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

Abstract 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.