Bioconjugation Strategies for Label-Free Optical Microcavity Sensors

Whispering gallery mode optical microcavities have significantly impacted the field of label-free optical biodetection. By combining the evanescent field generated by the microcavity with biomimetic surface chemistries, it is now possible to use the microcavities as not only biosensors, but as analytical tools to explore fundamental chemical and physical interactions of biomolecules and biomaterials. Here, we review the recent advancements of these applications from a surface chemistry perspective. For example, surface chemistries can be generated from a standard coating perspective, where active molecules, such as laser or fluorescent dyes can be embedded in a biomaterial matrix. Alternatively, direct and reverse grafting techniques can be used to tether biomolecules of interest to the surface to tune the surface properties (hydrophobicity/hydrophilicity, protein adsorption, cell adhesion, etc.). Finally, we discuss how to apply advancements in biomimetic chemistry from other sensor approaches to these devices to continue the development of new analytical tools. All of these developments rely on a firm understanding of how proper surface chemistries can be merged with whispering gallery mode optical microcavities to achieve not just a platform, but a precisely defined tool for a given application.