A Coulter-style, microfluidic sensor formed by stacking a plurality of substantially non-electrically conductive layers, typically formed from thin polymer films. Certain layers carry patterned electrodes that are arranged to permit their connection to an electrical interrogation circuit. Electrodes may be disposed in a 3-dimensional array in the sensor. A fluid path through the sensor includes an orifice sized to promote single-file travel of particles. The orifice may be defined by a tunnel passing through at least one layer. Particles entrained in an electrolytic carrier fluid may be detected, or otherwise characterized, by interrogation circuitry connected to the sensor. Certain sensors may include portions of a fluid path disposed parallel to the layers. In certain preferred embodiments, the sensor is carried by a cartridge, which is adapted to couple with an interrogation platform. Desirably, such coupling places the sensor in-circuit with operable interrogation electronics, as well as with a fluid-flow control device. Structure included in a cartridge may provide fluid sample loading, routing, and storage capabilities.