Cyclodextrin-mediated efficient antibody immobilization on upconversion nanoparticles for CKD biomarker sensing via luminescent lateral flow assay

Chronic kidney disease (CKD) is a progressive disease characterized by high rates of morbidity and mortality, often leading to various complications. Early home diagnosis and point-of-care prognosis are therefore crucial for monitoring CKD progression and managing patient outcomes. β2-microglobulin (B2M) levels offer a valuable indicator of renal function changes, however, their quantitative detection typically relies on sophisticated and costly laboratory instrumentation. Here, we present a universal and adaptable strategy for efficiently conjugating rare-earth-based nanoparticles with antibodies via a carboxymethyl β-cyclodextrin-mediated "self-assembly-followed-by-conjugation" approach. Cyclodextrin modification enhances the rigidity, hydrophilicity, and electrostatic repulsion of nanoparticles, significantly improving their colloidal stability and upconversion luminescence in aqueous solution. Moreover, the ample carboxyl groups on cyclodextrin offer multiple sites for covalent conjugation, resulting in a substantial enhancement in antibody loading capacity and improved immunoaffinity for biomarkers. Employing this methodology, we developed an antibody-conjugated nanoprobe for B2M and fabricated a fluorescent lateral flow strip. Subsequently, image acquisition and data analysis using a smartphone enabled sensitive and quantitative detection of B2M in artificial urine, achieving a detection limit of 2.7 ng/mL. This study provides a versatile strategy for the development of nanoparticle-based colorimetric/luminescent immunoassay probes.