Gold-nanoparticle-assisted self-assembly of chemical gradients with tunable sub-50 nm molecular domains

Abstract

A simple and efficient principle for nanopatterning with wide applicability in the sub-50 nanometer regime is chemisorption of nanoparticles; at homogeneous substrates, particles carrying surface charge may spontaneously self-organize due to the electrostatic repulsion between adjacent particles. Guided by this principle, a method is presented to design, self-assemble, and chemically functionalize gradient nanopatterns where the size of molecular domains can be tuned to match the level corresponding to single protein binding events. To modulate the binding of negatively charged gold nanoparticles both locally (<100 nm) and globally (>100 μm) onto a single modified gold substrate, ion diffusion is used to achieve spatial control of the particles' mutual electrostatic interactions. By subsequent tailoring of different molecules to surface-immobilized particles and the void areas surrounding them, nanopatterns are obtained with variable chemical domains along the gradient surface. Fimbriated Escherichia coli bacteria are bound to gradient nanopatterns with similar molecular composition and macroscopic contact angle, but different sizes of nanoscopic presentation of adhesive (hydrophobic) and repellent poly(ethylene) glycol (PEG) domains. It is shown that small hydrophobic domains, similar in size to the diameter of the bacterial fimbriae, supported firmly attached bacteria resembling catch-bond binding, whereas a high number of loosely adhered bacteria are observed on larger hydrophobic domains. Chemical gradients with the resolution needed to address complex biological binding events at the single protein level are prepared using surface-deposited gold nanoparticles as a versatile template for orthogonal chemical modifications. The effect of hydrophobic domain arrangement on the sub-50 nm scale is shown to influence binding of fimbriae carrying E. coli bacteria. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.