Research

, Volume: 14( 1) DOI: 10.37532/ 2320-1967.2022 .14(1).154

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A Facile Microwave-Assisted Synthesis of Sodium Alginate-Coated ZnO and CuO Nanoparticles and their Antimicrobial Effects

*Correspondence:

S. M. SathiyaDepartment of Physics, Arul Anandar College (Autonomous), Karumathur, Madurai, Tamil Nadu, India.,Tel: 9443751487; E-mail:sathiya.martin@gmail.com

Abstract

A facile, green, microwave-assisted co-precipitation technique was used for synthesizing Zinc Oxide (ZnO) and Copper Oxide (CuO) Nanoparticles (NPs) in the presence of a bio-polymer Sodium Alginate (SA) as stabilizer and reducer and the mechanism of the formation of NPs was examined. The analysis of the results showed that there is a strong interaction between the hydroxyl and carboxyl groups of SA with the nanostructured metal oxides. These NPs showed considerable antibacterial activities in both Pseudomonas aeruginosa and Bacillus subtilis. Strong affinity toward hydroxyl and negatively charged carboxyl groups in SA of the NPs with the cell walls of bacterial strains leads to reduction in the bacterial survival significantly. When compared to Gram-positive, both the NPs had better activity against Gram-negative bacterial cultures. The CuO NPs showed maximum zone of inhibition than ZnO NPs due to its intrinsic microbicidal properties.

Keywords

Alginate; Stabilizer; Antibacterial

Introducton

Nanoparticles (NPs) exhibit novel properties for various applications. Critics and others have however, raised questions about the potential toxicity of such materials on living organisms due to either intentional or unintentional contact with them [1,2]. It is also well- known that the reported results of contact on living organisms of NPs are sometimes conflicting [3,4]. Thus, the development of new material at low toxicity in the preparation of NPs attracts an increasing attention [5]. However, stabilization of the NPs, a key role for productive existence of the NPs without aggregation, is an important issue [6- 8].Naturally available polysaccharides are widely used for this purpose.They include chitosan, oligosaccharide, inulin, soluble starch, and xylan, used in the green preparation of metal oxides as reducing and stabilizing agent. Sodium Alginate (SA), an anionic medicinal bio-polymer and sodium salt of alginic acid, is one such natural polysaccharide with an un-branched copolymer with homopolymeric blocks of α-1,4-linked- D mannuronic acid (M block) and β-1,4-linked-L-guloronic acid (G block) units arranged in an irregular block-wise pattern of varying proportions of GG, MG and MM blocks [9-13].

Polymer incorporated metal oxide-based NPs have tremendous scope because of their potential applications not only in the bio-medical field but also in various important fields such as environment, energy and information technology. There has been a great deal of interest in making polymer incorporated metal oxide-based NPs because the impregnation of metal oxide into a polymer matrix can introduce novel properties to the NPs. According to Raveendran et. al., glucose was used as the reducing agent and starch as the protecting agent for the preparation of Au, Ag, and Au–Ag nanoparticles by an environmentally benign method in water for biological application . In recent years, metal oxides have been extensively used as antibacterial agents towards many pathogens. Among the various metal oxides, Zinc Oxide (ZnO) and Copper Oxide (CuO) nanocrystalline materials have been extensively studied because of their potential anti-bacterial properties, low toxicity and cost effectiveness. In the synthesis of the NPs, the carboxyl groups of the polymer matrix can electrostatically interact with metal ions and form a complex.

To the best of our knowledge, the microwave assisted co-precipitation technique for preparing well-dispersed nanocrystalline metal oxide in natural polymeric media has not been reported. Hence, we prepared a simple, rapid and totally green, one-pot approach of nanocrystalline metal oxide (ZnO-CuO) NPs using SA and investigated the antibacterial properties against Pseudomonas aeruginosa and Bacillus subtilis. These have been done after establishing their stabilization, morphologies, and mechanism of their formation.

