Using Biomolecular Recognition to Selectively Self-Assemble Microscale Components onto Patterned Substrates

  • Author / Creator
    Olsen, Trevor AS
  • Modern nanofabrication technology in the 21st century has continued year after year to push the boundaries of what is possible at the nanoscale. With the advent of molecular electronics, single electron devices, nanoelectromechanical systems (NEMS), and other nanotechnologies, the near future will see a requirement for the die-to-substrate assembly of components that are much smaller than conventional robotic pick-and-place technologies can accommodate. Many researchers have proposed the mechanism of self-assembly to replace robotic pick-and-place technologies and meet the micro/nanoscale assembly needs of some future technologies. Presented here is a biologically inspired approach for the selective self-assembly of micron-scale components onto lithographically patterned target sites on a substrate. Two mechanisms of selective adhesion through biomolecular recognition are explored and tested in this thesis: the strong protein-ligand interaction between avidin and biotin, and the hybridization interaction that occurs between two complementary single-stranded DNA oligonucleotides. Other than the benefits in scale, the method of integration by self-assembly may be advantageous for its parallel nature, 3D capabilities, and the ability to integrate devices made from incompatible processing technologies into a single platform (heterogeneous integration). Square silicon microtiles with widths ranging from 5 µm to 25 µm were chosen to be test devices (model ‘nanochips’) for the assembly. These devices, fabricated from silicon-on-insulator (SOI) substrates, were coated with a thin film of gold on one side, deposited by sputtering. A buffered oxide underetch of the buried SiO2 layer left the microtiles attached to the SOI handle substrate only by narrow SiO2 pillars. This allowed for facile release of the microtiles into solution from the front side of the substrate by ultrasound fracture of the SiO2 pillars in a bath sonicator. In the initial demonstration, self-assembled monolayers (SAMs) were employed to functionalize both the microtiles and the gold pads with biotin and avidin, respectively. Preliminary experiments employed commercially functionalized gold nanoparticles and polystyrene microspheres to develop reliable procedures for forming avidin and biotin SAMs on gold. After the gold-coated microtiles were functionalized with a biotin SAM and a target substrate had its gold pads functionalized with an avidin SAM, the microtiles were released into a solution of phosphate buffered saline (PBS) containing a low concentration of polysorbate 20. The avidin-functionalized target substrate was then placed in this solution. Self-assembly of the microtiles onto the substrate was achieved by intermittently stirring the solution over 24 hours. In the most successful demonstration, 5 µm square microtiles were self-assembled onto patterned 5 µm square gold pads on the target substrate. After rinsing, the avidin-biotin self-assembly method yielded 2.0% of the total target pads covered by assembled microtiles at a selectivity ratio of 7.3:1 in favour of microtiles affixed to the target pads as opposed to the surrounding silicon substrate. DNA-driven self-assembly of the microtiles was also successfully demonstrated at a lower yield using similar procedures.

  • Subjects / Keywords
  • Graduation date
    Spring 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.