Surface Plasmon Coupled Phosphorescence (SPCP)

Photoluminescence modification of europium(III)-doped MAl2O4 (M = Zn, Mg) spinels induced by Ag@SiO2 core-shell nanoparticles

In recent years, there has been an increasing interest in developing new inorganic compounds with exceptional properties for advanced materials. Specifically, compounds containing europium have attracted much attention due to their luminescent properties. These compounds are used in electronics, biotechnology, medicine, and catalysis. Eu is known for its characteristic red emission, which can be influenced by the environment. This study investigates the surface-enhancement luminescence of europium-doped spinel oxides using modified surface with silver (Ag@SiO2 core-shell) nanoparticles as the enhancers. The europium-doped spinels were synthesized through a sol-gel method, and characterization techniques were used to analyze their structure and morphology. Photoluminescence spectra exhibited characteristic Eu3+ transitions, with the hypersensitive transition being the most prominent. The interaction with an Ag@SiO2 modified-surface led to a significant increase in photoluminescence. The study also analyzed the photoluminescence excitation and lifetimes of the oxides, leading to a 7.3-fold increase in photoluminescence. The improvements observed in the luminescence of these tailor-made materials show their potential interest in next-generation technologies.

Surface Plasmon-Coupled Dual Emission Platform for Ultrafast Oxygen Monitoring after SARS-CoV-2 Infection

The outbreak of the COVID-19 pandemic has had a major impact on the health and well-being of people with its long-term effect on lung function and oxygen uptake. In this work, we present a unique approach to augment the phosphorescence signal from phosphorescent gold(III) complexes based on a surface plasmon-coupled emission platform and use it for designing a ratiometric sensor with high sensitivity and ultrafast response time for monitoring oxygen uptake in SARS-CoV-2-recovered patients. Two monocyclometalated Au(III) complexes, one having exclusively phosphorescence emission (λ_PL = 578 nm) and the other having dual emission, fluorescence (λ_PL = 417 nm) and phosphorescence (λ_PL = 579 nm), were studied using the surface plasmon-coupled dual emission (SPCDE) platform for the first time, which showed 27-fold and 17-fold enhancements, respectively. The latter complex having the dual emission was then used for the fabrication of a ratiometric sensor for studying the oxygen quenching of phosphorescence emission with the fluorescence emission acting as an internal standard. Low-cost poly (methyl methacrylate) (PMMA) and biodegradable wood were used to fabricate the microfluidic chips for oxygen monitoring. The sensor showed a high sensitivity with a limit of detection ∼ 0.1%. Furthermore, real-time oxygen sensing was carried out and the response time of the sensor was calculated to be ∼0.2 s. The sensor chip was used for monitoring the oxygen uptake in SARS-CoV-2-recovered study participants, to assess their lung function post the viral infection.

Green synthesis of gold nanoparticle/gelatin/protein nanogels with enhanced bioluminescence/biofluorescence

Here we report the green synthesis of gelatin/protein hybrid nanogels containing gold nanoparticles (AuNPs) that collectively exhibit metal-enhanced luminescence/fluorescence (MEL/MEF). The gelatin/protein nanogels, prepared by genipin cross-linking of preformed gelatin/protein polyion complexes (PICs), exhibited sizes ranging between 50 and 200 nm, depending on the weight ratio of gelatin and protein. These nanogels serve as reducing and stabilizing agents for the AuNPs, allowing for nucleation in a gel network that exhibits colloidal stability and MEL/MEF. AuNP/gelatin/HRP and AuNP/gelatin/LTF nanogels presented an ~11-fold enhancement of bioluminescence in an HRP-luminol system and a ~50-fold fluorescence enhancement when compared to free LTF in cell uptake experiments. These hybrid nanogels show promise for optically enhanced diagnosis and other therapeutic applications.

