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Although plasmonic and photonic crystal substrates represent fertile ground for plasmon-enhanced fluorescence, Raman scattering, and surface-enhanced Raman scattering based diagnostic tool development, extracting quantifiable Raman information from strongly fluorescent analytes without photobleaching, signal gating, or multi-step sample preparation has remained a long-standing challenge. In this work, we introduce Fluorescence Enabled Raman Amplification (FERA) as a mechanism that triggers the resonances of a photonic crystal surface and plasmonic nanoparticles via the molecular emission of a fluorescence-emitting radiating dipole, which, in turn, feeds back into molecular Raman scattering of the same molecules. This self-reinforcing feedback mechanism of FERA is experimentally demonstrated using multiple lasers and objectives and validated through COMSOL Multiphysics simulations. While the mesoscopic engineering presented valuable insights toward the generation of intense photonic-plasmonic hotspots, the microscopic engineering demonstrates the functionality of the radiating dipole as a dynamic entity with tailorable electronic and vibrational energy levels. By offering a simple, scalable, and label-compatible approach to photonic crystal-enhanced fluorescence in the transmittance mode and FERA in the reflectance mode, our study represents a pathway in the design of multifunctional plasmonic-photonic substrates and invites further exploration into light-matter interactions at the nanoscale. 

The requirements of augmented signal contrast provided by nanoparticle tags in biosensor microscopy-based point-of-care technologies for cancer and infectious disease diagnostics can be addressed through metallo-dielectric nanoarchitectures that enhance optical scattering and absorption to provide digital resolution detection of single tags with simple instrumentation. Photonic Resonator Interferometric Scattering Microscopy (PRISM) enables label-free visualization of nanometer-scale analytes such as extracellular vesicles and virions, and its applicability can be extended to biomolecular analyte counting through nanoparticle tags. Here, we present template-free, linker-less cryosoret nano-assemblies fabricated via adiabatic cooling (−196 °C) as plasmonic nano-antennas that provide high scattering contrast in PRISM. Plasmonic Ag and Au nanomaterials and their cryosorets are evaluated through imaging experiments and simulations based on the finite element method to understand the photo-plasmonic coupling effect at the surface of a photonic crystal (PC) interface. The Ag and Au cryosorets provide at most 8.29-fold and 6.77-fold higher signal contrast compared to their singlet counterpart. Through the simulations, the averaged field magnitude enhancements of 2.77-fold and 3.68-fold are observed for Ag and Au cryosorets when interfacing with PCs compared to bare glass substrates. The hybrid coupling between the localized Mie and delocalized Bragg plasmons of cryosorets and the underlying PC's guided mode resonance provides insights for developing nano-assembly-based nano-tags for biosensing applications.