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.