Thermal conduction is the transport of energy due to random molecular motion across a temperature gradient. This property is vital as it governs every heat transfer problem in engineering and basic science research. As such, there has been rapid development of technology particularly with a focus on heat transfer in nanostructures, wires, and macromolecules. For instance, for one to understand a biological reaction in living cells and transport of thermal energy in biological systems, measurement of temperature and thermal properties is important. Previous research in the field reveals that thermal characterization of cells is vital to obtain critical knowledge for screening, diagnostics, basic and clinical science, and the pharmaceutical industry. At present, there are several thermal-analysis techniques available for measuring the thermodynamic and thermophysical properties of biological samples. However, temperature change within the cells is usually small. Moreover, such temperature change is transient due to the thermo-influence by the extracellular environment, making temperature change difficult to measure using conventional temperature detection methods.
Some techniques incorporate a thermal couple (25μm) or sensor to improve efficiency. However, the accuracy of such technique is questionable due to the sensor size. Specifically, measurement of transient temperature remains to be confirmed for the development of micro-thermocouple sensors of size 2μm to 20μm. Consequently, a much more precise and faster-response technique is required to measure intracellular transient temperature changes in real-time. In this regard, University of North Texas researchers: Ramesh Shrestha (PhD), Rohini Atluri (PhD candidate), Professor Denise Perry Simmons, and Professor Tae-Youl Choi in collaboration with Professor Dongsik Kim at POSTECH in South Korea developed a novel technique that utilizes a laser point heat source for temporal temperature rise in a micro-pipette thermal sensor. Specifically, they proposed a technique that could characterize heat conduction of a measured sample, the Jurkat cell, thus measuring the sample’s thermal conductivity. Their work is currently published in the research journal, International Journal of Heat and Mass Transfer.
In their approach, the research team incorporated the computational model in COMSOL to solve for the transient temperature and used the multi-parameter fitting of the experimental data using MATLAB. To address the influence of a Jurkat cell’s chemical composition on thermal conductivity (TC), the researchers compared three structural models for prediction of effective TC in heterogeneous materials thereby determining the weight percentage of the Jurkat cell. Lastly, they validated the accuracy of the measurement technique, itself, by measuring polyethylene microspheres and observed 1% deviation from published data.
The authors reported that when considering water and protein as the major constituents, they found that a combination of Maxwell-Euken and Effective Medium Theory modeling provided the closest approximation to published weight percent data and, therefore, was recommended for prediction of the cell composition. Moreover, following their approach, thermal conductivity for the microsphere was determined to be 0.327 W/(mK) by the MPTS technique with reproducibility of 98% and accuracy with less than 1% error, in good agreement with the published data.
In summary, the study presented a new characterization technique for measuring the thermal properties of a single biological cell. The study further demonstrated the validity of the MPTS technique in measuring the spherical microparticles by measuring industry standard polyethylene microspheres. Remarkably, the presented technique was reported to be mechanically non-invasive for characterization of thermal conductivity of microscale materials. In a statement to Advances in Engineering, Professor Tae-Youl Choi explained their developed thermal conductivity measurement using the MPTS is a unique technique for the characterization of thermal properties and temperature measurement of microspheres and single biological cells. This work was supported by National Science Foundation (award number: 1906553).
R. Shrestha, R. Atluri, D.P. Simmons, D.S. Kim, T.Y. Choi. Thermal conductivity of a Jurkat cell measured by a transient laser point heating method. International Journal of Heat and Mass Transfer: volume 160 (2020) 120161.