Measurements of micro bubble nucleation temperatures in DNA solutions

Measurements of micro bubble nucleation temperature in single-stranded DNA (ssDNA) solution with four different concentrations (0.4, 1, 6.4 and 10 mu g mu l(-1)) and under different heat fluxes are presented in this paper. A micro thermal bubble was generated periodically by a micro bubble actuator under pulse-heating conditions. The bubble nucleation temperature was measured by employing a micro Pt heater as a self-sensing resistive temperature sensor, and the voltage signal was recorded by a 100 MHz high-speed digitizer. By examining the temporal temperature variation of the micro heater during the pulse-heating period, one can observe a 'V' shape temperature change for the cases when bubble nucleation occur-red, which was speculated to be the beginning of bubble nucleation. It is found that (1) the onset bubble nucleation temperature increases with the DNA concentration and (2) at a fixed concentration, the bubble nucleation temperature increases with the heat flux from the micro heater. Based on a transient 3D heat conduction model, it is found that the size of the superheated region in the fluid just before bubble nucleation is comparable to the feature size of the micro heater, and. relatively independent of the ssDNA concentration and heat flux.