GoKawiilA cancer cell (nucleus in blue, cellular ‘skeleton’ in green). Scientists have devised nanosensors that can measure the temperature inside cancer cells, including the cell nuclei.Credit: Howard Vindin, The University of Sydney/Science Photo Library
To check your temperature, doctors place a thermometer under your tongue. Researchers have now created a thermometer small enough to check the temperature of a single living cell, and even individual cellular regions, such as the nucleus. Once refined, similar technologies could help scientists to study metabolism and other chemical reactions of life on the smallest scale. The work was reported last Wednesday in Science Advances1.
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Before now, the best cell thermometers were nanodiamonds with defects known as nitrogen-vacancy centres. But each diamond is slightly different, meaning that readings are not consistent across sensors.
The authors of the new paper created an alternative: molecular quantum nanosensors. The team embedded molecules of a hydrocarbon compound called pentacene into a crystal. Then they tumbled the crystal to break it into smaller particles, coating them in a polymer during this process to prevent clumping and maintain their safety to cells. The final sensors were either 200 or 500 nanometers across, a small fraction of the diameter of a human red blood cell.
These sensors are considered quantum because their behaviour depends on ‘superpositions’ between particular quantum states of the pentacene molecules’ electrons — that is, the electrons are occupying multiple states at once.
Green light, red light
Shining green lasers at the sensors made them glow red. But simultaneously stimulating the sensors with microwaves at certain frequencies slightly dimmed their glow. The temperature of the sensors’ surroundings (and, by extension, the sensors themselves) affects the dim-inducing frequency. The authors worked out the precise relationship between the frequency that triggered dimming and temperature, allowing them to infer one from the other.
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To get the sensors inside cells, the scientists either bathed cancer cells in solutions containing the sensors until they were absorbed or injected them into the nuclei. The team then applied their laser-and-microwave system to the sensors and noted which frequencies of microwaves caused them to dim, an index of cellular temperature.