Plasmon-Rich BCZT Nanoparticles in the Photonic Crystal-Coupled Emission Platform for Cavity Hotspot-Driven Attomolar Sensing

Abstract

The unique functionality of metallic and dielectric nanomaterials to generate intense electromagnetic field localization termed "hotspots" has been exploited in numerous luminescencebased biosensing applications. To obtain an amplified, sharply directional, and polarized emission, tunable size and shape morphologies have been evaluated in the surface plasmon-coupled emission (SPCE) platform. Although such studies have significantly facilitated the biosensor modalities, inevitable parasitic Ohmic losses in metal-dependent SPCE platforms have remained a significant bottleneck. In this context, recently, a dielectric-based photonic crystal-coupled emission (PCCE) platform is being explored for point-of-care diagnostics as it facilitates overcoming the limitations of conventional fluorescence and SPCE technologies. However, despite the utility of myriad metallo-dielectric hybrid nanoarchitectures and interfaces in SPCE and PCCE platforms to augment the photoplasmonic coupling efficiency, the expected fluorescence intensity remains compromised due to the presence of metallic components. In this background, we demonstrate the utility of high refractive index (HRI), ferroelectric, and biocompatible perovskite Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT) nanoparticles (NPs) for significantly augmenting the fluorescence of fluorophores. While nano-BCZT yielded 100-fold fluorescence enhancement in the lossy SPCE platform, >1000-fold enhancement is demonstrated in the lossless PCCE platform due to the generation of multifold nanocavities with copious hotspots. The localized density of states of radiating dipoles is maximized with effective coherent and collective photon coupling in a highly desirable nano-BCZT, graphene oxide, and one-dimensional photonic crystal ensemble. Consequently, this state-of-the-art ensemble presents an unaccustomed enhancement due to the judicious synergy of all-dielectric HRI NPs, π-plasmons, and internal optical modes which have been utilized for sensing a weakly fluorescent TPYP3 molecule at attomolar limit of detection. This all-dielectric-based PCCE platform opens up possibilities of using fluorophores with low quantum yield for sensing purposes. The sustainable nanoengineering technique developed here for photoplasmonic application opens opportunities for investigating such next-generation all-dielectric metasurfaces for point-of-care diagnostics and biosensing.

Review of Gold Nanoparticles in Surface Plasmon-Coupled Emission Technology: Effect of Shape, Hollow Nanostructures, Nano-Assembly, Metal–Dielectric and Heterometallic Nanohybrids

“…The metal-fluorophore system effectively constitutes a resonant hybrid termed ‘plasmophore’ (plasmon + fluorophore) because emitted photons from the radiating dipoles trigger newer charge density perturbation pathways to generate plasmons that finally radiate into the far-field, carrying the attributes of both the metal and the fluorophore species [ 4 , 24 ]. In the process, the newer channels of radiative decay rate are realized with high photostability and dwindled lifetime [ 27 , 28 , 29 ]. This field of research has evolved into metal-enhanced fluorescence (MEF) where the conventional limitations of low sensitivity in fluorescence spectrophotometry are circumvented.…”