Thermal-lens effect of low-density lipoprotein lyotropic-like aggregates investigated by using the Z-scan technique 

The thermal nonlinear optical response of human normal and copper-oxidized low-density lipoproteins (LDLs) were investigated by using the Z-scan technique, as a function of temperature and concentration of LDL particles. The results show that the Z-scan signals from normal LDL are characteristic of a sample with negative thermo-optical coefficient. The amplitude of the Z-scan signal increases linearly with the LDL concentration, following the usual Beer-Lambert law. On the other hand, oxidized LDLs do not show thermal nonlinear optical response. This behaviour can be attributed to an absorbing element that is modified by the oxidative process. On the other hand, changes in the physical state of the cores and conformation of the ApoB100 protein, due to an increase in temperature, seems to enhance the native LDL thermal nonlinear optical response.