Magnetic field facilitated-colorimetric aptasensor for selective and sensitive detection of Staphylococcus aureus...

Colorimetric detection of pathogenic bacteria (such as S. aureus) in complex sample confronts challenges regarding sensitivity, selectivity, and accuracy. In this paper, a magnetic field facilitated (MFF)-colorimetric aptasensor was proposed for S. aureus detection based on magnetic separation and nanoenzyme-facilitated chromogenic reaction. The vancomycin-functionalized magnetic chitosan (CS-MNPs-Van) was introduced to capture and isolate S. aureus from the complex matrix through magnetic field separation. The zinc/cobalt infinite coordination polymers (Zn/Co ICPs) was rapidly prepared with a green synthesis technology at room temperature. It was directly functionalized with aptamer through interactions of Zn²⁺/Co²⁺ and phosphate backbone, large surface area and π-π stacking reactions, avoiding the tedious chemical modification. The aptamer-labeled Zn/Co ICPs (Zn/Co ICPs-Apt) exhibited not only the excellent peroxidase-like activity, but also the good specificity toward the captured S. aureus to generate CS-MNPs-Van@S. aureus@Zn/Co ICPs-Apt complexes. The residual unreacted Zn/Co ICPs-Apt catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue oxTMB, which can be distinguished with naked eyes. The S. aureus concentration showed a negative correlation with the absorbance (A_{652 nm}) in the range of 1.8 × 10¹ to 1.8 × 10⁵ CFU/mL, with a detection limit of 4 CFU/mL. The MFF-colorimetric aptasensor presents advantages of high sensitivity, good selectivity, low matrix interference and naked visualization without complicated devices, making it competitive candidate for on-site and large-scale detection of pathogens.