Metal-Dielectric Interfacial Engineering with Mesoporous Nano- Carbon Florets for 1000-Fold Fluorescence Enhancements: Smartphone-Enabled Visual Detection of Perindopril Erbumine at a Single-molecular Level

Metallic nanosystems with strong surface plasmon resonance have been a predominant choice for surface plasmon-coupled emission (SPCE), leading to a plethora of sensing and diagnostic applications. The Ohmic losses and strong isotropic scattering of the emissive photons in such systems still remain major challenges that limit the sensitivity, reliability, and magnitude of enhancements. Consequently, rational designing of non-plasmonic dielectric interfaces and their hybrids that suppress these drawbacks without compromising the radiative decay pathways is highly desirable. Here, we present dielectric-based nanostructured carbon florets (NCFs), exhibiting precisely tailored porosities and surface morphologies for enhanced light entrapment, thereby achieving plasmon-free generation of electromagnetic (EM) hotspots. The hard-carbon sp2 framework of NCF, together with its morphology resembling conical microcavities, thus represents the first all-carbon system, providing 310-fold SPCE enhancements. Such enhancements achieved in cavity configuration present a fundamental departure from those obtained through conventional plasmonic interfaces that work best in spacer and extended cavities. This underlines the importance of the extensive surface area (745.62 m2/g) and high absorbance (>0.9) of NCF. Besides showcasing the detailed morphological dependence of SPCE, the NCF also acts as a versatile support for anchoring plasmonic Ag and interfacing with pi-plasmon rich GO. Such a multi-component hybrid combines the benefits of several radiative pathways for realizing unprecedented 1000-fold SPCE enhancements. Consequently, this substrate has been utilized for the detection of pathologically important PE at single-molecular attomolar levels (1 x 10-19 M) with excellent linearity (R2 = 0.996) and high reliability (RSD: 2.07) over a wide concentration range spanning 16 orders of magnitude (0.1 aM-1 mM). The demonstration of such detection with smartphone-based platforms expands opportunities for the internet-of-things, besides unraveling newer possibilities for metal-dielectric interfacial engineering.