Shell-Isolated Nanoparticle-Enhanced Phosphorescence

Abstract

The emerging field of plasmonics has promoted applications of optical technology, especially in plasmon-enhanced spectroscopy (PES). However, in plasmon-enhanced fluorescence (PEF), "metal loss" could significantly quench the fluorescence during the process, which dramatically limits its applications in analysis and high-resolution imaging. In this report, silver core silica shell-isolated nanoparticles (Ag@SiO NPs or SHINs) with a tunable thickness of shell are used to investigate the interactions between NPs and emitters by constructing coupling and noncoupling modes. The plasmonic coupling mode between Ag@SiO NPs and Ag film reveals an exceeding integrating spectral intensity enhancement of 330 and about 124 times that of the radiative emission rate acceleration for shell-isolated nanoparticle enhanced phosphorescence (SHINEP). The experimental findings are supported by theoretical calculations using the finite-element method (FEM). Hence, the SHINEP may provide a novel approach for understanding the interaction of plasmon and phosphorescence, and it holds great potential in surface detection analysis and singlet-oxygen-based clinical therapy.

Plasmonic Core–Shell Nanomaterials and their Applications in Spectroscopies

“…Therefore, shell isolated mode was also applied to enhance the phosphorescence intensity of Ru(bpy) 3 2+ bonded to the substrate surface. [108] We first covalent bonded the molecule to the noncoupling and coupling substrates, then synthesized the shell-isolated NPs Ag@SiO 2 with the silica shell of 2 nm/6 nm/10 nm/20 nm to enhance the spectra. In combination of the transient spectra, we were able to gain the different lifetime of the Ru(bpy) 3 2+ molecules as well.…”

The critical role of shell in enhanced fluorescence of metal-dielectric core-shell nanoparticles

“…42,43,50,51 In the dielectric shell case, the tunability limits are set between Re ε c = −2ε h for r s → r c and Re ε c = −2ε s for r c → 0, 50 and the resulting tunability is narrower and typically of the order of ∼ 100 nm. For the same reason, initial search of fluorescence enhancement focused more on metal shell particles, whereas the use of metal-dielectric core-shell particles, apart of some preliminary work, 45,46,[52][53][54][55][56][57][58][59][60] has still remained to be underestimated in the current literature.…”

“…We searched for experimentally feasible metal-dielectric core-shell configurations with common Au and Ag cores and widely available dielectric shell materials (SiO 2 , Al 2 O 3 , ZnO) whose refractive indices are higher than that of the host medium (air or water), for optimal fluorescence enhancements. The outcome is that, in spite of relatively narrow tunability of the LSPR wavelength of those particles, there is still enough of design flexibility left for optimally designed nanoparticles to enable (i) comparable or even larger fluorescence enhancement as metal shells 61 and (ii) significantly enhanced fluorescence compared to homogeneous metal particles, 45,46,[58][59][60] due to the efficient tailoring of the electric nearfield and fluorescence decay rates by dielectric shell. Furthermore, the dielectric shell of a metal-dielectric core-shell nanoparticle (also called shell-isolated nanoparticle 60 ) provides a convenient way to separate the fluorescence emitter and the metallic component with a predetermined distance, thus avoiding the quenching problem.…”

“…The outcome is that, in spite of relatively narrow tunability of the LSPR wavelength of those particles, there is still enough of design flexibility left for optimally designed nanoparticles to enable (i) comparable or even larger fluorescence enhancement as metal shells 61 and (ii) significantly enhanced fluorescence compared to homogeneous metal particles, 45,46,[58][59][60] due to the efficient tailoring of the electric nearfield and fluorescence decay rates by dielectric shell. Furthermore, the dielectric shell of a metal-dielectric core-shell nanoparticle (also called shell-isolated nanoparticle 60 ) provides a convenient way to separate the fluorescence emitter and the metallic component with a predetermined distance, thus avoiding the quenching problem. 12, 45,52,57,62,63 In our simulations, we have employed a rigorous and computationally fast transfer matrix method, which can be viewed as an extension of the theory for homogeneous particles [20][21][22][23] to a multilayered case with an arbitrary number of layers, to obtain the radiative and nonradiative decay rates, 24,25 the electric field distribution, 64 and, as a result, the fluorescence enhancement factor.…”

Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

“…The excitation of surface plasmons significantly affects the intensity of the electric field in the proximity of the illuminated plasmonic nanoparticles—a very large enhancement of the electromagnetic field may be induced in some places in the proximity of the illuminated plasmonic nanostructures (Wei et al, 2018). This electric field enhancement leads to a significant increase in the efficiency of a number of optical processes for molecules in the proximity of the plasmonic nanostructures, such as: fluorescence (Touahir et al, 2010; Wang et al, 2012), phosphorescence (Meng et al, 2018), second harmonic generation (Brolo et al, 2002), Raman scattering (Brolo et al, 2002; Wang et al, 2013; Zhang et al, 2014), Raman optical activity (Osinska et al, 2010), hyper-Raman scattering (Hulteen et al, 2006), coherent anti-Stokes Raman scattering (Brolo et al, 2002), and infrared absorption (Imae and Torii, 2000). From the practical point of view, what is most important is the enhancement of the efficiency of Raman scattering generation induced by the plasmonic systems–this effect is called surface-enhanced Raman scattering (SERS).…”