Z-scan method to measure the nonlinear optical behavior of cells for evaluating the cytotoxic effects of chemotherapy and hyperthermia treatments

The effects of new treatments must be investigated in vitro before using clinically or in vivo. The aim of this study was to
introduce the Z-scan technique as a fast, accurate, inexpensive, and safe in vitro method to distinguish the cytotoxic effects of
various treatments. C6 and OLN-93 cell lines were prepared and treated with Temozolomide (TMZ), radiofrequency hyperthermia
(HT), and chemo-hyperthermia (HT+TMZ). The cytotoxic effects of different treatments on both cell lines were evaluated
using colony formation assay and Z-scan method. The results of colony assay showed that the surviving fraction (SF) of C6 cells
treated with TMZ, HT, and HT + TMZ were significantly decreased compared to the control group. Whereas, hyperthermia
treatment had no significant effect on the SF of OLN-93 cells. The results of Z-scan technique indicated that the control group of
C6 cells had the negative nonlinear refractive index (n2). Whereas, the C6 cells treated with HT, TMZ, and HT + TMZ had the
positive n2 index. The sign of n2 index in the control and HT groups of OLN-93 cells was positive but treatment of cells with
TMZ and HT + TMZ changed the sign of it.Moreover, with increasing the cytotoxic effects of different treatments, the SF value
of both cell lines decreased and the magnitude of n2 index increased. The results of Z-scan technique were completely in line with
the results of colony assay. Therefore, Z-scan method could distinguish the cytotoxic effects of various treatments by examining
the nonlinear optical properties of the samples