DNA Hybridization Measured with Graphene Transistor Arrays

Arrays of field-effect transistors are fabricated from chemical vapor deposition grown graphene (GFETs) and label-free detection of DNA hybridization performed down to femtomolar concentrations. A process is developed for large-area graphene sheets, which includes a thin Al₂ O₃ layer, protecting the graphene from contamination during photolithographic patterning and a SiO_x capping for biocompatibility. It enables fabrication of high-quality transistor arrays, exhibiting stable close-to-zero Dirac point voltages under ambient conditions. Passivation of the as-fabricated chip with a layer composed of two different oxides avoids direct electrochemical contact between the DNA solutions and the graphene layer during hybridization detection. DNA probe molecules are electrostatically immobilized via poly-l-lysine coating of the chip surface. Adsorption of this positively charged polymer induces a positive shift of the Dirac point and subsequent immobilization of negatively charged DNA probes induces a negative shift. Spatially resolved hybridization of DNA sequences is performed on the GFET arrays. End-point as well as real-time in situ measurements of hybridization are achieved. A detection limit of 10 fm is observed for hybridization of 20-nucleotide DNA targets. Typical voltage signals are around 100 mV and spurious drifts below 1 mV per hour.