A Label-Free Optical Biosensor Based on Ordered Porous Layer Interferometry for IgG Quantification in Milk.

Abstract

Background: Immunoglobulin G (IgG) levels in milk are critical indicators of dairy quality. Conventional measurement methods require labeling and complex sample pretreatment, limiting their practical use for real-time monitoring.

Objective: This study aimed to develop a label-free optical biosensor based on ordered porous layer interferometry (OPLI) for the rapid quantification of IgG in milk at different processing stages.

Methods: Test portions were directly applied to the flow tank, where protein A from Staphylococcus aureus was immobilized as a functional ligand via chemical conjugation. Conditions for ligand immobilization, flow rate, contact time, and sensor regeneration were optimized to minimize nonspecific binding and enhance accuracy.

Results: The OPLI biosensor demonstrated a linear quantification range of 0.44 μg/mL to 5 mg/mL, with a limit of quantification of 0.44 μg/mL. This dynamic range effectively covers the IgG content from raw milk to finished milk. The method showed high reproducibility, with an instrumental response relative standard deviation (RSD) of 0.05% and an average RSD of 12.1% across batches. The biosensor was successfully applied throughout raw milk and final milk production, facilitating IgG calibration for consumer milk.

Conclusion: The OPLI-based biosensor offers a sensitive, real-time and wide-range analytical method for IgG analysis, enabling effective quality control in dairy production.

Highlights: The study developed a label-free biosensor for IgG detection in milk, with a linear quantification range of 0.44 μg/mL to 5 mg/mL and high reproducibility. The biosensor is applicable across all stages of dairy production for IgG quality assessment.