ROS-generation and cellular uptake behavior of amino-silica nanoparticles arisen from their uploading by both iron-oxides and hexamolybdenum clusters

Silica-Based Materials Containing Inorganic Red/NIR Emitters and Their Application in Biomedicine

The low absorption of biological substances and living tissues in the red/near-infrared region (therapeutic window) makes luminophores emitting in the range of ~650-1350 nm favorable for in vitro and in vivo imaging. In contrast to commonly used organic dyes, inorganic red/NIR emitters, including ruthenium complexes, quantum dots, lanthanide compounds, and octahedral cluster complexes of molybdenum and tungsten, not only exhibit excellent emission in the desired region but also possess additional functional properties, such as photosensitization of the singlet oxygen generation process, upconversion luminescence, photoactivated effects, and so on. However, despite their outstanding functional applicability, they share the same drawback-instability in aqueous media under physiological conditions, especially without additional modifications. One of the most effective and thus widely used types of modification is incorporation into silica, which is (1) easy to obtain, (2) biocompatible, and (3) non-toxic. In addition, the variety of morphological characteristics, along with simple surface modification, provides room for creativity in the development of various multifunctional diagnostic/therapeutic platforms. In this review, we have highlighted biomedical applications of silica-based materials containing red/NIR-emitting compounds.

Specific nanoarchitecture of silica nanoparticles codoped with the oppositely charged Mn2+ and Ru2+ complexes for dual paramagnetic-luminescent contrasting effects

The silica nanoparticles (SNs) co-doped with paramagnetic ([Mn(HL)]^n-,) and luminescent ([Ru(dipy)₃]²⁺) complexes are represented. The specific distribution of [Mn(HL)]^n- within the SNs allows to achieve about ten-fold enhancing in magnetic relaxivities in comparison with those of [Mn(HL)]^n- in solutions. The leaching of [Mn(HL)]^n- from the shell can be minimized through the co-doping of [Ru(dipy)₃]²⁺ into the core of the SNs. The co-doped SNs exhibit colloid stability in aqueous solutions, including those modeling a blood serum. The surface of the co-doped SNs was also decorated by amino- and carboxy-groups. The cytotoxicity, hemoagglutination and hemolytic activities of the co-doped SNs are on the levels convenient for "in vivo" studies, although the amino-decorated SNs cause more noticeable agglutination and suppression of cell viability. The co-doped SNs being intravenously injected into mice allows to reveal their biodistribution in both ex vivo and in vivo conditions through confocal microscopy and magnetic resonance imaging correspondingly.

A review on functional nanoarchitectonics nanocomposites based on octahedral metal atom clusters (Nb6, Mo6, Ta6, W6, Re6): inorganic 0D and 2D powders and films

This review is dedicated to various functional nanoarchitectonic nanocomposites based on molecular octahedral metal atom clusters (Nb₆, Mo₆, Ta₆, W₆, Re₆). Powder and film nanocomposites with two-dimensional, one-dimensional and zero-dimensional morphologies are presented, as well as film matrices from organic polymers to inorganic layered oxides. The high potential and synergetic effects of these nanocomposites for biotechnology applications, photovoltaic, solar control, catalytic, photonic and sensor applications are demonstrated. This review also provides a basic level of understanding how nanocomposites are characterized and processed using different techniques and methods. The main objective of this review would be to provide guiding significance for the design of new high-performance nanocomposites based on transition metal atom clusters.

Enhancement of photoactivity and cellular uptake of (Bu4N)2[Mo6I8(CH3COO)6] complex by loading on porous MCM-41 support. Photodynamic studies as an anticancer agent

The incorporation by ionic assembly of the hexanuclear molybdenum cluster (Bu₄N)₂[Mo₆I₈(CH₃CO₂)₆] (1) in amino-decorated mesoporous silica nanoparticles MCM-41, has yielded the new molybdenum-based hybrid photosensitizer 1@MCM-41. The new photoactive material presents a high porosity, due to the intrinsic high specific surface area of MCM-41 nanoparticles (989 m² g^-1) which is responsible for the good dispersion of the hexamolybdenum clusters on the nanoparticles surface, as observed by STEM analysis. The hybrid photosensitizer can generate efficiently singlet oxygen, which was demonstrated by using the benchmark photooxygenation reaction of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) in water. The photodynamic therapy activity has been tested using LED light as an irradiation source (λ_irr ~ 400-700 nm; 15.6 mW/cm²). The results show a good activity of the hybrid photosensitizer against human cervical cancer (HeLa) cells, reducing up to 70 % their viability after 20 min of irradiation, whereas low cytotoxicity is detected in the darkness. The main finding of this research is that the incorporation of molybdenum complexes at porous MCM-41 supports enhances their photoactivity and improves cellular uptake, compared to free clusters.

