A novel optical fiber immunosensor for detection of heart failure marker ST2 based on MoS₂-modified D-shaped ExTFG

A D-Shaped, excessively tilted fiber grating (ExTFG) immunosensor modified with molybdenum disulfide (MoS₂) was developed for label-free and specific detection of growth-stimulated expressed gene 2 protein (ST2), a critical biomarker for heart failure. The D-Shaped ExTFG sensor was fabricated by side-polishing an ExTFG along its slow axis to enhance refractive index (RI) sensitivity. It was subsequently biofunctionalized with MoS₂ and anti-ST2 monoclonal antibodies (anti-ST2 MAbs) for ST2 immunoassays. The RI sensitivities of the sensor after side-polishing and MoS₂ coating were thoroughly investigated. Additionally, the immunodetection properties of the sensor were evaluated across varying concentrations of ST2 antigen solutions, as well as its specificity and clinical performance in serum samples from healthy individuals and patients. Experimental results revealed that the sensitivity of the MoS₂-modified D-Shaped ExTFG immunosensor for ST2 reached 0.335 nm/[log(mg/mL)] over a wide linear testing range of 1 ng/mL to 1000 ng/mL, with a detection limit of 0.472 ng/mL. This represents an improvement of approximately 86 % compared to the ExTFG without D-Shaped modification and demonstrates excellent specificity for ST2 biomarkers even in complex clinical sera. The MoS₂-modified D-Shaped ExTFG immunosensor exhibits notable advantages, including stability, practical usability, and high clinical specificity, making it a promising candidate for biomedical and other analytical applications.