A washing-less biosensor based on the dual functions of magnetic separation and signal output of magnetic nanoparticles for the rapid and visual detection of enrofloxacin

Abstract

Background

There is an urgent need for in-situ detection of antibiotic residues to enhance both food safety and environmental sustainability. Although various biosensing methods have been elaborately designed and achieved extremely high sensitivities, they are always complicated and require sophisticated instruments, making them unsuitable for on-site application. Herein, a simple and washing-less biosensor that took full advantage of magnetic nanoparticles (MNs), i.e., magnetic separation and signal output, was developed for the rapid and sensitive detection of enrofloxacin (ENR) residues.

Results

The surface of MNs with diameters of approximately 20 nm (MN₂₀) and 130 nm (MN₁₃₀) were modified with ENR and antibodies to prepare MN₂₀-ENR and immunomagnetic nanoparticles (IMN₁₃₀), respectively. In the absence of ENR, the MN₂₀-ENR analogues were captured on the surface of IMN₁₃₀, forming “MN₂₀-ENR-IMN₁₃₀” complexes, which were larger in volume and could be quickly separated in a magnetic field. While in the presence of ENR, the target ENR competed for the binding sites on IMN₁₃₀ surface, inhibiting the formation of the “MN₂₀-ENR-IMN₁₃₀” structures. Therefore, the separation speed significantly slowed down. Qualitative or semi-quantitative determination of ENR residues could be achieved via visual observation of the color changes, while quantitative detection was also achieved with the aid of a microplate reader or merely a smartphone. The developed method enabled sensitive, selective and rapid detection of ENR with a limit of detection of 0.18 ng mL^-1 and a detection time of 25 min.

Significance

This method uses MNs for both magnetic separation and signal output, simplifies the detection process and eliminates the use of sophisticated instruments, providing a powerful tool for the rapid and in-situ detection ENR residues in various fields such as food safety and environmental protection.