27 September 2011

Multifunctional nanocomposites for theranostics

Researchers around Photonics4Life partner Prof. Nikolai Khlebtsov from Institute of Biochemistry and Physiology of Plants and Microorganisms (IBPPM RAS), Saratov, Russia, have fabricated, characterized, and tested hybrid nanoparticles consisting of a gold-silver nanocage core and a mesoporous silica shell doped with a photodynamic sensitizer in vitro and ex vivo.

Multifunctional nanoparticles that combine therapeutic and diagnostic modalities are a new trend in nanobiotechnology. One attractive option for theranostic applications are systems that combine the unique optical properties of plasmonic nanoparticles1 and the advantages of mesoporous silica functionalized with an appropriate photosensitizer. However up to date, there is limited data available on such materials.

The group from together with colleagues from SSU suggested nanoparticles consisting of a gold-silver (Au-Ag) nanocage core and a mesoporous silica (SiO2) shell that is doped with the photodynamic sensitizer ytterbium-hematoporphyrin (Yb-HP).The synthesis of such composites includes four basic steps. First, silver nanocubes are prepared by the sulfide-mediated polyol method.Then, these cubes serve as templates to create partly hollow Au-Ag alloyed structures called nanocages, whose formation is accompanied by controllable red shift of the plasmon resonance from 435nm to 650–900nm. Finally, the third and fourth steps involve fabricating a mesoporous silica shell (20–120nm) doped with Yb-HP molecules.

Transmission electron microscope images of (a) silver nanocubes, (b) Au-Ag nanocages, and (c) composite silica-coated nanocages. The insets in (b) show the box and cage particle morphologies. Images (d) and (e) show cuvettes with 1: final nanocomposites Au-Ag/SiO2/Yb-HP; 2: silica-coated particles Au-Ag/SiO2; and 3: free Yb-HP solution under white and UV light excitation respectively. The scale bars in the insets are 50nm.

Figure 1 shows images of cuvettes with silver nanocubes, Au-Ag nanocages, and silica-coated nanocages. Straightforward evidence for the successful functionalization of the composite particles with Yb-HP is provided by the photo on the right, bottom, which shows cuvettes containing the nanocomposites with and without attached Yb-HP, and with free Yb-HP molecules. Under white light illumination, cuvettes 1 and 2 show a blue-green color while 3 looks faint pink because of selective absorption near 400nm. When irradiated with a UV lamp, cuvettes 1 and 3 exhibit intense pink fluorescent emission whereas 2 remains blue. Additional evidence for the successful functionalization of the particles was obtained from measurements of singlet oxygen (1O2) generation.

The scientists used IR luminescence for the ex vivo detection of Au-Ag/SiO2/Yb–HP nanoparticles in different organs taken from tumor-bearing mice. To assess the potential of the particles as theranostic agents, they examined the viability of HeLa cells in the presence of free Yb-HP and nanocomposites with and without light treatment. Khlebtsov and his team observed enhanced killing of HeLa cells incubated with the particles and irradiated with a 625nm LED.

According to the biochemist the hybrid nanoparticles combine several promising theranostic modalities: an easily tunable plasmon resonance across the 650–950nm spectral band with possible use in photothermolysis; a mesoporous silica shell that preserves the plasmon resonance from an aggregation shift and provides a convenient possibility of surface or volume functionalization with various molecular probes; and a combination of singlet oxygen generation with IR-luminescence band of Yb-HP, which can be used for optically controlled photodynamic therapy.

The researchers are now attempting to fabricate silica-coated Au-Ag nanocages and Au nanorods functionalized with hematoporphyrin, which they plan to characterize using transmission electron microscopy, absorption and fluorescent spectroscopy, and other methods. These nanocomposites will be tested soon as potential antimicrobial agents against several pathogenic bacteria.

Round Robin Experiment

Raman spectroscopy has already proved its effectiveness in many cases for medical diagnostics such as for cancer, cardiovascular diseases and infections. However, there are no standards in the different working groups, e.g. for sample preparation, implementation of the Raman experiments, spectra pre-treatment, data evaluation, etc.In a round robin experiment, the required groundwork will take place in order to define standardised Raman measurement methods, which will be fundamental for establishing Raman spectroscopy for clinical diagnostic procedures.

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