Superior resonant nanocavities engineering on photonic crystal-coupled emission platform for detection of femtomolar iodide and zeptomolar cortisol

Abstract

Although luminescence spectroscopy has been a promising sensing technology with widespread applications in point-of-care diagnostics and chem-bio detection, it fundamentally suffers from low signal collection efficiency, considerable background noise, poor photostability, and intrinsic omnidirectional emission properties. In this regard, surface plasmon-coupled emission (SPCE), a versatile plasmon-enhanced detection platform with > 50 % signal collection efficiency, high directionality, and polarization has previously been explored to amplify the limit of detection of desired analytes. However, high Ohmic loss in metal-dependent plasmonic platforms has remained an inevitable challenge. Here, we develop a hybrid nanocavity interface on a template-free and loss less photonic crystal-coupled emission (PCCE) platform by quintessential integration of high refractive index (HRI) dielectric Nd2O3 �Huygens sources� and sharp-edged silver nanoprisms (AgNPrs). While efficient forward light scattering characteristics of Nd2O3 -nanorods (NRs) present 460-fold emission enhancements in PCCE, the tunable localized plasmon resonances of NPrs display high electromagnetic field confinement at sharp nanotips and protrusions boosting the enhancements to 947-fold. The judicious use of AgNPr metal- Nd2O3 dielectric hybrid resonances in conjugation with surface trapped Bloch surface waves of one-dimensional photonic crystal (1DPhC) displayed unprecedented > 1300-fold enhancements. The experimental results are validated by excellent correlations with numerical calculations. The multifold hotspots generated by zero and non-zero nanogaps between the co-assembly of NPrs, NRs and 1DPhCs are used for (i) determination of hyper and hypothyroidism levels through monitoring concentration of iodide (I-) ions and (ii) single molecule detection (zeptomolar) of the stress hormone, cortisol through synthesized cortisol-rhodamine B conjugate obtained using a simple esterification reaction.