Crystal harvesting out of native crystallization drops (hanging- and/or sitting-drop geometries) can sometimes be severely hampered by the propensity of crystals to stick to their crystallization surface. Here are some tips on how to approach the problem:
OPERATE ON THE PLASTIC RATHER THAN ON THE CRYSTAL!
Take a sturdy needle (like one of the microneedles from a Hampton kit, or a very thin syringe needle, or an accupuncture needle) and stick the needle into the plastic a bit away from the crystal. Push hard. If you’re using polarizers, you may be abe to visualize the stress forces in the plastic by the shifting of the colors. The basic idea is to stress the plastic under the crystal without touching the crystal in any way. By digging and twisting, one can generate little movements across the plastic which can be enough to free the crystal. Sometimes you have to push quite hard, and to wiggle the needle a bit. Beware, however, as the needle can slip and ruin the crystallization drop.
COAT THE CRYSTALLIZATION SURFACE WITH A THIN LAYER OF GREASE
If working with the 'sitting-drop' geometry, one can coat the sitting drop depressions with a thin layer of vacuum grease. You only need a very thin layer of the grease (i.e. keep wiping off with a KimWipe until the grease is almost completely gone). Upon crystal harvesting, the crystals will have the tendency to slide right off the grease. One may opt for Vaseline or petroleum jelly rather than silicone-based grease.
COAT THE CRYSTALLIZATION SURFACE WITH SILICON
You can try various siliconizing fluids such as AquaSil (Hampton Research). Such a product will not melt the plastic of the crystallization plate as opposed to eg. Repelcote.
CHANGE CRYSTALLIZATION PLATE
You can also try plates made from COC (cyclic olefins), such as the "UVP" plates made by SwissCi (sold by lots of companies including us). They are less sticky than polystyrene plates. COC is halfway between polystyrene and polypropylene. Polypropylene is even less sticky than COC but is not rigid, therefore harder to dispense to automatically. You can get plates made of "clarified polypropylene" from Emerald, and you can also get polypropylene "bridges" that you place in Linbro wells. I think Hampton still sells them.
If you have good and bad crystals in the same drop, I've had success pushing a crummy crystal into a good crystal and having it release that way.
CRYSTALLIZATION WITH AGAROSE AS AN ADDITIVE
Crystals form inside the very soft gel and they are hold in place by this meshwork. So, they are mechanically protected and do not fall down onto the bottom of the sitting-drop well. A final concentration of 0.1-0.2 % (w/v) agarose is sufficient. When you harvest a crystal cut generously around it with a microtool, pick it up (e.g. using a nylon loop) and do not mind if some agarose comes with it. Reference: Biertmpfel, C.; Basquin, J.; Suck, D. & Sauter, C. Crystallization of biological macromolecules using agarose gel. Acta Crystallogr D Biol Crystallogr, 2002, 58, 1657-9 PMID: 12351881
FLOATING DROP CRYSTALLIZATION METHOD
References 1. Application of a two-liquid system to sitting-drop vapour-diffusion protein crystallization. Adachi, H. et al, Acta Cryst. (2003) D59, 194-196 2. Promotion of large protein crystal growth with stirring solution. Adachi, H. et al. Jpn. J. Appl. Phys. Vol. 41 (2002) pp.1025-1027 3. Two-liquid hanging-drop vapour-diffusion technique of protein crystallization. Hiroaki Adachi et al. Japanese Journal of Applied Physics. Vol. 43, No. 1A/B, 2004, pp.L79-L81. Here is a web link to the fluid on the Hampton Research web site. http://hamptonresearch.com/product_detail.aspx?cid=4&sid=185&pid=32 HR2-797 100% Fluorinert FC-70 Fluid 100 ml
Put a small piece of dry ice on the opposite side of the plastic from the crystal. Perhaps the difference in thermal expansive coefficient will let the crystal(s) break away. Don't overdo it though. This is a trick that Gary Gilliland taught me.
‘IN-PLATE’ DIFFRACTION EXPERIMENTS
-i hope i understood correctly, but basically leave the crystal in-situ and put the whole ensemble in an x-ray beam. somehow. you may see plastic scatter. never tried it, all theoretical. perhaps custom-cut a tray so you can break the well away when the xtal grows. or put something down there to grow on, then pick it out... would love to know if any of that works! -You might want to contact Luc Ferrer from ESRF in Grenoble or read his publications. I know they were developping robotisation for in plate shooting, but you probably will need to set up new trials in a particular type of plate. -You can collect data on your crystal still in the drop, on our beamline (FIP-BM30A at the ESRF) if you are interested. Provided space group is not P1.... We do that routinely. MITEGEN MICROTOOLS
The MiTeGen microtools kit: http://mitegen.com/products/microtools/microtools_kit1.shtml comes with a "MicroSaw", which is a 10-micron thick kapton saw that is intended for this purpose. That is, you don't pry the crystal off the surface, but rather rest this saw against the surface, bring it over to the edge of the stuck crystal and then work it back and forth until you have cut underneath the crystal. PIPETTING techniques I had a similar story like yours.Then I added a drop of 10ul simulated mother liquot which contains much higher concentrations of all components in the normal mother liquot. Sometimes, the crystals attached to the plastic would float to the surface. If not, take another 10ul, but blew it to the bottom plastic with a pippetman back and forth, and some crystals would also leave the plastic(But you have to be very careful to do this.)
GROW THE CRYSTALS ON A MICROTOOL MESH
For my PhD I once sonicated crystals off a glass surface; diffraction was fine; apparently this was the standard approach for papain when Jan Drenth solved it long ago.