A novel electrochemical platform based on mesoporous silica/titania and gold nanoparticles for simultaneous determination of norepinephrine and dopamine.

An amorphous and mesoporous silica/titania (SiTi) material was synthesized by sol-gel method and its surface was modified with gold nanoparticles (AuNP) previously stabilized in a chitosan solution. The presence of small AuNP, with diameter lower than 10 nm was confirmed by transmission electron microscopy (TEM) and UV-Vis spectroscopy. Carbon paste electrodes were prepared to test the electrochemical properties by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in [Fe(CN)6]3-/4- solution probe whereby the material silica-titania/gold nanoparticles (SiTi/AuNP) showed a huge improvement in the redox peak current and low charge transfer resistance. This electrode presented a good response for both norepinephrine and dopamine by means of square wave voltammetry (SWV) measurements; great sensitivity for both analytes, in an extensive linear range, was obtained. The limits of detection were 0.35 µmol L-1 and 0.57 µmol L-1 for norepinephrine and dopamine, respectively. Additionally, this electrode showed high selectivity for both analytes and it was applied in the simultaneous determination of norepinephrine and dopamine. The sensor was also tested in simulated biological fluids presenting a good recovery. The SWV electrochemical response of norepinephrine was also investigated in the presence of possible interferers such as uric acid, ascorbic acid and glucose and there was no significant interference. The prepared electrode also exhibits good reproducibility for norepinephrine detection, with relative standard deviation of 5.19%.

Sensitive simultaneous voltammetric determination of the herbicides diuron and isoproturon at a platinum/chitosan bio-based sensing platform.

Phenylurea herbicides are persistent contaminants, which leads their transport to the surface and ground waters, affecting human and aquatic organisms. Different analytical methods have been reported for the detection of phenylureas; however, several of them are expensive, time-consuming, and require complex pretreatment steps. Here, we show a simple method for the simultaneous electrochemical determination of two phenylurea herbicides by differential pulse adsorptive stripping voltammetry (DPAdSV) using a modified platinum/chitosan electrode. The one-step synthesized platinum/chitosan PtNPs/CS was successfully characterized by TEM, XRPD, and FT-IR, and applied through the sensing platform designated as PtNPs/CS/GCE. This bio-based modified electrode is proposed for the first time for the individual and/or simultaneous electrochemical detection of the phenylurea herbicides diuron and isoproturon compounds extensively used worldwide that present a very similar chemical structure. Electrochemical and interfacial characteristics of the modified electrode were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the oxidation mechanism of diuron and isoproturon occurs in two different pathways, with a peak-to-peak definition of ca. 0.15 V. Under differential pulse adsorptive stripping voltammetry (DPAdSV) optimized conditions, the limit of detection (LOD) was estimated as 7 µg L-1 for isoproturon and 20 µg L-1 for diuron (Ed = +0.8 V; td = 100 s). The proposed method was successfully applied to the determination of both analytes in river water samples, at three different levels, with a recovery range of 90-110%. The employment of the bio-based sensing platform PtNPs/CS/GCE allows a novel and easy analytical method to the multi-component phenylurea herbicides detection.