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

Abstract

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.

Mesoporous Silica Nanoparticles in Bioimaging

“…FRET quenching was reduced on DOX release, enabling a useful direct imaging of this. Work by Kitajima et al reported the internal coupling of the phosphorescent transition metal complex bis(2,2′-bipyridine)-(5-maleimide-1,10-phenanthroline) ruthenium(II) within the pores channel of the MSNs for oxygen sensing both in vitro and in vivo [ 135 ]. Compared to direct excitation of the molecular ruthenium analogue, these nanoparticles demonstrated significant reduced levels of singlet oxygen ( 1 O 2 ) generation, reducing cytotoxicity and providing the potential to probe oxygen levels in vitro and in vivo.…”

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

“…It is well known that the diffusion sphere of singlet oxygen is related to its lifetime. 32 In our previous research, singlet oxygen generated in the pores of the MSNs exhibited a short lifetime, 28 and therefore they were quenched within the pores before leaching out. Thus, pM-Rus showed negligible cytotoxicity upon photoirradiation, even when 1 O 2 was generated.…”

Strategies to promote permeation and vectorization, and reduce cytotoxicity of metal complex luminophores for bioimaging and intracellular sensing

“…Critically, the particles were less toxic compared to the free complex which demonstrates another benefit of using particle vehicles. 119 More recently Wang et al reported silicate particles of 52 nm diameter encapsulating Ru(II)tris-phenanthroline complex and surface modified using silane chemistry, with N,N 0bis(carboxypropyl)-9,9 0 -biacridine (BAC), a Cl À sensor. In this case the metal complex provided the reference signal and ratiometric emission sensing of chloride at the particles was investigated in cells.…”