No abstract

Charge transport through molecular structures is interesting both scientifically and technologically. To date, DNA is the only type of polymer that transports significant currents over distances of more than a few nanometers in individual molecules. For molecular electronics, DNA derivatives are by far more promising than native DNA due to their improved charge-transport properties. Here, the synthesis of several unique DNA derivatives along with electrical characterization and theoretical models is surveyed. The derivatives include double stranded poly(G)-poly(C) DNA molecules, four stranded G4-DNA, metal-DNA hybrid molecular wires, and other DNA molecules that are modified either at the bases or at the backbone. The electrical characteristics of these nanostructures, studied experimentally by electrostatic force microscopy, conductive atomic force microscopy, and scanning tunneling microscopy and spectroscopy, are reviewed.

Since their discovery, liposomes have been widely employed in biomedical research. These nano-size spherical vesicles consisting one or few phospholipid bilayers surrounding an aqueous core are capable of carrying a wide variety of bioactive compounds, including drugs, peptides, nucleic acids, proteins and others. Despite considerable success achieved in synthesis of liposome constructs containing bioactive compounds, preparation of ligand-targeted liposomes comprising large quantities of encapsulated proteins that are capable of affecting pathological cells still remains a big challenge. Here we described a novel method for preparation of small (80-90 nm in diameter) unilamellar liposomes containing very large quantities (thousands of protein molecules per liposome) of heme-containing cytochrome c, highly fluorescent mCherry and highly toxic PE40 (Pseudomonas aeruginosa Exotoxin A domain). Efficient encapsulation of the proteins was achieved through electrostatic interaction between positively charged proteins (at pH lower than pI) and negatively charged liposome membrane. The proteoliposomes containing large quantities of mCherry or PE40 and functionalized with designed ankyrin repeat protein (DARPin)_9-29, which targets human epidermal growth factor receptor 2 (HER2) were shown to specifically stain and kill in sub-nanomolar concentrations HER2-positive cells, overexpressing HER2, respectively. Specific staining and eradication of the receptor-positive cells demonstrated here makes the DARPin-functionalized liposomes carrying large quantities of fluorescent and/or toxic proteins a promising candidate for tumor detection and therapy.

We have demonstrated that designed ankyrin repeat protein (DARPin) _9-29, which specifically targets human epidermal growth factor receptor 2 (HER2), binds tightly to gold mini nanorods (GNRs). Molecular dynamic simulations showed that a single layer of DARPin_9-29 molecules is formed on the surface of the nanorod and that conjugation with the nanorod does not involve the protein's domain responsible for specific binding to HER2. The nanorod-DARPin (DARPin-GNR) conjugate is specifically bound (in nanomolar concentrations) to human breast adenocarcinoma SK-BR-3 cells overexpressing HER2. Illumination by near-infrared light (850 nm) led to almost complete eradication of the conjugate-treated SK-BR-3 cells; the viability of epithelial human breast cancer cells expressing normal amounts of the receptor was much less affected by the illumination. The results reported here pave the way toward application of DARPin-GNR conjugates in phototherapy of cancer.

Metal-mediated base-paired DNA has long been investigated for basic scientific pursuit and for nanoelectronics purposes. Particularly attractive in these domains is the Ag +intercalated polycytosine DNA duplex. Extensive studies of this molecule have led to our current understanding of its self-assembly properties, high thermodynamic and structural stability, and high longitudinal conductivity. However, a high-resolution morphological characterization of long Ag + -intercalated polycytosine DNA has hitherto not been carried out. Furthermore, the electronic level structure of this molecule has not been studied before. Here we present a scanning tunneling microscopy and spectroscopy study of this intriguing nanowire. Its temperature-independent morphological and electronic properties suggest substantial stability, while its emergent electronic levels and energy gap provide the basis for its high conductivity.