A method and apparatus for electrically monitoring a time-varying liquid droplet whose conductivity is continuously modulated by osmoregulation response of cells. According to the method, the droplet impedance or conductance is monitored over time as the droplet shrinks due to evaporation. The monitoring data is then compared to calibration data which is obtained by monitoring a reference droplet. The result of the comparison is then used to determine the concentration of viable (live) biological material contained in the droplet.