Methods for detecting an analyte

A method, comprising:

• introducing a liquid sample comprising multiple particles into an inlet of a device, said device comprising a cartridge having:
• a microfluidic channel including an inlet and a detection region in fluid communication with the inlet;
• a microfluidic flow path having an at least partially deformable wall and in fluid communication with the detection region of the channel;
• and
• a cap having:
• a sealing member configured to seal with the inlet and form a fluid circuit including the inlet, the microfluidic channel, and the microfluidic flow path, wherein the cap and cartridge are configured to close after forming the fluid circuit, thereby forming a contiguous liquid slug enclosed by the channel and bounded at a first end and a second end by a transport fluid, which is substantially immiscible with the liquid sample, and having a second end;
• sealing the inlet with the sealing member of the cap thereby forming a closed fluid circuit such that the transport fluid provides fluid communication between the first end and the second end of the liquid slug;
• forming a mixture comprising at least a portion of the liquid sample and an optical label;
• and
• applying a differential pressure to the first and second ends of the liquid slug via the transport fluid by reducing a thickness of the at least partially deformable wall by an actuator configured to subject a portion of the at least partially deformable wall to a localized compressive force and thereby moving the liquid slug within the fluid circuit and controlling the location of the liquid slug;
• forming a complex comprising one of the multiple particles and the optical label;
• and
• detecting the complex present within the mixture, wherein the detecting occurs in the detection region of the device.