## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Ablation** \\ **Condition** \\ \end{tabular} & **20 (Degree)** & \
\begin{tabular}{c} **Orientation** \\ **(hkl)** \\ \end{tabular} & **G.S (nm)** &
\begin{tabular}{c} **FWHM** \\ **(Degree)** \\ \end{tabular} & **Phase** \\ \hline \multirow{2}{*}{200 mJ} & 35.4 & 101 & 41.67 & 0.2 & anatase TiO\({}_{2}\) \\  & 38.8 & 112 & 46.77 & 0.18 & anatase TiO\({}_{2}\) \\  & 45 & \(-\)403 & 44.46 & 0.19 & \(\beta\)-TiO\({}_{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: XRD parameters of TiO\({}_{2}\) NPs. Figure 4: FTIR spectra of TiO\({}_{2}\) NPs synthesized: (a) 80 mJ; (b) 200 mJ. Figure 5: XRD patterns of TiO\({}_{2}\) NPs. Figure 7 shows TEM image of TiO\({}_{2}\) NPs prepared at 80 mJ laser energy with a 20 min ablation time. The images revealed that particle size ranged from 2 nm to 23 nm with spherical shaped particles. TEM images in Figures 6 and 7 indicated a reduction in the particle size with increasing laser ablation times. Moreover, the increase in the ablation time results in more ablated mass and high absorption peak, and thereby increases the NPs concentration in the result colloidal solution. The results showed a reduction in the ablation rate with time, which results from the fact that the suspension solution diffracts and/or absorbs a significant portion of incident laser energy and therefore, less energy is absorbed by the target. This process leads to a laser-particles interaction within the solution which causes a smaller particle size formation. Figure 8a shows the optical density of bacterial culture growths in the presence of TiO\({}_{2}\) NPs. The optical density was dropped slightly as the concentrations of TiO\({}_{2}\) NPs increased in all types of the tested pathogens. Figure 8b shows that the best-used concentration of TiO\({}_{2}\) NPs for inhibiting the growth of both strains was found to be 1000 \(\mu\)g mL\({}^{-1}\). The inhibition rates of TiO\({}_{2}\) NPs at 400 \(\mu\)g mL\({}^{-1}\) were 21%, 3.5%, 5.3%, and 4.9% for _E. coli_, _S. aureus_, _P. aeruginosa_, and _P. vulgaris_, respectively. The effect of TiO\({}_{2}\) NPs against G-positive bacteria was less than for G-negative bacteria, due to the difference in membrane structures of bacteria. The inhibition rates of TiO\({}_{2}\) NPs at 600 \(\mu\)g mL\({}^{-1}\) are 34%, 13.7%, 8.6%, and 14.04% for _E. coli_, _S. aureus_, _P. aeruginosa_, and _P. vulgaris_, respectively. On the other hand, the inhibition rates of TiO\({}_{2}\) NPs at 1000 \(\mu\)g mL\({}^{-1}\) were 42%, 25.5%, 15.05%, and 30.5% for _E. coli_, _S. aureus_, _P. aeruginosa_, and _P. vulgaris_, respectively. TiO\({}_{2}\) was found to  
Figure 6: **(a)** TEM image of TiO\({}_{2}\) NPs prepared at the following laser conditions (80 mJ; 10 min) and (b) size distribution histogram. Figure 7: **(a)** TEM image of TiO\({}_{2}\) NPs prepared under the following laser conditions (80 mJ; 20 min) and (b) size distribution histogram. be very effective against _E. coli_ among all bacterium types. This effect may be explained by the fact that metal oxide NPs carry a positive charge while the microorganisms carry negative charges; this causes an electromagnetic attraction between microorganisms and metal oxide NPs, leading to the microorganism's oxidization and finally death [33; 34; 35]. Figure 9 shows the suppressive effect of amoxicillin against _E. coli_ and _S. aureus_ with and without TiO\({}_{2}\) NPs. The optical density of cultures was found to break down as the combination of nanoparticles with amoxicillin increased, which confirms the antibacterial effect of amoxicillin enhancement in the presence of nanoparticles. The combined impact of nanoparticles and amoxicillin is due to the cell wall lysis action of the amoxicillin and the DNA binding activity of the nanoparticles [36; 37]. Figure 10 shows the inhibition rate of amoxicillin of about 74.8% against _E. coli_ and 76.28% against _S. aureus_.