Experimental and theoretical data support the easy reduction of Au3+ into self-stabilized nanoparticles by citrus flavonoids.

This paper describes the immobilization of nickel (II) phthalocyanine‐tetrasulfonic acid tetrasodium salt (NiTsPc) in 3‐n‐propyl(3‐methylpyridinium) silsesquioxane chloride (Si3Pic+Cl−). This hybrid material was synthetized and characterized by 29Si NMR CP‐MAS, FTIR and DRS. The modified material, designated as Si3Pic+Cl−/NiTsPc, was used to build carbon paste electrodes to determine sulfanilamide (SFL) by differential pulse voltammetry. The modified electrode showed a higher current response when compared to the bare carbon paste electrode. The evaluation of SFL was possible in the presence of salicylic acid, commonly used in solid ointment compositions in a high concentration. Theoretical calculations using density functional theory were done aiming to shed light at dimerization process at SFL. The oxidation peak increased with increasing concentrations of SFL in the range of 35–301 μmol L−1. The LOD and LOQ values obtained were 12 and 35 μmol L−1 of SFL, respectively. The novel electrochemical sensor was successfully applied for the determination of SFL in pet drug samples, urine and serum through the standard addition method. Validation was performed through a comparison with values obtained by the molecular absorption spectrometry method and there were no significant differences in the results, as confirmed by the statistical paired t‐test. This demonstrates the promise of a new approach for analytical application in clinical and drug samples of sulfonamide compounds.

This work reports the characterization and application of a new electrochemical platform modified with gold nanoparticles (AuNP) and functionalized multi-walled carbon nanotubes (f-MWCNT) film to determine melatonin (MEL), a critical sleep inductor neurohormone categorized by the U.S. Food and Drug Administration as a nutritional supplement. The AuNP were synthesized and stabilized by 3-n-propyl-(4-methylpyridinium) silsesquioxane chloride (Si4Pic+Cl−), presenting an electrostatic stabilization and a material with a positive surface charge. Thermogravimetric analysis, Fourier transform-infrared spectroscopy, Raman spectroscopy, and zeta (ζ) potential indicated the insertion of oxygenated functional groups and a superficial negative charge for f-MWCNT. The GCE/f-MWCNT-AuNP-Si4Pic+Cl− platform showed an electrocatalytic profile and a current increase of ca. 7.5 times. Voltammograms were obtained by square wave voltammetry; the current increased with successive additions of MEL in the linear range of 4.9 to 55.5 μmol L−1. The values of LOD and LOQ were 1.6 and 4.7 μmol L−1, respectively. The standard addition was used to quantify MEL in simulated saliva, blood serum, and urine samples. Statistical tests showed no significant differences between the data collected by voltammetry and the comparative technique, molecular absorption spectrometry. It can be concluded that the new method provides novel perspectives for MEL sensing

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