## 3 Results and Discussion
### ECIS Measurement  
ECIS results are shown in Figures 4 and 5 in response to the exposure of different concentrations (0, 1, 5, 10, and 50 mM) of MgO/Mg(OH)\({}_{2}\) NPs, respectively, on hFOB 1.19 cells. Cells were utilized after three passages to obtain high throughput results through ECIS experiments. Cells were incubated for 24 h on microelectrodes of the ECIS array for the control group (0 mM) and the experimental groups (1, 5, 10, and 50 mM) to evaluate the cytotoxicity of different concentrations of MgO/Mg(OH)\({}_{2}\) NPs upon exposure. Figures 4 and 5 illustrate an increase in impedance at 24 h due to the cell proliferation and formation of the monolayer of the cells. Further, a drop in the impedance for an hour has been observed after 24 h in the samples due to the change of the culture media of the control group and the experimental groups before exposure of the concentrations of MgO/Mg(OH)\({}_{2}\) NPs.  
Figure 4 shows the ECIS impedance response to hFOB 1.19 cells upon exposure of different concentrations of MgO NPs for 24 h. At a 0 mM concentration of MgO NPs, a constant monolayer of cells was observed due to rapid cell proliferation, resulting in an increase impedance that saturated at 8700 \(\Omega\) after 24 h. For the lower concentration (1 mM) of MgO NPs, increased cell proliferation and formation of a monolayer of cells have been observed, which resulted in an increased impedance that saturated at 8600 \(\Omega\) after 24 h. Nearly similar impedance results for 1 mM concentrations of MgO NPs and control group (0 mM) indicates the negligible amount of cytotoxicity to the hFOB 1.19 cells. However, at concentrations of 5, 10, and 50 mM, a subsequent decrease in the impedance to 8300.4, 8200, and 8080 \(\Omega\) was reported, respectively, as compared to control group (0 mM) and 1 mM concentration of MgO NPs. The decrease in impedance demonstrates increased cytotoxicity in hFOB 1.19 cells, mainly due to cell death that has been confirmed with the live-cell images of hFOB 1.19 cells on microelectrodes upon exposure, as shown in Figure 2.  
Figure 5 shows the ECIS impedance response to hFOB 1.19 cells upon exposure to different concentrations (0, 1, 5, 10, and 50 mM) of Mg(OH)\({}_{2}\) NPs for 24 h. At 0 mM concentration, a constant monolayer of cells was identified with rapid cell proliferation with an increase of impedance that saturated at 8400 \(\Omega\) after 24 h. Exposure to a lower concentration, such as 1 mM, cell proliferation and formation of a monolayer of cells with an increased impedance that saturated at 8130 \(\Omega\) after 24 h was observed. However, at the concentrations of 5, 10, and 50 mM, subsequent decreases in the impedance to 7890, 7830, and 7810 \(\Omega\) were reported, respectively, as compared to control group (0 mM) and 1 mM concentrations of Mg(OH)\({}_{2}\) NPs. A subsequent decrease in the impedance results reveals increased cytotoxicity with the higher concentrations of 5, 10, and 50 mM of Mg(OH)\({}_{2}\) NPs. Cytotoxicity was also confirmed with the live-cell images of hFOB 1.19 cells on microelectrodes upon exposure, as shown in Figure 3. To access the level of cytotoxicity among the different concentrations of MgO and Mg(OH)\({}_{2}\) NPs for 24 h, ECIS impedance responses of hFOB 1.19 cells upon exposure have been compared. The combined results of ECIS impedance and the live images depict that 1 mM concentrations of MgO NPs are less toxic to hFOB 1.19 cells as compared to 1 mM concentrations of Mg(OH)\({}_{2}\) NPs.