## 3 Results
### Synthesis and Characterization of CaS nanoclusters
#### 3.1.3 Effect of CaS Nanostructures (NS) in Carcinoma Cells  
The insert in the upper right-hand side of Figure 5 represents the results of the measurements of carcinoma cell density at different times following a single CaS NS dose. The plots labeled S\({}_{1}\), S\({}_{2}\), and S\({}_{3}\) represent the average carcinoma cell density on each sample at the indicated times following the dose of CaS NS in a DMSO dispersion. The results from two independent controls, labeled C\({}_{1}\) and C\({}_{2}\), are also included in the figure. One of the control samples, C\({}_{1}\), was fed with equal volumes of DMSO in the media as the S\({}_{1}\), S\({}_{2}\), and S\({}_{3}\) samples, while the other control sample, C\({}_{2}\), was fed with normal media. The general trend found was an increase in carcinoma cell density in the first 24 h in all samples. The density of cells started to decrease about 48 h following the CaS dose, while the density of cells in the two controls increased during this period. The average rate of decrease in the cell density of samples exposed to CaS is (0.7 \(\pm\) 0.2) cells/mm\({}^{2}\) per hour. We conclude that CaS nanostructures reduce carcinoma cell proliferation. However, they appear to act somewhat slower than the CaS clusters, where the inhibition in cancer cell proliferation was found immediately following the dose.  
The gray bars in the upper and lower panels of Figure 6 summarize the effect of a single CaS dose on the average density of carcinoma cells and the number of dead carcinoma cells, respectively, as a function of time. The white bars in the upper and lower panel of Figure 6 represent the average density of cells and the number of dead carcinoma cells in the controls. Each reported value represents the average of the 15 independent measurements performed each day on different regions of samples S\({}_{1}\), S\({}_{2}\), and S\({}_{3}\). The error bars represent the standard error of the measurements.  
The average density of carcinoma cells increased monotonically in the first 48 h following the CaS NS dose. The density of cells fed with CaS in the media started to decrease at about 48 h following the CaS dose. The rate of increase of the density of cells in the first 72 h was about (0.4 \(\pm\) 0.1) (cells/mm\({}^{2}\)) per hour, slightly lower than the rate ofgrowth of carcinoma cells in the control, which was estimated to be (0.50 \(\pm\) 0.04) cells per mm\({}^{2}\) per hour in the same time range.  
There was a well-defined decrease in the density of cells between 48 and 72 h following the dose. The number of dead cells in this group, on the other hand, increased from 100,000 to 150,000 to over 400,000 in the first 48, 72, and 96 h, respectively, following the single dose of CaS. The rate of increase in the number of dead cells was (3.8 \(\pm\) 0.8) \(\times\) 10\({}^{3}\) cells/h. The marked decrease in the density of cells and sharp increase in the number of dead cells was not observed in the carcinoma cells used as a control. We conclude that CaS induce cell death within 48 h following a single dose.  
The density of cells as a function of hours following a second dose of CaS is illustrated in the insert in Figure 6. The gray and light-colored bars represent the density cells exposed to a second dose of CaS and control, respectively. Both cell samples were sub-cultivated from cells exposed to a single CaS dose, as described in the previous paragraphs. Cell growth was followed for a period of 48 h. The number of control cells increased to about 100 cells/mm\({}^{2}\) in the first 48 h. The number of cells exposed to a second dose did not reach this cell density in this period.