Multichannel QCM-Based System for Continuous Monitoring of Bacterial Biofilm Growth

Quartz crystal microbalance (QCM) sensors are becoming a good alternative to analytical methods for the measurement of bacterial growth in liquid media culture. For this purpose, two essential resonance parameters allow the monitoring of biofilm formation: the series resonance frequency shift and the change of the resistance at this frequency. Nevertheless, several problems arise in determining these parameters, as their relative variation is very small. This means that an accurate procedure must be implemented for the measurement of the QCM resonance parameters, including the automatic calibration of the frequency response effects of the measurement circuits and the automatic compensation of the static electrical capacitance of the QCM. In this article, a novel multichannel system for on-line monitoring of biofilm formation based on QCM sensors is proposed. QCM resonance parameters are determined from the electrical impedance analysis by means of an auto-balanced impedance bridge. This configuration has allowed the implementation of an affordable multichannel measurement instrument. Obtained results, based on binary mixtures of water-glycerol measurements and real microorganism experiments, are in good agreement with the theoretical behavior. These results show the great potential of this instrument to be used for monitoring microbial growth and biofilm formation.