My protein is crystallized in 1-2 days. The fact it is so quick might affect the quality of the crystals. I am planning to slow down the growth in hope that it will yield better crystals.
I am doing hanging and sitting drop (vapour diffusion) in 24-well Linbro plates.
The classical method is to add some oil to the reservoir, this will cover its surface and slow down evaporation
Unless you have tested the diffraction you cant say that its bad thing. overlaying oil, adding glycerol to reservoir, reducing protein concentration, varying drop ratios might help.
You can also lower the temperature by placing your plates at 15, 8 or 4 ° C, this will also limit the rate of diffusion and hence the rate of crystal growth, without changing your crystallization conditions
There is another pretty easy way to slow the growth down if you rely on vapour diffusion with its different geometries. After the appearance on nuclei (tiny crystals), transfer the cover slip to another well with lower precipitant concentration.
I second Salam's suggestion to layer oil over the reservoir. Specifically, a mixture of paraffin oil (which is impermeable to water vapor) and silicone oil (which allows transmission of water vapour) works quite well.
The 1:1 mixture of these two oils is commonly referred to as Al's oil. I would suggest if you are working in 24-well plates, and your reservoir is ~0.5-1mL, layer ~200-400uL oil over the reservoir when setting up your trays.
Simply using larger drops may also help, as they will have a lower surface area to volume ratio and hence will equilibrate more slowly.
Do you have any reason apart from the fast growth to suspect that your crystals are poor quality (e.g. obvious imperfections/defects, multiple intergrown crystals, etc)?
You should consider the possibility to switch to free interface diffusion technique, and eventually to use agarose or silica gels to slow down the mass transport process.
See Garcia-Ruiz JM or Giegè R for gel techniques and Chayen N for moving from a technique to another.
Just to note: I had a protein that crystallised immediately after pipetting and it was perfect. Nothing is guarantee. Anyway to slow down crystallisation, get less protein, less precipitant concentration (do a fine screen), store the plate in a room at lower temperature, change the volume of the drop..
You’ve gotten several good comments already but perhaps these thoughts may also help. As noted by others, I think 1-2 days is fine and means you have gotten very nice conditions for forming crystals – how well do they diffract? But if you want more control then consider separating nucleation from growth, which I did not see mentioned. Find conditions that do not allow de novo crystals to grow by creating plates with gradients of protein and precipitant approaching the region that is now providing crystals. Then you can streak seed into these conditions by touching a cat whisker to your fresh crystals and then streaking it across the drop. If you have conditions for crystal growth but not nucleation (which typically requires higher concentrations than growth), then you will see crystals only in the line of your streak. At this point, you can pick great tiny crystals and macro-seed or use the whisker to go through multiple drops till you only have a few nucleation sites, and you will see some nice crystals and hopefully suitable diffraction.
You need increase the solubility of your protein. To do that just increase by steps the NaCl concentration (Salting-in effect). This allow you a fine tunning of your ptrotein solubility. Good Luck
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