Precipitant-Free Crystallization of Protein Molecules Induced by Incision on Substrate

Nucleation of protein crystals has been shown to be facilitated by substrates decorated with both nano- to micro-scale hierarchical undulations and spatially varying surface potential. In fact, on such surfaces, several proteins were found to crystallize without having to use any precipitant in contrast to all other homogeneous and heterogeneous systems in which precipitant is an essential ingredient for nucleation. While these surfaces were so patterned whole through the area that was brought in contact with the protein solution, it was not clear exactly to what extent the surfaces were required to be patterned to trigger nucleation without use of any precipitant. Here we show that a simple incision may be enough on an otherwise smooth surface for this purpose. In particular, the substrate used here is a smooth silicone film with its surface plasma oxidized to create a thin crust of silica. An incision is then generated on this surface using a sharp razor blade. The silica crust being brittle leads to random nano- microscopic undulations at the vicinity of the incision. These undulations along with surface charge can induce protein crystal nucleation without precipitant.