The growth of <i>Pseudomonas aeruginosa</i> PAO1 biofilms on ZnSe internal reflection elements (IREs) was compared with their growth on TiO<sub>2</sub>-coated ZnSe over several days using attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy. The effect of the TiO<sub>2</sub> coating on the IR spectra of reference compounds and cell suspensions was determined to aid in the interpretation of the data. The presence of TiO<sub>2</sub> on the surface of a ZnSe IRE tripled the size of the amide II peak and facilitated the detection of pyoverdin production due to its increased adsorption on the coated surface. A 50% increase in the length of the lag phase was observed for PAO1 growth on TiO<sub>2</sub>-coated surfaces as compared to growth on ZnSe. Biofilms on both surfaces exhibited a growth maximum for all components, followed by restructuring at the surface characterized by a decrease in the signal. The composition of biofilms grown on TiO<sub>2</sub> was relatively constant after the restructuring phase, while the extracellular polymeric substance (EPS) component of the biofilms grown on ZnSe gradually increased. The peak due to the carbohydrate component of EPS was much larger in the spectra of biofilms than in those of planktonic cells. The increase of the pyoverdin signal over time in the spectra of the biofilms on TiO<sub>2</sub> closely followed the overall increase in biomass. However, no signal from pyoverdin was detected in the presence of ferric ions.

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