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Strong electric field enhancement can be achieved in metal-insulator-metal (MIM) configuration where a thin dielectric layer is in between two metal layers. Here MIM nanostructures with intrinsic electromagnetic hot spots accessible for analytes are fabricated by oblique angle deposition (OAD). Firstly, silver nanoparticles are produced by OAD on a flat silver mirror with a thin dielectric over-layer. The broadband absorption peak of this particle-on-film system can be tuned by varying the particle size in order to fit a given excitation laser source for SERS (surface-enhanced Raman scattering). Then we deposit MIM nanoparticles on three-dimensionally structured silicon by an equivalent OAD method. By two-photon induced luminescence imaging and Raman measurements, we demonstrate strong and uniform field enhancement over the proposed substrate which is a good candidate for SERS application.

UCNP-based drug delivery systems commonly rely on stimuli-sensitive auxiliaries, lacking a straightforward manipulation strategy. Here we designed Yb3+-enhanced upconversion/mesoporous silica nanocomposites (UCNP@SiO2) for consecutive cell imaging, photothermal drug delivery and cancer therapy. Core UCNPs (NaYbF4: 2% Er3+) were synthesized and coated with mesoporous silica, whose high-efficiency photothermal properties were verified in vitro. Then doxorubicin hydrochloride (DOX) was loaded on the UCNP@SiO2 and successfully triggered to release by a 975 nm laser of 150 mW or 300 mW. Before the therapy, we used a much lower laser power of 15 mW (which would cause little DOX release) for UCNP-probed fluorescence imaging of Hela cells and affirmed a favorable cell uptake of nanocomposites. Subsequently, cell viability assay and PI stain have demonstrated that the 300 mW laser could manipulate drug delivery of UCNP@SiO2-DOX and cause a severe loss of cell viability. The Yb3+-enhanced UCNP@SiO2 shows a great potential in simultaneous biomedical imaging and photothermal-triggered on-site drug delivery for chemotherapy of cancer.

Upconversion nanoparticles (UCNPs) is a class of promising probes widely used in protein molecules imaging due to the no photobleaching and non-blinking emission. However, it is still remained challenging to synthesize a type of ultra-small but bright UCNPs. In this paper, a new class of efficient sub-5-nm upconversion nanodots (UCNDs) was elaborately designed and experimentally demonstrated. The proposed uniform UCNDs comprise two parts: a 3.5-nm Ln3+-doped ZrO2 core and 0.5-nm NaYF4 shell. The emission intensity of the proposed UCNDs was measured to be more than 10 times brighter than that of the conventional 10-nm NaYF4 UCNPs. Under 300 kW·cm−2 irradiance excitation, the 15 mol% Er3+-doped UCNDs exhibit an 18-fold enhanced intensity and one fifth emission lifetime compared to the 0.5 mol% Er3+-doped ones. Using the biocompatible UCNDs, the aptamer-mediated proteins-targeted imaging was performed and demonstrated high efficiency. These ultra-small, efficient UCNDs would have great potentials in rapid scanning and cellular imaging.