Ultrasensitive and rapid fluorescence immunoassay for Listeria monocytogenes detection using size-compatible magnetic beads and core-shell quantum dots

A rapid and ultrasensitive fluorescence immunoassay for Listeria monocytogenes detection was developed by integrating antibody-conjugated magnetic beads (MBs-Ab1) and core–shell CdSe@ZnS quantum dots (QDs-Ab2). Covalent conjugation methods ensured stable antibody immobilization while preserving the structural and optical properties of the carriers. The ∼1 μm magnetic beads demonstrated superior capture efficiency (∼96 % in 10 min) and high specificity against L. monocytogenes. Core–shell QDs enabled robust fluorescence signaling with a sharp emission at ∼555 nm. The assay achieved a linear response over 1–10⁴ CFU/mL and an exceptional limit of detection of 0.26 CFU/mL, surpassing existing fluorescence-based methods. The total assay time was only 35 min. High reproducibility and minimal background fluorescence further confirmed the system's analytical reliability. This performance is attributed to compatible particle size, covalent conjugation chemistry, high quantum yield fluorophores, and efficient magnetic separation. Future efforts will focus on enhancing the long-term stability of the bioconjugates and validating assay performance using complex real-world samples—critical steps toward translating this proof-of-concept into a practical diagnostic platform.