Nano-zirconia – Evaluation of its antioxidant and anticancer activity

Highlights

• Synthesis of smaller size tetragonal nano-ZrO₂ by Eucalyptus globulus leaves extract

• ZrO₂ NPs shows high anti-oxidant activity.

• ZrO₂ NPs are more cytotoxic to A549 compared to HCT116 carcinoma cell lines.

• ZrO₂ NPs can be used as a potential anti-cancer agent.

Abstract

Bioactivity of nanomaterials largely depends on its size, shape and crystalline nature. In this work, the smaller sized spherical shaped nano-zirconia (ZrO₂ NPs) (of ~ 9 to 11 nm) was fabricated and studied its biological activity especially antioxidant and cytotoxicity against human colon carcinoma (HCT-116) and human lung carcinoma (A-549) cell lines. To have its real applications in biological aspects readily available Eucalyptus globulus (E. globulus) leaf extract was used as an effective capping and reducing agent for its synthesis. The prepared ZrO₂ NPs was characterized by using different sophisticated instrumentations such as UV–visible spectrophotometer, XRD, FTIR, TEM, SAED, EDX, DLS and fluorescence spectroscopy. Cellular mitochondrial activity i.e. cell viability was measured by MTT assay and anti-oxidant activity was determined by DPPH assay. The smaller sized ZrO₂ NPs showed strong antioxidant activity as well as cytotoxicity on human cancer cell lines. Comparative cytotoxic studies were conducted on human cancerous cell lines using different techniques. Results confirmed the efficient anti-cancer activities of the fabricated ZrO₂ NPs towards the tested cell lines as well as efficient anti-oxidant activity. This is the first study in which E. globulus leaf extract was used to synthesize smaller spherical shaped ZrO₂ NPs for improved bioactivity i.e. antioxidant and cytotoxicity.

Introduction

Environmentally friendly nano regime materials were developed for the past few years with the aim of low-cost production using simple green technologies. Nano zirconia (ZrO₂ NPs) are widely used in various photocatalytic, piezoelectric applications, as a catalyst in various organic reactions [1] and industries for ceramics, dental and optical coatings [2], [3]. The cytotoxic activity of nanoparticles mainly depends on its size and shape [4], [5]. Various chemical methods such as solvothermal method, hydrothermal method [6], [7], [8], [9], [10], aqueous precipitation method [11], sol-gel method [12], [13], [14], thermal decomposition methods [15], [16], [17] and pyrolysis of zirconium oxychloride salt organic precursors have been applied to prepare ZrO₂ NPs [18]. These methods are more effective for the controlling the shape and size of nanoparticles but often results in the formation of mixed crystal phases [19], [20], [21]. However, all these methods require high temperature, costly and environmentally hazardous chemical precursors during synthesis processes [22], [23].

Green synthesis has been adopted nowadays as the best alternative to the above-mentioned methods to synthesize nanomaterials because these methods are simple, fast and environmentally safety procedures. Reports based on this energy sustaining process are very less. Bansal et al. reported the biosynthesis of ZrO₂ NPs by using fungus Fusarium oxysporum at neutral pH [24]. Phytosynthesis (plant extract based) of ZrO₂ NPs was first reported by researchers using Curcuma longa tuber extract [25]. Researchers have performed the cytotoxicity of ZrO₂ NPs [5], [26], but as per our knowledge, no cytotoxicity study for green synthesized ZrO₂ NPs is available in the literature.

In the present work, first time we reported green synthesized Nano zirconia with smaller size range using leaf extract of Eucalyptus globulus (E. globulus). Also, its anti-oxidant activity was monitored by using DPPH (1,1,diphenyl-2-picryl hydrazyl) assay and cytotoxic efficiency was studied by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay against cancer cell lines such as human colon carcinoma (HCT-116) and human lung carcinoma (A-549) cell lines.