A graphene biosensor is formed on an electrically insulating substrate with a single-layer graphene sheet arranged between two metallic electrodes. The graphene sheet is in electrical contact with the metallic electrodes. The graphene sheet has perforations creating edges in the graphene sheet. The perforations may be holes on a micrometer scale or in a nanometer scale. The biosensor can be configured as an ISFET. The graphene sheet may comprise affinity probes immobilized on the edges for attaching specific molecules to the graphene sheet. Several graphene sheets may be arranged in a microarray with different affinity probes on different graphene sheets. The sensor may also be arranged on the distal end of a catheter for in situ measurements in a body vessel.
