Voltammetric kinetic discrimination of two sequential proton-coupled electron transfers in serotonin oxidation: Electrochemical interrogation of a serotonin intermediate

Electrochemical Sensing Platform Based on Metal Nanoparticles for Epinephrine and Serotonin

A sensing platform based on nanocomposite materials composed of gold metal nanoparticles (AuNPs) and conducting polymer (CP) matrix has been developed for serotonin and epinephrine detection. The CP-AuNPs nanocomposite materials have been synthesized onto glassy carbon electrodes (GCE) by using novel electrochemical procedures based on sinusoidal currents (SC). The SC procedures ensured good control of the metal nanoparticles distribution, increased electrochemical surface area, and enhanced analytical performance. The proposed sensing platform displayed good analytical performance toward serotonin and epinephrine detection. A wide linear analytical response toward epinephrine in the range from 10 to 640 μM and a low detection limit of 1.4 μM epinephrine has been obtained. The sensing platform has also displayed a linear response toward serotonin in the range from 10 to 320 μM, with a detection limit of 5.7 μM serotonin. The sensing platform has been successfully applied in the analysis of epinephrine and serotonin in real samples of tap water and urine with good accuracy.

Cl-/Cl3- Redox Voltammetry to Recognize the Interfacial Layer on Positively Electrified Carbon in "Water-in-Salt" Electrolytes

A "Water-in-Salt" electrolyte solution (WiSE) is a promising aqueous medium for lithium-ion batteries containing highly concentrated electrolytes. For the increased kinetic overpotential of water oxidation in WiSE, the formation of an interfacial layer (IFL) on a positively electrified electrode is crucial. Nonetheless, most related studies have been restricted to theoretical approaches. In this Article, we voltammetrically study the Cl^-/Cl₃^-/Cl₂ redox reaction on Pt and glassy carbon (GC) electrodes in WiSE containing LiTFSI (WiSE_LiTFSI) and demonstrate that careful monitoring of Cl^-/Cl₃^- redox voltammetry can allow recognition of an IFL formed on a positively electrified electrode. The voltammetric wave attributed to the electro-oxidation of Cl^- on a GC electrode was negatively more shifted as the molal concentration of LiTFSI was increased from 0.5 to 6 m, while there was no shift on Pt. Also, there was voltammetric resolution into two peaks associated with Cl^-/Cl₃^- and Cl₃^-/Cl₂ on the GC electrode in WiSE_LiTFSI, while only unresolved, one redox-paired voltammograms were observed on Pt, regardless of the molal concentration of LiTFSI. These two main voltammetric features indicate the LiTFSI-induced IFL coupled with Cl^- and Cl₃^- on a GC electrode induced by an applied potential of ∼2 V versus the point of zero charge (PZC). We found other halide/halogen redox reactions did not show differentiated voltammetric behaviors in WiSE_LiTFSI, which demonstrates the uniqueness of the Cl^-/Cl₃^- redox reaction for recognizing the IFL formed on a positively charged electrode surface. Lastly, a strong interaction between the IFL and Cl species was also confirmed by XPS measurements.