Lanthanide metallohydrogel with multicolor luminescence for visual sensing and in situ treatment of bacterial infections

The real-time in situ monitoring of bacterial infections with the naked eye and the development of an on-demand drug delivery system according to the degree of bacterial infection are highly attractive, as they can effectively avoid the overuse of antibiotics. In this study, a smart luminescent hydrogel (4-PY/CIP-EuTb) was designed based on an amino acid derivative, ciprofloxacin (CIP), and lanthanide ions (Tb³⁺/Eu³⁺). This hydrogel can emit multicolor luminescence including blue from 4-PY/CIP, green from Tb³⁺, red from Eu³⁺ and white from the mixture of Tb³⁺ and Eu³⁺, respectively. The luminescence color of the 4-PY/CIP-EuTb hydrogel can be modulated by adjusting the emission wavelength or the ratio of metal ions. Notably, the luminescence color of this metallohydrogel varies with the pH values. During bacterial growth and metabolism, protons are produced, altering the acidity of the microenvironment at the site of bacterial infection. The increased acidity caused by bacterial growth can trigger a decrease in the coordination ability between CIP and lanthanide ions in the hydrogel. Consequently, the 4-PY/CIP-EuTb hydrogel with excellent pH-responsiveness can be used to visually sense bacterial infection. As the acidity increases，CIP in the hydrogel can be gradually released, and it can simultaneously kill the bacteria. Thus, a platform for real-time monitoring of bacterial infection and in situ killing of bacteria has been developed, which holds great promise as a valuable aid in clinical diagnosis and treatment.