Chapter 5
Zinc Oxide Nanostructures: Advances and Applications
Edited by Magnus Willander
Copyright © 2014 Pan Stanford Publishing Pte. Ltd.
ISBN
978-981-4411-33-2 (Hardcover), 978-981-4411-34-9 (eBook)
www.panstanford.com
ZnO Nanostructures: Toxicity and
Phototoxicity Characteristics in
Biological Samples
Zinc oxide nanoparticles (ZnO NPs) are emerging milestones
in the ongoing research in photodynamic therapy (PDT) with
tremendous multiple clinical applications, diagnostic as well as
anti-tumoricidal, in many microbial non-microbial treatments and
are front-runners in these applications due to their high quantum
yield, size-dependent tunable emission of wavelength over a wide
spectrum of light. Currently, the nano-dependent PDT technique
involving ZnO NPs and zinc oxide nanorods (ZnO NRs) is simple bio-
safe, biocompatible in dark, enhances endogenous luorescence,
noninvasive, and fast with their least permeability in normal cells,
Magnus Willander,
a
O. Nur,
a
M. Fakhr-e-Alam,
b
M. Atif,
c
and M. S. AlSalhi
c
a
Department of Science and Technology, Campus Norrköping,
Linköping University, SE-601 74 Norrköping, Sweden
b
Department of Physics, Faculty of Basic and Applied Sciences,
International Islamic University, Islamabad, Pakistan
c
King Saud University, Riyadh, Kingdom of Saudi Arabia
magwi@itn.liu.se
158
ZnO Nanostructures
but ZnO NRs with high surface-to-volume ratio and biocompatibility
can be used as an eficient photosensitizer carrier system and at the
same time provide intrinsic white light needed to achieve cancer
cell necrosis. In this current work, the authors demonstrate the
toxicity of different ZnO nanostructures alone and complex with
different photosensitizers (PS), e.g., aminolevulinic acid (ALA),
Photofrin
®
and protoporphyrin dimethyl ester (PPDME) by using
multiple malignant cell lines, e.g., hepatocellular carcinoma (HepG2),
rhabdomyosarcoma (RD), cervical (HeLa), melanoma (FM55P), and
foreskin ibroblast (AG1518) cells by applying multiple/various
techniques. In addition, ZnO NRs are prominent semiconducting and
piezoelectric materials that have multiple applications in the ield
of optoelectronics, biosensors, resonators, electric nanogenerators,
energy scavenging, and nanolasers [1–7]. Zinc oxide (ZnO) with its
semiconducting and piezoelectric properties exhibits bio-safety
and biocompatibility [8]. ZnO being a wide band gap (3.37 eV)
semiconductor, has large excitation binding energy (≈60 meV) at
room temperature, have applications in optronics [9, 10]. Moreover,
because of its electronic and optical properties ZnO nanostructures,
e.g., nanorods (NRs), nanotubes (NTs), nanoparticles (NPs), and
nanowires (NWs) are dominantly found in transparent electronics
devices [11]. ZnO nanostructures have attracted the attention of
researchers because of their potential applications in nanodevices,
e.g., nanobiotechnology one-dimensional nanostructures such as
nanotubes, nanowires, and nanoribbons [11–13]. In addition, the
role of nanoparticles in biomedical applications cannot be ignored,
e.g., targeted drug delivery, hyperthermic cancer treatment, gene
therapy, ultra-sensitive bio-agent detection and magnetic resonance
imaging (MRI) and overcoming of multidrug resistance [14]. In this
regard, different drug delivery systems were introduced for the
assessment of ZnO toxicity in dark as well as under exposure of
240 nm of UV light. Some of them are briely discussed here:
freestanding drug delivery
microinjection drug delivery
Different malignant cell lines/biological samples, such as
melanoma, foreskin ibroblast, breast carcinoma, hepatocellular
carcinoma, and RD, were used as in vitro experimental model due to
corresponding experimental equipment facility/availability. In this
current conducting experiment, toxicity of different nanomaterial
159
ZnO Nanostructures
structures, such as NRs, nanolakes (NFs), NPs, NPS, and NWs,
were analyzed for mentioned cell lines. It was investigated that
ZnO NRs have marvelous toxicity even in the absence of laser light
(in dark). Various nanomaterial structures are shown in Fig. 5.1.
Figure 5.1 (a) Zinc oxide nanowires, (b) zinc oxide (ZnO) nano-urchin,
(c) zinc oxide nanoparticles
, and (d) zinc oxide nanorods.
Many research experts agreed that zinc oxide nanomaterials, in
the presence of 10–20 J/cm
2
of UV light doses, showed the signiicant
amount of reactive oxygen species (ROS) which is responsible for
the cell killing effect [15]. It has been investigated that dimension
and size of nanomaterials is also dependent factor for cell toxicity,
sometimes signiicant loss in cellular viability were recorded due
to shape and dimension of ZnO NPs. In multiple publicized data,
it was found that the concentration of nanomaterials toward the
malignant cell line has a direct relationship with the killing of the
mentioned cells via cell membrane rupturing, lysosomal injury/
vascular blockade [16]. In this chapter, we focus the killing of cells
via photochemical reaction instead of mechanical stress/trauma,
which includes in PDT drawback. The schematic diagram of
photochemical reactions (Jablonski diagram) that lead to cell death/
cell apoptosis or necrosis is shown in Fig. 5.2.

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