A pico calorimeter with a highly sensitive sensor for detecting heat from a biological cell is developed and evaluated, and also the heat detection of a single brown fat cell has been demonstrated. The measurement principle relies on resonant frequency tracking of a resonator in temperature variation due to the heat from the sample; the resonator is placed in vacuum, and heat is conducted from the sample in the microfluidic channel via a heat guide. This configuration can prevent heat loss from the resonator to the surroundings and damping in water. The heat resolution of the fabricated sensor is 5.2 pJ. Heat emissions from single cells are detected as pulsed or continuous in the absence and presence of stimulation, respectively.

A highly sensitive thermometer system for a living cell is proposed, fabricated, and evaluated. The system possesses a resonant thermal sensor surrounded by vacuum in a microfluidic chip. The measurement principle relies on resonant frequency tracking of the resonator in temperature variations due to the heat from a sample cell; the heat is conducted from the sample cell in the microfluidic channel via a heat guide connecting the resonator to a sample stage. This configuration can reduce heat loss from the resonator to the surroundings and damping in water. Two types of resonators are prepared, i.e., a cantilevered resonator and a double-supported resonator. The resonator sizes as a sensor are 30 × 50 × 1.5 μm in the cantilevered resonator, 30 × 75 × 0.40 μm in the double-supported one, respectively. The temperature and thermal resolutions of 79 μK and 1.90 nW, respectively, are achieved using the double-supported resonator. Two types of heat emissions from single brown fat cells are detected; one is continuous heat generation in the presence of chemical stimulation by a norepinephrine solution, and the other is pulsed without any stimulation.

Mammalian cells must produce heat to maintain body temperature and support other biological activities. Methods to measure a cell's thermogenic ability by inserting a thermometer into the cell or measuring the rate of oxygen consumption in a closed vessel can disturb its natural state. Here, we developed a noninvasive system for measuring a cell's heat production with a bimaterial microcantilever. This method is suitable for investigating the heat-generating properties of cells in their native state, because changes in cell temperature can be measured from the bending of the microcantilever, without damaging the cell and restricting its supply of dissolved oxygen. Thus, we were able to measure increases in cell temperature of <1 K in a small number of murine brown adipocytes (n = 4-7 cells) stimulated with norepinephrine, and observed a slow increase in temperature over several hours. This long-term heat production suggests that, in addition to converting fatty acids into heat energy, brown adipocytes may also adjust protein expression to raise their own temperature, to generate more heat. We expect this bimaterial microcantilever system to prove useful for determining a cell's state by measuring thermal characteristics.

This paper reports the piezoresistive performance of the two-dimensional (2D) material of vanadium (V)-doped molybdenum disulfide (MoS2) films based on sulfurization of sputtered Mo thin films. I–V characteristics indicate that V atom doping indeed decreases the resistivity of MoS2. Strain sensors based on V-doped MoS2 resistive elements were fabricated. By using a four-point bending method, a gauge factor (GF) of 140 under compressive and tensile strain conditions was obtained. The piezoresistive effect of V-doped MoS2 with different V sputtering conditions was also investigated. The doping method introducing V atoms as dopants is found to play an important role in enhancing piezoresistive performance.

This review presents two types of cantilever beams employed as highly sensitive temperature sensors. One type is fabricated from composite materials and is operated in the deflection mode. The second type, used as a temperature sensor and presented in this review, is a resonant cantilever beam. The materials used for the fabrication of the bimaterial cantilever beam are silicon or silicon nitride and thin metallic films such as gold or aluminum. When the temperature changes, the different coefficients of thermal expansion of the metal and silicon cause the sensor to deflect. Considering the models of temperature measurement for biological cells, the heat should be applied locally at the tip of the cantilever beam. Formulas for the calculation of the deflection as a function of incident power applied at the free end of the cantilever beam operated in a liquid are presented in this review. The natural convective heat transfer coefficient was estimated by using the mathematical model and experimental values. For biological applications, the cantilever beam temperature sensor was operated in a liquid, and the heat transfer coefficients were between 381 and 642 W/m 2 K when the temperature applied to the cantilever's free end varied from 28 to 71.8 • C. The resonant cantilever beam was also demonstrated as a sensitive temperature sensor for biological applications. As a thermogenic sample, brown fat cells (BFCs), which are related to metabolic heat production, are employed. The working principle of the resonator cantilever beam temperature sensor is based on the shift in resonant frequency in response to temperature changes. The resonant frequency and the temperature coefficient were 960 kHz and 22.0 ppm/K, respectively. The measurements were performed by stimulating the activity of BFCs by flowing a norepinephrine (NE) solution (1 μM).