(358a) Directed Dielectrophoretic Assembly of Thin Highly Organized Photoreactive Biocoatings of Cyanobacteria

Authors: 
Bernal, O. I., North Carolina State University
Flickinger, M. C., Golden LEAF Biomanufacturing Training and Education Center (BTEC)
Velev, O. D., North Carolina State University



The use of dielectrophoresis (DEP) for the fabrication of monolayer coatings of photoreactive cyanobacteria and adhesive polymers on flexible polyester sheets is being investigated to optimize photoreactivity, gas transport, light scattering and self-shading in future thin coating photobioreactors by precisely controlling cell packing and orientation. DEP is being used to fabricate 1-cell thick coatings of Synechococcus PCC 7002 to study light absorption and scattering, cell packing, and reactivity after drying and rehydration. This organism can be genetically modified to produce fuel precursors from CO2 with simultaneous energy capture from sunlight and O2 production. Adhesion is triggered by priming a surface-activated polyester substrate with a layer-by-layer (l-b-l) assembled film of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonic acid) (PSS) [general composition (PAH-PSS)3PAH]. The effects of voltage, frequency, electrolyte concentration and pH during the DEP assembly demonstrate the means to fabricate viable chains and monolayers of Synechococcus in suspension, and deposit on polyelectrolyte-coated polyester sheets permanent ordered biocoatings that remain aligned after the electric field is turned off. Photoreactivity (measured as reflectance, absorptance and transmittance using an integrating sphere) of DEP coatings of Synechococcus PCC 7002 show significantly decreased light scattering and enhanced transmittance indicating reduced self-shading compared to suspension cultures. Analysis of confocal laser scanning microscopy (CLSM) images allows accurate measurement of cell dimensions for predicting optimal cell packing density and for electrostatic simulations of chain assembly. Numerical simulations of chain and monolayer assembly in suspension show that field intensity is strongest between adjacent cells in chains and drives chains together to form monolayers. Total electrostatic energy calculations predict energetically favorable intermediate cell ordering motifs and reveal mechanisms of coating assembly by comparing simulation results with experimental observations. Future work will be focused on microstructure characterization of the DEP coatings, development of methods for photoreactivity analysis and development of layer-by-layer (l-b-l) DEP-based methods for fabrication of multi-layered coatings combining different types of photosynthetic organisms. These methods will be used to construct highly reactive, robust, structured cellular biomimetic materials capable of being dried and when rehydrated harvest light in a broad range of wavelengths and remain reactive for 1000s of hours.