MXene-Gold Nanoparticles/Reduced Graphene Oxide/Carbon Nanofibers (AuNPs/rGO-CNFs)-Modified Screen-Printed Carbon Electrode for the Voltammetric Determination of Indole-3-Acetic Acid

Indole-3-acetic acid (IAA) is an important plant hormone and its rapid determination is useful for evaluating plant growth and physiological status. In this work, a screen-printed carbon electrode (SPCE) modified with a composite of MXene, gold nanoparticles (AuNPs), and reduced graphene oxide/carbon nanofibers (rGO-CNFs) incorporating an electrospun carbon-nanofiber network was developed for the voltammetric determination of IAA. The composite was characterized by morphological, structural, and chemical analyses. The modified electrode showed a larger electrochemically active area and lower charge-transfer resistance than the bare SPCE. Under optimized conditions, least-squares regression over 0.05–125 µM based on six concentration levels gave a slope of 1.060 ± 0.016 µA µM−1, a limit of detection (LOD) of 12.1 nM, and a limit of quantification (LOQ) of 40.3 nM. In buffered model solutions, the electrode showed acceptable selectivity, fabrication repeatability, and short-term electrochemical stability. These results support the MXene-AuNPs/rGO-CNFs-modified SPCE as a low-cost platform for IAA determination, while validation in real plant matrices remains necessary.