Whispering-gallery mode-based optical biosensing: A review on development and applications in ultrasensitive biological detection and bioimaging

Biological detection and bioimaging based on specific optical signal changes have succeeded in recent decades. Likewise, a plethora of strategies have emerged to enhance detection sensitivity. Notably, whispering gallery mode (WGM)-based optical biosensing has attracted significant attention due to its high sensitivity and label-free nature. In this review, we present the characterization parameters of WGM resonators in detail and elucidate their relationship with ultrasensitive biological detection and bioimaging. Then, we present emerging design principles and functionalization strategies of WGM resonators. Finally, we thoroughly describe the recent advances of WGM-based optical biosensing technology in different biosensing applications. Thus, we aim to offer fresh insights and stimulate interest among researchers from various domains toward developing and utilizing WGM resonators for biosensing purposes.