A cartridge assembly, and method of using the same, is provided. The assembly includes a sample processing card and a substrate attached thereto. The card has an injection port for receiving a test sample; at least one metering chamber; a mixing material source for introducing mixing material(s) to the metering chamber; fluid communication channels fluidly connecting the injection port and the mixing material source to the metering chamber; and at least one output port for delivering the test sample to a sensor (e.g., GMR sensor). The substrate has associated therewith: the sensor for sensing analytes in the test sample; electrical contact portions for an electrical connection with a reader unit; and a memory chip. The assembly further includes a pneumatic interface with port(s) and corresponding communication channel(s) fluidly connected to card. The interface connects with an off-board pneumatic system and enables application of positive and negative pressurized fluid to the card to move the test sample and one or more mixing materials therein and to the sensor.