Gold Nanoparticle-Coated Magnetic Graphene Oxide as a Dual-Mode Immunochromatographic Biosensor for Enrofloxacin Residue Analysis in Food Samples

Enrofloxacin (ENR) is a commonly used veterinary antibiotic and poses a health risk when present as residues in food. This study describes a dual-mode immunochromatographic test strip (DITS) biosensor for the detection of ENR residues in food. Magnetic graphene oxide nanoparticles (MGO-NPs) are two-dimensional magnetic nanomaterials with a large specific surface area and fine biocompatibility, which can better provide more adsorption points for biological antibodies. Gold nanoparticles (AuNPs) can stimulate the localized surface plasmon resonance effect under laser irradiation, which will increase the temperature to achieve photothermal conversion. The photothermal conversion efficiency of MGO-NPs can be effectively enhanced by combining AuNPs with MGO-NPs to form MGO@Au nanocomposites (MGO@Au-NCs). Then, MGO@Au-NCs were combined with an ENR monoclonal antibody to form the MGO@Au@Ab probe, and the MGO@Au@Ab-DITS biosensor was developed. The biosensor was employed to assess ENR samples spanning concentrations from 0 to 1000 μg/mL. Sample solutions containing ENR were mixed with the MGO@Au@Ab solution, deposited on the test strip's sample pad, and analyzed using both colorimetric and photothermal methods employing an 808 nm infrared laser in a photothermal infrared imaging instrument. The results show that the sensitivity of the photothermal mode sensor is 0.0159°C whereas, the standard deviation (SD) and limit of detection (LOD) is 0.058 and 10.89 μg/mL, respectively with quantification limit (LOQ) of 36.31 μg/mL. In colorimetric mode, the sensitivity of the developed sensor is 5.222 au, with SD, LOD and LOQ of 40.13, 23.05 μg/mL, and76.85 μg/mL, respectively. This innovative MGO@Au@Ab-DITS system has been effectively applied to detect ENR residues in food samples such as juice and milk, laying the groundwork for the detection of other drug residues in food.