  Mycotoxins comprise a frequent type of toxins present in food and feed. The
problem of mycotoxin contamination has been recently aggravated due to the
increased complexity of the farm-to-fork chains, resulting in negative effects
on human and animal health and, consequently, economics. The easy-to-use,
on-site, on-demand, and rapid monitoring of mycotoxins in food/feed is highly
desired. In this work, we report on an advanced mycotoxin biosensor based on an
array of graphene field-effect transistors integrated on a single silicon chip.
A specifically designed aptamer against Ochratoxin A (OTA) was used as a
recognition element, where it was covalently attached to graphene surface via
pyrenebutanoic acid, succinimidyl ester (PBASE) chemistry. Namely, an electric
field stimulation was used to promote more efficient {\pi}-{\pi} stacking of
PBASE to graphene. The specific G-rich aptamer strand suggest its {\pi}-{\pi}
stacking on graphene in free-standing regime and reconfiguration in
G-quadruplex during binding an OTA molecule. This realistic behavior of the
aptamer is sensitive to the ionic strength of the analyte solution,
demonstrating a 10-fold increase in sensitivity at low ionic strengths. The
graphene-aptamer sensors reported here demonstrate fast assay with the lowest
detection limit of 1.4 pM for OTA within a response time as low as 10 s, which
is more than 30 times faster compared to any other reported aptamer-based
methods for mycotoxin detection. The sensors hold comparable performance when
operated in real-time within a complex matrix of wine without additional
time-consuming pre-treatment.
