Cronobacter sakazakii (C. sakazakii) is a food pathogen that has drawn attention in the area of food safety, especially in relation to infant formula and other food matrices. However, the typical methods for detecting C. sakazakii can be tedious, time-consuming, and need complex tools and equipment, which restricts their use for quick detection. As a result, sensitive and quick detection techniques are essential. In the present study, a new type of optical fiber biosensor was developed, which combines CeCoMOF@Ag@MoS₂ nanomaterials and gold nanorods (AuNRs). The sensor adopts a multimode fiber (MMF)–lanthanum-doped fiber (LDF)–MMF (MLM) fiber structure, and the integration of CeCoMOF, Ag@MoS₂, and AuNRs combines the structural advantages of the porous framework with the plasmonic response of the metallic nanostructures, providing a composite sensing interface for optical fiber LSPR detection and measuring the refractive-index sensitivity of different concentrations of C. sakazakii. The sensing interface was designed by integrating CeCoMOF@Ag@MoS₂ and AuNRs on the probe surface to optimize the LSPR response and provide a suitable platform for antibody functionalization. The probe was subsequently functionalized with monoclonal antibodies against C. sakazakii to facilitate target recognition. According to the experimental findings, the developed sensor’s detection range is 1 × 10⁰–1 × 10⁷ CFU/mL, the sensitivity is 5.1447 nm/[CFU/mL], and the detection limit is 0.78 CFU/mL. Moreover, the sensor has good repeatability, stability, selectivity, and reusability. The performance of the suggested sensor was analyzed in terms of sensing capabilities with starch-based matrix under the conditions tested. Note that the enhanced performance is not just due to La doping but due to the combined effect of the multi-tapered MLM structure, La doping and the nanomaterial–antibody interaction.