Cell–material interactions are crucial for many biomedical applications, including medical implants, tissue engineering, and biosensors. For implants, while the adhesion of eukaryotic host cells is desirable, bacterial adhesion often leads to infections. Surface free energy (SFE) is an important parameter that controls short- and long-term eukaryotic and prokaryotic cell adhesion. Understanding its effect at a fundamental level is essential for designing materials that minimize bacterial adhesion. Most cell adhesion studies for implants have focused on correlating surface wettability with mammalian cell adhesion and are restricted to short-term time scales. In this work, we used quartz crystal microbalance with dissipation monitoring (QCM-D) and electrical impedance analysis to characterize the adhesion and detachment of S. cerevisiae and E. coli, serving as model eukaryotic and prokaryotic cells within extended time scales. Measurements were performed on surfaces displaying different surface energies (Au, SiO2, and silanized SiO2). Our results demonstrate that tuning the surface free energy of materials is a useful strategy for selectively promoting eukaryotic cell adhesion and preventing bacterial adhesion. Specifically, we show that under flow and steady-state conditions and within time scales up to ∼10 h, a high SFE, especially its polar component, enhances S. cerevisiae adhesion and hinders E. coli adhesion. In the long term, however, both cells tend to detach, but less detachment occurs on surfaces with a high dispersive SFE contribution. The conclusions on S. cerevisiae are also valid for a second eukaryotic cell type, being the human embryonic kidney (HEK) cells on which we performed the same analysis for comparison. Furthermore, each cell adhesion phase is associated with unique cytoskeletal viscoelastic states, which are cell-type-specific and surface free energy-dependent and provide insights into the underlying adhesion mechanisms.

This paper reports a multifunctional platform based on a nanocomposite hydrogel combining poly(ethylene glycol), with rhodamine B‐containing silica nanoparticles (RhB@SiO2), as temperature sensors, and gold nanorods (AuNRs) as plasmonic heaters. This composite material acts as a light‐addressable cellular matrix able to induce 3D temperature gradients locally and dynamically using the localized surface plasmon resonance (LSPR) of AuNRs under near‐infrared (NIR) laser illumination. At the same time, the temperature changes are probed locally by monitoring changes of the RhB@SiO2 NPs fluorescence. As a result of plasmonic heating, and, depending on the preparation protocol, the light‐addressable hydrogel also deforms controllably and reversibly, allowing mechanical and thermal cellular stimulation in a 3D matrix. The hydrogel deformation is quantified by means of inline holographic microscopy. This approach makes it possible to accurately and locally control and simultaneously measure temperature gradients and deformation in soft, 3D deformable materials and will enable novel platforms for studying cellular thermo‐ and mechanobiology.

In this article, we report on the development of a flow cell optimized for the heat‐transfer method, a versatile biosensing technique. The design of the flow cell ensures that the heat flow is focused with minimal heat loss through the surroundings of the cell. This results in a more stable measuring signal and an improved sensitivity of the measuring technique. The sensor was characterized by performing background measurements in air, water, and phosphate buffered saline (PBS) solution. Heat flow through the setup was simulated using COMSOL in order to provide insight in the contribution of convection to the heat flow and recommendations for possible future improvements to the cell. Additionally, a two‐step algorithm for calculating thermal resistance was defined, allowing the user to accurately derive thermal conductivity from experimental data. Finally, the potential of the flow cell for bacteria (Escherichia coli) detection was assessed and compared with the results obtained in the original HTM setup in a similar experiment. This experiment demonstrates that we were able to improve the limit‐of‐detection (LoD) to 2.10 × 104 colony forming units (CFU) mL−1 by changing the geometry of the measuring cell. Sensor setup for thermal biodetection experiments a directed heat flow.

The preparation of gold nanoparticles through reduction of chloroauric acid by trisodium citrate, also known as the Turkevich synthesis, was analyzed both ex situ and in situ. In situ experiments consist of dynamically tracking second and third harmonic light scattering and multiphoton luminescence. By complementing in situ data with ex situ quenching experiments, which enabled further UV−vis−NIR spectroscopy, as well as transmission electron microscopy (TEM) and dynamic light scattering (DLS) characterization, we obtained new insight into the mechanistic process of gold nanoparticle growth. Our results reveal that the growth proceeds through a metastable state of aggregation and offer additional evidence for a sharp transition from metallic molecular cluster to plasmonic nanoparticle behavior in the initial stage of the process. While multiphoton luminescence can be used as a marker for this transition, second and third harmonic scatterings reveal surface and bulk information such as size, shape, and the presence of aggregates.

Understanding microbial adhesion and retention is crucial for controlling many processes, including biofilm formation, antimicrobial therapy as well as cell sorting and cell detection platforms. Cell detachment is inextricably linked to cell adhesion and retention and plays an important part in the mechanisms involved in these processes. Physico-chemical and biological forces play a crucial role in microbial adhesion interactions and altering the medium ionic strength offers a potential means for modulating these interactions. Real-time studies on the effect of ionic strength on microbial adhesion are often limited to short-term bacterial adhesion. Therefore, there is a need, not only for long-term bacterial adhesion studies, but also for similar studies focusing on eukaryotic microbes, such as yeast. Hereby, we monitored, in real-time, S. cerevisiae adhesion on gold and silica as examples of surfaces with different surface charge properties to disclose long-term adhesion, retention and detachment as a function of ionic strength using quartz crystal microbalance with dissipation monitoring. Our results show that short-and long-term cell adhesion levels in terms of mass-loading increase with increasing ionic strength, while cells dispersed in a medium of higher ionic strength experience longer retention and detachment times. The positive correlation between the cell zeta potential and ionic strength suggests that zeta potential plays a role on cell retention and detachment. These trends are similar for measurements on silica and gold, with shorter retention and detachment times for silica due to strong short-range repulsions originating from a high electron-donicity. Furthermore, the results are comparable with measurements in standard yeast culture medium, implying that the overall effect of ionic strength applies for cells in nutrientrich and nutrient-deficient media.