The quest for auxiliary plasmonic materials with lossless properties began in the past decade. In the current study, a unique plasmonic response is demonstrated from a stratified high refractive index (HRI)–graphene oxide (GO) and low refractive index (LRI)–polymethyl methacrylate (PMMA) multistack. Graphene oxide plasmon-coupled emission (GraPE) reveals the existence of strong surface states on the terminating layer of the photonic crystal (PC) framework. The chemical defects in GO thin film are conducive for unraveling plasmon hybridization within and across the multistack. We have achieved a unique assortment of metal-dielectric-metal (MDM) ensuing a zero-normal steering emission on account of solitons as well as directional GraPE. This has been theoretically established and experimentally demonstrated with a metal-free design. The angle-dependent reflectivity plots, electric field energy (EFI) profiles, and finite-difference time-domain (FDTD) analysis from the simulations strongly support plasmonic modes with giant Purcell factors (PFs). The architecture presented prospects for the replacement of metal-dependent MDM and surface plasmon-coupled emission (SPCE) technology with low cost, easy to fabricate, tunable soliton [graphene oxide plasmon-coupled soliton emission (GraSE)], and plasmon [GraPE] engineering for diverse biosensing applications. The superiority of the GraPE platform for achieving 1.95 pg mL–1 limit of detection of human IFN-γ is validated experimentally. A variety of nanoparticles encompassing metals, intermetallics, rare-earth, and low-dimensional carbon–plasmonic hybrids were used to comprehend PF and cavity hot-spot contribution resulting in 900-fold fluorescence emission enhancements on a lossless substrate, thereby opening the door to unique light–matter interactions for next-gen plasmonic and biomedical technologies.

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Conventionally, nanoassemblies are synthesized using widely adopted template-based approaches. External stimuli such as electric and magnetic fields and light-induced reactions have recently been investigated. The exploration using a temperature gradient in this spotlight is very nascent. In this context, soret colloids are nanoparticle (NP) assemblies obtained via adiabatic cooling at −18 °C. They have found widespread utility in surface plasmon-coupled emission (SPCE) and surface-enhanced Raman scattering (SERS) for sensing analytes and ions of biological and environmental concern. However, the drawback of the current methodology for obtaining enhanced tunability in functional properties for large-scale production has remained a bottleneck hitherto on account of the significant time (2 h) needed for building precise nanoassemblies. In this direction, a rapid, one-pot, and cost-effective adiabatic cooling methodology to obtain precise nanoassemblies with exceptionally tunable optical and morphological properties is experimentally demonstrated in this work. Thermodiffusion of homogeneous gold (Au) and silver (Ag) nanoparticles using adiabatic cooling at cryoshift temperatures (−80, −150, and −196 °C (or liquid N 2 )) significantly lowered the time from 2 h to 3 min for obtaining structurally and functionally tunable nanoassemblies. This methodology aids in the realization of hotspots of first, second, third, and fourth generations, which are nanoregimes of high electric-field intensity. The innovative fourth-generation hotspots (a horizon toward Nano 4.0) were distinctively generated and studied by mounting the cryosorets on SPCE substrates. The dual dependence of nanoassembly formation on time and cooling temperature is elaborately discussed for the first time in this study. The abundant field intensity and synergistic plasmon hybridization between metallic Ag, dielectric TiO 2 nanorods, and graphene oxide π-plasmons assisted in the realization of single-molecule detection. The sensing is achieved using a cost-effective smartphone-based technology that is amenable to resource-limited settings. This work opens a window to accomplish precise nanoassemblies of different sizes, shapes, material properties, numbers of particles by modulating the adiabatic cooling time and temperature, for use in biosensing, photonics, and interdisciplinary applications.

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Engineering photo-plasmonic platforms with heterometallic nanohybrids are of paramount significance for realizing augmented sensitivity in fluorescence-based analytical detection. Although myriad nanomaterials with versatile functionalities have been explored in this regard in the surface plasmon-coupled emission (SPCE) interface, light harvesting using nano-antennas synthesized via sustainable bio-inspired routes still remains a high priority in current research. Our study provides a rational design for in situ fabrication of nanoparticles of silver, gold, and their plasmonic hybrids using biocompatible, non-hazardous sericin protein (obtained Bombyx mori) as the reducing and capping agent. The one-pot, user-eco-friendly technology demonstrated here utilizes UV irradiation to promote the photo-induced electron transfer mechanism, thereby yielding nanomaterials of tunable optoelectronic functionalities. The resulting homometallic and heterometallic nanohybrids with robust localized surface plasmon resonances (LSPR) showed strong light-confining attributes when interfaced with the propagating surface plasmon polaritons (SPPs) of the SPCE platform, thereby yielding tunable, highly directional, polarized, and amplified fluorescence emission. The experimentally obtained emission profiles displayed an excellent correlation with the theoretically obtained dispersion diagrams validating the spectro-plasmonic results. The abundant hotspots from AgAu nanocubes presented in excess of 1300-fold dequenched fluorescence enhancement and were utilized for cost-effective and real-time mobile phone-based sensing of biologically relevant mefenamic acid at an attomolar limit of detection. We believe that this superior biosensing performance accomplished using the frugal bioinspired nano-engineering at hybrid interfaces would open new doors for developing nanofabrication protocols with the quintessential awareness of the principles of green nanotechnology, consequently eliminating hazardous chemicals and solvents in the development of point-of-care diagnostic tools.

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