DNA-Biofunctionalization of CTAC-Capped Gold Nanocubes.

Clinical diagnostics and disease control are fields that strongly depend on technologies for rapid, sensitive, and selective detection of biological or chemical analytes. Nanoparticles have become an integral part in various biomedical detection devices and nanotherapeutics. An increasing focus is laid on gold nanoparticles as they express less cytotoxicity, high stability, and hold unique optical properties with the ability of signal transduction of biological recognition events with enhanced analytical performance. Strong electromagnetic field enhancements can be found in close proximity to the nanoparticle that can be exploited to enhance signals for e.g., metal-enhanced fluorescence or Raman spectroscopy. Even stronger field enhancements can be achieved with sharp-edged nanoparticles, which are synthesized with the help of facet blocking agents, such as cetyltrimethylammonium bromide/chloride (CTAB/CTAC). However, chemical modification of the nanoparticle surface is necessary to reduce the particle's cytotoxicity, stabilize it against aggregation, and to bioconjugate it with biomolecules to increase its biocompatibility and/or specificity for analytical applications. Here, a reliable two-step protocol following a ligand exchange with bis (p-sulfonatophenyl) phenyl phosphine (BSPP) as the intermediate capping-agent is demonstrated, which results in the reliable biofunctionalization of CTAC-capped gold nanocubes with thiol-modified DNA. The functionalized nanocubes have been characterized regarding their electric potential, plasmonic properties, and stability against high concentrations of NaCl and MgCl2.

Loop-mediated amplification as promising on-site detection approach for Legionella pneumophila and Legionella spp.

Recently Legionella pneumophila is the main causative waterborne organism of severe respiratory infections. Additionally, other Legionella species are documented as human pathogens. In our work, we describe a rapid detection method which combines two advantages for sensitive and specific detection of the genus Legionella: the fast isothermal amplification method "Loop-mediated isothermal AMPlification" (LAMP), and a colorimetric detection method using the metal indicator hydroxynaphtol blue (HBN) which allows to determine an optical signal with a simple readout (with the naked eye). Moreover, we present two approaches for minimizing the assay volume using a stationary microchip LAMP and droplet digital-based LAMP (ddLAMP) as promising highly sensitive setups.

AFM-Based Probing of the Flexibility and Surface Attachment of Immobilized DNA Origami.

The flexible and precise immobilization of self-organizing DNA nanostructures represents a key step in the integration of DNA-based material for potential electronic or sensor applications. However, the involved processes have still not been well studied and are not yet fully understood. Thus, we investigated the potential for the mechanical manipulation of DNA origami by atomic force microscopy (AFM) in order to study the interaction between intramolecular flexibility and surface-attachment forces. AFM is particularly suitable for nanoscale manipulation. Previous studies showed the potential for pushing, bending, and cutting double-stranded DNA (dsDNA) with an AFM tip. Understanding the involved parameters may enable control over different processes such as nanointegration, precise cutting, and stretching of preassembled DNA origami. We demonstrate the defined manipulation and flexibility of DNA origami immobilized on mica in the nanometer range: controlled cutting, folding, and stretching as a function of the magnesium concentration.