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The study explores carbon quantum dots (C-dots) as potential candidates for enhancing the signal sensitivity of an electrochemical sensor devised for biologically important molecule, such as uric acid (UA). The C-dots were evaluated for their electrochemical characteristics in combination with Fe3O4 nanoparticles (Fe3O4 NPs), which were applied as the primary electro-catalytic promoter. The hybrid nanocomposite (C-dots/Fe3O4 HCs) formation was achieved by facilitating the adsorption of C-dots over Fe3O4 NPs using amine-carbonyl interactions. Unlike, one pot method, the proposed strategy enables aggregation-free coverage of Fe3O4 NPs with highly conductive layer of C-dots that can act as conduction centres to support ultra-fast electron transfer kinetics to satisfy the need of high signal sensitivity. The hybrid composite demonstrated remarkable signal improvement when tested against the electrochemical oxidation of UA. The heighten current response and lower over-potential values enabled development of a DC-amperometric (DC-AMP) sensor for UA with a linear working range of 0.01 to 0.145 mu M and signal sensitivity measurable up to 6.0 x 10(-9) M. The said improvement was manifested as a synergetic outcome of active redox couple (Fe (III/II)), larger surface area of Fe3O4 NPs engulfed with a layer of highly conductive C-dots acting as efficient charge sensitisers.

This study describes the hydrothermal synthesis of NiO, CuO and Co3O4 nanostructures using acetylsalicylic acid (ASA) as a growth-controlling/directing agent. The as-synthesised nanostructures were shown to possess unique structural features and distinct morphologies, portraying the efficiency of ASA as a suitable growth modifier. The formed metal oxide nanostructures, when used for electrode modification purposes, exhibited excellent electrocatalytic capabilities against the oxidation of nelbuphine hydrochloride (NAL) in aqueous buffer solution. The modified electrodes exhibited distinct electrochemical characteristics, with CuO-based electrodes exhibiting a superior signal sensitivity and lower over-potential value compared to the NiO and Co3O4 nanostructures. The study further explores the variation in the observed electro-catalytic oxidation signal referenced to the distinct morphologies of the metal oxides nanostructures. The CuO-based electrode was selected for the sensitive quantification of NAL in aqueous solution over the linear range 0.001-2.25 mu M. The electrode demonstrated excellent working linearity, with signal sensitivity achieved down to 1 x 10(-4) mu M. Moreover, the successful quantification of NAL in complex matrices, such as human urine and clinical waste water, further reflected the analytical capability of the proposed sensor.

This study describes the development of a new ITO-based electrode used for the electrochemical determination of N-acetyl-L-cysteine (NAC). The electrode system relies on in situ grown CuO nanostructures over the ITO substrate, which provide a relatively greater contact and enables effective electron facilitation during the electrocatalytic oxidation of NAC in an aqueous medium. In situ growth of the CuO nanostructures was achieved using a simple hydrothermal process with the application of succinic acid as an effective growth template. The grown layer of CuO possessed a dense population of highly ordered nanostructures with a high degree of structural uniformity. The study evaluates the potential of the newly developed ITO-based electrode against the bare GCE and an electrode modified via the direct deposition of the same CuO nanostructures synthesised under similar hydrothermal conditions. The electrochemical oxidation of NAC over the newly developed electrode demonstrated low-over potential value and good working linearity in the range from 0.01 to 0.28 mu M. The electrode system was found to be sensitive up to 1.2 x 10(-3) mu M (S/N = 3) with charge transfer co-efficient (alpha) and diffusion co-efficient (D) values of 0.65 and 1.62 x 10(-2) cm(2) s(-1), respectively. Moreover, the developed electrode system demonstrated excellent working capability when utilised for the determination of NAC from a pharmaceutical formulation obtained from a local pharmacy.

