Non-Interventional and High-Precision Temperature Measurement Biochips for Long-Term Monitoring the Temperature Fluctuations of Individual Cells

Abstract

Monitoring the thermal responses of individual cells to external stimuli is essential for studies of cell metabolism, organelle function, and drug screening. Fluorescent temperature probes are usually employed to measure the temperatures of individual cells; however, they have some unavoidable problems, such as, poor stability caused by their sensitivity to the chemical composition of the solution and the limitation in their measurement time due to the short fluorescence lifetime. Here, we demonstrate a stable, non-interventional, and high-precision temperature-measurement chip that can monitor the temperature fluctuations of individual cells subject to external stimuli and over a normal cell life cycle as long as several days. To improve the temperature resolution, we designed temperature sensors made of Pd–Cr thin-film thermocouples, a freestanding Si3N4 platform, and a dual-temperature control system. Our experimental results confirm the feasibility of using this cellular temperature-measurement chip to detect local temperature fluctuations of individual cells that are 0.3–1.5 K higher than the ambient temperature for HeLa cells in different proliferation cycles. In the future, we plan to integrate this chip with other single-cell technologies and apply it to research related to cellular heat-stress response.

Thermal Probing Techniques for a Single Live Cell

“…In sharp contrast, if the same TFTC was made on a 400 nm thick, freestanding Si 3 N 4 thin-film, and the same measurement was repeated, the local temperature increment was 30 times higher than that on the Si wafer. Similarly, a local temperature increment peak was recorded at a focal point of an incident laser beam up to 2400 K, which was 100 times higher than that measured with the same sensors made on thick Si wafers [ 88 ]. The large difference measured in the sensitivity of the same TFTC sensors was attributed to the dissipation effect of heat.…”

“…The development of a freestanding Si 3 N 4 thin-film window platform significantly improved the thermal sensitivity of the built-in micro-TC arrays for sensing individual cells. Recently, Han et al applied such a platform and observed local temperature increments of individual HeLa cells in the range of 10–50 mK [ 88 ].…”

“…When sensing the temperature of a single cell, the micro-/nano-TFTC produces a DC voltage in the sub-microvolt to a few microvolt range [ 21 , 88 ], so the measurement system requires a nanovoltmeter. A multiplexer that offers an opening operation through measurement of the sensors on a time scale in a controlled manner is required for multiple sensors, such as an array of 100 TFTC sensors [ 77 , 81 ].…”

“…Later, Li et al improved on this strategy, achieving near-real-time 2D mapping of the local temperatures of the region under test with a delay of only a few seconds [ 81 ]. This is very helpful for monitoring the temperature of a single cell, as it has been shown that a cell changes its temperature at a slow rate of tens of minutes [ 21 , 88 ]. A near-real-time 2D map of the temperatures within a single cell, for example, may provide valuable clues for understanding the dynamic biochemical reactions inside the cell, or may provide criteria for modifying the parameters of an ongoing experiment.…”

“…The surface of the sensors and substrate can then be covered with a proper oxide layer of a few nanometers in thickness. In other cases, modifying these surfaces with a molecular layer of organic material may be the best option [ 88 ].…”