Dual-signal fluorescent-colorimetric aptasensor for tobramycin detection in milk based on fluorescent magnetic...

Tobramycin (TOB) is an aminoglycoside antibiotic employed in human and veterinary medicine whose residues in food raise safety concerns. To resolve this issue, we developed a dual-mode aptamer-based sensor for sensitive TOB detection via fluorescence and colorimetric signals. The platform utilizes fluorescent magnetic nanoparticles (FMNs) conjugated with anti-TOB aptamers and gold nanoparticles (AuNPs). In the absence of TOB, AuNPs associate with FMN-Apt, causing fluorescence quenching. Upon TOB binding, aptamer-target recognition interrupts the complex, restoring fluorescence. Concurrently, magnetic separation and enhancer treatment reduces matrix interference and promotes AuNPs growth, causing a color change from red to blue-gray. The fluorescent and colorimetric modes attained detection limits of 1.03 nM and 2.45 nM, respectively, exhibiting enhanced sensitivity relative to previously documented techniques. The sensor was validated using TOB-spiked milk varieties and human serum without pretreatment, with recoveries of 94.05-106.42%, highlighting its potential for practical preliminary TOB monitoring in food safety and clinical applications.