Novel low-cost drug-delivery vehicles Functionalising nanoparticles (NPs) to reversibly bind ligands paves the way to biomedical applications such as drug delivery. Scientists made major progress with inexpensive, inert and non-toxic silica to support the effort. Health © Thinkstock The EU-funded training project 'Dynamic libraries for the synthesis of new multifunctional silica striped nanoparticles' (TRANSFORMERSURFACES) sought to dramatically expand the possibilities for functionalisation and eliminate toxicity. Specifically, scientists set out to develop new surfaces on silica NPs. They consist of molecular monolayers in patterns (primarily stripes) that can be reversibly functionalised with ligands. Researchers exploited dynamic combinatorial chemistry and the creation of dynamic combinatorial libraries, powerful tools for discovery. The library members can be thrown together in a test tube where they continuously exchange building blocks with each other, giving rise to unexpected combinations. Previously, partners developed striped gold NPs with the ability to diffuse through cell membranes without creating transient holes (porating) associated with leakage and cytotoxicity. Substituting silica for gold would significantly reduce costs. Further, silica is transparent and has no intrinsic photochemical properties such that subsequent integration with fluorescent molecules would not cause interference in terms of signal source. Finally, silica is inert and thus highly biocompatible. A large portion of the research effort focused on synthesis of dynamic libraries and investigation of bond reversibility. The team selected iminic bonds, where imines contain a carbon-nitrogen double bond. Techniques used to characterise the morphology of self-assembled monolayers on gold NPs are not as easily applied to silica. For example, scanning tunnelling microscopy cannot be used because silica is not conductive. The team used atomic force microscopy with very good results. Scientists were also awarded five days of beam time at the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) neutron source to conduct materials characterisation experiments. In addition, researchers used nuclear magnetic resonance to study the ligand on the surface of the functionalised silica NPs. In order to assess reversibility, the team hydrolysed the double (iminic) bond and verified the presence of the molecules on the surface. TRANSFORMERSURFACES focused on understanding the mechanism and the conditions of assembly of molecules on the silica NP surfaces with an eye on biological experiments. The foundations are strong and demonstrate the potential for future development of novel drug-delivery systems at a low cost and with next to no cytotoxicity. Keywords Nanoparticle, drug delivery, silica, striped nanoparticles, dynamic combinatorial chemistry
