Understanding the Carbon-Bio Interface: Influence of Surface Chemistry and Buffer Composition on the Adsorption of Phospholipid Liposomes at Carbon Surfaces.

Surface active phospholipids are present in fluids of biological relevance, and their adsorption may condition and determine the response of carbon and nanocarbon surfaces when they are immersed in physiological media. In this work, the adsorption and assembly of liposomes at carbon interfaces were investigated to understand the effect of surface termination on the extent and mode of assembly of lipid aggregates. Liposomes of natural lipids were prepared from a mixture of phosphatidylcholine (PC) and phosphatidylserine (PS), and their hydrodynamic size and surface zeta potential were studied as a function of pH. Adsorption was investigated at graphitic amorphous carbon surfaces (a-C) and at these surfaces after oxidative treatments (a-C:O). Infrared surface spectroscopy experiments show that PC/PS liposomes adsorb at a-C surfaces exclusively, independently of pH, while no adsorption is observed at a-C:O materials. Nanogravimetry and fluorescence imaging experiments in solution indicate that adsorption at a-C occurs as supported intact vesicles. Interestingly, PC/PS adsorption at oxidized surfaces was observed only in the presence of a dication such as Ca2+, a behavior that was attributed to screening of surface-liposome repulsive electrostatic interactions. Vesicle rupture experiments show that lipids adsorb as monolayers on graphitic surfaces, whereas adsorbate structures correspond to bilayers in the case of oxidized carbons. These results therefore demonstrate a strong dependence of adsorbate structure on both carbon chemistry and buffer composition. These findings have important implications for the design of carbon nanoparticles, carbon electrodes, or carbon coatings for applications in biology and medicine.

Modulation of Protein Fouling and Interfacial Properties at Carbon Surfaces via Immobilization of Glycans Using Aryldiazonium Chemistry.

Carbon materials and nanomaterials are of great interest for biological applications such as implantable devices and nanoparticle vectors, however, to realize their potential it is critical to control formation and composition of the protein corona in biological media. In this work, protein adsorption studies were carried out at carbon surfaces functionalized with aryldiazonium layers bearing mono- and di-saccharide glycosides. Surface IR reflectance absorption spectroscopy and quartz crystal microbalance were used to study adsorption of albumin, lysozyme and fibrinogen. Protein adsorption was found to decrease by 30-90% with respect to bare carbon surfaces; notably, enhanced rejection was observed in the case of the tested di-saccharide vs. simple mono-saccharides for near-physiological protein concentration values. ζ-potential measurements revealed that aryldiazonium chemistry results in the immobilization of phenylglycosides without a change in surface charge density, which is known to be important for protein adsorption. Multisolvent contact angle measurements were used to calculate surface free energy and acid-base polar components of bare and modified surfaces based on the van Oss-Chaudhury-Good model: results indicate that protein resistance in these phenylglycoside layers correlates positively with wetting behavior and Lewis basicity.

Enhanced Antifouling Properties of Carbohydrate Coated Poly(ether sulfone) Membranes.

Poly(ether sulfone) membranes (PES) were modified with biologically active monosaccharides and disaccharides using aryldiazonium chemistry as a mild, one-step, surface-modification strategy. We previously proposed the modification of carbon, metals, and alloys with monosaccharides using the same method; herein, we demonstrate modification of PES membranes and the effect of chemisorbed carbohydrate layers on their resistance to biofouling. Glycosylated PES surfaces were characterized using spectroscopic methods and tested against their ability to interact with specific carbohydrate-binding proteins. Galactose-, mannose-, and lactose-modified PES surfaces were exposed to Bovine Serum Albumin (BSA) solutions to assess unspecific protein adsorption in the laboratory and were found to adsorb significantly lower amounts of BSA compared to bare membranes. The ability of molecular carbohydrate layers to impart antifouling properties was further tested in the field via long-term immersive tests at a wastewater treatment plant. A combination of ATP content assays, infrared spectroscopic characterization and He-ion microscopy (HIM) imaging were used to investigate biomass accumulation at membranes. We show that, beyond laboratory applications and in the case of complex aqueous environments that are rich in biomass such as wastewater effluent, we observe significantly lower biofouling at carbohydrate-modified PES than at bare PES membrane surfaces.

Monodispersed molecular donors for bulk hetero-junction solar cells: from molecular properties to device performances.

The relations between the chemical-physical properties of novel designed monodispersed donors and their photovoltaic performances are discussed. The importance of intermolecular interactions is emphasized to figure out the achievement of high performing bulk hetero-junction solar cells which are solution processed.