Multiarchitecture-Based Plasmonic-Coupled Emission Employing Gold Nanoparticles: An Efficient Fluorescence Modulation and Biosensing Platform

Abstract

Surface plasmon-coupled emission (SPCE) is an efficient surface-enhanced fluorescence method based on the nearfield coupling process of surface plasmons and fluorophores. Based on this, we developed multiple coupling structures for an SPCE system by introducing gold nanoparticles (AuNPs) with different architectures by adjusting different modification methods and configurations. By assembling AuNPs on a gold substrate through electrostatic adsorption and spin-coating, 40-and 55-fold enhancements were obtained compared to free space (FS) emission, respectively. After theoretical simulations and the optimization of experimental conditions, a novel "hot-spot" plasmonic structure, an intense electromagnetic field within the system, plasmonic properties, and the coupled process were found to be mainly responsible for the diverse enhancement effects observed. For the spincoating deposition method, new enhancing systems with high efficiency can be easily built without complex modification. Additionally, the subsequent detection system based on the uniform modification of AuNPs through electrostatic adsorption is convenient to establish with high sensitivity and stability, which can broaden the application of SPCE in both fluorescence-based sensing and imaging. This AuNP-enhanced SPCE using an electrostatic adsorption method was designed as an immunosensor to prove feasibility.

Hottest Hotspots from the Coldest Cold: Welcome to Nano 4.0

“…Furthermore, our laboratory has examined the plasmonic interfacial functionality (basic research) of a variety of nanoscale materials in the SPCE platform toward applied optics and translational-based photonic biosensors. − In the past decade, several quintessential processes, material properties, and applications have been reported in SPCE. The study of materials such as plasmonic NPs (Ag, Au, Pt, and Pd), CNTs, low-dimensional carbon (0D, 1D, and 2D), plasmon-soliton architectures, high-refractive-index dielectric NPs and their plasmonic hybrids, to name a few, has enriched the understanding of the quantum emitter–photon coupling phenomenon in the nano regime. − Although there are different routes to synthesize varied NPs, the utility of nanoassemblies in SPCE had remained elusive on account of the nanogaps supported by them. Self-assembly is a widely used technique for the synthesis of nanoassemblies with collective functional properties .…”

“…(ii) AuNPs, by virtue of interband transitions and ohmic losses, quench the molecular emission from radiating dipoles present in their vicinity. Different methodologies have been explored in the past to overcome the quenching phenomenon. ,− Here, dequenching the intrinsically quenched emission in the presence of AuNPs using Au-based CSs is presented. The intense and uniform 3D electromagnetic hotspots rendered delocalized and localized plasmons, thereby surmounting the quenching phenomenon.…”

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

“…These studies unambiguously pointed to the advantages of the engineered morphologies with sharp edges (such as nanostars, nanoprims, and nanorods) and their hierarchical assemblies for providing high electromagnetic (EM) field confinement, leading to enhanced SPCE. − Our earlier studies in this direction contributed to this by reaffirming the structural advantages of nanovoids and nano-cavities for achieving significant plasmon-based enhancements. − These, in turn, have been utilized for ultrasensitive and reliable analytical detection through both vibrational Raman (SERS) and fluorescence (SPCE). − Furthermore, 118-fold SPCE enhancements have been demonstrated by minimizing Ohmic losses using high refraction index dielectrics in conjugation with metal nanostructures . In spite of such significant advancements in both fundamental aspects and the applications thereof, the major challenges in SPCE enhancements using metallic nanostructures have been (i) inevitable Ohmic losses along with radiative damping, ,, (ii) poor chemical stability, especially in real-time applications, ,, and (iii) extensive isotropic photon scattering that compromises the magnitude of SPCE enhancements. − As opposed to the variety of metal, non-metallic, dielectric, two-dimensional, and zero-dimensional substrates that have been investigated for SERS, substrates for SPCE have been primarily restricted to metallic and their composites. ,, Thus, a ubiquitous platform that synergistically couples the plasmonic advantages of metallic nanostructures while simultaneously minimizing the Ohmic and radiative losses is desirable for improving the quality factor and reliability of SPCE, thereby transforming it into a powerful ultrasensitive analytical technique. − Achieving this would provide distinct opportunities for portable and mobile phone-based detection capabilities catering to the internet-of-things. , …”

Sericin-Based Bio-Inspired Nano-Engineering of Heterometallic AgAu Nanocubes for Attomolar Mefenamic Acid Sensing in the Mobile Phone-Based Surface Plasmon-Coupled Interface

“…Recently, anisotropic Ag and Au nanomaterials with sharp edges, vertices, and cavities have been gaining increased attention for hotspot generation in plasmonics-based optical sensors. − However, it is important to note that both Ag and AuNPs have typical merits and demerits from a spectro-plasmonics point of view. − While AgNPs suffer from unavoidable chemical instability (absent in AuNPs), the usage of AuNPs in SPCE has remained a long-standing challenge on account of the well-known quenching phenomena (due to high Ohmic losses) in spite of their copious electron density (≈5.90 × 10 16 m –3 ). ,, In this context, fundamental explorations have been limited to Ag-based nanomaterials or composites due to comparatively negligible quenching rendered by them with the use of rhodamine moieties as luminophores. In the spatial range of <5 nm, the so-called zone of inactivity is prevalent in the case of gold due to large non-radiative decay channels supported by higher-order plasmonic modes. , In order to overcome such limitation of quenching with AuNPs, different approaches have been adopted, namely, (i) plasmon intermixing in nanocavities where the quenching is dequenched, (ii) core–shell metal–dielectric nanointerfaces, (iii) metal–dielectric-decorated nanorchitectures, (iv) nanostructures showcasing sharp protrusions such as tips and vertices supporting tip–core hybrid plasmon coupling, and (v) nanoshells and nanocages for generating cavity and void hotspots. , Although these strategies have demonstrated dequenched fluorescence emission, the synthetic routes adopted for nanofabrication are often not bio-inspired and not sustainable.…”