Elsevier

Applied Surface Science

Volume 575, 1 February 2022, 151764
Applied Surface Science

Full Length Article
Influence of erbium doping on zinc oxide nanoparticles: Structural, optical and antimicrobial activity

https://doi.org/10.1016/j.apsusc.2021.151764Get rights and content

Highlights

  • Pure and Er-doped ZnO were synthesized by a wet chemical method.

  • XRD shows that Er-doped ZnO at high at.% kept their hexagonal structure.

  • The optical band gap was improved as Er at.% increased.

  • Antimicrobial activity of Er-doped ZnO was tested against Staphylococcus aureus and Escherichia coli.

  • ANN model was trained with lab data, such model predicts absorbance with a 1–2% error.

Abstract

Antimicrobial activity of the Zn1-xErxO (0, 1, 5, 10 at.%) nanoparticles were tested against Staphylococcus aureus and Escherichia coli. The nanoparticles were successfully synthesized by wet chemical route, where polyvinyl alcohol and sucrose were used. The influence of erbium content in structural, optical, and antimicrobial activity was analyzed. The average crystallite size is under 15 nm for all the samples according to X-ray diffraction results, and no secondary phases were observed even at high erbium content. Optical results exhibit a blue shift in the ultra-violet region. The X-ray photoelectron spectroscopy analysis confirmed the variations of Zn/O ratio, together with particles size and band gap are key factor in antimicrobial properties. The microbiological essays exhibit to these nanoparticles as a high potential agent with antibacterial activity versus S. aureus, with lower impact in E. coli. The absorbance results of these assays were used in two theoretical approaches. At first, Gompertz model used in the regression analysis showed the best fit for bacterial growth. Additionally, an artificial neural network was trained to forecast the result of new experiments, showing a good performance.

Introduction

Highly multidrug-resistance (MDR) bacteria cause a high percentage of nosocomial infections (NIs). NIs have public health consequences given their potential to endanger patient safety, prolong hospitalization stay, and increase treatment cost, resulting in high mortality and morbidity rates [1]. The inability to act against MDR bacterial strains is a current concern because it represents a severe risk to human health worldwide [2]. Available antibiotics have many shortfalls that enforce the quest for novel and better materials against a wide spectrum of bacteria [3]. Recent strategies, including the use of metal oxide nanoparticles (MONPs) such as Ag2O, TiO2, CuO, MgO, and ZnO, has been receiving increased attention due to their broad-spectrum antimicrobial properties [4], [5], [6], [7], leading to new potential agents that effectively act against the bacterial strains associated with NIs.

MONPs exhibit effective action against a wide range of Gram-positive and Gram-negative bacterial strains due to their high photocatalytic activity, good biocompatibility, and non-toxicity [8], [9]. Among the MONPs evaluated so far, zinc oxide (ZnO) has proved to be an efficient antibacterial agent because of its ability to over-accumulate reactive oxygen species (ROS) and metal ions to disrupt normal bacterial cell homeostasis [10], [11]. Additionally, bacteria exposure to the ZnO nanoparticles results in cell envelope rupturing, increased cellular internalization, and mechanical damage [12]. However, the individual performance of ZnO for efficient application remains limited. Therefore, the modification of ZnO has been explored as a promising route to enhance its antibacterial properties. ZnO is a multifunctional material due their physicochemical properties, which can be used in a wide variety of applications [13].

Rare earth elements have been recently employed as antibacterial materials due to their 4f shell electron configuration [14], [15]. In addition, ZnO is one of the best hosts for rare earth ions because of the very similar sizes of Zn2+ and rare-earth ions. Such a small size mismatch makes rare-earth ions easily replace Zn without affecting the crystal structure of ZnO. The electronic structure is also affected by the charge transfer between the valence band (VB) and the conduction band (CB) of ZnO and 4f or 5d electrons of rare earth metal [15].

Different studies have demonstrated the bactericidal properties of MONPs over a broad range of Gram-positive and Gram-negative bacteria such as Staphylococcus aureus and Escherichia coli [16], [17], [18]. S. aureus is a Gram-positive bacterium that causes a wide variety of clinical diseases [19]. Infections caused by this pathogen are common, both in community and hospital-acquired settings. S. aureus is also a leading cause of bacteremia, endocarditis, skin and soft tissue infections, bone and joint infections, and hospital-acquired infections [20]. E. coli is one of the most studied prokaryotic microorganisms worldwide and is an enteric bacterium, constituent of a fraction of the human microbiome [21]. Extraintestinal E. coli infections, such as urinary tract infections and neonatal sepsis, represent a substantial public health problem [22].

The aim of this work is to study the effect of the Er in the Zn1-xErxO (0, 1, 5, 10 at.%) nanoparticles as an antimicrobial agent against Staphylococcus aureus and Escherichia coli. The Zn1-xErxO (0, 1, 5, 10 at.%) particles were prepared using polyvinyl alcohol (PVA) and sucrose. The effect of the Er was studied by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), specific surface area (SBET), Field-emission scanning electron microscopy (FE-SEM), Ultraviolet–visible spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). The data obtained from antimicrobial kinetics was used to adjust the bacterial growth to several mathematical models. The data was also used to compute a model using an artificial neural network (ANN). This ANN model can be used to assess in future experiments the relevance of them, allowing the experimenter to decide whether to run them or not.

Section snippets

Nanomaterials synthesis

The Zn1-xErxO (0, 1, 5, 10 at.%) nanoparticles were prepared by a solution-polymerization method [23], in this work citric acid was used to improve the chemical reaction. Two solutions were prepared: (S1) the first solution with 0.4 g of PVA (PVA a.m.w.: 70000–1000) and 3.2 g of sucrose (C12H22O11) were dissolved in 100 mL of deionized water with stirring at 70 °C to dissolve PVA. The second solution (S2) includes the Zn(NO3)26H20 (98%) and Er(NO3)35H2O (99%) for each composition, which were

Structural characterization

The effect of the Er of structural parameters of the Zn1-xErxO (0, 1, 5, 10 at.%) nanoparticles was studied by X-ray diffraction (XRD). Fig. 2a shows the diffraction patterns of the as-prepared nanomaterials, where the crystalline structure of all the samples, exhibited by the presence of the main diffraction peaks (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0), (1 1 2) and (2 0 1) which are associated to the hexagonal wurtzite structure of ZnO according to the JCPDS # 36–1451, and space group P63

Conclusions

In summary, the Zn1-xErxO (0, 1, 5, 10 at.%) nanoparticles were prepared by the wet chemical method were PVA and sucrose were used as stabilizer and fuel, respectively. According to XRD results, the hexagonal wurtzite structure of the ZnO was kept even at high Er content. The lattice parameters show a slight contraction, then a strain is observed; this occurred at Er content below 5 at.%. The average crystallite size is under 20 nm for all the samples, being the sample with 5 at.% of Er the

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.

Acknowledgements

This work was partially funded by COECYTJAL through FODECYJAL Program and Tecnologico de Monterrey, through the Nutriomics and Emerging Technologies, Biomedical Engineering, Bioinformatics, Translational Omics, and Nanotechnology and Devices Design research groups. Also, A. Sanchez-Martinez acknowledges to CONACyT through Catedras project No. 67.

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