Biofunctionalized gold nanoparticles (AuNPs) or strongly luminescent semiconductor nanocrystals (quantum dots, QDs) are well suited for a broad variety of bioanalytical purposes, for medical diagnosis, and possibly even for medical treatment. However, all these applications require the solubility of the particles in an aqueous biological environment with sufficient colloidal stability. Thus, one of our projects aims at the synthesis and characterization of nanoparticles stabilized by polyethylene glycol (PEG), a polymer that is well known for its excellent biocompatibility. Recently, we have shown that the stability of PEGylated AuNPs in aqueous media strongly depends on the molecular structure of the spacer, which is used to couple the stabilizing PEG-ligands to the nanoparticle surface. Furthermore, in collaboration with the University Medical Center Hamburg-Eppendorf, we functionalized PEGylated AuNPs with a fragment of the neural cell adhesion molecule L1, which promotes regeneration of acute and chronic injury of the adult nervous system. Via in vitro cell culture experiments we demonstrated that the prepared L1/PEG-AuNP conjugates promote neurite outgrowth and survival of neurons from the central and peripheral nervous system. These observations raise the hope that, in combination with other therapeutic approaches, L1/PEG-functionalized AuNPs may become a useful tool to ameliorate the deficits resulting from acute and chronic injuries of the mammalian nervous system.
In another project we explore the synthesis of PEGylated CdSe/CdS-quantum-dots-quantum-rods (QDQRs) and, in collaboration with the Universities of Lübeck and Jena, we study their application as strongly luminescent probes for Two-Photon-Laser-Scanning-Microscopy (TPLSM). Because of their extremely high two-photon absorption cross sections these particles can easily be detected and tracked by TPLSM. Thus, these probes are well suited to study the interaction of nanoparticles with various cell types and their fate after uptake in vivo.