Photonic-crystal-enhanced fluorescence: Template-free gold cryosoret nanoassembly steering, dequenching, and augmenting the quenched emission from radiating dipoles

Abstract: Photonic-crystal-enhanced fluorescence (PCEF) has emerged as a versatile tool for medical diagnostics and analyte quantification. However, challenges with regard to low sensitivity, experimental artifacts, and negligible emission output in the “zone of inactivity” due to the quenching from plasmonic gold (Au) nanoparticles have remained a major bottleneck. Here, we report the distinct functionalities rendered by hybridizing the PC interface with the Au cryosoret nanoassemblies to not only dequench the quenched emission from radiating dipoles, but also yield augmented 200-fold steering fluorescence output. The performance of the platform is evaluated numerically using rigorous coupled-wave analysis (RCWA) and COMSOL Multiphysics simulations presenting good overlap with the experimentally obtained fluorescence signal, validating the radiating guided mode resonance model. Our approach incorporating the cryosoret nanoassemblies with three-dimensionally distributed nanogaps provides a method to realize integrated and abundant hot spots with insights into material interface engineering and potential applications for biosensing. Impact statement: Although surface plasmon-coupled emission (SPCE) technology has emerged as a resourceful tool for biosensing applications, it suffers from fundamental dissipative ohmic losses encountered with the underlying metal thin-film substrates. Challenges with regard to low sensitivity, experimental artifacts, and consequent negligible emission output in the “zone of inactivity” due to the quenching from plasmonic gold (Au) nanoparticles have remained a major bottleneck. In order to address this drawback, in this article, we demonstrate rational design, fabrication, and tunability of the lossless guided-mode resonance (GMR) of grating photonic crystals (PCs) to effectuate unprecedented steering fluorescence output that is not only dequenched, but also augmented. The synergistic approach utilizing the polarization selectivity of the PC and the hottest plasmonic hot spots of the Au cryosoret nanoassemblies presented newer insights from a materials engineering perspective substantiating the inferences from experiments (fluorescence) and simulations (RCWA). While the SPCE presented ~10-fold fluorescence enhancement, a ~200-fold enhancement in the photonic-crystal-coupled-enhanced steering (PCES) emission is demonstrated for identical conditions using the delocalized Bragg plasmons and localized Mie plasmons of the cryosorets fabricated via adiabatic cooling technology. We believe that this quench-free technology will lay the stepping stone for next-gen photoplasmonic devices for chem-biosensing applications.