We demonstrated that the nanostructures comprising silver cores and dense layers of Y(2)O(3):Er separated by a silica shell are an excellent model system to study the interaction between upconversion materials and metals in nanoscale. This architecture allows for versatile control of the Y(2)O(3):Er-metal interaction through control of the silica dielectric spacer thickness and the metal-core size. Finally, the nanoparticles are potentially interesting as fluorescent labels in, for instance (single particle), imaging experiments or bioassays which require low background or tissue penetrating wavelengths.
The temporal and spatial control over the delivery of materials such as siRNA into cells remains a significant technical challenge. We demonstrate the pulsed near-infrared (NIR) laser-dependent release of siRNA from coated 40 nm gold nanoshells. Tat-lipid coating mediates the cellular uptake of the nanomaterial at picomolar concentration, while spatiotemporal silencing of a reporter gene (green fluorescence protein) was studied using photomasking. The NIR laser-induced release of siRNA from the nanoshells is found to be power- and time-dependent, through surface-linker bond cleavage, while the escape of the siRNA from endosomes occurs above a critical pulse energy attributed to local heating and cavitation. NIR laser-controlled drug release from functional nanomaterials should facilitate more sophisticated developmental biology and therapeutic studies.
Nanorattles consisting of hydrophilic, rare-earth-doped NaYF(4) shells each containing a loose magnetic nanoparticle were fabricated through an ion-exchange process. The inner magnetic Fe(3)O(4) nanoparticles are coated with a SiO(2) layer to avoid iron leaching in acidic biological environments. This multifunctional mesoporous nanostructure with both upconversion luminescent and magnetic properties has excellent water dispersibility and a high drug-loading capacity. The material emits visible luminescence upon NIR excitation and can be directed by an external magnetic field to a specific target, making it an attractive system for a variety of biological applications. Measurements on cells incubated with the nanorattles show them to have low cytotoxicity and excellent cell imaging properties. In vivo experiments yield highly encouraging tumor shrinkage with the antitumor drug doxorubicin (DOX) and significantly enhanced tumor targeting in the presence of an applied magnetic field.
A simple, sensitive, and reproducible sensing technique is described for the unambiguous detection of unlabeled single-stranded DNA by surface-enhanced Raman spectroscopy (SERS). By self-assembling probe-tethered Ag nanoparticles to a moderately smooth Ag film using the complementary target species, electromagnetic “hot spots” are created which strongly enhance the Raman signal of the species present in the hot spot. These species can include a Raman label (a molecule with a very large Raman cross-section) that dominates the spectrum and generates highly reproducible signals. The self-assembly process does not take place in the absence of the target species. Consequently, a strong SERS signal is observed only in the presence of the target. The SERS signal was also absent in the presence of noncomplementary species. AFM analysis indicates that strong SERS signal intensity arises from only a few surface-bound nanoparticles which generate an enhancement factor ∼105−106 greater than the metal film alone. Notably, this nanoparticle−film DNA detection method does not require any chemical deposition of silver to read out the SERS spectrum from the surface-bound labels.
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