No abstract

We demonstrate, for the first time, the electrosynthesis of uniformly dispersed nickel hydroxide nanoparticles (NPs) on polycrystalline boron-doped diamond (pBDD). This has been achieved by electrogenerating OH -at the pBDD surface in the presence of Ni 2þ to create local conditions near the electrode where highly supersaturated (relative saturation ratio > 10 5 ) nickel hydroxide solutions are generated for short periods of time (approximately seconds). This results in the deposition of nickel hydroxide NPs directly on the electrode surface, as confirmed by X-ray photoelectron spectroscopy. The NPs have a reasonably homogeneous size distribution and are deposited uniformly across the heterogeneous pBDD surface. We show that by simply increasing the electrogeneration time and, hence, increasing both the local concentration of OH -and extent of the precipitation reaction, it is possible to increase the size of the NPs. For example, after 1 s, NPs with dimensions of 12 ( 3 nm form, whereas after 15 s, NPs of size ∼39 ( 9 nm result. Longer times result in larger particles, which form aggregated structures. The effect of nickel hydroxide NP size on electrocatalytic activity was investigated by measuring the steady-state current for the oxidation of glucose in alkaline media. For NPs g 25 nm in size, glucose oxidation is close to diffusion-controlled. However, for the smallest NPs produced (∼12 nm) the currents passed suggest kinetic limitations. For glucose at an effective surface coverage of nickel hydroxide of ∼20 nmol cm -2 , equivalent to 15 ng of nickel hydroxide, this functionalized electrode showed a sensitivity of 330 μA mM -1 cm -2 and a limit of detection of 400 nM. The latter represents one of the lowest limits of detection for glucose for nickel hydroxide-based electrodes. The electrocatalytic oxidation properties of this electrode toward methanol and ethanol was also found to be very efficient, yielding very high density currents of ∼1010 A g -1 for 0.5 M ethanol and 990 A g -1 for 0.47 M methanol.

Pseudocapacitive materials are highly capable to achieve high energy density integrated with high power electrostatic capacitive materials. However, finding a suitable electrostatic capacitive material to integrate with pseudocapacitive material in order to achieve high energy density with good rate capability is still a challenge. Herein, we are providing a novel synthetic approach starting from the synthesis of polypyrrole nanotubes (PPy-NTs) and ending up at the carbonization of PPy-NTs to obtain N-doped carbon nanotubes (N-CNTs). With highly porous nature of PPy-NTs and great graphitic texture with copious heteroatom functionalities, N-CNTs significantly promoted the faradic pseudocapacitors, demonstrating high single-electrode capacitance over 332 F/g(PPy-NTs) and 228 F/g(N-CNTs) in 1 M H2SO4 aqueous solution. Further, a novel asymmetric supercapacitor with PPy-NTs as positive and N-CNTs as negative electrode has been fabricated. This PPy-NTs//N-CNTs cell effectively provides high operation voltage (1.4 V) and hence high energy density over 28.95 Wh/kg (0.41 mWh/cm3) with a high power density of 7.75 kW/kg (113 mW/cm3) and cyclic stability of 89.98 % after 2000 cycles.

O presente trabalho de revisão aborda os mais recentes avanços na tecnologia de biossensores alcançados através da montagem de biomoléculas associada com nanopartículas de ouro na construção de dispositivos analíticos. Esta revisão está dividida de acordo com a biomolécula empregada no desenvolvimento de biossensores: (i) compostos imunológicos; (ii) DNA/RNA funcionais; e (iii) enzimas e proteínas Heme. A fim de facilitar a compreensão, cada seção foi subdividida de acordo com o modo de transdução. Os imunossensores contendo nanopartículas de ouro têm uma ampla gama de aplicações nos campos alimentício, ambiental, farmacêutico, químico e de diagnósticos clínicos. As nanopartículas foram empregadas para melhorar o sinal analítico ou a imobilização dos imunocompostos. Em outra seção, os biossensores DNA/ RNA empregando nanoestruturas de ouro como labels e biossensores label-free associados a nanoestruturas de ouro como transdutores foram sistematicamente relatados para a rápida identificação de patógenos, espécies de interesse ambiental e diagnóstico clínico. A inclusão de nanopartículas de ouro em eletrodos modificados aumenta a transferência de elétrons entre o transdutor e a biomolécula proporcionando um melhor desempenho quando enzimas e proteínas redox heme são usados. Biossensores para a detecção e quantificação de glicose e peróxido de hidrogênio foram também discutidos.The present review discusses the latest advances in biosensor technology achieved by the assembly of biomolecules associated with gold nanoparticles in analytical devices. This review is divided in sections according to the biomolecule employed in the biosensor development: (i) immunocompounds; (ii) DNA/RNA and functional DNA/RNA; and (iii) enzymes and Heme proteins. In order to facilitate the comprehension each section was subdivided according to the transduction mode. Gold nanoparticles based immunosensors have a wide range of applications in food, environmental, pharmaceutical, chemistry and clinical diagnostics. The nanoparticles were employed to improve whether the analytical signal or the immunocompounds immobilization. In another section, biosensors based on DNA/RNA biomolecules employing gold nanostructures as labels and label-free funtional DNA/RNA biosensors associated to gold nanostructures as tranducers were systematically reported for rapid identification of pathogens, species of environmental interest and clinical diagnostics, respectively. The inclusion of gold nanoparticles in modified electrodes itself enhances the electron transfer between the transducer and biomolecules leading to improved bioanalytical devices when redox enzymes and heme proteins are used. Biosensors for the detection and quantification of glucose and hydrogen peroxide are discussed as well.

Nanoparticles of a Prussian blue (PB) analogue, copper hexacyanoferrate, were synthesized by using ultrasonic radiation and characterized by spectroscopic and electrochemical techniques. The nanoparticles (ca. 10 nm diameter) were immobilized onto transparent indium tin oxide electrodes by electrostatic layer-by-layer deposition. These modified electrodes showed interesting electrochromic properties, changing the coloration during the redox process from brown to orange when oxidized. The nanostructured electrode presented high stability, in contrast to that observed for PB nanoparticles; this fact must be related to the maintenance of the electrostatic assembly because the oxidized compound, CuII/FeIII(CN)6, still possesses a negative excess of charge due to the high number of cyanide groups that link the nanoparticles with the polycation, assuring the integrity of the whole electrostatic assembled film.