A smartphone-assisted dual-mode colorimetric sensing system for on-site detection of ciprofloxacin: experimental and DFT insights

Abstract

The development of portable, cost-effective, and user-friendly analytical tools for one-site detection of ciprofloxacin (CIP) in complex matrices remains a significant challenge. Herein, we report a novel smartphone-assisted dual-mode colorimetric sensing platform based on an aluminum(III)–alizarin red S (Al(III)–(ARS)₂) chemosensing ensemble for the rapid and sensitive determination of CIP in aqueous media. The sensing strategy exploits the strong chelating ability of CIP toward Al(III) via its carboxylate and carbonyl groups, driving the formation of a ternary CIP–Al(III)–(ARS)₂ complex accompanied by a distinct color change from orange to pink. This color change is quantitatively monitored using both UV-Vis spectrophotometry and smartphone-based RGB image analysis, enabling complementary dual-mode detection. The proposed platform exhibits excellent analytical performance with linear ranges of 0.34–13.6 µM (UV-Vis) and 0.075–12 µM (smartphone-based analysis) and low limits of detection of 70 nM and 48 nM, respectively. Notably, the smartphone-assisted approach minimizes user subjectivity, enhances signal reproducibility, and enables rapid analysis within minutes. The method was successfully applied to real samples, including pharmaceutical formulations, environmental water, and human urine, achieving satisfactory recoveries (95.20–119.04%) and good precision (RSD: 1.02–6.09%). The sensing mechanism was validated by UV-visible and FT-IR spectroscopic analyses and further supported by DFT calculations.