Biopolymer Synthesis for Optical Photonic Crystals

Jessica Sinacola, Annette Shine, and Anne Skaja Robinson

University of Delaware
Department of Chemical Engineering
150 Academy Street
Newark, DE 19716

sinacola@che.udel.edu
(302) 831-6697

The transmission of certain frequencies of electromagnetic radiation can be controlled through the use of photonic crystals.  There are many optical devices, such as display screens and lasers, which could benefit from the development of a cost-effective photonic crystal tailored to visible light frequencies.  Generation of a photonic crystal suitable for optical applications can be accomplished by stacking several layers of polymer molecules oriented perpendicular to a surface.  The polymer must be monodisperse, contain functional groups that can be used for crosslinking and manipulation of polymer solubility, and exhibit rigid rod behavior under the film deposition conditions.  The rigid rod behavior of alpha helical proteins combined with the monodisperse nature of proteins produced from a cell make biopolymers strong candidates for optical photonic crystals.

De novo genes were constructed for two alpha helical proteins by head-to-tail ligation of synthetic DNA monomers.  The artificial genes were inserted into a plasmid that codes for an N-terminal S tag and a C-terminal polyhistidine tag, both of which can be used for protein identification and purification.  A 15 kDa glutamic acid rich protein, corresponding to 4 linked monomers, and a leucine rich protein, corresponding to 2 linked monomers, have been expressed at high levels in Escherichia coli.   Significant differences in solubility have been observed between the two polymers.  The glutamic acid rich protein resides overwhelming in the soluble fraction of the cell lysate, while the leucine rich protein resides entirely in the insoluble lysate fraction.  This indicates that the glutamic acid rich polymer may be preferred for ease of protein isolation and purification.  The glutamic acid rich polymer has been purified using immobilized metal affinity chromatography.  Current experiments are focusing on isolating larger genes and polymer secondary structure verification via circular dichroism spectra.