The study describes the application of CuO nanostructures as an effective electrode modifying material for the direct electrocatalytic oxidation of N-acetyl-L-cysteine (NAC). The CuO nanostructures were synthesized using hydrothermal growth method with the assistance of NAC, adipic acid (AS) and citric acid (CA) utilized as effective growth modifiers. The morphological characterization of the as-synthesized nanostructures reveled formation of highly distinct and attractive structural features signifying the efficient growth controlling and directing capabilities of the used modifiers. Although, all the fabricated nanostructures were known to possess electrocatalytic potential for the oxidation of NAC. However, the CA modified CuO nanostructures were noted to demonstrate greater sensitivity compared to its other competitors. The developed sensor system relies on the relatively high electro-active area and charged moieties associated with the surface of CA assisted CuO, thus creating a favorable environment for the faster diffusion of analyte towards catalyst surface. The developed sensor exhibited excellent working linearity in the selected concentration range of 0.1 to 5.0 mu M with estimated LOD value of 0.01 mu M. (C) 2016 Elsevier B.V. All rights reserved.

This study describes the application of gold nanocages (Au NCs) for the development of enzyme free electrochemical glucose sensor. The described sensor system is based on the direct modification of glassy carbon electrode (GCE) with Au NCs prepared using simple galvanic replacement reaction. The excellent sensitivity in this case was attributed to the high surface area (interior/exterior) and cavity confinement phenomena (cage effect) associated with Au NCs during the oxidation of glucose. The observed electro-catalytic cage confinement phenomena for Au NCs was elaborately studied using cyclic voltammetry(CV) against solid gold nanoparticles (Au NPs) modified electrode. In addition to this, the developed sensor system was found highly resistive towards interfering species such as uric acid (UA), ascorbic (AS), dopamine (DP) and monosaccharide like fructose (FC) and maltose (ML). The electro-catalytic affinity of Au NCs for the oxidation of glucose enabled development of highly sensitivity (2131 mu Acm (2) mM (1)) and selective sensor with lower detection limit estimated to be 0.1 mM and linear working range of 1.0-9.0 mM. (C) 2016 Elsevier B.V. All rights reserved.

This study demonstrates the fabrication of a highly sensitive electrochemical sensor designed for the quantification of 2,4,6-trinitrotoluene (TNT). The devised sensor system relies on the electro-catalytic reduction of TNT molecules achieved at the surface of palladium (Pd) and palladium-platinum (Pd-Pt) alloy nanostructure modified glassy carbon electrodes (GCEs). The electrode based reduction was studied in a competitive manner with Pd nanocubes (Pd NCs) in comparison to Pd hollow nanospheres (Pd HNS) and Pd-Pt alloy nanostructures (Pd-Pt NA). The experiments revealed Pd NCs to possess high catalytic capability in comparison to their other competitors where relatively greater signal sensitivity suggested the importance of shape-dependence electro-catalysis. The Pd NCs based sensor was found to be highly sensitive towards TNT molecules with detection limits up to 0.01 ppm and a working window of 0.1-7.0 ppm. Moreover, the Pd NCs based sensor demonstrated excellent selectivity in the presence of other common nitro-aromatic compounds. In addition, the excellent recoveries obtained in the real matrix environment (tap water) further promise the real-time application of the developed sensor for trace level detection of TNT.

The aim of this study was to reduce the highly toxic hexavalent chromium Cr(VI) into less toxic chromium Cr(III) species by using nickel nanoparticles (Ni NPs) as catalysts in order to provide safety to the aqueous environment. In the first phase Ni NPs were synthesized in ethylene glycol and capped with l-cysteine by a modified microwave irradiation method using NaOH as the accelerator. The formed Ni NPs were characterized by various techniques such as UV-Visible spectroscopy, Fourier Transform Infra-red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). In the second phase the formed Ni NPs were immobilized on glass surfaces and employed as catalyst for the reduction of Cr(VI) ions. According to observations, 99% reduction of Cr(VI) ions was achieved in the presence of 0.5 mg of Ni NPs catalyst in just five minutes as compared to nickel powder that showed only 16% reduction in 15 minutes. The study has a great impact on the aqueous pollution control of Cr(VI) especially caused by the discharge of waste water from several industries utilizing Cr(VI) containing salt as one of the essential gradients.