Ionic strength tunes yeast viscoelasticity and promotes trace-level cell detection

QCM‐D Viscoelastic and Adhesion Monitoring Facilitate Label‐Free and Strain‐Selective Bacterial Discrimination

“…The composition and dimensions of the sensor chips are specified in previous work. [23,40] The gold-and SiO 2 -coated crystals were cleaned by first exposing them to UV-ozone (UVO-Cleaner, Jelight Company Inc., CA, USA) for 15 min and 30 min, respectively. Afterward, the SiO 2 -coated chips were washed with 1% sodium dodecyl sulfate (SDS) solution (Sigma-Aldrich, Diegem, Belgium) and autoclave-sterilized Milli-Q water (resistivity 18.2 MΩcm at 25 °C).…”

“…Buffer solutions of various ionic strengths (0-299 mM) were prepared by serial dilutions of 10 Â PBS (1,491 mM, pH 7.4) in Milli-Q water. [23,40] To prepare 10 Â PBS, a mixture of 37.7 g NaCl (>99% purity), 4.4 g Na 2 HPO 4 (>99%), and 1 g KH 2 PO 4 (>99% purity) was dissolved in 500 mL of Milli-Q water and sterilized by autoclaving. All chemicals were purchased from Sigma-Aldrich (Overijse, Belgium).…”

“…Resazurin was prepared as described in the previous studies. [23,55] As a measurement principle, metabolically active bacteria reduce the blue resazurin solution to pink resorufin. Thus, the rate of resazurin conversion positively correlates with cell metabolic activity, and therefore cell viability.…”

“…While this difference is relatively small, the result is consistent with a similar study on yeast, which showed much larger differences in yeast resazurin reduction in 0 mM buffer compared to ion-rich buffers. [23] Figure 8f compares the fluorescence for cells in various ionic strengths and control samples, consisting of solutions of different ionic strengths (0, 149, and 299 mM) without cells. The control samples show similar fluorescence signals over the entire 4 h measurement time, proving that the salt concentration did not affect the results of the metabolic activity experiments.…”

“…[ 22 ] The ability to provide 3D information accurately is further enhanced by the availability of multiple overtones of the fundamental frequency and dissipation signals, with each overtone sensitive to events at different heights above the adhesion‐sensor surface. [ 23 ] Also, recent forms of the QCM‐D device allow for multiplex monitoring, using multiple flow cells, thus making simultaneous replicate monitoring of adhesion of treated and control samples possible. Furthermore, QCM‐D is label‐free, minimally invasive, and various physicochemical parameters, such as temperature, pH, and ionic strength, can easily be tuned during measurements.…”