One of the new techniques that permit the access to temperature rise at microscopic level is based on the exploitation of the biological dye Rhodamine B (Rhod-B). A TEM cell is used to apply a 1800 MHz RF signal to a 3 ml Rhod-B labeled culture medium. Experimental dosimetry shows that the concentration of Rhod-B can affect its fluorescence intensity. It is preferable to use concentrations of at least 10 μmol for better calibration of temperature measurements.