Femtomolar Detection of Spermidine Using Au Decorated SiO₂ Nanohybrid on Plasmon-Coupled Extended Cavity Nanointerface: A Smartphone-Based Fluorescence Dequenching Approach

Abstract

Coupling of photons with molecular emitters in different nanocavities have resulted in transformative plasmonic applications. The rapidly expanding field of surface plasmoncoupled emission (SPCE) has synergistically employed subwavelength optical properties of localized surface plasmon resonance (LSPR) supported by nanoparticles (NPs) and propagating surface plasmon polaritons assisted by metal thin films for diagnostic and point-of-care analysis. Gold nanoparticles (AuNPs) significantly quench the molecular emission from fluorescent molecules (at close distances <5 nm). More often, complex strategies are employed for providing a spacer layer around the AuNPs to avoid direct contact with fluorescent molecules, thereby preventing quenching. In this study we demonstrate a rapid and facile strategy with the use of Au-decorated SiO 2 NPs (AuSil), a metal (Au)-dielectric (SiO 2 ) hybrid material for dequenching the otherwise quenched fluorescence emission from radiating dipoles and to realize 88-fold enhancement using the SPCE platform. Different loading of AuNPs were studied to tailor fluorescence emission enhancements in spacer, cavity, and extended (ext.) cavity nanointerfaces. We also present femtomolar detection of spermidine using this nanohybrid in a highly desirable ext. cavity interface. This interface serves as an efficient coupling configuration with dual benefits of spacer and cavity architectures that has been widely explored hitherto. The multifold hot-spots rendered by the AuSil nanohybrids assist in augmented electromagnetic (EM)-field intensity that can be captured using a smartphone-based SPCE platform presenting excellent reliability and reproducibility in spermidine detection.

Plasmon-Coupled Directional Emission from Soluplus-Mediated AgAu Nanoparticles for Attomolar Sensing Using a Smartphone

“…The SPCE enhancements are modified significantly depending on the properties of the dye molecules, NPs, and metallic thin film used. In our earlier reports, 11,27,28 it was noted that on account of admixing of dye and NPs, the surface induced quenching of the dye by NPs compete with plasmonic coupling, thereby resulting in dwindled enhancements. In view of that, we have developed an extended (ext.)…”

“…cavity nanointerface is fabricated by first spin coating the PVA doped with RhB, followed by NPs doped in PVA. 27 We have used PVA as a polymer matrix throughout to maintain generality across the experiments, aiding in easy analysis and reliable comparison of the results. For ease of understanding, one can also assume ext.…”

“…24−26 Unlike complex core−shell geometries, simplistic metal-dielectric AuSil (silica decorated with gold) nanohybirds has been recently reported to overcome the quenching. 27 While this domain adopts metal-dielectric hybrid plasmonic resonances, another approach constitutes the applicability of a sharp-edged gold nanostar (AuNS) to surpass the quenching phenomenon. 28 Nevertheless, the SPCE enhancements has remained less than 200-fold, in the presence of AuNPs, in spite of all these modifications.…”

Chromogenic Chemodosimeter Based on Capped Silica Particles to Detect Spermine and Spermidine

“…Some of these probes are based on organic molecules that experiment changes in fluorescence color after reacting with the polyamines [22][23][24], whereas other protocols are based on the use of metallic or organic nanoparticles [25][26][27] (for more details see Table S1 in the Supplementary Material). However, even though mesoporous silica nanoparticles can also be used in the preparation of chromogenic or fluorogenic sensors [28], there is only one example in which this type of nanoparticles is used for detecting Spm and Spd [29] and, even in this case, the silica particles are decorated with Au that is responsible for the transduction mechanism. What is more, at the best of our knowledge, there are no examples of Spm or Spd detection using silica nanoparticles capped with molecular gates.…”

High‐Sensitivity Tunable Bloch Surface Waves’ Biosensor Using Nanocomposite Cap Layer

“…Recently, dielectric−plasmonic hybrids overcome the limitation of using all‐plasmonic or all‐dielectric materials and open up new perspectives in biosensing. [ 25,26 ] Particular attention is paid to dielectric−plasmonic Nc, which are customizable materials widely used in sensing. [ 27,28 ] In this article, we propose the Ag−TiO 2 Nc as a terminate layer.…”