Miniaturization of isothermal calorimeters provides an even wider range of possibilities.

The first isothermal calorimeter was devised and used in 1782–1783 by Lavoisier and Laplace to determine the heat produced during chemical changes. This was the ‘ice-calorimeter,’ in which a sufficient amount of ice was used to keep the temperature constant (Lavoisier & Laplace, 1780). These early scientists realized that the mass of liquid water produced by the melting ice was directly proportional to the heat selleck produced by the reaction taking place atop the ice. Many improvements have of course been made since the early 19th century. In addition, several other types of calorimeters have evolved besides the ones that operate isothermally – for example adiabatic, constant-volume, constant-pressure, heat loss and temperature (differential) scanning calorimeters (van Herwaarden, find more 2000). Some of them can also be used in the isothermal mode. In the isothermal approach, isothermal titration calorimetry has emerged as the broadly used standard for thermodynamic characterization of relatively fast reactions between molecules – for example ligand binding – especially for molecules of interest in biology (Cooper, 2003).

However, because isothermal titration calorimetry is mostly a tool for molecular studies, it is not covered here. This review focuses on IMC in microbiology for a wide variety of Acyl CoA dehydrogenase purposes including microorganism detection and discrimination, evaluation of microbial processes and determining the performance of antimicrobial agents. The term IMC is used here to refer to measurements in the microwatt range under essentially isothermal conditions (Wadsö, 2001). The related instruments are often called isothermal microcalorimeters. Most isothermal microcalorimeters are heat conduction calorimeters in which heat produced in the reaction vessel is allowed to flow to a heat sink, usually made of aluminum. Therefore,

so-called isothermal microcalorimeters are not truly isothermal, but allow small variations of the sample temperature (up to 0.1 °C). Variation in the sample temperature mostly does not affect the heat sink temperature significantly because the heat sink has a much higher heat capacity than the reaction vessel and its contents (usually × 100). In addition, the heat sink is often placed in a thermostat, ensuring its temperature stability. The heat transfer between the vessel and the heat sink takes place through a thermopile, allowing measurements of the heat produced or consumed (Wadsö & Goldberg, 2001). In other isothermal microcalorimeters, thermoelectric compensation is preferred to maintain isothermal conditions. Heat produced is compensated using Pelletier elements, and similarly, heat consumed is compensated either by an electric heater or by reversing the polarity of the Peltier elements (van Herwaarden, 2000).