Smartphone-Assisted Rapid Detection of Glyphosate Residues Using Water-Soluble Potassium-Sodium Mixed Poly(heptazine imide)-based ″On-Off-On″ Fluorescent Fibrous Strips

Glyphosate is a widely used pesticide exhibiting high environmental stability and potential ecological risks, which necessitates the development of convenient and rapid on-site detection techniques. Traditional methods, while sensitive, are constrained by high instrument costs and long analysis time, making them unsuitable for on-site applications. In this study, water-soluble potassium-sodium mixed poly(heptazine imide) (K,Na-PHI) was synthesized via molten salt synthesis using melamine, KOH, and NaOH as precursors. The resulting water-soluble material exhibited a nanobelt morphology with lateral dimensions of 10‒20 nm and lengths up to micrometers. A novel fluorescence sensing method was thus constructed based on K,Na-PHI, where Cu2+ quenched the fluorescence of K,Na-PHI, while glyphosate subsequently restored fluorescence through specific chelation with Cu2+, enabling the quantitative detection of glyphosate. This method exhibited a good linear response to glyphosate over the concentration ranges of 0.001‒0.2 mg/L and 0.2‒30 mg/L, respectively, with a detection limit of 0.5 μg/L. Subsequently, K,Na-PHI was immobilized onto electrospun polyacrylonitrile (PAN) nanofibrous membranes, fabricating K,Na-PHI/PAN fluorescent test strips for on-site detection. By leveraging smartphone color recognition capabilities, this platform successfully achieved real-time, visual, on-site detection of glyphosate (Minimum detectable concentration was 1 μg/L). This study provided an easy-to-operate, fast-responding, and highly sensitive new method for on-site pesticide residue detection, demonstrating significant potential for food safety monitoring applications.