Poster Presentation 1B-59

Activity and Lifetime of Urease Immobilized using Layer-by-Layer Nano Self-assembly on Silicon and Polydimethylsiloxane Microchannels

Scott R. Forrest, Wen Jie, Bill B. Elmore, James D. Palmer^*

Louisiana Tech University

Chemical Engineering Program

600 W. Arizona, P.O. Box 10348 TS

Ruston LA 71272

Phone: (318)257-2885

Fax: (318)257-2562

E-mail: jpalmer@coes.latech.edu

Urease enzyme was immobilized and layered onto the walls of silicon and polydimethylsiloxane (PDMS) microchannels. Silicon microchannels were produced using Inductive Coupling Plasma, resulting in high aspect ratio vertical sidewalls. PDMS microchannels were fabricated on silicon wafer molds. Enzyme immobilization was performed using layer-by-layer nano self-assembly. Alternating layers of oppositely charged polyelectrolytes, with a single enzyme layer “sandwiched” between them, were deposited on to the walls of the silicon microchannels. The polycations used were poly(ethylenimine) (PEI) and poly(allylamine) (PAH). The polyanions used were poly(styrenesulfonate) (PSS) and poly(vynilsulfate) (PVS). A urease concentration of 1 g/L was passed through the silicon channels with immobilized enzyme at various residence times to determine activity. Effluent concentration was measured using a UV/Vis spectrometer by monitoring the absorbance of a pH sensitive dye. PEI/PSS/PEI/Urease/PEI has demonstrated superior performance over other architectures tested. Urea conversions of over 80% were achieved with a residence time of 63 seconds on the first day of operation and 21 minutes after 11 days of operation. A first order rate constant was regressed from the data at every day tested, and the decrease in activity was fitted to an exponential decay model.