A magnetic relaxation switching and colorimetric dual-mode aptasensor for the rapid detection of florfenicol and florfenicol amine in eggs.

It is important to establish a sensitive and rapid screening detection method for Florfenicol (FF) residue in eggs. A magnetic relaxation switch (MRS) and colorimetric aptasensor were developed for the detection of FF based on aptamer-modified Au@Fe3O4 nanoparticles (NPs). Apt-Au@Fe3O4 NPs were played as a "switch" between dispersion and aggregation, with a concomitant change in the R2 (T2 relaxivity, 1/T2W) and the UV-vis absorption spectra. To improve the sensitivity and stability of the method, the aptamers modification, salt inducing aggregation, and reaction conditions were optimized. The molar ratio of aptamers to Au, the incubation time of aptamers modification, the molar ratio of NaCl to Au, the dilute ratio of Apt-Au@Fe3O4, and reaction time were optimized to be 2:1, 3 h, 15:1, 1:300 and 15 min, respectively. The working range and LOD of MRS analysis are 0.1-10 nM and 1.10 nM for Florfenicol amine (FFA), 4-40 nM and 5.65 nM for FF. Noticeably, the colorimetric analysis can also qualitatively analyze the FF and FFA. The working ranges and LOD were 5-40 µM (5 µM) and 10-40 µM (10 µM), respectively. Hence, the results indicated that this aptasensor could be a potential tool for the rapid detection of FF residue in food.