The probing of living cells in different colors over extended periods of time can be used to see the complicated processes that take place during carcinogenesis or heat stress, for example. Since most therapeutic laser tissue interactions are based on thermal effects a detailed characterization of thermal tissue damages in the cellular and sub-cellular levels is important. In order to study such microdosimetry laser-induced fluorescences of Quantum dots provide a suitable approach. Streptavidin conjugated Qdot 605 (Quantum Dot Corp., USA) were used in combination with the concanavalin A-biotin labeling system (Molecular Probes, NL) to observe membrane associated thermal lesions. Fluorescent Qdot conjugates are a promising alternative to organic dyes. The extinction coefficient of Qdot 605 streptavidin conjugate is 650,000 M(-1) cm(-1) at 600 nm. Red fluorescent Qdots 605 were selected because autofluorescence of cells in the red spectral range is not relevant. Fluorescence detection was performed with a confocal laser scan microscope LSM410 (Carl Zeiss, Germany). Breast cancer cells were used in the thermal stressing experiments performed at 40 degrees C, 42 degrees C, 45 degrees C, 50 degrees C or 56 degrees C for 30 min, each. In this methodical approach Qdot mediated labeling of heat stressed cells were demonstrated to show alterations of plasma membrane organizations and integrities, respectively.