A novel immunoassay applying lanthanide-based metal-organic frameworks to detect thrombomodulin in human serum for early vascular endothelial injury diagnosis.

Thrombomodulin (TM), a transmembrane glycoprotein, is a crucial biomarker for diagnosing cardiovascular diseases (CVDs). Highly sensitive and selective detection of TM is indispensable for achieving an early diagnosis of CVDs. In this work, a novel lanthanide-based metal-organic framework nanosheet (Eu-MOF NS) was synthesized via the solvothermal method. The obtained Eu-MOF NS exhibited the distinctive fluorescence of lanthanide metals when excited (375 nm), which could be quenched by 4-nitrophenol (4-NP) (absorption range of 375–425 nm) through the inner filter effect but not by 4-nitrophenyl phosphate (PNPP) (absorption range of 300–325 nm). Based on this, an immunofluorescence sensor was established. In the presence of TM, an enzyme-linked immune reaction triggers the formation of a capture antibody/TM/detection antibody sandwich complex, of which the alkaline phosphatase (ALP) conjugated to the secondary detection antibody could hydrolyze PNPP to 4-NP, leading to the disappearance of fluorescence. In contrast, when TM is absent, no 4-NP is produced, and the fluorescence of Eu-MOF could be detected. The sensor exhibited a satisfactory linear response to TM concentrations ranging from 20 pg mL⁻¹ to 1 × 10⁷ pg mL⁻¹, with a limit of detection (LOD) of 9.6 pg mL⁻¹. The proposed immunoassay demonstrated excellent stability, selectivity, and anti-interference capability, offering a promising new benchmark for the clinical practice of early CVDs diagnosis.