A highly sensitive Love-wave surface acoustic wave immunosensor for point-of-care detection of Cyfra21-1 in saliva

Decentralized biomarker testing is pivotal for cancer screening, risk evaluation, and longitudinal surveillance, yet most established assays remain laboratory-centric and are not suitable for point-of-care testing (POCT). Saliva has attracted extensive attention owing to its abundant bioinformation, non-invasive collection and easy sampling for disease screening. Herein, we developed a highly sensitive Love-wave surface acoustic wave (Love-SAW) immunosensor for the quantification of Cyfra21-1-a clinically established cytokeratin-19 fragment widely used in epithelial cancer management-in saliva and advanced it toward a chip-scale sensing platform readily integrable into portable POCT devices. The immunosensor employs a sandwich immunoassay, with signal amplification by gold nanoparticle-labelled antibodies. The sensing interface is engineered via cysteamine self-assembly on gold through Au-S coupling, followed by glutaraldehyde activation to enable covalent immobilization of the Cyfra21-1 coating antibody. Cyfra21-1 was measured in both PBS and artificial saliva samples, with a total assay time of approximately 20 min per sample. The Love-SAW immunosensor provided a dynamic detection range of 7.81-62.5 ng mL^-1 and a limit of detection of 4.9 ng mL^-1 for Cyfra21-1 detection in PBS, and demonstrated matrix-tolerant detection in spiked artificial saliva (15.62-125 ng mL^-1, LOD: 13.9 ng mL^-1). Quantification in spiked artificial saliva agreed well with ELISA, yielding good recoveries of 82.36%-106.60%. These results demonstrate that the gold-enhanced Love-SAW immunosensor enables highly sensitive, rapid and portable quantification of salivary biomarkers, providing a promising foundation for the development of compact and non-invasive POCT systems for disease screening.