Characterization of the Lipid Structure and Fluidity of Lipid Membranes on Epitaxial Graphene and Their Correlation to Graphene Features.

Graphene has been recognized as an enhanced platform for biosensors because of its high electron mobility. To integrate active membrane proteins into graphene-based materials for such applications, graphene's surface must be functionalized with lipids to mimic the biological environment of these proteins. Several studies have examined supported lipids on various types of graphene and obtained conflicting results for the lipid structure. Here, we present a correlative characterization technique based on fluorescence measurements in a Raman spectroscopy setup to study the lipid structure and dynamics on epitaxial graphene. Compared to other graphene variations, epitaxial graphene is grown on a substrate more conducive to production of electronics and offers unique topographic features. On the basis of experimental and computational results, we propose that a lipid sesquilayer (1.5 bilayer) forms on epitaxial graphene and demonstrate that the distinct surface features of epitaxial graphene affect the structure and diffusion of supported lipids.

Lipid-Functionalized Graphene Loaded with hMnSOD for Selective Inhibition of Cancer Cells.

Combination therapies utilize multiple mechanisms to target cancer cells to minimize cancer cell survival. Graphene provides an ideal platform for combination therapy due to its photothermal properties and high loading capacity for cancer-fighting molecules. Lipid functionalization of graphene extends its potential as a therapeutic platform by improving its biocompatibility and functionality. Previous studies involving graphene demonstrated its usage as a therapeutic vehicle; however, the effect of bare and engineered graphene structures on oxidative stress has not been comprehensively investigated. Because oxidative stress has been linked to cancer progression, it is vital to examine the generation of reactive oxygen species (ROS) in response to therapeutic platforms. This study functionalizes reduced graphene oxide (rGO) with lipids and the antioxidant enzyme human manganese superoxide dismutase (hMnSOD) and presents a detailed characterization of cellular responses to bare and functionalized rGO nanostructures in tumorigenic and nontumorigenic breast cell lines. Each cell type displayed distinct responses depending on whether they were normal, nonmetastatic, or metastatic cells. Bare rGO significantly reduced cell growth and substantially increased ROS production in all cell lines and instigated necrosis in metastatic breast cancer cells. Cell proliferation decreased in cancerous breast cells upon introduction of lipid-rGO, which correlated with peroxidation of lipids coating the rGO. In contrast, lipid-rGO nanostructures had minimal impact on proliferation and lipid peroxidation for normal breast cells. Lipid-rGO nanostructures with bound hMnSOD inhibited the proliferation of metastatic cancer cells while preventing necrosis and avoiding the negative side effects on normal cells associated with chemotherapeutic agents. Together, the results confirm the importance of functionalizing rGO for therapeutic applications and present an additional modality for the usage of graphene to selectively target cancer cells.

Artificial water channels enable fast and selective water permeation through water-wire networks.

Artificial water channels are synthetic molecules that aim to mimic the structural and functional features of biological water channels (aquaporins). Here we report on a cluster-forming organic nanoarchitecture, peptide-appended hybrid[4]arene (PAH[4]), as a new class of artificial water channels. Fluorescence experiments and simulations demonstrated that PAH[4]s can form, through lateral diffusion, clusters in lipid membranes that provide synergistic membrane-spanning paths for a rapid and selective water permeation through water-wire networks. Quantitative transport studies revealed that PAH[4]s can transport >109 water molecules per second per molecule, which is comparable to aquaporin water channels. The performance of these channels exceeds the upper bound limit of current desalination membranes by a factor of ~104, as illustrated by the water/NaCl permeability-selectivity trade-off curve. PAH[4]'s unique properties of a high water/solute permselectivity via cooperative water-wire formation could usher in an alternative design paradigm for permeable membrane materials in separations, energy production and barrier applications.

Author Correction: Artificial water channels enable fast and selective water permeation through water-wire networks.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.