Fabrication of polymeric nanorods using bilayer nanoimprint lithography.

Polymeric nanoparticles are becoming increasingly important in a variety of biological applications, such as biomolecular sensing, diagnostic imaging, and therapeutic drug delivery. For these applications, the mass production of multifunctional nanocomposite materials with precise control of particle size, shape, and composition is a significant challenge. For instance, the use of conventional bottom-up strategies (e.g., emulsion polymerization) to fabricate polymeric nanostructures with nonspherical geometry and a uniform size distribution is difficult because these methods are typically driven by the minimization of interfacial free energy that yields spherical particles with a size variation. Moreover, the formation of nanocomposite materials is difficult due to the challenge in assembling multiple components from large volume fractions of solvent. On the other hand, in the field of microelectronics, polymers as resist can be precisely patterned to have arbitrary shapes using state-of-the-art photo-, e-beam, and X-ray lithographic technologies. They are limited either by high cost, poor accessibility, slow speed, or radiation damage to functional polymers. In the past decade, many lowcost nanopatterning techniques have been invented to pattern polymer structures, such as nanoimprint lithography (NIL) and soft lithography, among many others. These methods are capable of making nanostructures of desired shape and size. However, it is not straightforward to produce large quantities of biofunctional nanoparticles using them. Most of these nanopatterning approaches, either imprinting or soft lithography, result in a residual layer that connects the periodic structures on a surface. Furthermore, they are limited