Journal of Materials Chemistry Blog

Functionalisation of graphene by adsorbed single-stranded DNA (ssDNA) enables the dispersion of graphene in aqueous solution.  The resulting composites are of great interest as biomaterials with applications in areas such as molecular diagnostics, biosensors and DNA sequencing. Hence, there is much to be gained from an improved understanding of the interaction between graphene and ssDNA.

In this hot paper, Manna and Pati use atomistic molecular dynamics (MD) simulation and density functional theory (DFT) to investigate the structural topology, energetics and electronic structure of ssDNA hybridized with graphene.  They find the adsorption process is influenced by competing π–π stacking interactions, which are highly dependent on the chemical nature of the nucleobase and the sequence type of the ssDNA.  Mixed nucleobase sequence ssDNA is proposed as a better candidate for dispersing graphene than ssDNA containing homologous base sequences.

This research provides a fundamental understanding of the adsorption of ssDNA on graphene, and therefore has important implications for the design of graphene-based biomaterials.

Theoretical understanding of single-stranded DNA assisted dispersion of graphene
J. Mater. Chem. B, 2013, 1, 91-100 DOI: 10.1039/C2TB00184E

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The use of antitumour drugs has always been problematic due to the risk of severe side-effects consistent with such cytotoxic compounds. A logical method of reducing side effects is to exercise more control over the deployment of drugs, ensuring that they are only delivered to cancer cells and not across the entire body. The first stage in the development of such a system is the design of biocompatible drug carriers.

Drug carriers must be designed in such a way that they do not interfere with the therapeutic action of the drug yet also be sufficiently resilient that their payload is not released before their cellular destination. A solution to this is to use a chemical trigger that exploits differences in the extracellular and intracellular environments. One such difference is redox potential. Inside the cell, the concentration of the thiol-containing tripeptide glutathione (GSH) is around one order of magnitude higher than it is outside the cell. Disulfides (-S-S-) can be rapidly degraded by GSH meaning that structures that contain them are extremly unstable inside the cell yet remain completely stable in the mildly oxidising conditions found in the extracellular milieu.

Ding et al. prepared micelles consisting of poly(ethylene glycol) (PEG) and poly(ε-benzyloxycarbonyl-L-lysine) (PZLL) linked by a disulfide group. Upon entering the cell, it was envisaged that the fission of the disulfide would greatly undermine the structural integrity of the micelle. The carriers formed were of the order of 100 nm in size and were loaded with the drug Doxorubicon (DOX). In a non-reducing environment more than 50% of the drug was held after sixty hours; in the presence of GSH less than 10% was held demonstrating the effectiveness of the trigger. In vitro efficacy of the micelles was demonstrated using cellular imaging and the biocompatibility of the micelles was found to be extremely high.

Biocompatible reduction-responsive polypeptide micelles as nanocarriers for enhanced chemotherapy efficacy in vitro

J. Mater. Chem. B, 2013, 1, 69.  DOI: 10.1039/c2tb00063f

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Nonviral vector-based delivery of genetic information into cells to manipulate their protein expression is of great interest for applications in regenerative medicine and the treatment of genetic diseases. Nanoparticles are a type of nonviral delivery vehicle that can be employed; however their contact with cells is, too a large extent, a diffusion limited process. Using magnetic forces to pull magnetic nanoparticles towards target cells is an established technique to overcome this. However, this can have the drawback that the nanoparticles form overly tight complexes with DNA, which can inhibit gene release. Stimuli-responsive polymer vectors can be used to tune DNA unpacking, by adapting to microenvironmental changes such as temperature, pH, light and redox.

In this hot paper, scientists from Tianjin University describe the preparation of magnetic/thermoresponsive nonviral vectors in the form of monodispersed magnetic nanoparticles (MNPs). The authors investigate the physicochemical properties of the MNP-polymer brushes/DNA nanocomplexes and the in vitro gene transfection of the MNPs-polymer brushes under a magnetic field with variable temperature conditions. Co-application of magnetic field and temperature stimuli was shown to enhance gene transfection efficiencies.

Combining magnetic field/temperature dual stimuli to significantly enhance gene transfection of nonviral vectors
J. Mater. Chem. B , 2013,1, 43-51.  DOI: 10.1039/c2tb00203e (free to read for a short time)

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