*3.2.3 Chemical doping*

*Nanoemulsions - Properties, Fabrications and Applications*

try, to water purification and to the textile industry [28].

obstructs growth of bacteria.

*3.2.1 Size and shape*

intensity [30].

*3.2.2 Surface and zeta potential*

ing other mechanisms [23] (**Figure 1**).

subsequent loss of viability (**Figure 1**).

the phosphotyrosine residues, which inhibits signal transduction and, ultimately,

**3.2 Nanoparticle characteristics and their influence of antimicrobial activity**

Other factors of the antimicrobial activity, has been sought to analyze what characteristics influence the microbial response to the action of the metal oxide nanoparticles. It is known of existing reports concerning the chemical-physics properties from the metal oxide nanoparticles, but taking into consideration factors like the shape, size, roughness, zeta potential and coatings, etc., that influence the resultant antimicrobial effectiveness [5, 10]. These results could have a mainly therapeutic application in medicine, but it can also be extended to the food indus-

Several reports mention that the size and shape are the most important factors to the antimicrobial activity [23, 29–31]. With respect to size there are findings where this is a crucial factor to damage the bacterial systems for many reasons. The sizes as <30 nm are factors that allows the accumulation and penetration into the bacteria causing damage and consequently leading to bacteria death (<10 nm) [23]. The same authors point out that metal oxide nanoparticles with a size greater than 10 nm promotes the permeability when coming into contact with bacteria [23]. In relation with this, the specific surface area by the nanoparticle size affects the surface to mass ratio affecting on surface reactivity. For this reason, they can also have influence in many direct mechanisms of toxicity against the bacteria and the

With respect to shape, it is by knowing that depending on the synthesis method,

it will obtain the form of the nanoparticle [32]. Numerous studies shown various forms obtained like spherical, rod-shaped, truncated triangular, nanotubes, nanorods, nanowires, nanosphere, nanoneedles, nanorings and nanocubic [23, 33, 34]. Evidence reports that needle-shaped metal oxides nanoparticles present higher antibacterial activity than cubic shaped, based on the optical and fluorescence

The relation between the surface nanoparticle/nanomaterial and bacterial adhesion has not been fully studied and there are few reports about it. Some studies report that the adsorption of bacterial proteins is promoting by the surface areato-mass ratio carry out the reduction in bacterial adhesion [35–37]. Surface nanomaterials have high degree of roughness, therefore bacteria cell membranes cannot adhere to the surface nanomaterial; so the bacteria adhesion is reduced [10, 38, 39]. The surface charge or zeta potential could be another property of the nanoparticle related with bacteria adhesion since it is important to mention that if the surfaces with negative charge are capable to decrease the interaction with bacteria charged negatively, the surface of nanomaterial with negative charge could obtain the same effect, compromising bacterial adhesion [10, 23, 40]. On the other hand, the electrostatic attraction occurs when the nanoparticles are positively charged promoting the accumulation in bacterial cell membrane, which is negatively charged and then they penetrate inside the bacteria trigger-

**18**

Nanoparticle chemical doping is a modification and functionalization around the surface of nanoparticles to regulate and control the interaction with bacteria and enhance their antimicrobial effect. Reports have shown this method as a factor to improve the presence of surface oxygen atoms that promote the production of reactive oxygen species (ROS) [23]. Similarly, the chemical functionalization increase of the surface-area-to-volume ratio results in increasing the antimicrobial potential activity [38]. Also, this procedure has prevented the agglomeration and the solubility in different solutions [10].
