Monodisperse Polymer Optical Microresonators as a Versatile Platform for Protein-Conjugated Biocompatible Optical Probes.

Optical microresonators have attracted increasing attention as next-generation miniature optical probes for biological sensing, but their practical applications remain limited by insufficient biocompatibility and limited chemical functionalizability at the surface. Here, we report polymer-based optical microresonators (MR) as a surface-functionalizable and biocompatible platform for covalently anchoring biofunctional molecules. Highly spherical and monodisperse polystyrene MR were prepared by inkjet printing and conjugated with guest molecules using Sulfo-SANPAH as a heterobifunctional cross-linker. This strategy enabled the stable surface conjugation of multiple classes of biomolecules, including ovalbumin proteins, IgG antibodies, and polylysine, even after repeated washing. MR retained sharp peaks of the whispering-gallery-mode resonance even after conjugation and immersion in water and a buffer solution, indicating their applicability to biologically relevant environments. Furthermore, IgG-conjugated MR were internalized by macrophage cells without causing visible cellular damage. These results establish polymer microresonators as a promising platform for biofunctional and biocompatible optical probes capable of operating in aqueous and cellular environments.