Surface Plasmon-Coupled Directional Enhanced Raman Scattering by Means of the Reverse Kretschmann Configuration

Surface-enhanced Raman scattering (SERS) is a unique analytical technique that provides fingerprint spectra, yet facing the obstacle of low collection efficiency. In this study, we demonstrated a simple approach to measure surface plasmon-coupled directional enhanced Raman scattering by means of the reverse Kretschmann configuration (RK-SPCR). Highly directional and p-polarized Raman scattering of 4-aminothiophenol (4-ATP) was observed on a nanoparticle-on-film substrate at 46° through the prism coupler with a sharp angle distribution (full width at half-maximum of ∼3.3°). Because of the improved collection efficiency, the Raman scattering signal was enhanced 30-fold over the conventional SERS mode; this was consistent with finite-difference time-domain simulations. The effect of nanoparticles on the coupling efficiency of propagated surface plasmons was investigated. Possessing straightforward implementation and directional enhancement of Raman scattering, RK-SPCR is anticipated to simplify SERS instruments and to be broadly applicable to biochemical assays.

Experimental and theoretical study of the distance dependence of metal-enhanced fluorescence, phosphorescence and delayed fluorescence in a single system

Distance dependent singlet and triplet metal-enhanced emission of eosin from silica coated silver island films (SiFs) has been studied by steady-state and time resolved fluorescence techniques, along with theoretical finite difference time domain (FDTD) numerical simulations, to understand how the thickness of the dielectric coating surrounding silver nanoparticles fundamentally affects luminescence enhancement. Our findings suggest that the distance dependence of metal-enhanced phenomena such as fluorescence, phosphorescence and delayed fluorescence is underpinned by the decay of the electric near-field, and depending on the actual silver silica sample embodiment, one can see either decreased or enhanced luminescence. These results not only expand our current MEF thinking but also suggest that one may well be able to approximate plasmon-enhanced luminescence values.

Spectral tuning of the phosphorescence from metalloporphyrins attached to gold nanorods

The spectral shape of the phosphorescence emission of organometallic porphyrin molecules is shown to be altered when these chromophores are incorporated into hybrid nanostructures with gold nanorods. This result shows that triplet-singlet transitions, which are (at least partially) dipolar forbidden, can be modified by the dipolar resonances of gold nanoparticles. By choosing nanorods of increasing aspect ratios, it is possible to match the long axis plasmon resonance of the nanorods to a specific phosphorescence transition. Consequently, the emission colour of the hybrids can be tuned.

Surface plasmon-coupled emission: what can directional fluorescence bring to the analytical sciences?

Surface plasmon-coupled emission (SPCE) arose from the integration of fluorescence and plasmonics, two rapidly expanding research fields. SPCE is revealing novel phenomena and has potential applications in bioanalysis, medical diagnostics, drug discovery, and genomics. In SPCE, excited fluorophores couple with surface plasmons on a continuous thin metal film; plasmophores radiate into a higher-refractive index medium with a narrow angular distribution. Because of the directional emission, the sensitivity of this technique can be greatly improved with high collection efficiency. This review describes the unique features of SPCE. In particular, we focus on recent advances in SPCE-based analytical platforms and their applications in DNA sensing and the detection of other biomolecules and chemicals.

RECENT ADVANCES IN METAL-ENHANCED OPTICAL PROPERTIES

Noble metal nanoparticles exhibit strong surface plasmon resonance (SPR) and have been utilized in many chemical, biological and electronic applications. Recent advances on metal-enhanced optical properties demonstrated that the quantum yield and photo-stability of the fluorophores can be significantly enhanced when they are in the proximity of the metal surface, that will benefit many fluorescence-based applications. In this review article we first discuss the fundamental concepts of metal-enhanced optical properties and the recent achievements of metal-enhanced fluorescence of organic fluorophores and quantum dots, as well as metal-enhanced phosphorescence of organic molecules and upconversion nanoparticles that have long life times. Finally, we present recent applications of metal-enhanced optical properties in biosensing and bioassays, photodynamic therapy and optoelectronics.