A variety of materials such as low dimensional carbon substrates (1D, 2D, and 3D), nanoprisms, nanocubes, proteins, ceramics, and DNA to name a few, have been explored in surface plasmon-coupled emission (SPCE) platform. While these offer new physicochemical insights, investigations have been limited to silver as primary plasmonic material. Although, gold nanoparticles (AuNPs) exhibit robust performance, its intrinsic property to quench the emission from radiating dipoles (at distances < 5 nm) has impeded its utility. Despite the use of metal-dielectric resonances (with Au decorated SiO2 NPs) and sharp nanotips (from Au nanostars) for dequenching the emission, the enhancements obtained has been less than 200-fold in SPCE platform. To address these long-standing challenges, we demonstrate the utility of gold soret colloids (AuSCs) and photonic crystal-coupled emission (PCCE) platform. The soret nano-assemblies synthesized using adiabatic cooling technique presented integrated hotspots when taken with high refractive index Nd2O3 ‘Huygens sources’. The collective and coherent coupling between localized Mie and delocalized Bragg plasmons (of sorets), dielectric plasmons (of Nd2O3), highly confined and intense Bloch surface waves (of PCCE platform) aided in realization of dequenched, as well as amplified > 1500-fold enhancements at the photoplasmonic nanocavity interface, presenting new opportunities for multidisciplinary applications.

Sustainable chemistry principles involve go-green approaches for the synthesis of nanomaterials. Recent interest has been toward the use of renewable raw materials as precursors for the reduction of metal ions to nanoparticles (NPs). However, utility of residues and byproducts for plasmonic applications that could potentially add an immense value in interfacial applications is rarely attempted. Here, the silkworm pupae that contain up to 40% proteins and are generally discarded as a byproduct after reeling the silk fibers were collected, and the proteins in them were extracted. The protein hence obtained is termed silkworm protein (SWP). A simple mixture of metal ions (Ag+ and Au3+) with SWP and exposure to UV irradiation at defined intervals of time presented unique nanogeometries for plasmonic applications. The frugal bioinspired nanoengineering protocol developed here paved the way for monometallic (AgNPs and AuNPs) and heterometallic (AgAu) nanohybrids with remarkable optical and morphological properties. The obtained sharp-edged NPs with intense transverse and longitudinal localized surface plasmon resonances were studied on metallic thin films sustaining propagating surface plasmon polaritons to generate amplified and integrated hotspots. This was utilized for realizing tunable, highly directional, p-polarized, and augmented surface plasmon-coupled emission using a mobile phone-based detector. The unaccustomed 1300-fold enhancement of dequenched fluorescence achieved for the first time was employed for attomolar mobile phone-based sensing of environmentally and biologically relevant zinc ions with excellent correlation in comparison with conventional and cost-intensive detectors. This frugal bio-nanoinspired technology is amenable for resource-scarce settings and enhances adoption at the bottom of the pyramid for point-of-care applications. We strongly believe that the disruptive engineering developed in this study would open new doors for exploring and utilizing waste byproducts from several other industries including sugar, paper, electronics, and aquaculture for high-end photonic biosensor development.

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The ability of plasmonic nanoparticles (NPs) to focus the impinging electromagnetic (EM) radiation to subwavelength regimes assists in the detection of molecules at extremely low concentrations. Numerous nanomaterials have been exploited in the surface plasmon-coupled emission (SPCE) technology, presenting quintessential physicochemical insights. However, seldom attention has been paid toward utilizing the biocompatible nanotechnology for substrate nanoengineering in SPCE. In this context, we present LYCOAT-based silver (Ag) NPs synthesized via a frugal disruptive approach by exposing a simple physical mixture of Ag+ ions and LYCOAT to UV irradiation. Variations in the time of UV exposure resulted in nanofractals and nanocubes of Ag presenting unique architectures for nanophotonic applications, where the biocompatible LYCOAT functions as both reducing and capping agents under ambient conditions. Nanomaterials synthesized in this approach were studied in spacer, cavity, and extended cavity nanointerfaces in the SPCE platform for obtaining tunable plasmonic coupling. The augmented >900-fold SPCE enhancements were utilized for mobile phone-based attomolar sensing of environmentally hazardous Hg2+ ions. The simple, realistic, and eco-friendly methodology adopted here for developing nanomaterials for photonic applications opens the door for exploring such next-generation bio-inspired nanomaterials for point-of-care diagnostic applications.

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.