Pt−Pd/NGPs hybrid was characterized by transmission electron microscopy, scanning electron microscope and X-ray diffraction. The electrochemical behavior of XA on Pt−Pd/NGPs/GCE was investigated by cyclic voltammetry and amperometric i-t. The Pt−Pd/NGPs modified electrode exhibited remarkably electrocatalytic activity towards the oxidation reaction of XA in phosphate buffer solution (pH=5.5). Under the optimal conditions, the determination of XA was accomplished by using amperometric i-t, the linear response range from 1.0×10−5∼1.2×10−4 M. The detection limit was 3.0×10−6 M (S/N=3). The proposed modified electrode showed good sensitivity, selectivity, and stability with applied to determine XA in human urine. [ABSTRACT FROM AUTHOR]

In this paper, ultrathin graphene (GN) nanosheets were uniformly decorated with nickel (Ni) nanoparticles, as confirmed by scanning electron microscopy and transmission electron microscopy. This GNNi hybrid exhibited excellent accumulation and catalytic capacity for the simultaneous detection of sunset yellow and tartrazine, two colorants commonly found mixed in foodstuffs. The electrochemical reaction mechanism of sunset yellow and tartrazine were studied in detail on the GNNi nanocomposite modified glassy carbon electrode. In square wave voltammetry measurements, the oxidation peak potentials of sunset yellow and tartrazine were separated by about 250 mV. This novel proposed voltammetric method has good selectivity which was successfully applied for the simultaneous determination of sunset yellow and tartrazine in some food sample extracts. [ABSTRACT FROM AUTHOR]

The nanocomposite (denoted as GR-AuNPs-CD-CS) of graphene (GR), gold nanoparticles (AuNPs), chitosan (CS) and β-cyclodextrin (β-CD) was prepared to modify a glassy carbon electrode. The as-modified electrode was explored for the ultrasensitive detection of dopamine (DA) and uric acid (UA). The modified electrode demonstrated linearly increased current response in the concentration range of 0.1-120 µm for DA and 0.05-70 µm for UA, with so far the best detection limit for DA and UA. Good stability and repeatability were further demonstrated for the as-made sensor. [ABSTRACT FROM AUTHOR]

A novel nonenzymatic H2O2 sensor based on a palladium nanoparticles/graphene (Pd-NPs/GN) hybrid nanostructures composite film modified glassy carbon electrode (GCE) was reported. The composites of graphene (GN) decorated with Pd nanoparticles have been prepared by simultaneously reducing graphite oxide (GO) and K2PdCl4 in one pot. The Pd-NPs were intended to enlarge the interplanar spacing of graphene nanosheets and were well dispersed on the surface or completely embedded into few-layer GN, which maintain their high surface area and prevent GN from aggregating. XPS analysis indicated that the surface Pd atoms are negatively charged, favoring the reduction process of H2O2. Moreover, the Pd-NPs/GN/GCE could remarkably decrease the overpotential and enhance the electron-transfer rate due to the good contact between Pd-NPs and GN sheets, and Pd-NPs have high catalytical effect for H2O2 reduction. Amperometric measurements allow observation of the electrochemical reduction of H2O2 at 0.5 V (vs. Ag/AgCl). The H2O2 reduction current is linear to its concentration in the range from 1×10−9 to 2×10−3 M, and the detection limit was found to be 2×10−10 M ( S/ N=3). The as-prepared nonenzymatic H2O2 sensor exhibits excellent repeatability, selectivity and long-term stability. [ABSTRACT FROM AUTHOR]

A Fe3O4 magnetic nanoparticles/reduced graphene oxide nanocomposite modified glassy carbon electrode (Fe3O4/r-GO/GCE) was further expanded into the design of a high performance electrochemical biosensing platform. First, direct electrochemistry of glucose oxidase(GOx) immobilized onto Fe3O4/r-GO/GCE and its biocatalytic activity toward glucose oxidation was investigated. Then, differential pulse voltammetry (DPV) was used to investigate the electrochemical oxidation behavior of four DNA free bases of guanine (G), adenine (A), thymine (T) and Cytosine (C) at Fe3O4/r-GO/GCE. In addition, a label-free electrochemical impedance spectroscopy (EIS) method of detection was developed for Immunoglobulin E (IgE) in which the binding of IgE-specific aptamers immobilized on Fe3O4/r-GO/GCE leads to impedance changes associated with IgE binding events. [ABSTRACT FROM AUTHOR]