An assay system comprising a self-contained microfluidic system and an associated reader device, wherein: the self-contained microfluidic system comprises: a sample input port for receiving a liquid sample to be assayed, the sample input port connected to at least one microfluidic channel, wherein each/said microfluidic channel(s) comprises one or more reagents deposited therein for use in conducting an assay and a detection zone for use in detecting any analyte which may be present in a sample or analyte reaction product; and each/said microfluidic channel(s) is in fluid communication with a compressible, gas-filled chamber downstream from each/said detection zone, wherein the microfluidic system is formed from three layers, a top, a middle and a bottom layer, which are sandwiched together in order to define each/said microfluidic channel(s) and said gas filled chamber, and wherein compressing or decompressing an external surface of said chamber causes gas to be expelled from or drawn into the chamber, which in turn causes movement of the liquid sample within said/each microfluidic channel; and a reader device for use with the microfluidic system, the reader device comprising: force control means for controlling compression or decompression of the gas filled chamber of the microfluidic system; and detection means for enabling detection of a desired analyte within a liquid sample introduced into the microfluidic cartridge, or analyte reaction product thereof; wherein the force control means comprises a piezoelectric bending actuator which is designed to directly or indirectly compress or decompress the outer surface of said gas filled chamber through displacement of the actuator. the self-contained microfluidic system comprises: a sample input port for receiving a liquid sample to be assayed, the sample input port connected to at least one microfluidic channel, wherein each/said microfluidic channel(s) comprises one or more reagents deposited therein for use in conducting an assay and a detection zone for use in detecting any analyte which may be present in a sample or analyte reaction product; and each/said microfluidic channel(s) is in fluid communication with a compressible, gas-filled chamber downstream from each/said detection zone, a sample input port for receiving a liquid sample to be assayed, the sample input port connected to at least one microfluidic channel, wherein each/said microfluidic channel(s) comprises one or more reagents deposited therein for use in conducting an assay and a detection zone for use in detecting any analyte which may be present in a sample or analyte reaction product; and each/said microfluidic channel(s) is in fluid communication with a compressible, gas-filled chamber downstream from each/said detection zone, wherein the microfluidic system is formed from three layers, a top, a middle and a bottom layer, which are sandwiched together in order to define each/said microfluidic channel(s) and said gas filled chamber, and wherein compressing or decompressing an external surface of said chamber causes gas to be expelled from or drawn into the chamber, which in turn causes movement of the liquid sample within said/each microfluidic channel; and a reader device for use with the microfluidic system, the reader device comprising: force control means for controlling compression or decompression of the gas filled chamber of the microfluidic system; and detection means for enabling detection of a desired analyte within a liquid sample introduced into the microfluidic cartridge, or analyte reaction product thereof; wherein the force control means comprises a piezoelectric bending actuator which is designed to directly or indirectly compress or decompress the outer surface of said gas filled chamber through displacement of the actuator. force control means for controlling compression or decompression of the gas filled chamber of the microfluidic system; and detection means for enabling detection of a desired analyte within a liquid sample introduced into the microfluidic cartridge, or analyte reaction product thereof; wherein the force control means comprises a piezoelectric bending actuator which is designed to directly or indirectly compress or decompress the outer surface of said gas filled chamber through displacement of the actuator.