Plasmonic Nanoantenna Enhanced Ultrasensitive Fluorescence Immunoassay Enabled by Super-hydrophobic Surface - Abstract Fluorescence immunoassay has been a mainstay in protein detection. Although advanced techniques like multi-photon excitation and time-resolved microscopy have been routinely performed to increase fluorescence intensity, unfortunately, these incremental changes alone cannot bring the fluorescence intensity level high enough for meeting the growing biomedical research needs for ultralow and ultrasensitive detection crucial for early diagnosis. A paradigm shift that fundamentally transforms existing fluorescence technology relying on linear fluorescence emission is necessary. One such transformative technique explores localized surface plasmon resonance (LSPR) in a nanoantenna to trigger the nonlinear fluorescence emission. This nonlinear optical process can enhance fluorescence intensity by several orders of magnitude, holding the promise to support high- resolution biosensing. However, the nanoantenna technique is still far from being routinely implemented in biological and biomedical fields due to a major obstacle not from plasmonics but from the mass transport: Most of nanoantennas typically rely on diffusion to capture interested molecules. The diffusion limit makes the nanoantenna-enhanced fluorescence only theoretically possible. This critical technology gap will be bridged by the technology proposed here. This project proposes a new technology by the fusion of the nanoantenna and super-hydrophobic surface to break the diffusion limit. Droplets over super-hydrophobic surfaces maintain quasi- spheres during evaporation and do not wet the surface. Now the droplet evaporation replaces the diffusion and concentrates molecules onto the sensitive regions of the nanoantenna, becoming the dominant mechanism of mass transfer. The combination of plasmonic nanostructures and super-hydrophobic surfaces offers a unique solution to the key challenge in the nanoantenna-based detection: difficulty in practically bringing molecules to nanostructures. The specific aims of this application are to test that the integration of nanoantenna with the super-hydrophobic surface is capable of enhancing (1) the fluorescence intensity; and (2) the fluorescence immunoassay's detection sensitivity. This research will contribute to the paradigm shift of fluorescence technology. Since chips with deposited nanoantenna can be viewed through a regular fluorescence microscope with much improved capability, the devices produced by this research can be readily implemented in existing analytical platforms with little additional cost, which will have a major impact on the biomedical field.
