This study describes a systematic investigation of the electrocatalytic activity of poly [Ni(salen)] films, as catalysts for the electrooxidation of Cn alcohols (Cn = methanol, ethanol, and glycerol) in alkaline medium. The [Ni(salen)] complex was electropolymerized on a glassy carbon surface and electrochemically activated in NaOH solution by cyclic voltammetry. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy results indicate that during the activation step the polymeric film hydrolyzes, leading to the formation of β-Ni(OH) 2 spherical nanoparticles, with an average size of 2.4 ± 0.5 nm, encapsulated with the poly[Ni(salen)] film. Electrochemical results obtained together with the in situ Fourier transform infrared spectroscopy confirm that the electrooxidation of methanol, ethanol, and glycerol occurs by involving a cycling oxidation of β-Ni(OH) 2 with the formation of β-NiOOH species, followed by the charge transfer to the alcohols, which regenerates β-Ni(OH) 2 . Analyses of the oxidation products at low potentials indicate that the major product obtained during the oxidation of methanol and glycerol is the formate, while the oxidation of ethanol leads to the formation of acetate. On the other hand, at high potentials (E = 0.6 V), there is evidence that the oxidation of Cn alcohols leads to carbonate ions as an important product.
Flexible, fully printed immunosensors
can meet the requirements
of precision nutrition, but this demands optimized molecular architectures
to reach the necessary sensitivity. Herein, we report on flexible
and label-free immunosensor chips made with tree-like gold dendrites
(AuDdrites) electrochemically formed by selective desorption of l-cysteine (L-cys) on (111) gold planes. Electrodeposition
was used because it is scalable and cost-effective for a rapid, direct
growth of Au hyperbranched dendritic structures. The 25-hydroxyvitamin
D3 (25(OH)D3) metabolite was detected within 15 min with a limit of
detection (LOD) of 0.03 ng mL–1. This high performance
was possible due to the careful optimization of the electroactive
layer and working conditions for square wave voltammetry (SWV). Electrocrystallization
was manipulated by controlling the deposition potential and the molar
ratio between HAuCl4 and L-cys. Metabolite
detection was performed on human serum and saliva samples with adequate
recovery between 97% and 100%. The immunosensors were stable and reproducible,
unresponsive to interference from other molecules in human serum and
saliva. They can be extended for use as wearable sensors with their
mechanical flexibility and possible customization.
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