Figure 8.

Effects of surfactants and enzymes on fixed P. fluorescens biofilms, as monitored in situ by QCM. (a,b) Time-dependent changes of (a) frequency and (b) dissipation during sequential incubation of a fixed biofilm (immobilized on a gold-coated QCM sensor) with (1) hard water, (2) detergent in hard water (F1), (3) enzymes and detergent in hard water (F1/2), (4) detergent in hard water (F1), (5) hard water, and (6) deionized water, shown in an exemplary result of 2 independent QCM measurements of separate QCM sensors with fixed biofilms. Arrows indicate initial dip in ΔF after ca. 3 min and second prominent dip after 2.5 h. For both ΔF and ΔD, signals from different overtones (n) of the main resonance are shown (squares: n = 3, circles: n = 5, triangles: n = 7, inverted triangles: n = 9, diamonds: n = 11, crosses: n = 13). (c) Plot of the ratio of dissipation and frequency changes over time for the third overtone, representing a measure for the mass-normalized softening of the biofilm surface.