Biocompatibilization of fluorescent nanodiamond

Over the past few years, fluorescent nanodiamonds (FNDs) have been recognized as an potential fluorophores for use in bioimaging, owing to their unique and attractive chemical and particularly spectral properties. FNDs are capable of fluorescing with almost quantitative quantum yields from point defects of crystall lattice – nitrogen-vacancy (NV) centers. In particular, the long-wavelength emission, no photobleaching, no photoblinking, and an exceptional resistance to chemical degradation make them almost ideal core for development of fluorescent probes. On the other hand, the improper colloidal properties of FND surface still represent an important issue in construction of bioimaging probes for intracellular applications.

We are developing methods enabling dense decoration of FND by biocompatible hydrophillic polymers. The polymers are grown directly from the nanoparticle surface and they contain alkyne or azide groups enabling the covalent attachment of targeting and/or reporting moieties. The research is performed in collaboration with Institute of Macromolecular Chemistry AS CR in Prague.

The schematic structure of a fluorescent diamond nanocrystal coated by silica shell (white), thin crosslinked aminopropyl-silica shell (pink), and PEG-alkyne layer (violet). Targeting molecules are attached to the nanoparticles.

Boosting the nanodiamond fluorescence

Fluorescent probes and sensors constructed from nanodiamonds have several optical advantages including extreme photostability of luminescent NV centers, favourable emmision wavelength, possible external influencing of luminescent spectra and good transparency. For preparation of fluorescent particles the irradiation by high-energy particles is used. The lattice vacancies are formed and after thermal recombination with nitrogen impurities, luminescent NV centers are formed. This process is widely used, however, the brighter particles containing higher concentration of NV centers are still urgently needed. Currently we focus on optimization of procedures leading to creation of NV centers and on control of optical properties of nanodiamond particles. Recently we revealed set of annealing conditions and oxidation procedures showing about one order of magnitude increase of luminescence intensity of nanodiamond particles. The research is performed in collaboration with Institute of Nuclear Physics AS CR, Institute of Physics AS CR and Czech Technical University.

Boosting the brightness of fluorescent nanodiamonds by optimization of annealing conditions. The figure shows normalized fluorescence intensity of NV centers from 45 nm nanodiamond particles as a function of annealing time and temperature. Black dots represent the individual points of the matrix of annealing conditions. Darker color represents brighter samples.

Virus-like particles

For many applications in biomedicine, highly monodisperse in size, biocompatible soft-matter particles are needed. Viral capsides and viral-like particles (VLPs) are an ultimate example of such structures. While colloids, polymers and dendrimers are all amorphous, all of VLPs are resolved at atomic resolution and are available in vast range of sizes and distinct shapes. Their constrained interior space enables packaging of cargoes

We take advantage from their large surface area and attach to them multivalent arrays of molecules for targeting to cancer cells and creation of new contrast agents for bioimaging methods. On VLPs we also synthesize plasmonic systems based on noble metals like gold or silver. For construction of these new materials we use currently bacteriophage Qß and polyomavirus VLPs as nanobuilding blocks. The research is performed in collaboration with Georgia Institute of Technology, USA (M.G. Finn), Case Western Reserve University, USA (N. Steinmetz) and Faculty of Science, Charles University in Prague (J. Forstova).

A view into the schematic model of self-assembled crystalline lattice formed by virus-like particles and gold nanoparticles. DNA molecules are used as programmable “molecular glue” connecting the particles. Author of graphics: Adolf Lachman.