Label-Free Silanization-Functionalized Optical Fiber Biosensor for Ultrasensitive Detection of Cancer Biomarker CD44

CD44, a well-established cancer biomarker, plays a critical role in tumor invasion and metastasis across multiple cancer types. However, the clinical utility of current CD44 detection platforms is hampered by the requirement for labeling and limited sensitivity, rendering trace-level detection complex and challenging, and thus necessitating the development of novel, label-free, and highly sensitive CD44 sensors. Herein, we propose a silanization-modified label-free fiber biosensor with enhanced sensitivity by tuning the dispersion turning point and high-selectivity CD44 recognition via targeted antibody immobilization. A differential tapering technique is adopted to fabricate the micro/nano-fibers with low propagation loss and high spectral contrast, which effectively addresses the drawbacks of traditional fabrication methods such as severe airflow interference and fragile microstructure. Furthermore, a robust covalent immobilization interface for antibodies is constructed via silanization treatment, endowing the sensor with reliable specific binding capability toward CD44. Ultimately, the optimized sensor operates within a dynamic range of 100 fM-6.05 nM, where it exhibits a linear wavelength shift of 3.6443 nm per decade increase in CD44 concentration and achieves a remarkably low detection limit of 0.19 pM. This represents a 1000-fold enhancement in sensitivity compared to existing CD44 detection methods. This highly sensitive and robust CD44 sensor holds significant potential for applications in diagnosis, staging, and prognosis of multiple cancer types.