<p>Monitoring cardiac troponin I (cTnI) concentration is of clinical and diagnostic importance, as the changes in its levels serve as a highly specific biomarker for myocardial injury and overall cardiac function. Here, we present the development of a long-period fiber grating (LPFG) based molecularly imprinted fiber optic (MIFO) sensor for the label-free and selective detection of cTnI. In this work, a hydrogel-based imprinted layer is employed for the selective recognition of cTnI in combination with LPFG optical transduction, enabling a compact, label-free, and fiber-integrated sensing platform. The sensor fabrication involved the polymerisation of a cTnI-containing hydrogel precursor directly on the grating region of the LPFG, followed by the selective etching of the embedded cTnI molecules to create molecularly imprinted recognition sites. Upon rebinding of target cTnI molecules, the hydrogel undergoes swelling, resulting in a measurable shift in the LP₀₇ resonant mode of the LPFG. This change enables sensitive and specific detection of cTnI, highlighting the potential of the sensor for real-time cardiac monitoring applications. The developed sensor demonstrated a broad detection range from 0.01 to 10 ng/mL, with a low limit of detection of 0.023 ng/mL. It exhibited selectivity towards cTnI, maintaining reliable performance even in the presence of potential interfering biomolecules. Additionally, the sensor exhibited a rapid response time and reusability, underscoring its suitability for diverse biomedical and clinical diagnostic applications.</p>