Patent ID: 8377635

Claim:
A method of controlling the flow of an aqueous fluid in a microfluidic device, which method comprises the steps of: (a) adding a fluid sample to a microfluidic device, which comprises an inlet region and a downstream detection zone which are connected by one or more channels, wherein at least one channel contains a fluid gate comprising a UCST (upper critical solubility temperature) polymer, wherein said UCST polymer is derived from the polymerization of a MEDSAH ([2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)ammonium hydroxide) monomer; (b) allowing the sample to be retained within the device for a period of time by the fluid gate by maintaining the temperature of the fluid gate below the USCT of the polymer such that the fluid gate is closed, followed by (c) applying heat to raise the temperature of the fluid gate above the USCT of the polymer such that the fluid gate opens and the fluid sample is able to flow across the fluid gate to a region downstream from said gate, wherein the cross-sectional area of the polymer is 50% or less of the channel cross-sectional area.