No abstract

Mid-infrared absorption spectroscopy has been used extensively to study the molecular properties of cell membranes and model systems. Most of these studies have been carried out on macroscopic samples or on samples a few micrometers in size, due to constraints on sensitivity and spatial resolution with conventional instruments that rely on far-field optics. Properties of membranes on the scale of nanometers, such as in-plane heterogeneity, have to date eluded investigation by this technique. In the present work, we demonstrate the capability to study single bilayers of phospholipids with near-field mid-infrared spectroscopy and imaging and achieve a spatial resolution of at least 40 nm, corresponding to a sample size of the order of a thousand molecules. The quality of the data and the observed spectral features are consistent with those reported from measurements of macroscopic samples and allow detailed analysis of molecular properties, including orientation and ordering of phospholipids. The work opens the way to the nanoscale characterization of the biological membranes for which phospholipid bilayers serve as a model.

Polymer-gated reservoirs built of an ordered porous anodic aluminum oxide (AAO) platform equipped with poly(N-isopropylacrylamide) (PNIPAM) brushes grafted from the surface using atom transfer radical polymerization were fabricated and studied. The brushes of different lengths were grafted from the AAO surface with pores having diameters of 30, 50, and 80 nm, respectively. Polymer brushes served as thermally responsive valves that can immediately open and close the pores just by crossing the PNIPAM lower critical solution temperature. Calcein was used as a model fluorescent molecule to follow a release process from the platform of the gated nanocontainers. The studied systems enable the burst release of the loaded substance, followed by diffusion-controlled release that depends on the pores' diameter. These platforms are characterized by a high loading capacity in comparison to polymer films and can be loaded repeatedly. Importantly, the opening/closing of the nanocontainers is reversible, and a pulsatile release can be easily realized. Such platforms combined with highly localized heating devices can find potential applications in many systems where small controlled amounts of substances have to be released on demand, such as lab-on-a-chip, total analysis, and nano/microfluidic systems.

Conjugated polyelectrolyte brushes grafted from a conductive surface and forming a 1D macromolecular pathway for charge transport are synthesized.

No abstract

Formation and characterization of polyacetylene-based brushes that exhibit exceptional long term stability in air is presented here.

Submicrometer-sized silica gel particles were coated with a polyanion and a polycation bearing thymine chromophores. The polymer-coated particles were found to selectively adsorb adenine and adenosine-5'-triphosphate (ATP), as compared to other nucleobases and nucleotides, respectively. The adsorption was enhanced by the irradiation of the particles in the presence of adenine which resulted in the molecular imprinting of adenine. ATP adsorption was strongly pH-dependent.

Understanding interactions between functional nanoparticles and lipid bilayers is important to many emerging biomedical and bioanalytical applications. In this paper, we report incorporation of hydrophobic cadmium sulphide quantum dots (CdS QDs) into mixed 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) liposomes, and into their supported bilayers (SLBs). The QDs were found embedded in the hydrophobic regions of the liposomes and the supported bilayers, which retained the QD fluorescent properties. In particular, we studied the effect of the QD size (2.7-5.4 nm in diameter) on the formation kinetics and structure of the supported POPC/POPE bilayers, monitored in situ using quartz crystal microbalance with dissipation monitoring (QCM-D), as the liposomes ruptured onto the substrate. The morphology of the obtained QD-lipid hybrid bilayers was studied using atomic force microscopy (AFM), and their structure by synchrotron X-ray reflectivity (XRR). It was shown that the incorporation of hydrophobic QDs promoted bilayer formation on the PEI cushion, evident from the rupture and fusion of the QD-endowed liposomes at a lower surface coverage compared to the liposomes without QDs. Furthermore, the degree of disruption in the supported bilayer structure caused by the QDs was found to be correlated with the QD size. Our results provide mechanistic insights into the kinetics of the rupturing and formation process of QD-endowed supported lipid bilayers via liposome fusion on polymer cushions.