Meniscus-Directed Assembly of Biologically Active Coatings of Cells, Microparticles, and Nanoparticles

Abstract

Convective assembly principles and techniques were used in two complementary studies for depositing close packed yeast-coated surfaces and gold nanoparticle wires. Convective assembly at high volume fraction was used for the rapid deposition of uniform, close-packed coatings of Saccharomyces cerevisiae onto glass slides. A computational model was developed to calculate the thickness profiles of such coatings for various experimental conditions. Both experimentation and numerical simulations demonstrated that the deposition process is strongly affected by the presence of sedimentation. The deposition device was inclined to increase the uniformity of the coatings by causing the cells to sediment toward the three-phase contact line. In accordance with the simulation, the experiments showed that both increasing the angle of the device and decreasing the angle between the slides increased the uniformity of the deposited coatings. Finally, the “convective-sedimentation†assembly method was used to deposit composite coatings of live cells and large latex particles as an example of biologically active composite coatings. These coatings were allowed to proliferate and demonstrate a proof-of-concept of a self-cleaning surface. Two methods were developed for the deposition of micro- and nanoparticles into linear assemblies that could be used in biosensors and biomaterials. In capillary-guided deposition, a capillary is withdrawn across a wettable substrate, resulting in the assembly of a particle line. We characterized the effects of particle concentration and withdrawal speed and correlated them to structure of the deposited assemblies. The particles are assembled into one of three different structures, depending on the particle volume fraction and deposition speed. We demonstrate that the metallic nanoparticle lines are Ohmically conductive. Using wedge-templated deposition, linear assemblies were deposited from sessile droplets on moderately hydrophobic surfaces. The particles convectively assemble at the freely-receding three-phase contact line and are pulled into a line against the wedge. The deposited lines can be long and narrow with a few breaks or significantly wider and shorter but unbroken. These methods could be used for engineered patterning of nanoparticle structures on surfaces.