Plasmonic aptasensor with antifouling dual-functional surface layer for lysozyme detection in food

Antifouling coatings are critically necessary for optical biosensors for various analytical application sectors, from medical diagnostics to foodborne pathogen detection. They help avoid non-specific protein/cell attachment on the active biosensor surface and catch the analytes directly in the complex media. Advances in antifouling plasmonic surfaces have been mainly focused on detecting clinical biomarkers in real biofluids, whereas developing antifouling coatings for direct analysis of analytes in complex media has been scarcely investigated for food quality control and safety. Herein, we propose a new low-fouling poly-l-lysine (PLL)-based surface layer for directly detecting an allergen protein, lysozyme, in the food matrix using surface plasmon resonance. The PLL-based polymer contains densely immobilized anionic oligopeptide side chains to create an electric charge-balanced layer able to repel the non-specific adsorption of undesired molecules on the biosensor surface. It also includes sparsely attached aptamer probes for capturing lysozyme directly in food sources with no pre-analytical sample treatment. We optimized the surface layer fabrication condition and tested the dual-functional surface to evaluate its ability to detect the target protein selectively. The developed analytical approach allowed for achieving a limit of detection of 0.04 μg mL−1 (2.95 nM) and a limit of quantification of 0.13 μg mL−1 (8.95 nM). Lysozyme was successfully quantified in milk samples using the plasmonic dual-functional aptasensor without sample pre-treatment or target isolation, illustrating the device's utility.