Direct antibiotic susceptibility tests (AST) are
essential for rapid detection of bacterial infection and
administration of appropriate antibiotics. Conventional
AST systems are usually slow as they rely on cell
growth for an indirect assessment of antibiotics’ effec-
tiveness. Therefore, a faster method is desirable, espe-
cially for emergency cases. In this work, we studied the
performance of label-free, droplet-based impedance sen-
sors for rapid characterization of the effects of ampicil-
lin (Amp) on Escherichia coli. Ampicillin damages cell
wall integrity and makes cells permeable (leaky). The
leakage results in significant increase of the electrical
conductance measured directly by the microfabricated
sensing unit. We studied the conductance signal as a
function of both antibiotic treatment time and dosage
and demonstrated susceptibility testing within 60 min.
These findings demonstrate the potential of droplet-
based electrical chips for the realization of electrical
antibiotic susceptibility testing (e-AST) for early-stage
diagnostic/treatment, and consequently, preventing anti-
biotic misuse/overuse.

• Droplet-based non-faradaic impedance sensors for assessment of susceptibility of Escherichia coli to ampicillin in 60 min