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Laser-induced crystallization is emerging as a promising technique to crystallize biomolecules like amino acids and proteins. The use of external materials as nucleants and novel seeding methods open new paths for protein crystallization. We report here the results of experiments that explore the effect of nucleants on laser-based crystallization of microlitre droplets of small molecules, amino acids, and proteins. The role of parameters like solute concentration, droplet volume, type and size of the nucleant, and laser power, are systematically investigated. In addition to crystallization of standard molecules like NaCl, KCl, and glycine, we demonstrate the crystallization of negatively (l-histidine), and positively (l-aspartic acid) charged amino acids and lysozyme protein. Single crystal X-ray diffraction and Raman spectroscopy studies unequivocally indicate that the nucleants do not alter the molecular structure of glycine, hydrogen bonding patterns, and packing. Localized vaporization of the solvent near the nucleant due to photothermal heating has enabled us to achieve rapid crystallization - within 3 s - at laser intensities of 0.1 MW cm, significantly lower than those reported earlier, with both saturated and unsaturated solutions. The outcome of the current experiments may be of utility in tackling various crystallization problems during the formation of crystals large enough to perform X-ray crystallography.

The structure based drug design has been limited by various factors that include protein crystallization, which is one of the most challenging tasks in this area. It has been proved unequivocally that X-ray crystallography is highly trusted technique for three dimensional structure determination of small-and macro-molecules. It has provided the definite solution for several key areas such as structure based drug design, site directed mutagenesis and elucidation of enzyme mechanisms. In X-ray crystallography, growing good quality of crystals for structure determination is always, the rate limiting step. Various approaches including laser induced crystallization technique has been reported to tackle this issue. We report on the crystallization of small-and macro-molecules under focused optical radiation from a femtosecond laser (λ = 800 nm). The efficacy of this technique is proved by crystallizing different samples such as sodium chloride and urea, and by comparing the results to those crystals obtained by conventional methods. In addition, the unique capability of the developed technique is demonstrated by crystallizing the three chalcone compounds that are difficult to crystallize using conventional methods. Furthermore, the developed technique is extended to crystallize protein molecule (lysozyme) and the results indicate that present technique is a potential alternative tool to crystallize biomolecules.

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