Materials and Methods

All reagents were of analytic quality and were used without additional purification. The solutions were prepared with Double Distilled Water (DDW). Copper (II) chloride dehydrate, CuCl2.2H2O (Merk, Mumbai, 99% purity), zinc acetate dehydrate, Zn(CH3COO)2.2H2O (Merk, Mumbai, 99% purity), Sodium Alginate with Mr ~ 48,000-186,000, (Loba Chemie, Mumbai) and sodium hydroxide [NaOH] procured from Merck, Mumbai (98% purity) were used in this work

Synthesis of ZnO and CuO nanoparticles

In a typical synthesis process, 1 g of SA was dissolved in 100 mL DDW under vigorous string. After the complete dissolution of SA, 0.3 M (6.5847 g) of Zn(CH3COO)2.2H2O was dissolved to the above solution. To adjust the pH to 10 of the solution, NaOH was added drop-wise to the above mixture. As the reaction progresses, the colour of the reaction mixture changed to milky white. After 2 hrs of continuous magnetic stirring, the reaction mixture was kept in the microwave oven (operated with frequency 2.45 GHz and electrical power 800 W) at 110ºC for 2 min. The solution as prepared was cooled down to room temperature within a short time interval after the reaction, centrifuged, and washed with DDW to remove the by-products.

Then, the obtained product was dried in an oven at 80ºC for 3 hrs, named as ZSA and used for characterization. The same experimental procedure was followed for the synthesis of CuO NPs (named as CSA), by adding 0.3 M (0.51144 g) of CuCl2.2H2O instead of Zn(CH3COO)2.2H2O.

Antimicrobial Activity (Well-diffusion Method)

The antibacterial activity of the as prepared samples of ZSA and CSA were done on the microorganisms by well-diffusion method. The samples of various aliquots of 100 µg/mL, 150 µg/mL, 200 µg/mL and stock solution (1 mg/mL) was dispersed in appropriate amount of DDW and constantly stirred until a uniform colloidal suspension was formed. 5.3 g of Muller Hinton agar was dissolved in 100 mL of DDW and kept at 121ºC for about 15-20 minutes for sterilization. Sterilized mixture was poured on the sterilized plates while the temperature of medium was bearable. To assess antimicrobial activity, an appropriate volume of Pseudomonas aeruginosa (P. Aeruginosa) and Bacilus subtilis (B. Subtilis) was poured into the nutrient broth medium and equal sizes of wells were created. Three concentration of 100, 150 and 200 µg/mL of samples were injected into the respective wells along with positive and negative control. For negative control, DDW was used and for positive control, tetracycline (30 µg/mL) was used for P. Aeruginosa, and cefuroxime (30 µg/mL) was used for B. Subtilis. The plates were kept overnight for incubation at 37ºC. After the incubation, the zone of inhibition was measured in millimeter (mm). For each concentration, measurements were made in triplicate and their mean value is taken into account for the antibacterial activity of the sample [17].

Characterization Techniques

X’Pert Powder PANalytical X-ray diffractometer was used to study X-Ray Diffraction (XRD) patterns. The scan rates were made in the range of 10-70º (2θ) with a step size of 0.02 o and a count time of 2 sec/step. Transmission Electron Microscopy (TEM) analysis was carried out at a 200 kV Tecnai G2 20 microscope, equipped with a LaB6 filament and a CCD camera. The sample for IR analysis was prepared by mixing KBr with 10% NP powder by weight and pressing into a vacuum pellet at 200 kg cm-2 for 1 min. For this purpose, KBr tablets were prepared from the sodium alginate biopolymer, CuO and ZnO NPs, and the FTIR spectrum was obtained in the range 400-4000 cm-1 with a (Bruker, Germany, Vertex 70) spectrophotometer. Zeta (ζ) potential values were measured using a zeta/nano particle analyser Zetasizer Nano Plus (Micromeritics Instrument corporation, USA). Before zeta potential measurements, all samples were sonicated for 5 minutes.