A Novel Apparatus for Measuring the Interfacial Shear Rheology of Biofilms while Measuring the Concentration of Redox Species in the Growth Media

This project discuses the design of a novel apparatus for measuring the interfacial rheological properties of a complex interface while measuring the concentration of redox species within the sub-phase. Preliminary measurements made using the apparatus are also presented. The objective of the preliminary experimentation was to simultaneously measure the interfacial shear rheology of Pseudimonas aeruginosa biofilm, while continuously measuring the concentration of pyocyanin (PYO) within the growth media using scanning electrochemical microscopy (SECM). The DWR-SECM apparatus described in this thesis allows for interfacial rheological measurements to be taken simultaneously with electrochemical concentration measurements in the sub-phase. In the case of P. aeruginosa, the interfacial rheological properties remain constant at low concentrations of PYO in the growth media. During the first 24 hours of growth, the PYO concentration rapidly increases. After 24 hours of biofilm growth, the PYO concentration becomes constant. Over the following 72 hours, both the interfacial storage and interfacial loss modulus increase two orders of magnitude or more. The large increase in the interfacial moduli of the biofilm shows a general trend consistent with other quorum-sensing, biofilm-growth patterns, as P. aeruginosa does not begin production of biofilm until a high enough concentration of quorum sensing molecules are detected within the growth media. Key Words: rheology, interfacial rheology, P. areguniosa, biofilm, pyocyanin, scanning electrochemical microscopy, SECM