Covalent functionalization for biomolecular recognition on vertically aligned carbon nanofibers

We compare two different strategies for covalently modifying carbon nanofibers with biological molecules such as DNA. One method begins with a photochemical reaction between the nanofibers and molecules bearing both a terminal olefin group and a protected amine group followed by deprotection to yield the free primary amine. The second method uses a chemical reaction of an aryldiazonium salt with the nanofibers followed by electrochemical reduction to the primary amine. Both methods then link the primary amines to thio-terminated DNA oligonucleotides. Our measurements show that both methods yield DNA-modified carbon nanofibers exhibiting excellent specificity and reversibility in binding to DNA probe molecules in solution having complementary vs noncomplementary sequences. Quantitative measurements show that 2.3 x 10(14) DNA molecules/cm(2) will hybridize to the DNA-modified nanofiber samples, approximately eight times higher than for a flat sample of glassy carbon functionalized in an identical manner. Similar results were obtained comparing the amount of avidin that specifically binds to biotin-modified surfaces of nanofibers and glassy carbon. Our results demonstrate the ability to covalently functionalize nanofibers via two different methods that both provide excellent biomolecular recognition properties. Since the photochemical method uses molecules that are highly insulating while the diazonium method uses molecules bearing aromatic groups that are expected to be conductive, these methods can be used to prepare biologically modified nanofibers with a range of electrical properties that may be useful for electrical sensing of specific biomolecules in solution.