Calorimetry of microbial growth using a thermopile based microreactor

A miniaturized calorimeter, based on silicon integrated thermopile chips, has been developed for the determination of growth-related heat production in microbial cultures. The calorimetric vessels consists of two independent sensors located within a thermostated aluminum frame, the heat sink, and covered by a 0.6 ml reaction chamber made of PTFE for improved thermal insulation. The second sensor was used as a reference to minimize temperature perturbations on the output signal. Baseline stability was better than 0.08 μW h−1. The Si thin-film membrane which supports the Al–Si thermopiles enabled an excellent dynamic response and a temperature resolution of 50 μK. The sensitivity for the heat power measurement was 0.39 V W−1. Batch measurements of Escherichia coli activity under different conditions have been performed. The thermal profiles matched the exponential growth kinetics usually found in batch cultures of bacteria. A simplified model based in the Monod equation is used to analyze the influence of oxygen depletion on cell growth.