Scanning nano-calorimeter

Current micro-calorimetry equipment requires large sample volumes. To overcome this limitations, a highly sensitive nano-calorimeter with reduced sample volume and decreased response time was developed (Winter, W. and Hohne, G.W.H., Thermochimica Acta, vol.403, p.43-53, 2003; Eframov, M. Yu et al., Thermochimica Acta, vol.412, p.13-23, 2004). Sensitivity is evinced by detection of phase transitions in liquid crystals, solutions of a phospholipid and solutions of the enzyme Glucoseoxidase. The nano-calorimeter is made of a cavity in an anisotropically etched silicon chip with a volume of about 100 nl to take in the liquid or gel-like sample. A membrane of Si₃N₄ of 1 μm thickness forms the bottom closure of the cavity. Amorphous germanium thermistors with a temperature sensitivity of 100 μK are placed onto the Si₃N₄ membrane and the silicon chip as well. This allows thermal flow measurements with power resolution of down to 1 nW and specific thermal capacity resolution down to 1 mJ/g. This high sensitivity of the nano-calorimeter allows the detection of denaturing temperatures of enzymes within hydrogel membranes.