Silica-Supported Assemblage of CuII Ions with Carbon Dots for Self-Boosting and Glutathione-Induced ROS Generation

The present work introduces coordinative binding of CuII ions with both amino-functionalized silica nanoparticles (SNs) and green-emitting carbon dots (CDs) as the pregrequisite for the CuII-assisted self-assembly of the CDs at the surface of the SNs. The produced composite SNs exhibit stable in time stimuli-responsive green fluorescence derived from the CuII-assisted assemblage of CDs. The fluorescence response of the composite SNs is sensitive to the complex formation with glutathione (GSH), enabling them to detect it with the lower limit of detection of 0.15 μM. The spin-trap-facilitated electron spin resonance technique indicated that the composite SNs are capable of self-boosting generation of ROS due to CuII→CuI reduction by carbon in low oxidation states as a part of the CDs. The intensity of the ESR signals is enhanced under the heating to 38 °C. The intensity is suppressed at the GSH concentration of 0.35 mM but is enhanced at 1.0 mM of glutathione, while it is suppressed once more at the highest intracellular concentration level of GSH (10 mM). These tendencies reveal the concentrations optimal for the scavenger or reductive potential of GSH. Flow cytometry and fluorescence and confocal microscopy methods revealed efficient cell internalization of SNs-NH2-CuII-CDs comparable with that of “free” CDs.

Phosphorescent NIR emitters for biomedicine: applications, advances and challenges

Application of NIR (near-infrared) emitting transition metal complexes in biomedicine is a rapidly developing area of research. Emission of this class of compounds in the "optical transparency windows" of biological tissues and the intrinsic sensitivity of their phosphorescence to oxygen resulted in the preparation of several commercial oxygen sensors capable of deep (up to whole-body) and quantitative mapping of oxygen gradients suitable for in vivo experimental studies. In addition to this achievement, the last decade has also witnessed the increased growth of successful alternative applications of NIR phosphors that include (i) site-specific in vitro and in vivo visualization of sophisticated biological models ranging from 3D cell cultures to intact animals; (ii) sensing of various biologically relevant analytes, such as pH, reactive oxygen and nitrogen species, RedOx agents, etc.; (iii) and several therapeutic applications such as photodynamic (PDT), photothermal (PTT), and photoactivated cancer (PACT) therapies as well as their combinations with other therapeutic and imaging modalities to yield new variants of combined therapies and theranostics. Nevertheless, emerging applications of these compounds in experimental biomedicine and their implementation as therapeutic agents practically applicable in PDT, PTT, and PACT face challenges related to a critically important improvement of their photophysical and physico-chemical characteristics. This review outlines the current state of the art and achievements of the last decade and stresses the most promising trends, major development prospects, and challenges in the design of NIR phosphors suitable for biomedical applications.

Surface modification of silica nanoparticles by hexarhenium anionic cluster complexes for pH-sensing and staining of cell nuclei

The surface deposition of luminescent anionic cluster complex [{Re₆S₈}(OH)₆]^4- advantages to the design and synthesis of composite luminescent silica nanoparticles (SNs) for intracellular imaging and sensing, while the encapsulation of the cluster units into SNs lacks for efficient luminescence. The deposition of the Re₆ clusters resulted from their assembly at the silica surface functionalized by amino-groups provides the synthetic route for the composite SNs with bright cluster-centered luminescence invariable in pH range from 4.0 to 12.0. The pH-dependent supramolecular assembly of the cluster units with polyethyleneimine (PEI) at the silica surface is an alternative route for the synthesis of the composite SNs with high cluster-centered luminescence sensitive to pH-changes within 4.0-6.0. The sensitivity derives from the pH-driven conformational changes of PEI chains resulting in the release of the clusters from the PEI-based confinement under the acidification within pH 6.0-4.0. The potential of the composite SNs in cellular contrasting has been also revealed by the cell viability and flow cytometry measurements. It has been found that the PEI-supported embedding of the cluster units facilitates cell internalization of the composite SNs as well as results in specific intracellular distribution manifested by efficient staining of the cell nuclei in the confocal images.