Steady heat conduction-based thermal conductivity measurement of single walled carbon nanotubes thin film using a micropipette thermal sensor

A micro-pipette thermal sensing technique for measuring the thermal conductivity of non-volatile fluids

This research work demonstrates an innovative technique to measure the thermal conductivity of a small volume of non-volatile liquids. The method utilizes a micro-pipette thermal sensor (MPTS) (tip diameter < 2 μm) and is based on laser point heating thermometry and transient heat transfer. A laser beam is irradiated at the sensor tip immersed in a few microliters of the test fluid and the transient temperature change is recorded with the sensor. This temperature change is dependent on the surrounding fluid's thermal properties, such as thermal conductivity and diffusivity. The numerical solution for transient temperature profile for a point source is obtained using the finite element method in the COMSOL software. To determine the optimizing parameters such as thermal conductivity and power absorbed at the sensor tip, the multi-parameter fitting technique is used in MATLAB, which will fit the COMSOL simulation result with the experimental data. Three liquids with known thermal conductivity were tested to verify that the technique can be used to determine the thermal conductivity with high accuracy, and in addition, the thermal conductivity of growth media and serum used for culturing cancer cells is estimated. With the sensor size of 1-2 μm, we demonstrate the possibility of using this described method as the MPTS technique for measuring the thermal properties of microfluidic samples and biological fluids.

Micromachined Chip Scale Thermal Sensor for Thermal Imaging

The lateral resolution of scanning thermal microscopy (SThM) has hitherto never approached that of mainstream atomic force microscopy, mainly due to poor performance of the thermal sensor. Herein, we report a nanomechanical system-based thermal sensor (thermocouple) that enables high lateral resolution that is often required in nanoscale thermal characterization in a wide range of applications. This thermocouple-based probe technology delivers excellent lateral resolution (∼20 nm), extended high-temperature measurements >700 °C without cantilever bending, and thermal sensitivity (∼0.04 °C). The origin of significantly improved figures-of-merit lies in the probe design that consists of a hollow silicon tip integrated with a vertically oriented thermocouple sensor at the apex (low thermal mass) which interacts with the sample through a metallic nanowire (50 nm diameter), thereby achieving high lateral resolution. The efficacy of this approach to SThM is demonstrated by imaging embedded metallic nanostructures in silica core-shell, metal nanostructures coated with polymer films, and metal-polymer interconnect structures. The nanoscale pitch and extremely small thermal mass of the probe promise significant improvements over existing methods and wide range of applications in several fields including semiconductor industry, biomedical imaging, and data storage.

High-Resolution Mapping of Thermal History in Polymer Nanocomposites: Gold Nanorods as Microscale Temperature Sensors

A technique is reported for measuring and mapping the maximum internal temperature of a structural epoxy resin with high spatial resolution via the optically detected shape transformation of embedded gold nanorods (AuNRs). Spatially resolved absorption spectra of the nanocomposites are used to determine the frequencies of surface plasmon resonances. From these frequencies the AuNR aspect ratio is calculated using a new analytical approximation for the Mie-Gans scattering theory, which takes into account coincident changes in the local dielectric. Despite changes in the chemical environment, the calculated aspect ratio of the embedded nanorods is found to decrease over time to a steady-state value that depends linearly on the temperature over the range of 100-200 °C. Thus, the optical absorption can be used to determine the maximum temperature experienced at a particular location when exposure times exceed the temperature-dependent relaxation time. The usefulness of this approach is demonstrated by mapping the temperature of an internally heated structural epoxy resin with 10 μm lateral spatial resolution.

A high precision apparatus for intracellular thermal response at single-cell level

In this work, a nanoprobe that is highly thermo-sensitive to tiny temperature changes was prepared based on a thermocouple metal junction. A series of electro-element apparatuses were integrated to accomplish single-cell temperature measurement. The temperature measurement probe (TMP) was constructed by tungsten (W), polyurethane (PU), and platinum (Pt). The tip size of TMP was characterized at less than 500 nm, and the tip angle was between 10 and 20° with the resistance in the range of 500 to 1500 Ω. The single-cell temperature measurement probes were calibrated and calculated with a Seebeck coefficient ranging from 6 to 8 μV °C(-1) at a precision of 0.1 °C. Monitoring the temperature at a single-cell level by inserting the TMP in marine lung epithelia (MLE)-12 cells displayed that the stimulation of lipopolysaccharide (LPS) and cobalt chloride induced different single-cell temperature fluctuation. This investigation could help reveal complex cellular functions and develop novel diagnoses.