A highly luminescent lanthanide-functionalized covalent organic framework for rapid and specific detection of 7-methylguanine for DNA methylation assessment†

Rapid and accurate detection of 7-methylguanine (m⁷Gua), a biomarker reflecting the degree of DNA methylation that occurs before or in the early stage of cancer, is of particular significance but remains a great challenge. Herein, a luminescent lanthanide-based covalent organic framework (Ln-COF) probe, namely DPA/Eu@ETTA-DHTA, is designed for the first time for the identification of m⁷Gua by assembling pyridine-2,6-dicarboxylic acid (DPA) as both an energy donor and a recognition molecule and Eu³⁺ ions as signal reporters into a stable COF matrix with high porosity and available binding sites. Significantly, the characteristic luminescence of Eu³⁺ ions can be turned on by the grafted DPA in the COF probe and effectively quenched by the addition of m⁷Gua via a competitive absorption process, thus achieving the sensing of m⁷Gua. Such a Ln-COF-based fluorescent platform presents high selectivity and a rapid response (<1 min) to m⁷Gua with a low detection limit (μM level) even in the presence of the main coexisting species in urine, allowing it to serve as a potentially practical probe for point-of-care monitoring of the level of m⁷Gua in human urine specimens. This study provides a convenient, time-saving, and economical approach for visual detection of m⁷Gua, and opens up new perspectives for the design of a luminescent COF-based probe for DNA methylation evaluation in diagnostics.