Polypeptide Nanorods/Nanotubes

Hatice Duran, Wolfgang Knoll

Poly(γ-benzyl-L-glutamate) (PBLG) is an electro-optic polymer –also called a non-linear optic polymer- whose electrical and optical properties are closely interrelated. This polymer is attractive not only because of its large intrinsic dipole moments and birefringency but also because its ester side chain may be easily modified. This provides the flexibility to further engineer the nanotube structure and behavior at the molecular level.

Patterning of Oriented PBLG Nanorods for Optical Bragg Sensors

in cooperation with U. Jonas and M. Steinhart*
(MPI for Microstructure Physics, Halle, Germany)

Polypeptide Nanorods via Surface-initiated Vapor Deposition Technique (SI-VDP)

In this process, gas phase monomer molecules (NCA) are condensed onto a initiator-immobilized well-ordered alumina template membrane surface leading to polymerization[1,2]. Aminopropyl triethoxysilane (APTE) was used as initiator. It is immobilized on the pore walls through liquid phase silanization. This initiator coated template membrane was then placed in a sealed glass tube furnace with a small amount of NCA monomer spread on the bottom. Since vapor-deposition polymerization involves a reaction between the NCA vapor species and surface-immobilized amine groups, by increasining the temperature above the melting point of NCA (96.5-97.5°C) and applying high vacuum, NCA monomers extensively polymerize through a ring opening polymerization mechanism. While monomers are polymerized within the nanopores, it is possible to tune the wall thickness of the resulting polymers by choosing the right polymerization conditions, particularly the polymerization time [3]. The free-standing PBLG nanorods were then obtained by selective removal/dissolution of the template via 45% HF etcher solution.

Schematic representation of Polypeptide (PBLG) nanotube formation by SI-VDP technique.

SEM images of PBLG nanorods obtained via SI-VDP at 105°C for 30min using 1.5X10-3mbar.

Periodic Patterning of oriented PBLG nanorodes within a binder polymer will be achieved through the combination of photolithography [4] and photopolymerization. The use of nanorods for making aligned nanotubes within the polymer matrix requires surface modification of the nanotube ends to strengthen the adhesion of the nanotube and patterned substrate interface. The open ends of the polymeric nanotubes will be functionalized with thiol-derivatized grafting groups that preferentially react with the photolithographically patterned substrate surface through amide linkages. Then, the alumina template consisting of PBLG nanorods with both ends functionalized will be sandwiched between two photolithographically patterned substrates in order to fix the nanorods to the substrate surfaces. Once the nanorods are grafted on to the substrate surfaces, then the alumina template will be etched away (%45 HF). After removing the alumina template, a highly reactive acrylate monomer (trimethylolpropane triacrylate) and the photoinitiator (RBAX) mixture will be loaded between the substrates. An UV light source will be used to photopolmerize monomer and initiator mixture. The multifunctional acrylate chosen for the study has the advantage of being highly reactive and of having a very low viscosity. Using this approach, the loading of monomer is much easier. Therefore, PBLG nanorods will be stabilized inside the polymer matrix even after removal of the alumina template. As a final stage, prepatterned substrates will be removed with a razor blade.

(a) PBLG nanorods formation, (b) and (c) nanorods ends functionalization, (d) substrate patterning by photolithography, (e) binding the nanorods on the substrates, etching away the alumina template, filling the gap with photoreactive monomer mixture, and UV photopolymerization, (f) removing the substrates.

In-Situ Sensing of Polypeptide Growth within Nanoporous Alumina Template (Optical Waveguide Spectroscopy)

in cooperation with U. Jonas and A.K.H. Lau

In the template-wetting method, an alumina template with uniform porosity was used as the mold. First, PBLG polymer melt was brought in contact with the template by spreading them on top of pores. Then, substrate was put in vacuum oven under Ar and temperature was set above the Tm of the monomer. Layer of the polymer melt covers the region near the pore wall so that most of the molecules are in direct contact with the pore wall. Ultimately, the pore walls were wetted completely by polymer melt, as a result of the spatial limitations and the different surface energies between pore wall and the polymer. Since the nanotubes are replicas of the template pores, their dimensions were arranged by using templates with proper pore diameters and depths.

Schematic representation of Polypeptide films formed inside pore walls of a thin anodic alumina membrane.

SEM images of PBLG Nanotubes via template wetting technique.

(a) Waveguide mode patterns of thin alumina film before (pink) and after functionalization with APTE (red) in 1mM methanol. (b) In-situ kinetics of APTE coating followed using the right-most guided mode in (a). Open diamonds are data, and red solid line is fitting with 2-step diffusion limited model.

References
[1] Chang, Y. –C. and Frank, C. W. “Grafting of poly(γ-benzyl-L-glutamate) on chemically modified silicon oxide surfaces”, Langmuir, 1996, 12, 5824-29
[2] Chang, Y. –C. and Frank, C. W. “Vapor deposition-polymerization of α-amino acid N-carboxy anhydride on the silicon (100) native oxide surface”, Langmuir, 1998, 14, 326-334
[3] Parthasarathy, R. V.; Martin, C. R. “Synthesis of polymeric microcapsule arrays and their use for enzyme immobilization”, Nature, 1994, 369, 298-301
[4] (a) Huang, S.; Mau, A. H. M. “Aligned carbon nanotubes patterned photolithographically by silver”, Appl. Phys. Lett., 2003, 82(5), 796-798 (b) Yang, Y.; Huang, S.; He, H.; Mau, A. W. H. and Dai, L. “Patterned growth of well-aligned carbon nanotubes: A photolithographic approach”, J. Am. Chem. Soc., 1999, 121, 10832-33 (c) Huang, S.; Dai, L., and Mau, A. “Controlled fabrication of aligned carbon nanotube patterns”, Physica B, 2002, 323, 333-335