Figure 1.

(a) Diagram of the sensor architecture. Circular sections on top of the graphene represent proteins embedded in a blocking layer, represented by curved lines. (b) A microscopy image showing an entire sensor surface. Red scalebar is 1 mm. There are fifteen graphene strips grouped into three groups of five, exposed through the silicon nitride protective layer. The center of the circuit is the gate measurement pad (pseudo-reference) and the large pad surrounding the graphene strips is the liquid gate (counter electrode). (c) Diagram of the sensor regions near the graphene. The double layer region is 0.3/$\sqrt{c_s}$ nm tall, where $c_s$ is the ionic strength of the bulk solution. The Donnan equilibrium region is the thickness of the combined protein and blocking layer on the surface. (d) Picture of the complete biosensor.