Development of a dual-mode immunoassay kit for periostin detection in exhaled breath condensate using α-NaYF₄@ZIF-67...

Periostin in exhaled breath condensate (EBC) is a well-recognized specific biomarker for non-invasive diagnosis of idiopathic pulmonary fibrosis (IPF). However, the development of intuitive and quantitative methods for periostin analysis remains technically challenging. Here, we developed a dual-mode immunoassay kit based on α-NaYF₄:Yb³⁺,Er³⁺ @ZIF-67 core-shell nanostructures for the direct capture and efficient monitoring of periostin. By regulating the shell thickness of ZIF-67 during the in-situ growth process, the optimized core-shell nanostructures were able to retain stable upconversion luminescence (UCL) performance and sensitive surface-enhanced Raman scattering (SERS) response simultaneously. Particularly, the ultrahigh surface area and unique mesoporous framework of the ZIF-67 shell effectively promoted the enrichment of target molecules, facilitating robust SERS property with an enhancement factor (EF) of 6.76 × 10⁷. Attributable to the reliable chemical enhancement effect within the immunostructures, the linear dynamic range of the system could span from 10^-8 to 10^-1 mg/mL. Although the intrinsic surface defects were passivated by the ZIF-67 shell, stronger interfacial non-radiative relaxation pathways were introduced and became dominant, resulting in a prolonged fluorescence lifetime from 0.232 to 0.646 ms but reduced UCL intensity. Even for the low-concentration periostin sample at 10^-8 mg/mL, a stable green fluorescence signal could still be reliably obtained. Following the assembly of the as-prepared dual-functional nanocomposites into an immunoassay kit combined with a well-designed dedicated filter and condensation sheet, clinical validation with artificial EBC samples confirmed the great potential of the proposed kit for the non-invasive diagnosis of IPF.