Foodborne　bacteria,　inducing　outbreaks　of　infection　or　poisoning,　have　posed　great　threats　to　food　safety.　Potentiometric　sensors　can　identify　bacteria　levels　in　food　by　measuring　medium＇s　pH　changes.　However,　most　of　these　sensors　face　the　limitation　of　low　sensitivity　and　high　cost.　In　this　paper,　we　developed　a　high-sensitivity　ion-sensitive　field-effect　transistor　sensor.　It　is　small　sized,　cost-efficient,　and　can　be　massively　fabricated　in　a　standard　65-nm　complementary　metal-oxide-semiconductor　process.　A　subthreshold　pH-to-time-to-voltage　conversion　scheme　was　proposed　to　improve　the　sensitivity.　Furthermore,　design　parameters,　such　as　chemical　sensing　area,　transistor　size,　and　discharging　time,　were　optimized　to　enhance　the　performance.　The　intrinsic　sensitivity　of　passivation　membrane　was　calculated　as　33.2　mV/pH.　It　was　amplified　to　123.8　mV/pH　with　a　0.01-pH　resolution,　which　greatly　exceeded　6.3　mV/pH　observed　in　a　traditional　source-follower　based　readout　structure.　The　sensing　system　was　applied　to　Escherichia　coli　(E.　coli)　detection　with　densities　ranging　from　14　to　140　cfu/mL.　Compared　to　the　conventional　direct　plate　countingmethod　(24　h),　more　efficient　sixfold　smaller　screening　time　(4　h)　was　achieved　to　differentiate　samples＇　E.　coli　levels.　The　demonstrated　portable,　time-saving,　and　low-cost　prescreen　system　has　great　potential　for　food　safety　detection.