Nucleation of Sub-Micrometer Protein Crystals in Square-Shaped Macroporous Silicon Structures

Abstract

Macroporous silicon substrates, with square-shaped pores, have been used to crystallize hen egg white lysozyme by the sitting drop vapor diffusion method. The X-ray diffraction technique was used to determine the tetragonal structure of the crystals. Use of an asymmetric anodization procedure to produce pore size gradients in porous structure, ranging from 400 nm to 1 μm, resulted in the formation of sub-micrometer-sized protein crystals within the macroporous structure. The presence of the crystals was observed by field emission scanning electron microscopy and confirmed by Raman and infrared spectroscopy. The present work provides experimental evidence of sub-micrometer crystal growth from pore corners and rough sides of the pore walls, attributed to the reduction of the potential energy for nucleation, in accordance with the different mathematical models developed so far.

Room Temperature Crystallization of Hydroxyapatite in Porous Silicon Structures

“…In order to observe the HA nucleation in different pore dimensions in MPS structures, n-type graded macropores were fabricated employing an experimental setup which involves the simultaneous application of an electric and magnetic field along with an auxiliary metal electrode electrically connected to the negative contact of the lateral electric field (cathode) applied onto Si substrate [6, 38]. This configuration leads to the formation of linear gradient in pore size and thickness.…”

“…One of the most important characteristics of PS is its high specific surface area [1–3], which was shown to have a nanostructured fractal (self-similar) surface [4] with tunable interconnected pores. It serves as an ideal substrate for crystal growth of different materials such as proteins [5, 6], oxides [7], semiconductors [8], metallic nanoparticles [9], and hydroxyapatites [2, 10]. Moreover, heterogeneous nucleation occurs more often than homogeneous nucleation.…”

Porous Si Partially Filled with Water Molecules—Crystal Structure, Energy Bands and Optical Properties from First Principles

“…Note that the square-shaped void of 5 * 5 µm is a quite typical geometry for macroporous Si (>50 nm) used for the fabrication of photonic crystals [47]. Recently, the square-shaped 400 * 400 nm Si pores were successfully realized for nucleation of sub-micrometer protein crystals in a silicon mesh [48]. In our opinion, the shape of a pore plays a relatively minor role compared with pore diameter, supercell dimension and porosity of porous Si.…”

“…1.7 and 1.66Å. For comparison, the inter-hydrogen distance in molecular hydrogen is ∼0.74Å and in the molecular ion H + 2 is 1.06Å [48]. From the crystal-chemical point of view, such a coordination geometry of hydrogen atoms seems to be rather problematic for practical implementation, though it explains a metal-like conductive behavior of this 4aSi structure that will be discussed below.…”

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

“…When the protein is crystallized on a heterogeneous surface consisting of surface patterns and defects, the free energy barrier for nucleation diminishes, thereby increasing the rate of nucleation [2]. Surface defects include nano-pores, nano-spheres, and particles-like silica particles, polystyrene particles, and so on-which have been found to induce nucleation [3][4][5][6][7][8][9][10]. In fact, nano-pores having a pore diameter similar to that of the radius of gyration of a specific protein [4][5][6][7][8] is found more suitable as nucleant for that specific protein than other surfaces consisting of pores of different other dimensions.…”