In this work, authors have developed a portable, sensitive, and quick-response fiber optic sensor that is capable of detection of Aflatoxins B1 (AFB1) quantitatively and qualitatively. Using multi-mode fiber (MMF) and multi-core fiber (MCF), the MMF-MCF-MCF-MMF fiber structure based on symmetric transverse offset splicing and waist-expanded taper is fabricated. The evanescent waves are enhanced to form a strong evanescent field by etching the fiber surface with hydrofluoric acid. To successfully excite the localized surface plasmon resonance phenomenon, gold nanoparticles are deposited on the optical fiber probe's surface. Further, to modify the fiber optic probes, Niobium carbide (Nb2CTx) MXene and AFB1 antibodies are functionalized. Nb2CTx MXene is employed to strengthen the biocompatibility of the sensor and increase the specific surface area of the fiber probe, while AFB1 antibody is used to identify AFB1 micro-biomolecules in a specific manner. The reproducibility, reusability, stability, and selectivity of the proposed fiber probe are tested and validated using various concentration of AFB1 solutions. Finally, the linear range, sensitivity, and limit of detection of the sensing probe are determined as 0 - 1000 nM, 11.7 nm/µM, and 26.41 nM, respectively. The sensor offers an indispensable technique, low-cost solution and portability for AFB1-specific detection in agricultural products and their byproducts with its novel optical fiber structure and superior detecting capability. It is also useful for marine species like fish and consequently affecting health of human body.