Eco-Friendly and Reusable CNT/Halloysite-Based Sensor for Electrochemical Ciprofloxacin Detection

Antibiotic residues in aquatic environments require sensing approaches that are not only analytically effective but also compatible with aqueous fabrication and reusable after regeneration. Here, we report a ciprofloxacin (CIP) electrochemical sensor based on commercial carbon screen-printed electrodes modified with carbon nanotubes (CNTs) and halloysite nanotubes (HTs). The modifier is prepared and deposited entirely from aqueous dispersions: CNTs provide conductive pathways, whereas naturally occurring halloysite supplies an inexpensive adsorptive phase that may favor local analyte adsorption. The optimized sensing layer exhibited a mean sensitivity of 0.2916μAμM−1 over the 4.2–34μM calibration range, with a relative standard deviation of 4.29% across three independently fabricated electrodes. An estimated limit of detection (LOD) of approximately 34 nM was calculated from the blank signal variability and calibration sensitivity. Measurements were intentionally performed at pH 7.0, representative of near-neutral aquatic matrices and avoiding acidification pretreatment. Although mildly acidic conditions may further favor CIP adsorption, the neutral-pH workflow provides a conservative and more sustainability-oriented assessment. Following sensing, a 10min UVA-assisted cleaning treatment reduced the residual CIP-related signal and enabled subsequent electrode reuse. The regenerated electrode retained approximately 82.4% of its initial sensitivity in the investigated lower concentration interval (4.2–17 μM), demonstrating substantial recovery of its analytical response after UVA treatment.