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

Effect of micelles and reverse micelles on nonlinear optical properties of potassium dichromate and Staphylococcus aureus treatment

© 2020 Elsevier B.V. Potassium dichromate (KD) is a common inorganic pigment used as a photosensitizer (PS) for photodynamic therapy (PDT). Numerous works in this area have so far reflected on organic dye and its colloidal system with linear absorption in PDT, while a few studies have been completed on potentials of nonlinear absorption (NLA) of inorganic KD for this type of treatment. Therefore, absorbance, nuclear magnetic resonance (NMR), and nonlinear optical (NLO) properties of KD and its formulations were described in detail. The pigment was also found to be positioned within the inner part of the droplet prepared with water, oil, and surfactant. The impact associated with the length of hydrocarbon-chain of anionic surfactant micelles and reverse micelles (RMs) on the NLO properties of KD was further investigated. The results revealed that the pigment had more interactions with the micelles prepared with a small-length-scale surfactant. The NLA and the second-order hyper-polarizabilities of KD were correspondingly proportional to the size of the RMs in an inverse manner. Moreover, encapsulation of the pigment in the RMs led to a reduction in the aggregation of the pigment and subsequently increased their NLA. Quantum calculations have been done to achive optimized geometry, dipole moment and band gap of KD and dimer of KD (2KD). It was demonstrated that using KD in a smaller size of RMs as PSs along with NLA via laser irradiation (LI) could be a very efficient method for treatment of Staphylococcus aureus (S.aureus)