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Calorimetry is the study of heat changing in a sample, and a differential scanner is a machine that measures this difference. Individual substances react differently to the addition of heat, so the differential scanning calorimetry technique can be used to identify the components of a sample. Uses of the differential scanning calorimetry method include testing biological samples like cerebrospinal fluid for the presence of proteins of medical interest.
Atoms stick together to form molecules using bonds made of energy. Heat is a form of energy that can break down, or "denature" these bonds. Individual substances begin to break down at a specific level of added heat energy. Scientists call this change in state a "phase transition."
The most commonly known example of phase transitions in everyday life is that of water. Once water loses heat in a freezer to reach freezing point, its liquid phase transitions into a solid phase, which is ice. On the other hand, when water reaches boiling point, its liquid phase transitions into a gas phase. The amount of heat that a substance can absorb before changing phase or breaking down is specific to that molecule, and if a machine is sensitive enough, it can identify these molecules through their reaction to heat.
A machine that uses differential scanning calorimetry to test samples needs to be able to add heat to the sample and also to keep track of the temperature and phase of the sample. The technique requires a reference sample to compare the heat readings of the sample to ensure accuracy, and the analyst that performs the differential scanning calorimetry test also usually tests what is called a blank. Often, a blank merely contains the liquid that the sample is dissolved in, so it can be subtracted from the sample for a more sensitive result.
Only a small amount of sample is generally needed for differential scanning calorimetry testing. This can be as little as 1 milliliter of liquid sample, which the analyst places into a tiny container called a cell; this, along with other cells containing the blank and the reference sample, are then loaded into the machine. The machine then adds heat energy to the three individual tests, which can be provided by increasing pressure inside the machine to heat the samples up.
Each result from the machine needs to be interpreted in comparison to the reference sample, so the analyst can see how much heat energy the unknown sample can absorb before breaking down. The technique can be sensitive enough to identify different biological molecules in a medical sample. If these molecules are associated with disease, whether through their presence or their levels, then this information can then be used to help diagnose disease.
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