Liquid coplanar-gate organic/graphene hybrid electronics for label-free detection of single and double-stranded DNA molecules

The label-free detection of DNA with simple device structure and materials helps rapid and effective diagnosis of various diseases. In this study, liquid coplanar-gate graphene field-effect transistors (GFETs) were employed to detect and further distinguish between single-stranded (SS) and double-stranded (DS) DNA molecules. Use of coplanar-gate structure simplified the fabrication steps for GFETs. The liquid coplanar-gate GFETs exhibited higher sensitivity for DNA detection compared to conventional bottom-gate GFETs because they have liquid dielectric layer that was preferred by aqueous DNA. The immobilization of 1-pyrenebutanoic acid succinimidyl ester (PASE) onto graphene surface via π-π interaction further enhanced the DNA sensing performances of GFETs. The base parts of the SS DNA molecules can be covalently linked to the succinimidyl ester group in PASE/graphene, thereby leading to n-doping of graphene by action of lone-pair electrons from nitrogen atoms in the base parts. On the other hand, the negatively charged phosphate groups of the DS DNA molecules exposed to graphene surface induced p-doping of graphene. Accordingly, it was possible to distinguish the single and double-stranded DNA molecules by electrical signals. The combined use of liquid coplanar-system and surface modification of graphene with PASE could decrease the detection limit of DNA molecules to 1 nM. The liquid coplanar-gate organic/graphene hybrid electronics platform developed here will allow rapid and convenient label-free detection of single and double stranded DNA molecules.