Ru-N coordination hydrogen-bonded organic frameworks with enhanced peroxidase-like activity for colorimetric determination of gastric cancer-related salivary D-amino acids.

Hydrogen-bonded organic frameworks (HOFs) are promising porous crystalline materials for sensing, but their weak intrinsic enzyme-like activity limits nanozyme applications. Herein, a Ru-functionalized HOF material (Ru-HOFs) was fabricated through Ru-N coordination. In this material, the HOFs framework anchors and stabilizes the Ru sites. The resulting Ru-HOFs exhibited enhanced peroxidase-like activity toward hydrogen peroxide (H2O2)-mediated oxidation of o-phenylenediamine (OPD), with favorable catalytic stability and substrate affinity. Density functional theory (DFT) calculations suggest that Ru-N coordination modulates the local electronic structure and provides a more favorable free-energy profile for H2O2 adsorption and subsequent activation. By coupling Ru-HOFs with D-amino acid oxidase (DAAO), a cascade colorimetric platform was developed for salivary D-proline (D-Pro) and D-alanine (D-Ala), two reported gastric cancer (GC)-related D-amino acids (DAAs). Under individual assay conditions, the platform showed linear ranges of 2-150 µmol L⁻¹ for D-Pro and 5-100 µmol L⁻¹ for D-Ala, with limits of detection of 0.6112 and 2.299 µmol L⁻¹, respectively. Smartphone-based red-green-blue (RGB) analysis enabled visual readout and quantitative determination under controlled conditions. Spiked saliva tests showed satisfactory recoveries, demonstrating the applicability of the proposed assay to saliva matrices for the analysis of reported GC-related salivary DAAs. This work also provides a useful strategy for constructing coordination-regulated HOF-based nanozymes with improved catalytic performance for colorimetric sensing applications.