Electrospun Cellulose Acetate Membranes Enable Low-Background Fluorescent Nanodiamond Lateral Flow Immunoassays for Highly Sensitive cTnI Detection

Lateral flow immunoassays (LFAs) are widely used because of their simplicity, rapid readout, and low cost; however, quantitative performance is often limited by insufficient signal intensity and background interference from the membrane substrate. This issue becomes more severe when high-brightness fluorescent nanolabels are introduced: conventional nitrocellulose (NC) membranes tend to exhibit autofluorescence and strong light scattering and can also promote nonspecific retention of nanoparticles, which elevates background and compromises quantitative reliability. Here, we present a “fluorescent nanodiamond–electrospun fibrous membrane” strategy, in which a fibrous electrospun cellulose acetate (ECA) membrane replaces the NC membrane and photostable nitrogen–vacancy center nanodiamonds (NVDs) serve as fluorescent labels. The uniform fibrous architecture of the ECA membrane reduces scattering and substrate-derived fluorescence; meanwhile, the fibrous network facilitates smoother convective wash-through, mitigating nonspecific adsorption and mechanical trapping of nanoparticles. As a result, unbound labels are more efficiently removed, leading to suppressed background signals and improved quantitative robustness. Using this platform, we achieved sensitive detection of cardiac troponin I (cTnI) with a limit of detection of ∼0.009 ng/mL, markedly better than conventional NC-based LFA strips. Clinical testing further confirms the diagnostic performance and consistency of the proposed approach. This work offers a simple route to enhance LFA sensitivity and quantification and is readily extendable to other point-of-care biosensing applications.