Non-invasive and label-free calorimetry could become a disruptive technique to study single cell metabolic heat production without altering the cell behavior, but it is currently limited by ...insufficient sensitivity. Here, we demonstrate microfluidic single-cell calorimetry with 0.2-nW sensitivity, representing more than ten-fold enhancement over previous record, which is enabled by (i) a low-noise thermometry platform with ultralow long-term (10-h) temperature noise (80 μK) and (ii) a microfluidic channel-in-vacuum design allowing cell flow and nutrient delivery while maintaining a low thermal conductance of 2.5 μW K
. Using Tetrahymena thermophila as an example, we demonstrate on-chip single-cell calorimetry measurement with metabolic heat rates ranging from 1 to 4 nW, which are found to correlate well with the cell size. Finally, we perform real-time monitoring of metabolic rate stimulation by introducing a mitochondrial uncoupling agent to the microchannel, enabling determination of the spare respiratory capacity of the cells.
Thermoregulation has substantial implications for energy consumption and human comfort and health. However, cooling technology has remained largely unchanged for more than a century and still relies ...on cooling the entire space regardless of the number of occupants. Personalized thermoregulation by thermoelectric devices (TEDs) can markedly reduce the cooling volume and meet individual cooling needs but has yet to be realized because of the lack of flexible TEDs with sustainable high cooling performance. Here, we demonstrate a wearable TED that can deliver more than 10°C cooling effect with a high coefficient of performance (COP > 1.5). Our TED is the first to achieve long-term active cooling with high flexibility, due to a novel design of double elastomer layers and high-ZT rigid TE pillars. Thermoregulation based on these devices may enable a shift from centralized cooling toward personalized cooling with the benefits of substantially lower energy consumption and improved human comfort.
Thermal cloaking and camouflage have attracted increasing attention with the progress of infrared surveillance technologies. Previous studies have been mainly focused on emissivity manipulation or ...using sophisticated thermal metamaterials. However, emissivity control is only applicable for objects that are warmer than the environment and lower emissivity is usually accompanied with high reflectance of the surrounding thermal signals if they have nonuniform temperature. Metamaterial‐based thermal camouflage holds great promise but their applications on human subjects are yet to be realized. Direct temperature control represents a more desirable strategy to realize dynamically adjustable camouflage within a wide ambient temperature range, but a wearable, portable, and adjustable thermo‐regulation system that is suitable for human subjects has not been developed. This work demonstrates a wearable and adaptive infrared camouflage device responding to the background temperature change based on the thermoelectric cooling and heating effect. The flexible thermoelectric device can realize the infrared camouflage effect to effectively shield the metabolic heat from skin within a wide range of background temperature: 7 °C below and 15 °C above the ambient temperature, showing promise for a broad range of potential applications, such as security, counter‐surveillance, and adaptive heat shielding and thermal control.
A wearable and adaptive thermal camouflage device is developed. The flexible device is capable of responding to the background temperature change based on the thermoelectric cooling and heating effect, thus achieving thermal camouflage on human skin to effectively shield the metabolic heat from the skin within a wide range of background temperature.
We adopted hollow 3D structures of transparent conducting oxides (TCO) for efficient emission control. TCO has high transmittance in the solar spectrum and tunable optical properties in the infrared ...regime due to their plasmonic property. The IR emissivity can be further adjusted by the geometry. Here, using solid and hollow triangles as an example, we modeled the spectral absorptance of 3D TCO structures with various carrier concentrations and geometrical factors. We showed that hollow triangular structures enhance the spectrally selective absorption, namely, high emittance in IR and low absorptance in the solar spectrum. This is because the large primary sizes of the triangles can interact strongly with the longer wavelength mid-IR while the small wall thickness of the hollow structures reduces the overall absorption volume for the shorter wavelength light in the near-IR and visible regimes. Further, by changing their angles, the hollow features can be used to tune the IR emissivity within a large range (from 0.14 to 0.8). The selective and tunable absorptance of 3D hollow structures of TCO may find applications in passive radiative cooling, solar thermal absorbing, and tunable windows glazing.
Heat is one of the most important aspects of living organisms. Metabolic heat production and evaporative heat dissipation protect warm-blooded animals from adverse weather conditions. Heat management ...devices provide thermal comfort to human by climate control or thermal camouflage effect by blocking heat emission from the human body. Further, metabolism in living organisms can be investigated by monitoring heat signature because the metabolic heat production represents the overall enthalpy change during metabolic reactions in organisms. This dissertation presents two state-of-the-art devices and demonstrates their applications: 1) a wearable thermoelectric device (TED) for personal thermoregulation and camouflage, and 2) high-resolution calorimeter for measurement of single-cell metabolic heat generation. Personalized cooling/heating by TEDs can drastically reduce energy consumption with small cooling volume, meet individual cooling needs and camouflage heat emission from the human body. However, a TED with sufficient flexibility and temperature regulation performance has yet to be realized because of lack of optimization of the thermal and mechanical design. In the first part of the dissertation, we demonstrated a wearable TED that can deliver over 10 °C cooling effect with a high coefficient of performance (COP>1.5). Our TED is the first to achieve long-term active cooling with high flexibility, thanks to a novel design of double elastomer layers embedding an air gap insulation and high-ZT rigid TE pillars. The TED was also applied to thermal camouflage using the large temperature regulation window, which enables to match the heat signature of human body with background temperature. The last part of the dissertation focuses on fundamental study of cellular metabolism using direct calorimetry techique. We developed high-resolution calorimeter sufficient to measure heat generation from a single cell for investigation of heterogeneous metabolic activities. This non-invasive and label-free calorimetry technic is optimized to study the cell metabolic heat production without alter the nature of cells. Our single-cell calorimeter achieved the power resolution as low as 0.6 nW using the innovative one-dimensional microfluidic tube design. Single-cell measurements using the calorimeter revealed that the relationship between metabolic rate and cell size of individual Tetrahymena follows the allometric scaling relationship.
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