ABSTRACT
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 biosafe, biocompatible in dark, enhances endogenous luorescence, noninvasive, and fast with their least permeability in normal cells,
but ZnO NRs with high surface-to-volume ratio and biocompatibility can be used as an eficient 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 briely 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
structures, such as NRs, nanolakes (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.
