A non-intrusive method for the measurement of water vapour sorption by bacterial spores

Single particle levitation (SPL) is used to measure the sorption and desorption of water vapour from microparticles comprising of Bacillus spores. Water gain is determined from increases in the weight-balancing levitation voltages. Spore water isotherms are compared to values previously reported using bulk gravimetric methods. Two salient differences are found between the SPL and bulk data: (1) greater osmotic swelling is observed in the SPL data; and (2) the SPL data exhibit open loop hysteresis while bulk data exhibit closed loop hysteresis.