Hi Yibin, MiTeGen offers different loops that make it easier to pick really tiny crystals which can be diffracted at the synchrotron.
If you would like to optimize small needles or rod shaped crystals, you may try an additive screen. You may also try to lower the rate of crystal growth. Perhaps increasing the amount of protein may help. Or you may also try macro-seeding,,,where you pick out one tiny crystal and seed it into the drop with same conditions. Good luck! --Subhangi
