Ellipsometric Measurement of Bacterial Films at Metal-Electrolyte Interfaces

Abstract

Ellipsometric measurements were used to monitor the formation of a bacterial cell film on polarized metal surfaces (Al-brass and Ti). Under cathodic polarization bacterial attachment was measured from changes in the ellipsometric angles. These were fitted to an effective medium model for a nonabsorbing bacterial film with an effective refractive index (nf ) of 1.38 and a thickness (df ) of 160 ± 10 nm. From the optical measurements a surface coverage of 17% was estimated, in agreement 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 formation was observed, which was assigned to the decrease in oxygen concentration due to the presence of bacteria. It is shown that the irreversible adhesion of bacteria to the surface can be monitored ellipsometrically. Electrophoretic mobility is proposed as one of the factors determining bacterial attachment. The high sensitivity of ellipsometry and its usefulness for the determination of growth of interfacial bacterial films is demonstrated.

New evidences on the catalase mechanism of microbial corrosion

“…The pre-oxidation treatment applied to the electrode surface should lead to the formation of a Cu 2 O film [26]. However, when chloride ions are present, as in the case here, Cu 2 O dissolves and a film rich in Cu(II) compounds is preferentially formed [24].…”

Reversible Binding of Metal Ions onto Bacterial Layers Revealed by Protonation-Induced ATR-FTIR Difference Spectroscopy

“…On the basis of the diamond refractive index ( n 1 = 2.4), the incidence angle (α = 45°) and the refractive index of bacterial cells ( n 2 ) estimated to be around 1.39, , the penetration depth ( d p ) of the evanescent wave at 1750 cm −1 (λ = 5.7 μm) and 1000 cm −1 (λ = 10 μm) is approximately 0.9 and 1.6 μm, respectively, as arises from application of the following equation: d p = normalλ 2 normalπ false[ n 1 2 sin 2 normalα − n 2 2 false] 1 / 2 …”

Elucidation of Functional Groups on Gram-Positive and Gram-Negative Bacterial Surfaces Using Infrared Spectroscopy

“…d p is given by where θ is the angle of incidence, λ is the wavelength of the infrared radiation, and n s and n c are refractive indices of sample and the ATR crystal, respectively. For example, the penetration depth for bacterial cells ( n s ∼ 1.39) in contact with a Ge ATR crystal ( n c = 4.0) that accepts the incident infrared beam at 60° is 339 nm at 1000 cm -1 and 188 nm at 1800 cm -1 . It should be noted that this is 1/e depth, and the absolute penetration of the evanescent wave can be greater than these estimates.…”