###### Abstract  
Laser ablation in liquid was utilized to prepare a TiO\({}_{2}\) NP suspension in in deionized distilled water using Q-switch Nd: YAG laser at various laser energies and ablation times. The samples were characterized using UV-visible absorption spectra obtained with a UV-visible spectrophotometer (UV-Vis.) Fourier transform infrared (FTIR), X-ray diffraction (XRD), and transmission electron microscope (TEM). While, UV-Vis spectra showed the characteristic band-to-band absorption peak of TiO\({}_{2}\) NPs in the UV range. FTIR analysis showed the existence of O-Ti-O bond. XRD patterns indicated the presence of (101) and (112) plane crystalline phases of TiO\({}_{2}\). TEM images showed a spherical-like structure of TiO\({}_{2}\) NPs with various size distributions depending on the ablation period. It was also found that there is a relationship between laser ablation time and TiO\({}_{2}\) NP size distribution, where longer ablation times led to the smaller size distribution. The antibacterial activity of TiO\({}_{2}\) NPs was evaluated with different species of bacteria such as _Escherichia coli_, _Pseudomonas aeruginosa_, _Proteins vulgaris_, and _Staphylococcus aureus_, using the liquid approach. The optimum activity of TiO\({}_{2}\) NPs is found to be against _E. coli_ at 1000 \(\upmu\)g mL\({}^{-1}\). Furthermore, adding, TiO\({}_{2}\) NPs (100 \(\upmu\)g mL\({}^{-1}\)) in the presence of amoxicillin has a synergic effect on _E. coli_ and _S. aureus_ growth, as measured by the well diffusion method. However, both _E. coli_ (11.6 \(\pm\) 0.57 mm) and _S. aureus_ (13.3 \(\pm\) 0.57 mm) were inhibited by this process. TiO\({}_{2}\) NPs; laser ablation in liquid; characterization; antibacterial activity +
Footnote †: journal: _Sci._
environmental remediation applications due to their abundance, low cost, high surface-area-to-volume ratio, non-toxicity, and unique physiochemical properties. It also has a unique photocatalytic activity and good thermal stability and biocompatibility to chemicals. It is well known that the antibacterial activity of TiO\({}_{2}\) NPs is highly influenced by their size, shape, and surface chemistry such as the abundance of surface defects which significantly impact the photocatalytic activity of the particles [7; 8; 9; 10; 11]. TiO\({}_{2}\) has been incorporated with several nanomaterials to work as an antimicrobial agent in several research works. For instance, Fe\({}_{3}\)O\({}_{4}\)-TiO\({}_{2}\) core/shell NPs were synthesized to restrain the bacterial growth of _Staphylococcus aureus_ which has a survival ratio that decreased from 82.4 to 7.13% after treatment. TiO\({}_{2}\) nanotubes were used to restrain _Escherichia coli_ bacteria and their survival ratio reduced by 97.53% [12]. The survival ratio of _Pseudomonas aeruginosa_ was also studied with TiO\({}_{2}\) NPs and their survival was found to be significantly reduced [13; 14]. [PERSON] et al. investigated the remarkable effect of using an external magnetic field during TiO\({}_{2}\) NPs preparation on the inhibition zone of _S. aureus_ and _E. coli_[15]. In addition, a variety of techniques have been utilized to prepare TiO\({}_{2}\) nanostructures with different sizes and shapes, among which laser-induced etching, laser ablation, nano-lithography, sol-gel methods, and more. Laser ablation in liquids has been considered to be a relatively fast, easy to manipulate, and cost-effective technique as compared to the aforementioned methods [16; 17]. For instance, [PERSON] et al. used the second harmonic generation of Nd: YAG laser working at 532 nm wavelength with a varying fluence of 1 to 10 J cm\({}^{-2}\) and ablation time ranging from 10 to 30 min [7]. Their results show particles formation with diameters of 5-7 nm and agglomerations of 100-200 nm, which increases with laser fluence.