Chitosan/calcium nanoparticles as advanced antimicrobial coating for paper documents

https://doi.org/10.1016/j.ijbiomac.2022.06.142Get rights and content

Highlights

  • Calcium/chitosan nanoparticles (Ca/CS NPs <100nm) were successfully prepared via the modified ionic gelation method

  • Ca/CS NPs displayed enhanced antibacterial and antifungal activity compared to bare chitosan nanoparticles.

  • Antimicrobial activities of chitosan and calcium/chitosan moieties were investigated through molecular docking analysis.

  • Paper protection potential of the Ca/CS NPs was evaluated through the antimicrobial analysis and the pH stability test.

Abstract

Preservation of paper-based historical artifacts against deterioration due to the presence of bacteria and fungi colonies has been one of the major issues for the importance of protecting the cultural heritage of humankind. Advances in nanotechnology have enabled the implementation of nanomaterials for this purpose. In this work, calcium/chitosan nanoparticles (Ca/CS NPs) were prepared and well-characterized to investigate their potential as a novel approach for preserving paper-based documents. Following the fundamental characterizations, it was found that Ca/CS NPs are spherical nanoparticles with ~65 nm average size and homogenous dispersion (PdI: 0.2). Besides, minimum inhibition concentration results revealed that Ca/CS NPs show a superior antimicrobial effect against specific bacteria and fungi strains commonly found on paper documents compared to the effect of bare chitosan nanoparticles (CS NPs). After the deposition of Ca/CS NPs onto the paper the pH level was increased and stabilized, and only a limited amount of microbial colony formation was observed for up to 20 days. Moreover, molecular docking analysis provided a better insight into the antibacterial and antifungal activities of these nanoparticles. The antimicrobial activity of CS NPs and Ca/CS NPs was investigated through their interactions with E. coli DNA gyrase B and C. albicans dihydrofolate reductase. The binding modes and all possible interactions of active sites were confirmed by in silico molecular docking method. Collectively, our findings revealed that the formulated Ca/CS NPs are promising candidates for preserving paper documents.

Introduction

In recent years, advances in nanotechnology have pioneered new research fields such as the conservation of paper-based artifacts using nanomaterials. The preservation of paper-based historical artifacts is a critical process, primarily based on neutralizing the acidity level of the artifact. The increase in the acidity of the artifacts over time causes deformations in the cellulose structure of the paper, thus causing the paper to deteriorate and lose its integrity. There has been an intense effort to prepare various micro/nanoformulations as deacidification agents developed by nanotechnology. Various deacidification agents such as magnesium hydroxide, calcium hydroxide, or calcium carbonate are used to remove the acidity of the paper [1], [2], [3], [4]. These agents all have diminished the acidity of paper-based materials and strengthened them. Although these approaches are useful and effective, they mainly focus on the papers' neutralization through specific alkali agents.

The presence of bacteria and fungi on paper-based materials also plays an important role in increasing acidity. The extracellular secretions of these microorganisms increase the acidity level in the cellulose structure and eventually lead to disruption of the paper [5]. Removing the bacteria and fungi colonies from the artifact can also be considered as an effective approach that will indirectly strengthen the cellulose structure and prevent increased acidity. Usage of well-investigated antimicrobial agents such as benzimidazole and sulfonamid derivatives can be an effective strategy to prevent microorganism growth [6], [7], [8], [9], [10]. Moreover, this antimicrobial activity can be improved either by using antimicrobial nanomaterials alone or coupled with specific antimicrobial agents [10], [11], [12]. In the sense of paper conservation, Ponce-Jimenez et al. proved that chitosan provides effective protection for the papers against deterioration [13]. Jia et al. prepared chitosan nanoparticles (CS NPs) around 75 nm using the ball milling method and demonstrated that CS NPs can provide a safe environment acting as antimicrobial agents as well as reinforcement materials [14]. These efforts indicate a strong need to develop novel nanostructures that can provide enhanced protection for paper-based documents.

In addition to the studies mentioned above, our approach is based on increasing the effectiveness of CS NPs by calcium decoration. Here, we prepared calcium/chitosan nanoparticles (Ca/CS NPs) to preserve paper-based library and archival materials. Following the fabrication of the nanoparticles, they were characterized by dynamic light scattering to determine their average size, zeta potential, and dispersity index. Also, morphological and chemical makeup analyses were performed by Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and Energy dispersive X-ray (EDX) spectroscopy, respectively. The deacidification effect of the nanoparticles was investigated via periodic pH level measurements on paper-based samples, and their antimicrobial activity was confirmed through the minimum inhibitory concentration (MIC) assay for specific bacteria and fungi strains. Moreover, the antimicrobial activity of chitosan and Ca/CS NPs at the molecular level was investigated. At the molecular level, DNA gyrase and dihydrofolate reductase (DHFR) are preferred as essential targets to elucidate the antimicrobial properties of the materials [15], [16], [17]. The binding modes and energies of the antibacterial DNA gyrase and antifungal Candida albicans dihydrofolate reductase receptors and the inhibition activities at the active sites of these receptors were determined through molecular docking technique. Finally, this antimicrobial effect was also tested after the nanoparticle coating on the paper-based samples. The resulting nanoparticles displayed a microorganism-free environment for up to 10 days for the paper-based sample.

Section snippets

Materials

Chitosan (75–85 % deacetylated, low molecular weight, CAS no. 9012-76-4), sodium tripolyphosphate (TPP, CAS no. 7758-29-4), and calcium hydroxide (CAS no.1305-62-0) were from Sigma–Aldrich. Acetic acid (CAS no. 64-19-7) was purchased from Merck. For antimicrobial tests, the nutrient broth (CAS no. 70122) was purchased from Sigma-Aldrich. The strains of Micrococcus luteus (ATCC 15307), Bacillus megaterium (ATCC 14581), Bacillus subtilis (ATCC 6051), Aspergillus niger (CRM-16404), Aspergillus

Physicochemical characterization of CS NPs and Ca/CS NPs

DLS results of the nanoparticles are presented in Table 1. The average particle size and PdI values of both CS NPs and Ca/CS NPs are <100 nm in size and have homogeneous dispersion. The association of calcium ions with the blank chitosan nanostructures resulted in a small increase in average particle size from 61.5 ± 0.4 nm to 66.7 ± 0.7 nm and PdI value from 0.1 to 0.2. Besides, the zeta potential value of Ca/CS was reported as 11.7 ± 0.9 mV, whereas it was 16.9 ± 0.6 mV for bare CS NPs These

Conclusion

CS NPs successfully prepared and decorated with calcium ions for the preservation of paper-based artifacts. Antifungal and antibacterial assays revealed that calcium decoration increased the antimicrobial activity of the nanoparticles, by lowering the required dosage and increasing the inhibitory effect. This antimicrobial activity also enabled pH stability to the paper-based artifacts.

The molecular docking results were also in accordance with the antimicrobial activity results. In particular,

CRediT authorship contribution statement

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be submitted to IJBIOMAC.

Acknowledgment

In this study, the support of The Scientific and Technological Research Council of Turkey (TUBITAK) (Project number: 2180454) was used. The authors would thank TUBITAK for their support. We would like to thank Anuipraya Kumar for allowing the Small Molecular Docking program. E.M. would like to acknowledge the support from the National Institute of Biomedical Imaging and Bioengineering (5T32EB009035).

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