Highly sensitive ac nanocalorimeter for microliter-scale liquids or biological samples

We developed an ultrasensitive ac nanocalorimeter for use with biological liquids by means of microfabrication technologies. The volume of the cell measurement is only 5 muL. This nanocalorimeter, tested on deionized water, allows the measurement of heat capacity variation above +/-150 nJ/K (resolution of +/-5x10(-6)) with an operating temperature ranging from -20 to 120 degreesC and a stability of 100 muK. Its use is demonstrated on diluted lysosyme solution measured at the frequency of 3 Hz. At 3 Hz, this ac calorimeter gives only the variation of the heat capacity during the denaturation, which allows complementary thermodynamic investigations as regards to classical differential scanning calorimetry measurements. (C) 2004 American Institute of Physics.