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Atomic force microscopy (AFM) and FTIR spectroscopy techniques have been exploited to investigate the inverted hexagonal phase (HII) of cardiolipin obtained by dehydration of a phospholipid water dispersion on a solid support. The characteristic cylinders of the HIIphase have been imaged by AFM and the effects of different preparation conditions (temperature and the presence of chemicals) on the structural parameters and on the presence of local nanoscale defects have been studied. It has been found that the measured repeat spacing of the HIIcylinders decreases upon increase of temperature and addition of pentachlorophenol (PCP), a chemical which is known to affect the structure and function of lipid bilayers. It has been shown that AFM can help in revealing some features of the mechanism of the inverted hexagonal phase formation, corroborating the results of a recent molecular dynamics study on the HIIphase formation from multilamellar phospholipid structures. [ABSTRACT FROM AUTHOR]

We are presenting a method for modulating the size of CdS nanoparticles by templating their formation with oligo(guanine)noligomers where nvaried from 5 to 20. The variation in template length resulted in observable changes in the size distribution of the CdS nanoparticles. Statistical analysis of AFM images showed a general trend whereby the CdS average height decreased for longer oligoGnand increased for shorter oligoGn. Concomitantly, shorter oligoGnyielded more dispersed populations, while longer oligoGngave less dispersed populations. This synthetic methodology could be extended to the synthesis of other nanoparticles and even to mixed-metal nanoparticles resulting in a powerful method for fine-tuning size-dependent properties. [ABSTRACT FROM AUTHOR]

The usual biophysical approach to the study of biological membranes is that of turning to model systems. From these models, general physical principles ruling the lateral membrane structure can be obtained. A promising model system is the supported lipid bilayer (SLB) which could foresee the simultaneous investigation of the structure and physical properties of lipid bilayers reconstituted with membrane proteins. A complete exploitation of the model system to retrieve biologically relevant information requires an in-depth knowledge of the possible effect that experimental parameters could have on the behavior of the SLB. Here we used atomic force microscopy (AFM) to study the effect of different types of substrates on the behavior of SLBs as far as their main phase transition is concerned. We found that different substrates (mica and silicon oxide) can affect in dissimilar ways the interleaflet coupling of the bilayer, which might represent a sort of lipid signaling allowing communication between receptors on the extracellular leaflet and cytoplasmic components. By decreasing the interaction between the SLB and the substrate the interleaflet coupling is preserved independently of the bilayer preparation strategy. Moreover, we investigated by time-lapse AFM an isothermal phase transition induced by a pH change on a SLB. We established that the presence of a pH gradient across the bilayer can weaken the strength of the interleaflet coupling which is present in symmetrical pH conditions. [ABSTRACT FROM AUTHOR]

We report an atomic force microscopy study on the lateral spatial redistribution of an integral membrane protein reconstituted in supported lipid bilayers (SLBs) subjected to a thermally induced phase transition. KcsA proteins were reconstituted in proteoliposomes of POPE/POPG (3:1, mol/mol), and SLBs, including the proteins, were then obtained by the vesicle fusion technique on mica. By decreasing the temperature, the lipid bilayer passed from a liquid disordered (ld) phase in which the proteins are homogeneously distributed to a coexistence of solid ordered (so) and lddomains with the proteins preferentially distributed in the lddomains. The inhomogeneous distribution eventually led to protein clustering. The obtained results are discussed in light of the role that the lipid/protein interaction can have in determining the function of integral membrane proteins. [ABSTRACT FROM AUTHOR]

Functional DNA scaffolds can be defined as DNA-based structures comprising chemical moieties facilitating and guiding the immobilization of additional nanocomponents. Due to the limited reactivity of DNA there is currently a need to develop rapid routes to expand its chemical repertoire and increase its versatility as a nanostructuring scaffold. We report a simple synthetic strategy for generating linear and stable double-stranded DNA scaffolds functionalized with multiple sites reactive towards free thiols, and the utility of this approach is demonstrated by immobilizing a model protein containing an accessible free thiol. This procedure is very versatile and could be easily expanded to other types of chemistries. This approach could also potentially be employed for the specific, oriented immobilization of various biomolecules and nanoparticles on predefined DNA architectures. [ABSTRACT FROM AUTHOR]

Self-assembly of proteins, peptides, DNA, and other biomolecules to semiconductor quantum dots (QD) is an attractive bioconjugation route that can circumvent many of the problems associated with covalent chemistry and subsequent purification. Polyhistidine sequences have been shown to facilitate self-assembly of proteins and peptides to ZnS-overcoated CdSe QDs via complexation to unoccupied coordination metal sites on the nanocrystal surface. We describe the synthesis and characterization of a thiol-reactive hexahistidine peptidic linker that can be chemically attached to thiolated-DNA oligomers and mediate their self-assembly to CdSe−ZnS core−shell QDs. The self-assembly of hexahistidine-appended DNA to QDs is probed with gel electrophoresis and fluorescence resonance energy transfer techniques, and the results confirm high-affinity conjugate formation with control over the average molar ratio of DNA assembled per QD. To demonstrate the potential of this reactive peptide linker strategy, a prototype QD−DNA−dye molecular beacon is self-assembled and tested against both specific and nonspecific target DNAs. This conjugation route is potentially versatile, as altering the reactivity of the peptide linker may allow targeting of different functional groups such as amines and facilitate self-assembly of other nanoparticle−biomolecule structures. [ABSTRACT FROM AUTHOR]