Ultrasensitive toltrazuril sulfone detection in eggs via a AuNPs/NH2-Ce-MOF-enhanced electrochemical immunosensor.

The widespread use of toltrazuril (TOL) as a low-toxicity anticoccidial agent in livestock production necessitates sensitive monitoring of its persistent metabolite, toltrazuril sulfone (TOS), which exhibits hepatotoxic and reproductive risks at subchronic exposure levels. Here, we proposed a novel electrochemical immunosensor for the ultrasensitive detection of TOS in eggs, utilizing a decorated amino-functionalized cerium metal-organic framework-gold nanoparticle (NH2-Ce-MOF/AuNP) nanocomposite. The NH2-Ce-MOF was synthesized via hydrothermal crystallization of (NH4)2Ce(NO3)6 and 2-aminoterephthalic acid, exhibiting exceptional stability and an expansive surface area. Compared to conventional electrodes, NH2-Ce-MOF-modified electrodes promoted AuNP nucleation and provided more active sites for HAuCl4 deposition, while also enhancing antibody binding, thereby improving the detection sensitivity of electrochemical immunosensors. Subsequently, electrodeposited HAuCl4 enhanced both electron transfer kinetics (charge transfer resistance decreased by 68% compared to a bare electrode) and bioreceptor loading capacity. Electrochemical evaluation demonstrated superior sensor performance, achieving a wide linear range of 0.05-100 ng mL-1 (R2 = 0.998) with an ultralow limit of detection of 33.2 pg mL-1 (S/N = 3), representing a 3-fold improvement over conventional enzyme-linked immunosorbent assays. The electrochemical immunosensor exhibited excellent selectivity and reproducibility (relative standard deviation <10%). This platform establishes a robust foundation for monitoring TOS residues and other hazardous contaminants in complex food matrices.