RavichandranSathishkumar, Subramanian Srinivasan^*
JKKN College of Pharmacy, Komarapalayam, Salem, Tamil Nadu, India
Department of Environmental Science, Periyar University, Salem, Tamil Nadu, India

Article history:

Received 26 April 2021

Revised 28 May 2021

Accepted 15 June 2021

Available online 30 June 2021

Keywords:

Zinc oxide nanoparticles

Plant extract

Microbes

Antimicrobial

Photocatalytic

In current science, nanotechnology is an important area for material science researchers due to their diversify applications in the field of material engineering, medical science, pharmaceutical science, etc. The biomedical applications of nanomaterials have been usage with the nanoscale dimension range of 1-100 nm. Recently, the zinc oxide nanoparticles (ZnO NPs) had been reported large band gap energy and binding energy which important physicochemical feature has potential applicable for various biological applications like anticancer, anti-diabetic, antibacterial, antifungal, wound healing, anti-inflammatory, antioxidant and optic, etc. Generally, the conventional method synthesis of ZnO NPs has involved toxic hazardous chemicals and afterwards which leads to myriad health risks as well as environment. However, the advantages of biogenic method synthesis of ZnO NPs is free chemical, eco-friendly and cost-effectively. The biological methods have been employed various resources of plants, bacteria, fungi and algae, etc. In this review is focused on the biogenic synthesis of ZnO NPs and their biomedical applications.

Nanomaterials are new emerging field of research and that nanoscale dimension of materials dealing with various biological applications such as sensors, catalysis, electrochemistry, optics, space industry, textile industries, pharmaceutics, biomedicals, cosmetics, health care, agriculture and food technology, (Ayelen Velez  et al., 2017; Fernandes et al., 2017; Sharif et al., 2017; Syedmoradi et al., 2017; Bera et al., 2016) etc. The metal oxide nanoparticles are promising materials as use biomedical applications due to their exhibit unique physicochemical and biological properties. In generally, nanoparticles synthesis have been use chemical method, which process is involving toxic chemicals for reducing and capping agent its leads to side effects in aquatic environment as well as human health care applications. Several methods have been proposed the synthesis of zinc oxide nanoparticles (ZnO NPs) such as precipitation, hydrothermal, vapor deposition, thermal decomposition, microwave, sol-gel, electrochemical depositions and laser ablation, (Kahouli et al., 2015; Mirzaei et al., 2017; Pulit-Prociak et al., 2016) etc. According to the literature survey have been reported, the toxic chemicals are used through the physical and chemical synthesis of ZnO NPs, which techniques are required high energy, and more expensive its leads hazardous to health risk (Vijayan et al., 2016). Thus, reasons recently several researchers have been focused on green chemistry method synthesis of ZnO NPs, because of their eco-friendly, less toxic chemical and one step synthesis of nanoparticles. The biogenic synthesis method use of plants, microorganisms like bacteria, fungi, algae, yeast and natural raw materials of vegetable and fruits are used for synthesis of nanoparticles (Rajendran et al., 2021; . In this biogenic method presence of some biomolecules or phytochemicals that react as both capping or stabilizing and reducing of metal oxide nanoparticles (Stankic et al., 2016; Khan et al., 2016). Fig. 1, shows graphical abstract of biogenic synthesis of ZnO NPs. In currently more researchers have been clearly reported, the highly considerable potential antimicrobial activity of green synthesized metal oxide NPs like SiO2, MgO, TiO2, CaO, CuO, Iron oxide and ZnO NPs.  In this review is focused on the biogenic synthesis of ZnO NPs and their biomedical applications.

2. 0. Biogenic synthesis of ZnO NPs using plant

Plant mediated synthesis of ZnO NPs have been using of leaf, fruit, stem and root because of they are exclusive presence of phytocompound that at act as capping and reducing or stabilizing agent of ZnO NPs. In this alternative method of plant parts mediated synthesis is a very less cost effective, ecofriendly and an easily to handling procedure. In moreover, the less involve of

Fig 1. Graphical abstract of biogenic mediated synthesis of Zno NPs

costly equipment as well as chemical precursor. Generally plant mediated synthesis of metal oxide or ZnO nanoparticles are most preferred because of highly purities, less toxic effect, stable and possible to large scale production. The phytochemicals of polyphenolic compounds, polysaccharides, terpenoids, alkaloids, vitamins, amino acids are secreted from plant parts which involve bio-reduction conversion reaction of metal oxide or metal ions to 0 valence ZnO NPs (Qu et al., 2011; Heinlaan et al., 2008).

