Core/shell nanoparticles: Synthesis, investigation of antimicrobial potential and photocatalytic degradation of Rhodamine B
Graphical Abstract
Introduction
Bacterial pathogenesis is becoming a major concern of diseases and infections in patients of all age groups ranging from infant to adults. The ability of bacterial pathogens to resist antibacterial agents and the immune system has increased the chances of oral and nosocomial infections. For instance, antibacterial agents such as penicillin and sulfonamide have failed against pathogenic bacteria [1]. The gradual and stable increase in the development of resistance to antimicrobial agents has led to the finding of new unconventional bactericidal agents. In the present scenario, Nanoparticles (NPs) are gaining attention towards the treatment of infections and diseases. Metallic NPs are known to be potential antibacterial agents against pathogenic bacteria [1]. To date, different metallic NPs such as silver, zinc, copper, iron, and magnesium have been extensively studied against pathogenic bacteria [[1], [2], [3]].
Metal oxide NPs (MONPs) depend upon the structural geometries of particles responsible for the types of applications such as conductors (metals), semiconductors or insulators. The widely used metal oxides are SnO2, ZnO, Cu2O, CoO, CrO, TiO2, PbO2, Al2O3, MnO, AgO, CeO2 and ZrO2. Metal oxide NPs were synthesized using different methods including co-precipitation, thermal decomposition, microemulsion, hydrothermal and sonochemical methods [4]. MONPs can be used in various fields such as heterogeneous catalysis, electrochromic and electromechanical sensors, pigments and dyes, energy storage devices, bioimaging, biosensors, solar cells, and drug carriers. Nevertheless, all the metallic NPs are dose-dependent and become toxic at higher concentrations. The implication of coating materials over MONPs with organic materials reduces the toxicity and increases the efficacy of MONPs.
Core/shell NPs are highly functional materials having improved properties and gained progressive attentions of various researchers [5,6]. The properties of core/shell NPs are quite diverse and adapted towards different application by changing core/shell material composition or type. Core/shell NPs are dual phase nanomaterials having central core structure and exterior shell made up of different components. These particles can unveil unique properties ascending from the blend of materials for core and shell, geometry, and design.
Furthermore, they have been functionalized in a way that the shell material can enhance the reactivity, thermal steadiness or oxidative state of the core material or an economic core material can be used to render a flexible but an expensive shell material [7]. Selecting the shell material for the core/shell NPs is strongly dependent on the application and purpose of NPs. Core/shell nanostructures can be distributed into several modules such as inorganic/inorganic, inorganic/organic, organic/inorganic and organic/organic core shell NPs. Different shapes of core/shell NPs have been synthesized based on research interests and unique properties. The tenacity of the covering over core particle are numerous, such as surface modification, functionality, durability, dispensability, organized release of the core and reduction in depletion of the expensive materials. Core/shell NPs have major advantages over simple NPs viz. less cytotoxicity, easy to discard and biocompatibility [8,9]. In some cases, NPs are lethal at higher concentrations to the host tissue; covering with a stable material will result in lowering of the toxicity and enhancement of the core property. Core/shell NPs are majorly used as biosensors and drug encapsulates in biomedicine [9,10].
Zirconium Oxide (ZrO2) is an excellent metal oxide NPs with a higher band gap of 4.3 to 5.0 eV, higher photocatalytic property and conductivity. ZrO2 NPs are widely used in electronic devices, ceramics, coating, and mixed with various metals to obtain a fragile alloy [11,12]. As a biomedical counterpart, ZrO2 is significantly used in making dental crowns, as dental fillings, and as replacement of Titanium (Ti) for localized reactions and pain [13,14]. Cobalt (Co) MOs is a promising magnetic nanomaterial gathering much attention and with enhanced optical, catalytic and magnetic properties. Co is extensively used in anode materials for rechargeable Li-ion batteries, catalysts, gas sensors and magnetic materials. Co2O4 (cobalt oxide) is a compelling p-type semiconductor having better interconnection with different particle dimensions. However, the robust magnetic contact between cobalt NPs and their preference for oxidation makes it challenging to achieve a steady colloidal substance [[15], [16], [17]]. Therefore, the use of organic stabilizers can be used to control the growth of NPs. The combination of Co2O4 and ZrO2 will give promising core shell nanomaterial with efficient antibacterial properties [18]. The present study has targeted to synthesize such Zirconium oxide (ZrO) NPs using simple sol-gel technique. Further, the core/shell NPs were tested for their inhibitory potential against the growth of pathogenic Gram negative and Gram positive pathogens namely, Escherichia coli, Staphylococcus aureus, Bacillus subitilis and Pseudomonas aeruginosa.
Core/shell nanoparticles are highly functional materials and the structural properties can be easily modified. The surface properties of the core shell nanoparticles by changing the composition of the materials and ratio of core shell material. Based on the core/shell material, the properties like reactivity, thermal stability can be modified. Thus, based on the core shell modification, they can be used in different applications such as biomedical and pharmaceutical applications, catalysis, electronics, enhancing photoluminescence, creating photonic crystals etc. [8]. Thus, rationally tuning the cores or shells of such materials, a range of core/shell NPs can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems. But the present study in the first and foremost report demonstrating the multiple application of Core/shell Zirconium NPs as antimicrobial and bioremediation application.
Section snippets
Chemicals and Microbial Cultures
Zirconyl Nitrate Hydrate (Zirconium oxynitrate) (ZrO(NO3)2.6H2O) was purchased from SRL (Maharashtra, India), Ammonium Hydroxide (NH3OH), Cobalt Chloride (CoCl2.6H2O), Potassium Hydroxide pellets (KOH) and Absolute Ethanol (C2H5OH) were purchased from Changshu Hongsheng Fine Chemicals Co., Ltd., China. Acetone (CH3)2CO) and other chemicals were purchased from Spectrum Chemicals (Cochin, India). Muller Hinton agar was obtained from HiMedia (India).
All the bacterial strains namely, Bacillus
Optical Studies
The initial characterization of ZrO2 and Co3O4@ZrO2 core shell was performed using UV Vis absorption spectra. The result of UV Vis analysis revealed the emission of broad peak at 456 nm and 277 nm for ZrO2 NPs while the absorption peak at 470 and 780 nm denoted the synthesis of Co3O4@ZrO2 core shell (Fig. 1a). The Surface Plasmon Resonance (SPR) at these wavelengths confirmed the synthesized NPs as ZrO2and Co3O4@ZrO2 core shell. In comparison with previous reports, the present result suggested
Conclusion
CoZ NPs were successfully designed and synthesized as core/shell Co3O4@ZrO2 NPs using a simple,reliable and cost effective sol-gel technique. The CoZ NPs were characterized by UV–Vis spectroscopy, FTIR, XRD and FESEM- EDAX analyses confirming the formation of spherical shaped NPs. The CoZ NPs were ~600 nm in size with crystalline structures. The core/shell NPs had excellent electrochemical properties of reduction as, revealed by the cyclic voltammogram. Overall, the present report is the first
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors extend their appreciation to the International Scientific Partnership Program ISPP at King Saud University for funding this research work through ISPP# 0081. The author would like to acknowledge CORX Lifesciences and Pharmaceutical Pvt. Ltd, Trichy, Tamil Nadu, India for helping to carry out this work and IGPRED (www.igpred.com) for providing insight and expertise on the research topic and for the assistance that greatly improved the manuscript.
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The authors are equally contributed this work.