Arrangement in a capillary driven microfluidic system for dissolving a reagent in a fluid

A method in a capillary driven microfluidic system for dissolving a reagent in a fluid, comprising:

• providing a fluid at a first end of a channel, whereby the fluid is drawn into the channel by capillary forces,
• controlling, by means of a valve arranged at a second end of the channel, a flow of the fluid in the channel to stop as it reaches the second end of the channel,
• wherein one or more structures holding a dried reagent are fluidly coupled to the channel, the one or more structures each having a width (W2) which is larger than a width (W1) of the channel, whereby, as fluid is drawn into the channel, the fluid enters the one or more structures from the channel, dissolves the dried reagent held therein, and diffuses back into the channel,
• controlling, by means of an actuator, the valve to open a predetermined time after the fluid has been provided to the channel, whereby the fluid with the reagent dissolved therein flows out of the channel.