Synthesis of ultrasmall cerium oxide nanoparticles in deep eutectic solvent and their application in an electrochemical sensor to detect dopamine in biological fluid.

A solvothermal synthesis of ultrasmall cerium oxide nanoparticles (USCeOxNPs) with an average size of 0.73 ± 0.07 nm using deep eutectic solvent (DES) as a stabilizing medium at a temperature of 90 ºC is reported. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) were used to morphologically characterize the USCeOxNPs. These revealed approximately spherical shapes with emission lines characteristic of cerium. Selected area electron diffraction (SAED) was used to determine the crystalline structure of the cerium oxide nanoparticles (CeO2NPs), revealing the presence of crystalline cubic structures. The USCeOxNPs-DES/CB film was characterized by scanning electron microscopy (SEM), which demonstrated the spherical characteristic of CB with layers slightly covered by DES residues. DES was characterized by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR), indicating its formation through hydrogen bonds between the precursors. An electrochemical sensor for dopamine (DA) determination in biological fluids was developed using the USCeOxNPs together with carbon black (CB). An enhanced current response was observed on DA voltammetric determination, and this can be attributed to the USCeOxNPs. This sensor displayed linear responses for DA in the range 5.0 × 10-7 mol L-1 to 3.2 × 10-4 mol L-1, with a limit of detection of 80 nmol L-1. Besides detectability, excellent performances were verified for repeatability and anti-interference. The sensor based on USCeOxNPs synthesized in DES in a simpler and environmentally friendly way was successfully applied to determine DA in biological matrix.

Enhancing the electrochemical sensitivity of hydroquinone using a hydrophobic deep eutectic solvent-based carbon paste electrode.

The present study reports the synthesis and characterization of hydrophobic deep eutectic solvents (HDES) based on fatty acids and tetrabutylammonium bromide (TBAB) or 1-octanol using Fourier transform infrared spectroscopy, and the analysis of the physicochemical properties (viscosity, density, electrical conductivity, and water content) of these solvents. A carbon paste electrode modified with 6.0% (m/m) decanoic acid and TBAB-based HDES was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The oxidation peak currents of the proposed electrode were enhanced by its high electrochemical activity, fast electron transfer rate, and high surface area, while a remarkable decrease was observed in the peak potential separation. The electrochemical determination of hydroquinone (H2Q) was carried out using square-wave adsorptive anodic stripping voltammetry (SWAdASV). The electrode response was found to be linear in the H2Q concentration range of 2.5 × 10-6-3.0 × 10-3 mol L-1, with the limit of detection (LOD) of 7.7 × 10-7 mol L-1. The method was successfully applied for H2Q determination in dermatological creams.