Microcalorimetry

Microcalorimetry comprises techniques that measure the heat released or absorbed by processes occurring in tiny samples. By detecting heat changes on the microjoule to millijoule scale, it provides direct, label-free information about reaction energetics, binding, adsorption, phase transitions, and metabolic or cellular activity. The field includes instruments designed for high sensitivity and real-time data, operating under isothermal conditions or during controlled heating and cooling.

Principles and instrumentation: A microcalorimeter compares a sample cell with a reference cell, maintaining thermal conditions and recording the differential heat flow as a function of time or temperature. The signal is a heat-flow rate, which can be integrated to obtain the heat exchanged (enthalpy) and analyzed to derive kinetic or thermodynamic parameters such as rate constants, binding enthalpies, or heat capacities. Calibration with standard reactions ensures accuracy and absolute heat measurements.

Techniques and applications: Isothermal microcalorimetry measures heat flow at constant temperature and is widely used to study enzyme kinetics, protein-ligand binding, and microbial growth; it can monitor processes continuously without labels. Differential scanning calorimetry and related methods record heat flow during heating or cooling to characterize glass transitions, melting, crystallization, and protein stability. Applications span biochemistry, pharmacology, materials science, energy storage, and environmental monitoring.

Advantages and limitations: Microcalorimetry offers high sensitivity, small sample requirements, and real-time, label-free measurements. Limitations include cost, the need for careful calibration and baseline stabilization, potential heat-transfer limitations for rapid processes, and data interpretation that depends on sample geometry and thermal properties.