A diatom/PdNPs nanocomposite carbon paste electrode for sensitive voltammetric determination of aloe emodin: electrodeposition, characterization, and oxidation mechanism.

Aloe emodin (AE, 1,8-dihydroxy-3-(hydroxymethyl)anthraquinone) is a naturally occurring anthraquinone derivative with well-documented anticancer, antiviral, and anti-inflammatory properties, making it an important target for sensitive analytical determination. In this study, a novel electrochemical sensor based on a diatom/palladium nanoparticle nanocomposite-modified carbon paste electrode (DA/PdNPs/CPE) was developed for the highly sensitive and selective determination of AE in herbal samples. The carbon paste electrode was first modified with purified diatomaceous earth (DA), and palladium nanoparticles (PdNPs) were subsequently electrodeposited onto the DA/CPE surface via chronoamperometry (CA) to yield the composite sensing platform. The fabricated electrode was thoroughly characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (FE-SEM/EDS), confirming enhanced electrical conductivity, reduced charge-transfer resistance, and uniform deposition of PdNPs across the electrode surface. Under optimized conditions, square-wave voltammetry (SWV) was employed for the quantitative determination of AE, yielding a linear response in the concentration ranges of 0.05-2.0 µM and 2.0-8.0 µM with a limit of detection (LOD) of 0.0064 µM and a limit of quantification (LOQ) of 0.0213 µM. The sensor demonstrated excellent precision (RSD = 2.52%) and reproducibility (RSD = 1.35%). The practical applicability of the sensor was validated by determining AE in a herbal vitamin supplement, with recovery values ranging from 100.17% to 100.50%, thereby confirming its suitability for real-sample analysis. Furthermore, the electrooxidation mechanism of AE on the modified electrode surface was investigated and detailed.