The potential of graphite, graphene, and amorphous carbon structures as DNA sensor platforms

Abstract

The potential of graphene, graphite and amorphous carbon as DNA sensor platforms was investigated. Therefore, different functionalization strategies to bind DNA strands to graphene, thin graphite and amorphous carbon were tested. Furthermore, ultrathin graphite flakes were electronically characterized as a first step in the development of sp2 carbon based sensors with electronic readout. The hydrogen-terminated edges and defect sites of carbon nanowalls (CNW), upstanding microplates made out of 4-6 stacked graphene sheets, were succesfully functionalized with single stranded DNA. DNA strands were covalently bonded using a fatty acid linker molecule. The fatty acid linker was attached to the CNW edges through a photochemical reaction. This was followed by the coupling of amino-labeled DNA to the carboxylic acid groups of the fatty acid linker, using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) as a mediator. Hybridization experiments in combination with fluorescence microscopy allowed for the clear differentiation between fully complementary target DNA and DNA with a single mismatch, out of a 29 nucleotides sequence. The optimal hybridization temperature to achieve high selectivity was found to be 60 °C. Furthermore, hybridized DNA could be denatured and rehybridized for at least 10 cycles. In order to increase the DNA functionalization levels, different functionalization routes that act upon the basal plane of sp2 carbon were tested. First, a noncovalent method, based on π-π stacking, was investigated. A pyrene-like molecule was used to π-stack with the aromatic structure of graphene and graphite. The pyrene-like molecule also contained a carboxylic acid group that was used to couple DNA with the known EDC-mediated reaction. However, different experiments using fluorescence microscopy, fluorescence spectroscopy and XPS could not prove the binding of DNA or the pyrene-like linker to the graphene or graphite surface. The functionalizing species are probably rinsed off by mild washing steps.