Microfludic protein crystallography techniques

A method of mixing a first fluid and a second fluid in adjustable portions in a microfluidic device, the method comprising:

• providing a microfluidic device comprising a first well, a plurality of first control channels disposed across the first well, and a second well;
• filling the first well with said first fluid;
• filling the second well with said second fluid;
• pressurizing at least one first control channel to divide the first well into a plurality of first chambers;
• and
• placing the first well in fluid communication with the second well, such that at least one of said first chambers is in fluid communication with the second well, thereby allowing the first fluid and second fluid to mix by free-interface diffusion in portions determined by the pressurized first control channels.

A method of mixing a first fluid and a second fluid at varying rates in a microfluidic device, the method comprising:

• providing a microfluidic device comprising a plurality of compound wells, wherein each compound well comprises a first well, a second well, and one or more microchannels connecting the first and second wells, wherein the amount, average length, and/or average cross sectional area of the microchannels vary between compound wells;
• filling the first wells with said first fluid;
• filling the second wells with said second fluid;
• and
• placing the first wells in fluid communication with the second wells via the microchannels, thereby allowing the first fluid and second fluid to mix by free-interface diffusion at rates that vary between compound wells.

A method of capturing, in a microfluidic device, a chemical gradient resulting from the diffusive mixing of a first fluid and a second fluid, the method comprising:

• providing a microfluidic device comprising a first well, at least one first control channel disposed across the first well, and a second well;
• filling the first well with said first fluid;
• filling the second well with said second fluid;
• placing the first well in fluid communication with the second well, thereby allowing the first fluid and second fluid to begin mixing by free-interface diffusion;
• and
• pressurizing at least one first control channel before mixing has completed, thereby dividing the first well into a plurality of first chambers, such that concentrations of the first fluid and second fluid differ between first chambers.