A very commonly applicable method for the green synthesis of ZnO NPs from plant parts such as leaves, stem, root and flowers,

etc. are collected and washed thoroughly washed with running tap water, its help to removal of unwanted materials and debris particles and then finally washed with deionized water. The plant parts were air dried at room temperature followed weighing and chopped into small pieces then crushing in a mortar pestle. Milli-Q water (or different solvents ethanol, methanol, etc.) is directly added to plant parts as desired concentration and then mixture solution was boiled under the continuous magnetic stirring. The solution is filtered and desired volume of plant parts extract is mixed with desired Mm concentration of zinc sulfate or zinc nitrate solution and then the mixture is boiled at desired temperature and time to achieve formation of ZnO NPs. After that incubation time the mixture solution turned into yellow color which is primarily conformation of the synthesized ZnO NPs. UV-Vis spectrophotometry is performed to confirmation of synthesized ZnO NPs and followed to mixture solution is centrifuged then collected pellet is air dried in hot air oven. In moreover, synthesized ZnO NPs are additionally characterized using of Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffractometer (XRD), Field Emission Scanning Electron Microscopy (FESEM) with Energy Dispersion Analysis of X-ray (EDAX), High-Resolution Transmission Electron Microscopy (HRTEM), Thermal-gravimetric Differential Thermal Analysis (TG-DTA), Photoluminescence Analysis (PL), Raman Spectroscopy, Attenuated total reflection (ATR), Dynamic Light Scattering (DLS), and Thermal-gravimetric Differential Thermal Analysis (TG-DTA) (Rajeshkumar et al., 2016; Ochieng et al., 2015; Qu et al., 2011).

Waseem Ahmad and DivyaKalra, have been reported the green synthesis of ZnO NPs using of Euphorbia hirta leaf extract. The ethanolic extraction of phytocompounds is clear revealed that presence of flavonoid, alkaloid, sponins, terpenoids and carbohydrate obtained from Euphorbia hirta extract. The X-ray diffraction pattern and SEM images are also revealed hexagonal structure and spherical aggregation observed. The synthesized ZnO NPs is potential against Gram positive bacteria of Staphylococcus aureus and fungi of Aspergillusniger, Cuboida, the result is suggested Euphorbia hirtamediated synthesized ZnO NPs is possible material for biological related applications. Another similar reported Sharma et al. using Carica papaya mediated synthesis of ZnO NPs surface morphology is revealed nanoflowers structure. The ZnO NPs was excellent biodegradation properties and exhibited good antibacterial activity against of Staphylococcus aureusand Pseudomonas aeruginosa(Ahmad, W and Kalra, D, 2020). Table. 1 showed recent reports of plant mediated synthesis of ZnO NPs.

2. 2. Biogenic synthesis of ZnO NPs using bacteria

Bacteria mediated synthesis of ZnO NPs is another important green synthesis approach but it has various disadvantages like broth culture careful monitoring from the contamination, difficult of microbial screening process, bacterial culture medium is also Very costly and production of nanoparticles undesirable size and shape

Table 1 Zinc oxide nanoparticles (ZnO NPs) biogenic synthesis using by plant part

The screened or selected bacterial culture is inoculated into an Erlenmeyer flask containing bacterial culture medium. After that incubation, various concentration of ZnO precursor (Zinc nitrate or zinc sulfate) is added and incubated at 37°C for 24hrs, until white precipitation deposit at bottom of conical flask that the conformed to formation of ZnO NPs. Then visual conformation followed to initial NPs bio-reduction can be monitored by using UV-Vis spectrophotometer. Separation of NPs, the bacterial culture medium is transferred into centrifuge tubes and centrifuged at 3000 rpm for 15 min, after that process pellets were collected and washed with distilled water for the further application process (Ahmed et al., 2017).

ZnO NPs is synthesized from Aeromonashydrophilathroughthe biogenic approach method. In this rout of synthesized ZnO NPs surface morphologies were revealed smooth and spherical in shape which performed antimicrobial activity against both bacteria and fungi. ZnO NPs maximum zone of inhibition was showed against Pseudomonas aeruginosa and Aspergillusflavus which proved potential antimicrobial properties of synthesized ZnO NPs (Jayaseelan et al., 2012). In furthermore, similar research report the synthesis of ZnO NPs using by B. licheniformisthrough an eco-friendly method which is revealed nanoflowersZnO NPs and it showed potential photocatalytic activity the degradation of Methylene blue dye (Raliya et al., 2013). Another researcher has been reported through the biosynthesis of ZnO NPs using of Lactobacillus plantarum TA4, which HR-TEM images of biosynthesized ZnO NPs showed irregular flower like pattern of ZnO NPs supernatant (CFS) and cell-biomass (CB) with particles size ranges between 291.1 and 191.8 respectively. Biosynthesized ZnO NPs was potential bactericidal activity against pathogenic bacteria of Pseudomonas aeruginosa, Bacillus subtilis, and Helicobacter pylori. Biocompatibility experiment was performed the synthesized ZnO NPs by using of Vero cell line (Yusof et al., 2020).

