vapour diffusion screen set-up

Vapour diffusion techniques such as the sitting drop, hanging drop, and sandwich drop are the most widely used techniques for protein crystallisation screening and optimisation.

TTP Labtech’s mosquito Crystal offers fast, flexible and accurate nanoliter dispensing of protein/reagent drops for all vapour diffusion techniques. Using mosquito Crystal for setting up vapour diffusion techniques has distinct advantages in multiple user research laboratories and academic groups, as both set-ups are easily automated without the need for changes in instrument configuration.

Using accurate and repeatable X, Y and Z movements, smaller drops can be positioned very accurately. mosquito’s positive displacement technology also handles a range of viscosities and its disposable micropipettes guarantee zero cross-contamination.

TTP Labtech’s mosquito can set up 96-well screen plates within 2 minutes. Its nanolitre volume dispensing optimises the number of conditions that can be screened with a limited amount of protein.

Sitting drop

In this technique, a drop of protein and a drop of crystallisation reagent are placed on top of one another in a subwell next to a larger well containing the precipitant. The advantages of this vapour diffusion technique are its simplicity and speed of set-up. TTP Labtech’s mosquito has tightly toleranced and relatively short pipette tips, which allow it  to place drops very accurately in the centre of the subwells of any standard crystallization plate.

Hanging drop

Here, a drop of protein and a drop of crystallisation reagent are placed on top of one another on a cover plate and this is inverted over a reagent reservoir. The hanging drop technique enables viewing of crystals without optical interference from the plate, however, droplet volume is limited compared to the sitting drop method. TTP Labtech’s mosquito allows users to create several multi-component drops per well allowing different constructs, volume ratios or protein concentrations to be assessed at the same time.

Sandwich drop

Here drops of protein sample mixed with precipitant solution are sandwiched between two cover slips. This method is rarely used, but does have the advantage of reducing the exposed surface area of the drop thus slowing down the rate at which the precipitant reservoir solution draws water from the droplet allowing slower nucleation.

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