The Ag nanoparticles-SiO2–ZnO film sandwiched structure was fabricated by depositing ZnO films on silica substrates which had been implanted by Ag ions. Enhancement of emission of the sandwiched structure was observed. The enhancement emission is caused by the resonant coupling between the surface plasmons of Ag and the spontaneous emission of ZnO. The enhancement mechanism is confirmed by optical absorption spectra, transmission electron microscopy, and time-resolved photoluminescence. The key is to deposit ZnO on Ag nanoparticles covered with silica to prevent oxidation of Ag by direct contact with ZnO. This structure will be very useful for highly efficient optoelectronic devices.
A convenient nanotechnique is reported to tailor the light emission properties of organic emitter poly͓2-methoxy-5-͑2Ј-ethyl-hexyloxy͒-p-phenylene vinylene͔ ͑MEH-PPV͒ by coupling to resonance-tuned silver nanoantenna arrays. It is revealed experimentally and theoretically that the enhanced photoluminescence from the MEH-PPV/silver nanoantenna complex may originate from the energy transfer effect in the surface plasmon resonance coupling between the MEH-PPV and silver nanocaps and from local electromagnetic field enhancement of nanogaps between the silver nanocaps in the background of the light-emitting MEH-PPV. The results are corroborated by the finite difference time domain simulation results.
Fluorescence imaging has been widely used as a powerful tool for in situ and real-time visualization of important analytes and biological events in live samples with remarkably high selectivity, sensitivity, and spatial resolution. Compared with one-photon fluorescence imaging, two-photon fluorescence imaging exhibits predominant advantages of minimal photodamage to samples, deep tissue penetration, and outstanding resolution. Recently, the aggregation-induced emission (AIE) materials have become a preferred choice in two-photon fluorescence biological imaging because of its unique bright fluorescence in solid and aggregate states and strong resistance to photobleaching. In this review, we will exclusively summarize the applications of AIE-active materials in two-photon fluorescence imaging with some representative examples from four aspects: fluorescence detection, in vitro cell imaging, ex vivo tissue imaging, and in vivo vascular imaging. In addition, the current challenges and future development directions of AIE-active materials for two-photon bioimaging are briefly discussed.
Patterned silver nanocap arrays (PSNAs) prepared on porous anodic alumina templates by a simple coating technique yield enhanced sensitivity and stability in cellular fluorescence imaging. Microstructural analysis, surface-enhanced Raman scattering mapping, and finite difference time domain simulation indicate that the hot spots are evenly distributed on the substrate. Ag1522 or Chinese Hamster Ovary cells are labeled by phalloidin-fluorscein isothiocyanate (P-FITC) on the cytoskeletons and the fluorescence signals from the fluorophores bound on the cell cytoskeletons on the PSNAs are enhanced 8-fold compared to those on glass used in conventional imaging. In addition to the intensity enhancement, the photostability is improved dramatically. Spectral analysis suggests that the PSNAs can create more excitons in the light-emitting P-FITC because of plasmon resonance energy transfer from the silver nanocaps to the nearby P-FITC. They can also act as plasmonic antennae by converting a part of the nonradiative near-field emission from the fluorophores to the far field consequently enhancing the emission.
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