Polystyrene microsphere monolayer assembled on glass slide for label-free OIRD immunoassay with enhanced sensitivity

Oblique-incidence reflectivity difference (OIRD) is a newly established method to monitor various surface processes and shows great prospect for real-time and label-free immunoassay , yet its sensitivity needs essential improvement to meet the requirement of practical applications. In this work, a label-free OIRD immunoassay biochip was developed with improved sensitivity by using standard glass slide coated with polystyrene (PS) microsphere monolayer as the substrate. The immunoassay sensitivity of this biochip was found to be greatly improved compared with the conventional biochip built on glass slide. Further on-chip ELISA and optical calculation suggests that the improvement is not only associated with high capture efficiency of this biochip towards its target, but is also benefited from the porous PS monolayer enhanced intrinsic OIRD sensitivity via optical interference enhancement and effective dielectric constant effect. This work may provide valuable insight into the development of high performance label-free OIRD bio-detection devices.