Temperature is a crucial parameter that affects many physical, chemical and biological processes. However, measuring temperature at the nanometer scale, where many of these processes take place, is not an easy task. Conventional thermometers are too bulky and invasive to probe the temperature of nanoscale objects such as cells, molecules or nanomaterials.
Fortunately, scientists have developed a new class of thermometers that can overcome these limitations: nano-thermometers. These are tiny particles that can sense and report temperature changes by emitting light of different colors or intensities. Nano-thermometers can be incorporated into the systems being studied, such as biological tissues, chemical reactions or electronic devices, without disturbing their normal functioning.
How do nano-thermometers work?
Nano-thermometers are based on the principle of luminescence, which is the emission of light by certain materials when they are excited by an external source of energy. The source of energy can be heat, electricity, light or even an electron beam. The luminescent materials used for nano-thermometers are usually doped with rare earth ions, such as europium (Eu3+), which have specific optical properties that depend on temperature.
For example, researchers at the Ulsan National Institute of Science and Technology (UNIST) in South Korea have developed nano-thermometers based on cathodoluminescence (CL) spectroscopy . This technique uses a transmission electron microscope (TEM) to generate an electron beam that excites the nanoparticles doped with europium ions. The nanoparticles then emit light of different wavelengths and intensities depending on their temperature. By measuring the ratio of two emission bands from europium ions, the researchers can calculate the temperature of the nanoparticles with an accuracy of about 4°C and a spatial resolution of 100 nanometers.
Another example is the Thermal Magnetic Imaging and Control (Thermal MagIC) project at the National Institute of Standards and Technology (NIST) in the USA . This project aims to design and build nano-thermometers that can measure temperature changes by using magnetic signals instead of light. The nano-thermometers are composed of magnetic nanoparticles that change their orientation when exposed to a magnetic field. The orientation of the nanoparticles affects their ability to absorb or reflect microwaves, which can be detected by a remote sensing system. The researchers expect to achieve a temperature measurement accuracy of 25 millikelvin and a spatial resolution of 100 micrometers.
What are the applications of nano-thermometers?
Nano-thermometers have a wide range of potential applications in various fields where temperature plays a critical role. Some examples are:
- Medicine: Nano-thermometers can be used to monitor the temperature of living cells and tissues, which can reveal important information about their health and function . For instance, nano-thermometers can help diagnose diseases such as cancer or inflammation, which are associated with abnormal temperature patterns. Nano-thermometers can also be used to control the delivery of drugs or genes to specific cells by triggering their release at a desired temperature.
- Refrigeration: Nano-thermometers can be used to improve the efficiency and performance of refrigeration systems, which rely on phase transitions of fluids or gases at different temperatures . For example, nano-thermometers can help optimize the cooling cycle by detecting the optimal temperature for each phase transition. Nano-thermometers can also help prevent overheating or freezing of components by providing real-time feedback on their thermal state.
- Biology: Nano-thermometers can be used to study the thermodynamics of biological processes at the molecular level, such as enzyme reactions, protein folding or DNA replication . For example, nano-thermometers can help measure the activation energy or entropy changes involved in these processes, which can reveal their mechanisms and kinetics. Nano-thermometers can also help understand how organisms adapt to different thermal environments by measuring their thermal responses.
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