Monitoring of the Viscoelastic Behaviour of Bacterial Biofilms Exploiting an Accurate QCM System

The presence of bacteria forming biofilm is pervasive in our daily life and may lead to beneficial effects or, more frequently, to adverse consequences. The monitoring of the biofilm formation process and of the related physical parameters, is essential not only for the investigation of the biofilm internal structure but also because it offers the possibility to take prompt actions to either control or counteract the growth process. In this paper the measurement problem related to the real-time monitoring of biofilm growth through Quartz Crystal Microbalance (QCM) is analyzed. After a theoretical analysis, experimental data are discussed, consisting in the long-term monitoring of the activity of Pseudomonas fluorescens bacteria. The developed prototype measurement system is based on a Mecham bridge oscillator topology and allows to accurately monitor the quartz resonance frequency and the motional resistance in real time. In particular, the bacteria adhesion process, the biofilm growth and the complex impact which has on the QCM response, related to the soft particles and media attached on the quartz surface is analyzed. The presented results demonstrate the suitability of the developed system for this kind of applications. The excellent stability and frequency resolution of the measurement system allows for the analysis of biological processes and is a useful tool for collecting information concerning the physical characteristics of the observed biological media.