Phosphonated mesoporous silica nanoparticles bearing ruthenium complexes used as molecular probes for tracking oxygen levels in cells and tissues.

Molecular oxygen plays an important role in living organisms. Its concentration and fluctuation in cells or tissues are related to many diseases. Therefore, there is a need for molecular systems that can be used to detect and quantify oxygen levels in vitro and in vivo. In this study, we synthesized phosphonated mesoporous silica nanoparticles bearing ruthenium complexes in their pores (pM-Rus) and evaluated their photophysical and biological properties. The pM-Rus were highly soluble in water and showed robust phosphorescence under hypoxic conditions, while the addition of oxygen suppressed this emission. Cellular experiments revealed that pM-Rus with a size of 100 nm showed efficient cellular uptake to emit phosphorescence in hypoxic cells. In addition, pM-Rus have negligible toxicity to cells due to the blockage of direct contact between ruthenium complexes and intracellular biomolecules and the deactivation of singlet oxygen (1O2) generated by photoexcitation of ruthenium complexes before leaking out of the pores. Animal experiments confirmed that pM-Rus showed robust emission at hypoxic regions in mice. Thus, pM-Rus are promising oxygen probes for living systems.

Aggregate Formation of BODIPY-Tethered Oligonucleotides That Led to Efficient Intracellular Penetration and Gene Regulation.

Exogenous nucleic acids showed low efficiency regarding cellular uptake and low stability in biological conditions; therefore, a number of techniques have been developed to improve their basic properties. One of the best solutions is the application of nanosized particles consisting of oligonucleotides that penetrate the cell membrane without any additives and exhibit high stability in cells. In this report, we employed a simple approach to address the basic properties of nanoparticles of oligonucleotides in biological systems. We prepared BODIPY-labeled oligonucleotides that carried an exclusive modification at the strand end. BODIPY shows high hydrophobicity and fluorescent emission; therefore, the oligonucleotides formed nanosized aggregates in aqueous solution and their behaviors in cells or tissues were easily tracked. Detailed experiments revealed that aggregate formation was indispensable for the high cellular uptake of the oligonucleotides via scavenger-receptor-mediated endocytosis. In addition, the aggregates provided an efficient gene regulation in living cells and tumor tissues transplanted into mice.

Biological reduction of nitroimidazole-functionalized gold nanorods for photoacoustic imaging of tumor hypoxia.

Tumor-selective accumulation of gold nanorods (GNR) has been demonstrated for visualization of tumor hypoxia by photoacoustic imaging. We prepared GNRs with hypoxia-targeting nitroimidazole units (G-NI) on their surface. Biological experiments revealed that G-NI produced a strong photoacoustic signal in hypoxic tumor cells and tissues.

Confinement of Singlet Oxygen Generated from Ruthenium Complex-Based Oxygen Sensor in the Pores of Mesoporous Silica Nanoparticles.

We synthesized mesoporous silica nanoparticles bearing ruthenium complexes in their pores (MSN-Ru) and characterized their photochemical properties. The ruthenium complexes that were immobilized in the pores showed oxygen-dependent phosphorescence, similar to the complexes that were not tethered to nanoparticles. Cellular imaging and in vivo experiments revealed that hypoxic cells and tissues could be visualized by monitoring the phosphorescence of MSN-Ru. Our most important finding was that the toxic effect of singlet oxygen (1O2), which was generated by excitation of the complexes, was effectively suppressed by the deactivation before leaking out from the pores. In addition, we observed a negligible toxic effect of the ruthenium complexes themselves due to the blockage of their direct interaction with intracellular biomolecules. Thus, MSN-Ru is a promising molecular probe of oxygen levels in living cells and tissues.

Tracking the Oxygen Status in the Cell Nucleus with a Hoechst-Tagged Phosphorescent Ruthenium Complex.

Molecular oxygen in living cells is distributed and consumed inhomogeneously, depending on the activity of each organelle. Therefore, tractable methods that can be used to monitor the oxygen status in each organelle are needed to understand cellular function. Here we report the design of a new oxygen-sensing probe for use in the cell nucleus. We prepared "Ru-Hoechsts", each consisting of a phosphorescent ruthenium complex linked to a Hoechst 33258 moiety, and characterized their properties as oxygen sensors. The Hoechst unit shows strong DNA-binding properties in the nucleus, and the ruthenium complex shows oxygen-dependent phosphorescence. Thus, Ru-Hoechsts accumulated in the cell nucleus and showed oxygen-dependent signals that could be monitored. Of the Ru-Hoechsts prepared in this study, Ru-Hoechst b, in which the ruthenium complex and the Hoechst unit were linked through a hexyl chain, showed the most suitable properties for monitoring the oxygen status. Ru-Hoechsts are probes with high potential for visualizing oxygen fluctuations in the nucleus.

Confined Singlet Oxygen in Mesoporous Silica Nanoparticles: Selective Photochemical Oxidation of Small Molecules in Living Cells.

Chemical conversion of specific bioactive molecules by external stimuli in living cells is a powerful noninvasive tool for clarification of biomolecular interactions and to control cellular functions. However, in chaotic biological environments, it has been difficult to induce arbitrary photochemical reactions on specific molecules because of their poor molecular selectivity. Here we report a selective and nontoxic photochemical reaction system utilizing photoactivated mesoporous silica nanoparticles to control biological functions. Methylene blue modification within nanoparticle pores for photosensitization produced singlet oxygen confined to the pore that could mediate selective oxidation of small molecules without any damage to living cells. This intracellular photochemical system produced bioactive molecules in situ and remotely controlled the cell cycle phase. We also confirmed that this photoreaction could be applied to control cell cycle phase in tumor tissue transplanted in mice. The cell cycle phase in the cells in mice, to which our system was administered, was arrested at the G2/M phase upon photoirradiation. We demonstrate a simple and promising method for the exogenous conversion of an intracellular biomolecule to another functional compound.