  We have developed a novel, all-electronic biosensor for opioids that consists
of an engineered mu opioid receptor protein, with high binding affinity for
opioids, chemically bonded to a graphene field-effect transistor to read out
ligand binding. A variant of the receptor protein that provided chemical
recognition was computationally redesigned to enhance its solubility and
stability in an aqueous environment. A shadow mask process was developed to
fabricate arrays of hundreds of graphene transistors with average mobility of
~1500 cm2 V-1 s-1 and yield exceeding 98%. The biosensor exhibits high
sensitivity and selectivity for the target naltrexone, an opioid receptor
antagonist, with a detection limit of 10 pg/mL.