Table 2 Bacterial mediated biogenic synthesis of zinc oxide nanoparticles (ZnO NPs)

2. 3. Biogenic synthesis of ZnO NPs using algae

Photosynthetic organism of marine algae unicellular forms (ex. Brown algae). Marine algae can be classified based on the pigment present like chlorophytes presence of green pigment, Phaeophyta with brown pigment and Rhodophyta containing red pigment. Algae extract solution presence of proteins, carbohydrates, oil, minerals, fats, bioactive compounds like antioxidants (tocopherols, polyphenols) and pigments such as chlorophylls, phycobilins, and carotenoids which bioactive compounds potentially capping and reducing or stabilizing agents of biosynthesized NPs (Sharma et al., 2016; Michalak and Chojnacka, 2015; Thema et al., 2015).  Marine algae mediated synthesis of ZnO NPs has been reported very limit of research papers. In this method, algae mediated synthesis of ZnO NPs is involves steps such as metal precursor, algae extract and desired time incubation of algal extract solution with precursor. After that process color change is visually observed it’s to be conformed the formation ZnO NPs.  Rajiv et al., have been reported, the green synthesis of ZnO NPs using of Sargassummuticum and S. myriocystumunder to the family of Sargassaceae. Biosynthesized ZnO NPs results of XRD and FESEM are revealed hexagonal wurtzite structure with presence of sulfated polysaccharides and hydroxyl group. Yung et al., have been reported green synthesis of ZnO NPs using of freshwater algae C. reinhardtii (FACHB-479), C. pyrenoidosa (FACHB-9) and P. subcapitata (FACHB-271) (Rajiv et al., 2013). Table 3 illustrates algae mediated synthesis of ZnO NPs

Table 3 Algae mediated Biogenic synthesis of zinc oxide nanoparticles (ZnO NPs)

2. 4. Biogenic synthesis of ZnO NPs using fungus

Fungal extracellular mediated synthesis of ZnO NPs is highly preference because of their metal bioaccumulation, high metal tolerance, large scale production, downstream process and low cost effective (Pati et al., 2014). Bacterial strain compared to fungal culture mediated synthesis of ZnO NPs is easy to maintain and can be culturing, fast growth in the laboratory at room temperature conditions. Moreover, biologically mediated synthesized ZnO NPs has been gained more importance due to their non-toxic and biocompatibility.

Table 4 Mycological mediated synthesis of zinc oxide nanoparticles (ZnO NPs)

Pavani et al., have been reported, fungal mediated synthesized of ZnO NPs using Aspergillusfumigatus that DLS analysis exhibited the size range of 1.2 to 6.8 and with the average particles size of 3.8 nm. Another similar report have been using of Aspergillusfumigatus for the synthesis of ZnO NPs. The NPs size range of 54.8–82.6 nm were evaluated by SEM analysis and XRD analysis to be calculated average particle size of 29 nm through followed Debye-Sherrerequation method. Primary and secondary compounds such as alcohol, amine, and aromatic nitro and also to be confirmed the NPs formation by FTIR analysis (Pavani et al., 2012). Table 4 represents the recent reports of fungal mediated synthesis of ZnO NPs.

3.Conclusion

In this review mainly summarized on the eco-friendly biosynthesis approach of ZnO NPs by using of plants and microbes source in the last decade. Green route of biosynthesis NPs has containing the bioactive compounds that can be act as reducing and stabilizing agents and also size and shape control manner. Among different biological pattern synthesis of ZnO NPs which through the microorganism mediated synthesis is not an ease industrial scale production because of their highly requirements of aseptic conditions and high cost effective of culture medium as well as maintenance. Therefore, generally plant extract mediated synthesis of NPs has been possessing several advantageous over compared to microorganisms due to the less biohazard, ease handling and single step process. Phytosynthesis of ZnO NPs needs to be more research due to the huge availability of plant species and become potential candidate as phytonanofabication. In further more research needs to be exploring actual mechanism of phytosynthesis of ZnO NPs and their biological applications.

        Funding: The authors received no specific funding for this work.

        Conflicts of Interest: None

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