Integrated Metallo-Dielectric 3D Hotspots From High Refractive Index Nanodiamond-Plasmonic Gold Cryosoret Nano-Assemblies for Photonic Crystal Enhanced Fluorescence

Hybridizing fluorescent reporters with gold nanoparticles (AuNPs) presents challenges associated with surface-induced quenching in the “zone of inactivity,” compromising the functionality of related point-of-care diagnostic tools. Nano-assembly of high refractive index (HRI) dielectric and plasmonic NPs yields augmented electric and magnetic resonances that are not achievable with the individual counterparts. Here, several long-standing challenges associated with conventional photon-emitting reporters are addressed by integrating HRI dielectric fluorescent nanodiamonds (NDs) with metallo-dielectric nano-assemblies. An adiabatic cooling (−196 °C) driven nano-assembly method is used to synthesize AuND cryosoret (AuNDCS) nano-assemblies. More than 600-fold enhancement of the emission from the nitrogen vacancy of AuNDCS is demonstrated when interfaced with a photonic crystal through interaction with the radiating guided mode resonance. Experimental results are corroborated with extensive simulations of a variety of nano-constructs, including monomers (0D), dimers (1D), trimers (2D), and tetramers (3D) to visualize the electric and magnetic field hotspots. The fluorescence enhancement is utilized to detect a cancer-specific target biomarker, micro-RNA 375, with femtomolar-level detection limits, using the AuNDCS as a molecular tag. The PC-enhanced fluorescence detection instrument does not require prisms, objectives, or cooled photodetectors, resulting in a compact and inexpensive system that would be suitable for environments outside of conventional diagnostic laboratories.