Differential scanning calorimetry measures the change in heat in a sample to identify its components, including biological molecules in medical samples. Heat can break bonds and cause phase transitions, which vary for each molecule. The technique requires a reference sample and a blank, and only a small amount of sample is needed. Results are interpreted against the reference sample to identify the unknown sample’s heat absorption before breaking. This information can be used to diagnose diseases.
Calorimetry is the study of the change in heat 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 technique of differential scanning calorimetry can be used to identify the components of a sample. Uses of the differential scanning calorimetry method include analyzing biological samples such as cerebrospinal fluid for the presence of proteins of medical interest.
Atoms join together to form molecules using bonds made of energy. Heat is a form of energy that can break, or “denature” these bonds. Individual substances begin to degrade at a specific level of added heat energy. Scientists call this change of state a “phase transition.”
The best known example of phase transitions in everyday life is that of water. Once water loses heat in a freezer to reach its freezing point, its liquid phase turns into a solid phase, which is ice. On the other hand, when water reaches its boiling point, its liquid phase changes into a gaseous phase. The amount of heat 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 by their reaction to the heat.
A machine that uses differential scanning calorimetry to test samples must be able to add heat to the sample and also 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 performing the differential scanning calorimeter test usually also tests for what is called a blank. Often, a blank simply contains the liquid in which the sample is dissolved, so it can be subtracted from the sample for a more sensitive result.
Generally only a small amount of sample is 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; these, together with other cells containing the blank and the reference sample, are then loaded into the machine. The machine then adds thermal energy to the three individual tests, which can be supplied by increasing the pressure within the machine to heat the samples.
Each result of the machine must be interpreted against the reference sample, so that the analyst can see how much heat energy the unknown sample can absorb before breaking. The technique can be sensitive enough to identify different biological molecules in a medical sample. If these molecules are associated with the disease, either by their presence or levels, then this information can be used to help diagnose the disease.
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