Length-Dependent Diblock DNA with Poly-cytosine (Poly-C) as High-Affinity Anchors on Graphene Oxide

DNA-functionalized graphene oxide (GO) is a popular system for biosensor development and directed materials assembly. Compared to covalent attachment, simple physisorption of DNA has been more popular, and a DNA sequence with a strong affinity on GO is highly desirable. Recently, we found that poly-cytosine (poly-C) DNA can strongly adsorb on many common nanomaterials, including GO. To identify an optimal length of poly-C DNA, we herein designed a series of diblock DNA sequences containing between 0 and 30 cytosines. The displacement of a random sequenced DNA by poly-C DNA was demonstrated, confirming the desired diblock structure on GO with the poly-C block anchoring on the surface and the other block available for hybridization. The adsorption density of poly-C containing DNA did not vary much as the length of the poly-C block increased, suggesting the conformation of the anchoring DNA on the GO was quite independent of the DNA length. With a longer poly-C block, the efficiency of surface hybridization of the other block increased, while nonspecific adsorption of noncomplementary DNA was inhibited more. Compared to poly-adenine (poly-A)-containing DNAs, which were previously used for the same purpose, poly-C DNA adsorption is more stable. Using four types of 15-mer DNA homopolymers as the intended anchoring sequences, the C₁₅ DNA had the best hybridization efficiency. This work has suggested the optimal length for the poly-C block to be 15-mer or longer, and it has provided interesting insights into the DNA/GO biointerface.