ELLIPSOMETRIC MEASUREMENT OF BACTERIAL FILMS AT METAL-ELECTROLYTE INTERFACES

Ellipsometric measurements were used to monitor the formation of a bac terial cell film on polarized metal surfaces (Al-brass and Ti). Under cathodic polarization bacterial attachment was measured from changes i n the ellipsometric angles. These were fitted to an effective medium m odel for a nonabsorbing bacterial film with an effective refractive in dex (n(f)) of 1.38 and a thickness (d(f)) of 160 +/- 10 nm. From the o ptical measurements a surface coverage of 17% was estimated, in agreem ent with direct microscopic observations. The influence of bacteria on the formation of oxide films was monitored by ellipsometry following the film growth in situ. a strong inhibition of metal oxide film forma tion was observed, which was assigned to the decrease in oxygen concen tration due to the presence of bacteria. It is shown that the irrevers ible adhesion of bacteria to the surface can be monitored ellipsometri cally. Electrophoretic mobility is proposed as one of the factors dete rmining bacterial attachment. The high sensitivity of ellipsometry and its usefulness for the determination of growth of interfacial bacteri al films is demonstrated.