Irradiation of super-saturated agarose gels with low-powered lasers causes the nucleation of crystals with both spatial and temporal control
Crystallization is a very important tool for chemists; it is used as both a purification technique and a method of obtaining structural information. Its biggest downfall, however, is that it remains something of a dark art. It is widely acknowledged that the starting point is the most difficult part of crystallization, more specifically, controlling the nucleation of crystals, which usually occurs around a speck of dust or a 'seed crystal'.
A technique known as non-photochemical laser-induced nucleation (NPLIN), which uses low-energy lasers to nucleate crystals in aqueous solutions has been known for several years, but now Andrew Alexander and co-workers from the University of Edinburgh have shown1 how it can be used to nucleate crystals in gels, which gives both spatial and temporal control. They prepared agarose gels saturated with potassium chloride and then irradiated them through a mask to produce patterns of nucleated crystals.
The precise mechanism by which laser irradiation causes crystal nucleation is unclear, but the method has potential as a routine tool in, for example, the crystallization of proteins. Importantly, the power of the laser light used is far too low to cause photochemical damage to most compounds. The technique might also be used to nucleate crystals in three dimensions by inducing nucleation at the intersection of two low-power lasers.
Duffus, C. Camp, P. J. & Alexander, A. J. Spatial control of crystal nucleation in agarose gel. J. Am. Chem. Soc. 10.1021/ja905232m (2009).