Using two-phase (water-toluene) reduction of AuC14-by sodium borohydride in the presence of an alkanethiol, solutions of 1-3 nm gold particles bearing a surface coating of thiol have been prepared and characterised; this novel material can be handled as a simple chemical compound.

Stable functionalised gold nanoparticles are prepared by simultaneous reduction of tetrachloroaurate ions and attachment of bifunctional organic thiol molecules to the growing gold nuclei leading to a material whose chemical behaviour is characterised by the vacant functionality of the bifunctional thiol ligand.

Based on protein folding considerations, a pentapeptide ligand, CALNN, which converts citrate-stabilized gold nanoparticles into extremely stable, water-soluble gold nanoparticles with some chemical properties analogous to those of proteins, has been designed. These peptide-capped gold nanoparticles can be freeze-dried and stored as powders that can be subsequently redissolved to yield stable aqueous dispersions. Filtration, size-exclusion chromatography, ion-exchange chromatography, electrophoresis, and centrifugation can be applied to these particles. The effect of 58 different peptide sequences on the electrolyte-induced aggregation of the nanoparticles was studied. The stabilities conferred by these peptide ligands depended on their length, hydrophobicity, and charge and in some cases resulted in further improved stability compared with CALNN, yielding detailed design criteria for peptide capping ligands. A simple strategy for the introduction of recognition groups is proposed and demonstrated with biotin and Strep-tag II.

The preparation of materials with aligned porosity in the micrometre range is of technological importance for a wide range of applications in organic electronics, microfluidics, molecular filtration and biomaterials. Here, we demonstrate a generic method for the preparation of aligned materials using polymers, nanoparticles or mixtures of these components as building blocks. Directional freezing is used to align the structural elements, either in the form of three-dimensional porous structures or as two-dimensional oriented surface patterns. This simple technique can be used to generate a diverse array of complex structures such as polymer-inorganic nanocomposites, aligned gold microwires and microwire networks, porous composite microfibres and biaxially aligned composite networks. The process does not involve any chemical reaction, thus avoiding potential complications associated with by-products or purification procedures.

Understanding and controlling the interactions between nanoscale objects and living cells is of great importance for arising diagnostic and therapeutic applications of nanoparticles and for nanotoxicology studies. Here we report a detailed transmission electron microscopy (TEM) study of the uptake of ca. 16 nm surface-modified gold nanoparticles by human fibroblast cells (HeLa cells). It is demonstrated that the well-established endosomal route of cellular uptake can be bypassed to a significant extent by controlling the uptake mechanism either via the delivery of the nanoparticles by liposomes or by surface modification of the nanoparticles with so-called cell penetrating peptides (CPPs). Successful nuclear targeting is demonstrated using surface modification with a cocktail of CPPs and a peptide acting as a nuclear localization signal (NLS).