Lipid cubic phases as stable nanochannel network structures for protein biochip development: X-ray diffraction study

Biocompatible nanochannel and mesoporous structures of a three-dimensional (3D) periodicity, facilitating protein entrapment at native conformations, constitute organized protective media of interest for the fast developing fields of protein biochips and affinity biosensors. Three-dimensional periodic nanochannel structures possessing reactive chemical groups, surface-exposed to the aqueous phase, are formed here in self-assembled mixtures of a nonlamellar lipid glycerylmonooleate (MO) and a maleimide(triethylene glycol)ether lipid (MTEG) under physiological hydration conditions and are investigated by high-resolution time-resolved synchrotron X-ray diffraction in the interval from 3 to 96 degreesC. The mechanism of formation and the structural parameters of two nonlamellar cubic phases Q(224) and Q(229) (of space groups Pn3m and Im3m) are monitored. The structural phase behavior of the MO/MTEG-based immunocubosome and proteocubosome mixtures, obtained upon incubation with immunoglobulin Fab fragments, whole IgG, albumin, transferrin, and fibrinogen at high concentrations, indicates that the cubic lattices exist in excess water as nanostructured channel networks. With the particular lipid composition of interest, the protein type only finely tunes these channel networks and they appear to be stable over a broad temperature interval. A new mechanism of protein entrapment within the 3D cubosome lipid networks is proposed.