Surface plasmon coupled emission (SPCE) is a novel analytical technique in which the isotropic emission of a fluorophore is combined with the surface plasmon resonance of a Ag (or Au) thin film to yield highly directional emission from the so-called plasmaphore and thus greatly increased sensitivity. Here we report a 40-fold amplification of rhodamine B (RhB) fluorophore when graphene is used as the spacer layer in a conventional Ag-based SPCE setup. In addition to protecting the Ag thin film from oxidation, the highly impermeable graphene facilitated π–π stacking interactions with the RhB molecules that resulted in an efficient radiated emission from the plasmaphore. In addition, we found that the plasmaphore emission was more sensitively dependent on the in-plane crystallinity (measured by coherence length L a) of the graphene spacer layer than its thickness. This study describes the unique features of graphene as a spacer layer for SPCE-based analytical platforms and its potential applications in chem-bio sensing and detection.

Extremely thin layers of MoS 2 , WS 2 , and BN have come to the fore as a "beyond graphene" class of emerging 2Dmaterials that display many interesting properties and have wide technological applications. In this study, we report the first time engineering of these novel nano 2D-materials as efficient spacer layer components in silver (Ag) based thin-film stacks that generated up to 17-fold enhancement in the emission intensity of rhodamine B (RhB) fluorophore molecules; based on the surface plasmon coupled emission (SPCE) platform. The exceptional mechanical, thermal, and chemical stability of these 2D-spacer layers enabled effective surface passivation of Ag thin-films. The superior signal enhancements observed from the different 2D-spacer substrates may be attributed to optimal changes in radiative decay rates of excited RhB states. In a manner not reported before, we demonstrate the tunability of SPCE signal enhancements, on choosing spacer materials of appropriate refractive index. In this work, we further present a detailed comparison between MoS 2 / WS 2 /BN, and also nanocarbon allotropes like graphene and C 60 , which we have previously reported as high-performance spacers in biosensing applications. The low-cost fabrication of Ag-(MoS 2 /WS 2 /BN) thin-film architectures, synergistically coupled with superior fluorescence signals produced by SPCE, promises the application of these portable platforms for the detection of various biochemical analytes with very high levels of sensitivity.

In this study, we present the use of C60 as an active spacer material on a silver (Ag) based surface plasmon coupled emission (SPCE) platform. In addition to its primary role of protecting the Ag thin film from oxidation, the incorporation of C60 facilitated the achievement of 30-fold enhancement in the emission intensity of rhodamine b (RhB) fluorophore. The high signal yield was attributed to the unique π-π interactions between C60 thin films and RhB, which enabled efficient transfer of energy of RhB emission to Ag plasmon modes. Furthermore, minor variations in the C60 film thickness yielded large changes in the enhancement and angularity properties of the SPCE signal, which can be exploited for sensing applications. Finally, the low-cost fabrication process of the Ag-C60 thin film stacks render C60 based SPCE substrates ideal, for the economic and simplistic detection of analytes.

The relatively low sensitivity of fluorescence detection schemes, which are mainly limited by the isotropic nature of fluorophore emission, can be overcome by utilizing surface plasmon coupled emission (SPCE). In this study, we demonstrate directional emission from fluorophores on flexible Ag-C60 SPCE sensor platforms for point-of-care sensing, in healthcare and forensic sensing scenarios, with at least 10 times higher sensitivity than traditional fluorescence sensing schemes. Adopting the highly sensitive Ag-C60 SPCE platform based on glass and novel low-cost flexible substrates, we report the unambiguous detection of acid-fast Mycobacterium tuberculosis (Mtb) bacteria at densities as low as 20 Mtb mm(-2); from non-acid-fast bacteria (e.g., E. coli and S. aureus), and the specific on-site detection of acid-fast sperm cells in human semen samples. In combination with the directional emission and high-sensitivity of SPCE platforms, we also demonstrate the utility of smartphones that can replace expensive and cumbersome detectors to enable rapid hand-held detection of analytes in resource-limited settings; a much needed critical advance to biosensors, for developing countries.

The instantaneous isolation of green fluorescent colloidal quantum dots of iron selenide capped with biocompatible oleic acid is reported in this study. These iron-containing quantum dots also serve as a safe alternative to the conventionally used metalchalcogenide systems in which the heavy metal component is usually toxic. The isolated colored colloidal solutions exhibited intense green fluorescence on exposure to ultraviolet light, which was also confirmed by photoluminescence spectroscopy. The isolated product was subjected to dynamic light scattering and transmission electron microscopy, and the particles were found to exhibit spherical morphology with an average diameter of 6-8 nm, confirming the isolation of quantum dots. The isolated iron selenide quantum dots have promising potential towards bioimaging and sensing, due to the biocompatible coating of oleic acid and iron, which also allows possibility of further chemical derivatization.