The experimental sensing of bubble nucleation in a nanochannel reactor requires an advanced detection scheme. We report on the detailed characterization of an ultrasensitive fluidic device that has been used to detect the translocation of small particles through a sensing microchannel. The device connects a fluidic circuit to the gate of a metal-oxide-semiconductor field-effect transistor (MOSFET) and detects particles by monitoring the MOSFET drain current modulation instead of the modulation in the ionic current through the sensing channel. The minimum volume ratio of the particle to the sensing channel detected is 0.006%, which is about ten times smaller than the lowest detected volume ratio previously reported in the literature. This volume ratio is detected at a noise level of about 0.6% of the baseline MOSFET drain current, clearly showing the amplification effects from the fluidic circuits and the MOSFETs. We characterized the device sensitivity as a function of the MOSFET gate potential and show that its sensitivity is higher when the MOSFET is operating below its threshold gate voltage than when it is operating above the threshold voltage. In addition, we demonstrated that the device sensitivity linearly increases with the applied electrical bias across the fluidic circuit. We demonstrate the application of the device concept as a particle sensor for polystyrene and glass beads on a variety of micro/nano length scales.