Ferrite magnetic nanoparticles (MNPs) were functionalized with a variety of silanes bearing different functional endgroups to render them stable with respect to aggregation and keep them well-dispersed in aqueous media. The MNPs were prepared by the thermal decomposition method, widely used for the synthesis of monodisperse nanoparticles with controllable size. This method makes use of a hydrophobic surfactant to passivate the surface, which results in nanoparticles that are solely dispersible in nonpolar solvents. For use in biological applications, these nanoparticles need to be made water-dispersible. Therefore, a new procedure was developed on the basis of the exchange of the hydrophobic surface ligands with silanes bearing different endgroups to decorate ferrite magnetic nanoparticles with diverse functionalities. By this means, we could easily determine the influence of the endgroup on the nanoparticle stability and water-dispersibility. Amino-, carboxylic acid-and poly(ethylene glycol)-terminated silanes were found to render the MNPs highly stable and water-dispersible because of electrostatic and/or steric repulsion. The silane molecules were also found to form a protective layer against mild acid and alkaline environments. The ligand exchange on the nanoparticle surface was thoroughly characterized using SQUID, TEM, XPS, DLS, TGA, FTIR, UV-vis, and zeta potential measurements. The presented approach provides a generic strategy to functionalize magnetic ferrite nanoparticles and to form stable dispersions in aqueous media, which facilitates the use of these magnetic nanoparticles in biological applications.

An affinity biosensor interface of a biosensor is the interface between the sample and the transducer surface and is therefore of the utmost importance for the general performance of a biosensor. For immunosensor applications the affinity biosensor interface consists of antibodies, which are preferably covalently attached to the transducer surface. In this paper the properties and the enhanced performance of an affinity biosensor interface based on mixed self-assembled monolayers (SAMs) on gold are discussed. Mixed SAMs consist of two different functionalities, which allow attachment of bioreceptor molecules and avoid nonspecific adsorption. In this work, mixed SAMs of thiols with carboxylic and hydroxyl or poly-(ethylene glycol) groups are characterized with contact angle measurements, cyclic voltammetry, and grazing-angle Fourier transform infrared spectroscopy. It is found that the various mixed SAMs exhibit acceptable coverage and structural properties. Most importantly, surface plasmon resonance measurements clearly show the enhanced performance of these mixed SAMs with regard to sensitivity, stability, and selectivity compared to commercially available affinity biosensor interfaces. This superiority is experimentally demonstrated by evaluating the amount of immobilized antibodies, the recognition of antigens by the immobilized antibody, and the nonspecific adsorption of IgG molecules on the antibody-coated surfaces.

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Today's proteomic analyses are generating increasing numbers of biomarkers, making it essential to possess highly specific probes able to recognize those targets. Antibodies are considered to be the first choice as molecular recognition units due to their target specificity and affinity, which make them excellent probes in biosensor development. However several problems such as difficult directional immobilization, unstable behavior, loss of specificity and steric hindrance, may arise from using these large molecules. Luckily, protein engineering techniques offer designed antibody formats suitable for biomarker analysis. Minimization strategies of antibodies into Fab fragments, scFv or even single-domain antibody fragments like VH, VL or VHHs are reviewed. Not only the size of the probe but also other issues like choice of immobilization tag, type of solid support and probe stability are of critical importance in assay development for biosensing. In this respect, multiple approaches to specifically orient and couple antibody fragments in a generic one-step procedure directly on a biosensor substrate are discussed.

f Emergence of drug-resistant bacteria represents a high, unmet medical need, and discovery of new antibacterials acting on new bacterial targets is strongly needed. ATP synthase has been validated as an antibacterial target in Mycobacterium tuberculosis, where its activity can be specifically blocked by the diarylquinoline TMC207. However, potency of TMC207 is restricted to mycobacteria with little or no effect on the growth of other Gram-positive or Gram-negative bacteria. Here, we identify diarylquinolines with activity against key Gram-positive pathogens, significantly extending the antibacterial spectrum of the diarylquinoline class of drugs. These compounds inhibited growth of Staphylococcus aureus in planktonic state as well as in metabolically resting bacteria grown in a biofilm culture. Furthermore, time-kill experiments showed that the selected hits are rapidly bactericidal. Drug-resistant mutations were mapped to the ATP synthase enzyme, and biochemical analysis as well as drug-target interaction studies reveal ATP synthase as a target for these compounds. Moreover, knockdown of the ATP synthase expression strongly suppressed growth of S. aureus, revealing a crucial role of this target in bacterial growth and metabolism. Our data represent a proof of principle for using the diarylquinoline class of antibacterials in key Gram-positive pathogens. Our results suggest that broadening the antibacterial spectrum for this chemical class is possible without drifting off from the target. Development of the diarylquinolines class may represent a promising strategy for combating Gram-positive pathogens.