Page 51 - ACCB 2020

Nanotechnology for Combating Microbial Contamination. do Nascimento et al

sewage effl uent, and therefore, the contamination of the factant dodecyl-trimethylammonium chloride (DTAC)
environment is unavoidable (130–133), and the sewage with positively charged groups can combine with the
contamination by nanoparticles has been also obser- bacterial surface through electrostatic interactions and
ved through various reports (134–137). Therefore, as consequently cause an antibacterial effect. Brayner et
compared to the other contaminants, nanoparticles are al (97) studied the effect of ZnO nanoparticles on bacte-
also important contaminants for nanotechnologists. Va- rial growth. They used the SDS surfactant for regulating
rious parameters are affecting their properties including the shape of ZnO nanoparticles. Furthermore, they ob-
size, shape, and most importantly the surface coating served that the SDS surfactant used was contributing to
(138,139). Therefore, it is inevitable that nanomaterials the toxicity. The observed toxicity might be due to the
are under the scanner of the U.S. Environmental Pro- denaturation of bacterial protein by SDS. By composi-
tection Agency. There are various initiatives undertaken tion Tween 20 does not have any charged group and the-
by scientists across the globe dealing with the study of refore, does not affect the ZnO toxicity. The combined
the fate of nanomaterials in the ecosystem especially in effect of ZnO NPs with adsorbed Tween 20 is additive.
aquatic systems (140). The additive effect might be due to the dissolved Zn
ions and the surfactant (155).
According to a report, after 21 day exposure of citric
acid coated silver nanoparticles on Daphnia magna, According to the study performed by Sayes et al (156),
the reproductive toxicity at the concentrations of 10 μg surfactants were shown to decrease the toxicity of
Ag/L (141) was demonstrated. Similar results were also single-walled carbon nanotube. The mechanism lying
found after the exposure of sulfi dized AgNPs on Cae- behind such observation might be in the surface adsorp-
norhabditis elegans (142). Interestingly, silver nanopar- tion of surfactant on the nanoparticle surface thereby
ticles were found to be more toxic to the algal (Pseu- conditioning the nanoparticle surface, fi nally affecting
dokirchneriella subcapitata) growth than platinum the cytotoxicity (157). The reason behind this output
nanoparticles (143). Gold nanoparticles also reported might include the interaction between nanoparticles and
to induce the reactive oxygen species (ROS), expres- bacteria through steric hindrance and charge repulsion
sion of genes involved in oxidative and general cellular thereby decreasing the toxicity of nanoparticles (158).
stress such as glutathione S-transferase (GST), catala- Furthermore, through attachment to the nanoparticle
se (CAT), heat shock protein 70 (HSP70), and meta- surface, the surfactant modifi es the surface charge of the
llothionein1 (MT1) (144). All of these studies indicate nanoparticles, resulting in the alterations in their pro-
that though nanoparticles can help us in the treatment of perties and toxicity (159,160). Additionally, humic acid
water, they can also be harmful after their accumulation has also been reported to markedly reduce the toxicity
or release in the aquatic environment. of nanoparticles (161–163). On the other hand, it has
been reported to increase nanoparticle toxicity (164). A
5.1. Interaction of nanoparticles with surfactants recent study by Wang et al (165) also found the simi-
and organic compound in water and wastewater lar results suggesting the alleviative property of humic
Many times researchers use surfactants for either stabili- acid on PVP-coated AgNP, in an alga (Raphidocelissub
zing or modifying nanoparticles (145–148) and therefo- capitata), a cladoceran species (Chydorus sphaericus),
re, surfactants exist with nanoparticles. Surfactants are and a freshwater fi sh larva (Danio rerio). Bisphenol A
mostly chemicals, and hence they add to the properties (BPA), an organic compound, mimics the hormone es-
of nanoparticles. In summary, they will certainly affect trogen thereby disrupting the endocrine system. There-
the environment. Adsorption of surfactant on the surfa- fore, it could show a harmful effect on human health
ce of nanoparticles is a critical step for the application (166,167). It can also be found in water bodies as a con-
of nanoparticles as a superior sorbent in the treatment of taminant. However, the BPA may interact with TiO NP
2
wastewater (131,149). They also play a role in deciding when it could be used as a drug carrier. Furthermore,
the hazard associated with their use along with nanoma- Shi et al(168) investigated the activity of both TiO NP
2
terials to which they are bound (131,150–152). and BPA, both independently and in combination with
L-02 cells, human embryo hepatocytes. The authors ob-
Surfactants have been used as antibacterial agents for a served that both TiO NP and BPA alone did not show
2
long time (153). It has been demonstrated that the bac- signifi cant damage to DNA and chromosome. Howe-
terial surface is negatively charged due to the hydroly- ver, a combination of both of them induced much rise in
sis of the surface groups (154); thus, the cationic sur- oxidative stress, double-strand breaks in DNA, and for-

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Rev. Asoc. Col. Cienc.(Col.), 2020; 32: 42-62.