Crystallization of Proteins: Principles and Methods - Molecules: Nucleation, Aggregation and Crystallization - page 121

Fig. 5. Schematic representation of the three techniques of vapor diffusion: the hanging
drop, where the crystallizing drop is hung over a reservoir of crystallizing solution; the
sandwich drop, where the crystallizing drop is sandwiched between two coverslips over a
reservoir of crystallizing agent; the sitting drop, where the crystallizing drop is placed on
a bridge in the crystallizing solution.

Sandwich drop

The sample solution is mixed with the precipitant and placed in the mid-
dle of two cover slides with different dimensions, such that the drop is
sandwiched between the glass cover slides.
Figure 6 illustrates a 24-well plate used for vapor diffusion trials. The
volume of reservoir in usually 0.5-1 ml. The rims of the wells are
greased with vacuum grease. The protein and the crystallizing agent are
normally mixed in a 1:1 ratio on a cover slip. The volumes of the drop
can vary between 2 and 10 µ l. The cover slip is then inverted and sealed

over the well.

Liquid-liquid interface diffusion

Liquid-liquid interface diffusion also referred to as free interface diffusion
(FID), crystallization is another technique used for growing protein crys-
tals. This technique is commonly performed in small capillaries, the
geometry of which reduces undesirable convective effects. It consists of a