Sticky crystals: Difference between revisions

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!

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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

One may want to try plates made from COC (cyclic olefins), such as the "UVP" plates made by SwissCi. 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 not recommended for crystallization robots.  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.

CRYSTAL BOWLING

If you have good and bad crystals in the same drop, one may try to push crummy crystals into a good crystal, thus creating the necessary leverage to release the useful crystals from their growth position.  

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Crystals grown in the presence of 0.1-0.2 % (w/v) agarose will grow inside the soft agarose gel.

PMID: 12351881

'FLOATING-DROP' CRYSTALLIZATION METHOD  

References:

-Application of a two-liquid system to sitting-drop vapour-diffusion protein crystallization. -Adachi, H. et al, Acta Cryst. (2003) D59, 194-196

HR2-797        100% Fluorinert FC-70 Fluid    100 ml

MICROSEEDING   

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DRY-ICE trick

‘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.

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

SONICATION