Electrostatic-responsive Microdroplet Lasers for Ultrasensitive Molecular Detection

Electrostatics plays a critical function in most biomolecules, therefore monitoring subtle biomolecular bindings and dynamics via the electrostatic changes of biomolecules at biointerfaces has been an attractive topic recently and has provided the basis in diagnosis and biomedical science. Here we present a bioelectrostatic responsive microlaser based on liquid crystal (LC) droplet and explored its application for ultrasensitive detection of negatively charged biomolecules. Whispering gallery mode (WGM) lasing from positively charged LC microdroplets was applied as the optical resonator, where the lasing wavelength shift was employed as a sensing parameter. With the dual impacts from whispering-gallery mode and liquid crystal, molecular binding signals will be amplified in such LC droplet sensors. It is found that molecular electrostatic changes at the biointerface of droplet triggered wavelength shift in lasing spectra. The total wavelength shift increased proportionally with the adhering target concentrations. Compared to a conventional polarized optical microscope, significant improvements in sensitivity and dynamic range by four orders of magnitude were achieved. Our work indicated that the surface-to-volume ratio plays a critical role in the detection sensitivity in WGM laser-based microsensors. Finally, bovine serum albumin and specific biosensing using streptavidin and biotin were exploited to demonstrate the potential applications of microlasers with a detection limit on the order of 1 pM. We anticipate this approach will open new possibilities for the ultrasensitive label-free detection of charged biomolecules and molecular interactions by providing a lower detection limit than conventional methods.