A ratiometric colorimetric sensor for Escherichia coli detection based on the coordination between zirconium-tetraphenylporphyrin tetrasulfonic acid hydrate metal–organic frameworks and copper ions

Abstract

Escherichia coli (E. coli) is one of the most prevalent foodborne pathogens, releasing toxic substances and causing infectious and life-threatening diseases. Thus, the rapid and sensitive detection of E. coli is essential for safeguarding human health. Herein, a ratiometric colorimetric sensor was constructed for detecting E. coli, utilizing the coordination between zirconium (Zr)-tetraphenylporphyrin tetrasulfonic acid (TPPS) hydrate metal–organic frameworks (Zr-TMs) and copper ions (Cu²⁺). E. coli can capture and convert external Cu²⁺ into Cu⁺ through its distinctive metabolic activities. This capability further enhances the coordination interaction between the porphyrin ligands in Zr-TMs and the metal ions. As a result, the ultraviolet–visible (UV–vis) absorption spectral properties of Zr-TMs changed, exhibiting an enhanced absorption peak at 413 nm (A₄₁₃) and a weakened peak at 434 nm (A₄₃₄). By monitoring the increase in ratio of A₄₁₃ to A₄₃₄, this sensor achieved rapid and sensitive detection of E. coli at concentrations ranging from 10² to 10⁷ CFU/mL within 63 min, with a detection limit of 19 CFU/mL. The color of the solution gradually changed from green to colorless. This proposed ratiometric method utilized the opposite changes in the two UV–vis absorption peak signals (A₄₁₃ and A₄₃₄) generated by the Zr-TMs probes, improving detection accuracy and achieving visual analysis. Additionally, this method accurately identified E. coli in milk samples, demonstrating substantial potential for detecting pathogenic bacteria in food.