The study of cell proliferation is of great importance for medical and biological research, as well as for industrial applications. To render the proliferation process accurately over time, real-time cell proliferation assay methods are required. This work presents a novel real-time and label-free approach for monitoring cell proliferation by continuously measuring changes in thermal properties that occur at the sensor interface during the process. The sensor consists of a single planar resistive structure deposited on a thin foil substrate, integrated at the bottom of a cell culture reservoir. During measurement, the structure is excited with square wave current pulses. Meanwhile, the temperature-induced voltage change measured over the structure is used to derive variations in the number of cells at the interface. This principle is demonstrated first by performing cell sedimentation measurements to quantify the presence of cells at the sensor interface in the absence of cell growth. Later, cell proliferation experiments were performed, whereby parameters such as the available nutrient content and the cell starting concentration were modified. Results from these experiments show that the thermal-based sensor is able to accurately measure variations in the number of cells at the interface. Moreover, the influence of the modified parameters could be observed in the obtained proliferation curves. These findings highlight the potential for the presented thermal method to be incorporated in a standardized well plate format for high-throughput monitoring of cell proliferation.

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This work explores the feasibility of coupling two different techniques, the impedance and the transient plane source (TPS) principle, to quantify the moisture content and its compositional parameters simultaneously. The sensor is realized directly on textiles with the use of printing and coating technology. Impedance measurements use the fluid's electrical properties, while the TPS measurements are based on the thermal effusivity of the liquid. Impedance and TPS measurements show equal competency in measuring the fluid volume with a lowest measurable quantity of 0.5 μL, enabling ultralow volume passive measurements for sweat analysis. Both sensor principles were tested by monitoring the drying of a wet cloth and the measurements show perfect repeatability and accuracy. Nevertheless, when the biofluid property changes, the TPS sensor does not reflect this information on its readings, whereas, on the other hand, impedance can provide information on compositional changes. However, since the volume of the fluid changes simultaneously, one cannot differentiate between a volume change and a compositional change from impedance measurements alone. Therefore, we show in this work that we can apply impedance to measure the compositional properties; meanwhile, the TPS measurements accurately carry out volume measurements irrespective of the interferences from its compositional variations. To prove this, both of these techniques are applied for the quantification and composition monitoring of sweat, showing the capability to measure moisture content and compositional parameters simultaneously. TPS measurements can also be an indicator of the local temperature of the medium confined by the sensor, and it does not influence the fluid parameters. Compiling both impedance and thermal sensors in a single platform triggers smart wearable prospects of metering the liquid volume and simultaneously analyzing other compositional changes and body temperature. Finally, the repeatability and stability of the sensor readings and the washability of the device are tested. This device could be a potential sensing tool in real-life applications, such as wound monitoring and sweat analysis, and could be a promising addition toward future smart wearable sensors.