Channel-forming activity of syringomycin E in two mercury-supported biomimetic membranes.

The lipodepsipeptide syringomycin E (SR-E) interacts with two mercury-supported biomimetic membranes, which consist of a self-assembled phospholipid monolayer (SAM) and of a tethered bilayer lipid membrane (tBLM) separated from the mercury surface by a hydrophilic tetraethyleneoxy (TEO) spacer that acts as an ionic reservoir. SR-E interacts more rapidly and effectively with a SAM of dioleoylphosphatidylserine (DOPS) than with one of dioleoylphosphatidylcholine (DOPC). The proximal lipid monolayer of the tBLM has no polar head region, being linked to the TEO spacer via an ether bond, while the distal monolayer consists of either a DOPC or a DOPS leaflet. The ion flow into or out of the spacer through the lipid bilayer moiety of the tBLM was monitored by potential step chronocoulometry and cyclic voltammetry. With the distal monolayer bathed by aqueous 0.1M KCl and 0.8µM SR-E, an ion flow in two stages was monitored with DOPC at pH3 and 5.4 and with DOPS at pH3, while a single stage was observed with DOPS at pH5.4. This behavior was compared with that already described at conventional bilayer lipid membranes. The sigmoidal shape of the chronocoulometric charge transients points to an aggregation of SR-E monomers forming an ion channel via a mechanism of nucleation and growth. The ion flow is mainly determined by potassium ions, and is inhibited by calcium ions. The contribution to the transmembrane potential from the distal leaflet depends more on the nature of the lipid than that of the ion channel.

Graphene Oxide/Silver Nanoparticles Platforms for the Detection and Discrimination of Native and Fibrillar Lysozyme: A Combined QCM and SERS Approach.

We propose a sensing platform based on graphene oxide/silver nanoparticles arrays (GO/AgNPs) for the detection and discrimination of the native and toxic fibrillar forms of an amyloid-prone protein, lysozyme, by means of a combination of Quartz Crystal Microbalance (QCM) and Surface Enhanced Raman Scattering (SERS) measurements. The GO/AgNPs layer system was obtained by Langmuir-Blodgett assembly of the silver nanoparticles followed by controlled adsorption of GO sheets on the AgNPs array. The adsorption of native and fibrillar lysozyme was followed by means of QCM, the measurements provided the kinetics and the mechanism of adsorption as a function of protein concentration as well as the mass and thickness of the adsorbed protein on both nanoplatforms. The morphology of the protein layer was characterized by Confocal Laser Scanning Microscopy experiments on Thioflavine T-stained samples. SERS experiments performed on arrays of bare AgNPs and of GO coated AgNP after native, or fibrillar, lysozyme adsorption allowed for the discrimination of the native form and toxic fibrillar structure of lysozyme. Results from combined QCM/SERS studies indicate a general construction paradigm for an efficient sensing platform with high selectivity and low detection limit for native and amyloid lysozyme.