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

Abstract

Metallic nanosystems with strong surface plasmon resonance have been a predominant choice for surface plasmoncoupled 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 nonplasmonic 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 sp 2 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 m 2 /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 π-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 × 10 −19 M) with excellent linearity (R 2 = 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.

Biosensing Technologies: A Focus Review on Recent Advancements in Surface Plasmon Coupled Emission

“…In order to enhance the sensitivity of the detection devices, different nano-engineering techniques have been investigated and explored over the SPCE platform using myriad nanomaterials, including metallic nanomaterials (Ag, Au, Pt, Cu), dielectric nanomaterials (Nd 2 O 3 , SiO 2 , TiO 2 , TiC, TiN, TiCN), ferromagnetic nanomaterials (Fe 2 O 3 , Nd 2 O 3 -Ag or NdAg nanohybrids), homometallic and heterometallic, bi-, tri-, tetra-metallic nanohybrids, as well as graphene Dirac fermions and other 2-dimensional material-sustaining partially propagating plasmons, etc. [ 9 , 10 , 55 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ]. The EM field intensity in the spatial regions of nanogaps between the NPs and the metallic thin film is dependent on several factors, such as the shape (rods, triangles, urchins, spheres, cubes stars, and wires), size (<10 nm, 10 nm–100 nm, >100 nm), architecture (core-shell, decorated), surface roughness, nature of adjacently situated plasmonic and/or dielectric NPs as well as the immediate environment and its refractive index [ 92 , 93 , 94 , 95 , 96 , 97 ].…”

“…Extensive theoretical analysis of the utility of such nanomaterials for efficient photo-plasmonic hotspot generation have been carried out using discrete dipole approximation (DDA) [ 10 ], finite-difference time-domain (FDTD) [ 9 , 48 , 71 , 74 ] and COMSOL Multiphysics simulations [ 34 , 98 ] to obtain a comprehensive understanding of the hotspot behavior. These explorations have assisted in the realization of new opto-electronic phenomena at nano-dimensions, such as Casimir force, Rabi splitting, Fabry-Perot photonic mode-coupling, Fano resonance, quantum confinement and the Purcell effect in the SPCE platform, rendering scientific insights into physicochemical interactions at advanced interfaces [ 9 , 11 , 55 ]. These research studies have resulted in the development of intriguing biosensing platforms, thereby supporting translational photonics research in addition to providing newer insights from the basic (simulations) and applied research perspectives.…”

“…This has assisted in the realization of 60-fold SPCE enhancements; following which, several other nano-architectures with numerous sizes, shapes and assemblies have been examined in the SPCE platform for achieving amplified SPCE enhancements [ 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. Such synergy of fluorescence spectroscopy and applied nano-research with effective nano-engineering strategies has advanced the spectro-plasmonic modalities in the SPCE platform with newer applications and processes including, but not limited to: ultra-high sensitivity [ 41 , 42 , 43 ], CNT-assisted augmented coupling [ 44 ], cardiovascular disease and food biomarker monitoring [ 45 ], fluorescent polymer brushes for large angle studies [ 46 ], interfacial molecular beacon-related explorations [ 47 ], cavity-void plasmon coupling in nano-assemblies sustaining Bragg and Mie plasmons [ 48 ], adsorption-desorption analysis [ 49 ], lightning-rod effect [ 50 ], graphene π-plasmon hybrid coupling [ 51 , 52 , 53 , 54 ], mesoporous carbon florets for photon cascading in nanocavity [ 55 ], lower-to-higher aggregates coupling [ 56 ], magneto-plasmonics [ 57 ], PLEDs [ 58 ], simultaneous multianalyte sensing [ 59 ] and other cost-effective biosensing applications [ 60 , 61 , 62 , 63 , 64 , 65 , 66 ]. In spite of these developments, the three major long-standing limitations of the SPCE technology development have been: (i) a moderate increase in the SPCE signal intensity [ 67 , 68 , 6...…”

Photonic Crystal Enhanced Fluorescence: A Review on Design Strategies and Applications

“…To complement these advances, it is now firmly established that emission from fluorophores can be drastically modulated by placing them in the proximity of nanostructures that significantly alter their local density of states (LDoS) and photostability in the near-field [ 48 , 51 , 52 , 53 , 54 ]. In order to accomplish this, a variety of micro and nano-systems have been demonstrated [ 55 , 56 , 57 , 58 , 59 ]. In recent years, the research and development pertaining to the interaction of fluorescent moieties with plasmonic/metallic nanoparticles have exponentially improved with novel applications [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ].…”

Cost-Effective and Facile Fabrication of a Tattoo Paper-Based SERS Substrate and Its Application in Pesticide Sensing on Fruit Surfaces

“…However, since Raman signals are inherently weak, SERS, which can achieve high sensitivity combined with electromagnetic amplification, was developed [ 17 , 18 , 19 , 21 , 22 ]. Conductive NP clusters focus irradiated lasers and generate high plasmonic hotspots that allow SERS to detect even a single molecule [ 23 , 24 , 25 ]. Since they are based on electromagnetic amplification using conductive nanostructures, SERS devices are usually fabricated using sophisticated micro/nanostructure fabrication processes based on rigid substrates, such as silicon and quartz [ 20 , 26 , 27 ].…”