Fast and sensitive non-enzymatic glucose concentration determination using an electroactive anionic clay-modified electrode

Development of a portable electroanalytical method using nickel modified screen-printed carbon electrode for ethinylestradiol determination in organic fertilizers

Urine and struvite are organic fertilizers that have all nutritional requirements for the growth of a plant. However, these fertilizers may contain some emerging organic contaminants, such as ethinylestradiol, which is one of the most common hormones found in aquatic environments and can cause several changes in living organisms. Thus, the present study developed a fast, sensitive, inexpensive, and portable method for determining ethinylestradiol in urine and struvite, using square wave voltammetry (SWV) and screen-printed carbon electrodes modified with electrodeposited nickel film (SPCE-Ni). The electrodeposition of the nickel film on the screen-printed electrode was performed by cyclic voltammetry and optimized using complete factorial design 2³ and central composite design. The parameters optimized for SPCE-Ni were: number of cycles (1000); scan rate (5 V s^-1) and Ni²⁺ concentration (9.4 mmol L^-1). The operational parameters of the SWV for ethinylestradiol analysis were also optimized by experimental designs and obtained the following optimal values: step potential (10 mV), modulation amplitude (40 mV), and frequency (20 Hz). The method used 0.1 mol L^-1 BR buffer (pH 8.0) as support electrolyte and presented a limit of detection of 0.052 µmol L^-1 (R² = 0.996). Ethinylestradiol recovery test in struvite, human urine, synthetic urine, and pharmaceutical tablets ranged from 93.9% to 107.5%, indicating that there is no matrix effect. Furthermore, an interference test was performed with several drugs did not show any significant changes in the ethinylestradiol analytical signal, guaranteeing a greater precision of the method. These results reinforce the possibility of applying the proposed method in loco with a practical and fast way, without the need to use significant amounts of sample.

Synthesis and characterization of graphene quantum dots/CoNiAl-layered double-hydroxide nanocomposite: Application as a glucose sensor

In the present work, a novel nanocomposite based on the graphene quantum dots and CoNiAl-layered double-hydroxide was successfully synthesized by co-precipitation method. To achieve the morphological, structural and compositional information, the resulted nanocomposite was characterized by scanning electron microscopy X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and photoluminescence. Then, the nanocomposite was used as a modifier to fabricate a modified carbon paste electrode as a non-enzymatic sensor for glucose determination. Electrochemical behavior and determination of glucose at the nanocomposite modified carbon paste electrode were investigated by cyclic voltammetry and chronoamperometry methods, respectively. The prepared sensor offered good electrocatalytic properties, fast response time, high reproducibility and stability. At the optimum conditions, the constructed sensor exhibits wide linear range; 0.01-14.0 mM with a detection limit of 6 μM (S/N = 3) and high sensitivity of 48.717 μAmM^-1. Finally, the sensor was successfully applied to determine the glucose in real samples which demonstrated its applicability.