Nanoworld Institute, University of Genoa and Fondazione EL.B.A., Italy.AbstractA new in situ μGISAXS technique was used to study at ESRF the nucleation and growth mechanisms of lysozyme microcrystals with and without the thin Langmuir-Blodgett lysozyme film surface. Following recent studies on thaumatin crystal growth only in presence of LB monolayers (1.2) , in this work ultrasmall Lysozyme microcrystals are grown by classical hanging vapor diffusion and by its modification using homologous protein thin-film template displaying a long-range order. Intensity fluctuations in the μGISAXS pattern versus time for the LB-induced crystallization process appears associated to rapid seed formation and crystal growth, while the classical method continuous shift of intensity in the Yoneda region is compatible with slow crystal growth. The nucleation and growth mechanisms of lysozyme microcrystals are thereby studied at the thin lysozyme film surface by the new in situ μGISAXS technique developed at the microfocus beamline of the European Synchrotron Radiation in Grenoble. New insight on the nucleation and crystallization processes appear to emerge.Pechkova, E., Gebhardt, R., Riekel, C. & Nicolini, C. , In Situ GISAXS: I. Experimental Setup for Submicron Study of Protein Nucleation and Growth, Biophysical Journal(2010) doi:10.1016/j.bpj.2010.03.069 in pressGebhardt, R., Pechkova, E., Riekel, C. & Nicolini, C., In Situ mGISAXS: II. Thaumatin Crystal Growth Kinetic, Biophysical Journal(2010), doi:10.1016/j.bpj.2010.03, in press