An AuNF-modified optical fiber LSPR biosensor for sensitive and wide-range 5-HT detection.

Serotonin (5-hydroxytryptamine, 5-HT) is a critical biomarker for carcinoid tumor diagnosis, yet its precise quantification in clinical settings remains challenging. Herein, we develop a high-performance optical fiber localized surface plasmon resonance (LSPR) biosensor functionalized with in situ grown gold nanoflowers (AuNFs). The hierarchical branched architecture of AuNFs concentrates electromagnetic fields into dense nanoscale "hotspots", delivering a ∼2.2-fold signal amplification compared to spherical AuNPs. Integrated with a specific 5-HT aptamer, the sensor achieves a wide linear range (10-1000 ng mL-1) and a low limit of detection (7.06 ng mL-1), seamlessly covering physiological to pathological concentrations. Validation in human serum confirms excellent accuracy with recoveries of 99.9-102.9%. This label-free, rapid, and cost-effective platform offers a highly promising tool for point-of-care carcinoid screening and neuroendocrine biomarker monitoring.