Agriculture Reference
In-Depth Information
13.5.2 Zinc Oxide
Zinc oxide (ZnO) nanoparticles have unique optical, catalytic, semiconducting,
piezoelectric, and magnetic properties, all reasons why it has been widely produced
and technologically applied (Li et al.
2011a
,
b
).
Tang et al. (
2014
) explored the toxicity of ZnO nanoparticles (nano-ZnO) and
Zn
2+
to
Anabaena
sp., cyanobacteria. Results showed that nano-ZnO and Zn
2+
could inhibit
Anabaena
sp. growth with the EC
50
(concentration for 50 % of
maximal effect) of 0.74
0.01 mg L
1
, respectively. Nano-ZnO
had more damage to the cell membrane than Zn
2+
did, which could be proven by the
malondialdehyde content in
Anabaena
sp. cells.
Brayner et al. (
2006
) reported studies of biocidal effects and cellular internali-
zation of ZnO nanoparticles on
E. coli
bacteria. They used synthesized ZnO
nanoparticles, in diethylene glycol (DEG) medium by forced hydrolysis of ionic
Zn
2+
salts. Particle size and shape were controlled by the addition of small mole-
cules and macromolecules such as tri-
n
-octylphosphine oxide, sodium dodecyl
sulfate, polyoxyethylene stearyl ether, and bovine serum albumin.
The presence of these nanoparticles at a concentration between 10
2
0.01 and 0.3
and
10
3
M caused 100 % inhibition of bacterial growth. Concentrations between
3.0
10
3
and 1.5
10
3
M inhibited bacterial growth by 85 %. For concentra-
3.0
10
3
and 10
3
M, an increase of
E. coli
colonies was observed.
Cellular internalization of these nanoparticles was observed. One prediction made
by the authors through these results was that this increase was metabolism-
dependent, because bacteria can metabolize Zn
2+
as an oligoelement, which
showed that ZnO nanoparticles were not toxic for
E. coli
at the concentrations used.
Brayner et al. (
2010
) also evaluated the ZnO nanoparticles toxicity to
Anabaena
flos
-
aquae
and the euglenoid
Euglena gracilis
. The nanoparticles were synthesized
in DEG medium by forced hydrolysis of zinc acetate, the general procedure
involving addition of zinc acetate to 80 mL of polyol and H
2
O to reach a final
concentration between 0.06 and 0.63 mol L
1
. The hydrolysis ratio was varied from
10 to 80, and protective agents such as TOPO and Brij-76 were added to zinc
acetate and polyol solution with concentrations between 10
2
and 10
1
Mto
control particle size and shape. For ZnO prepared without protective agent addition,
spherical submicrometer-sized nanoparticles were observed. After the increase of
the hydrolysis ratio from 10 to 30, nanorods were formed (30
tions between 1.5
<
length
<
100 nm).
At
H
¼
300, particles with crown morphology were also observed. For ZnO pre-
pared with TOPO, using
H
¼
2, very small spherical nanoparticles were obtained
(
d
¼
2.0
0.4 nm). At
H
¼
10, spherical nanoparticles with narrow size distribution
were observed (
d
¼
15.0
0.7 nm). For 30
<
H
<
70, nanorods were also formed,
and the length varied from 30
length
200 nm. Finally, for ZnO prepared with
<
<
Brij-76, for
H
2, 30, and 70, agglomerates were obtained by coalescence of
spherical nanoparticles. The sizes of these agglomerates were 100
¼
10 nm for
H
¼
2, 150
10 nm for
H
¼
30, and 300
25 nm for
H
¼
70. On the other hand, for
H
¼
10, nanocubes and nanorods forming nanobelts were formed.
