Improved antifungal activity and stability of chitosan nanofibers using cellulose nanocrystal on banknote papers

Highlights

• Using new combination of nanomaterials as anti-fungal.

• Obtaining good results by using both nanomaterials as anti-fungal.

• Investigation of the effect of CNC and CNF as anti-fungal agents on the banknote paper alone.

• The results could open up the new windows to use as anti-fungal bio-nanomaterials in paper making or banknotes applications.

• Using very important test on the cell growing that we call it MTT.

Abstract

Microorganisms can spread on the surface of banknotes and cause many infectious diseases. Chitosan nanofibers (CNFs) and cellulose nanocrystals (CNCs) are nanomaterials, which can affect the antimicrobial properties. In this study, the fungal species that grew on the surfaces of collected banknotes from different places were identified. To examine the antifungal effect of the both nanomaterials on the banknotes, the stable coatings using CNFs and CNCs emulsions were prepared by roller coating. The results revealed that the most colonies in the banknotes obtained from the bakeries and butcheries were Aspergillus sp., whereas the colonies in bus terminals and the hospitals were Aspergillus niger and Penicillium, respectively. The results showed that the CNCs had no antifungal effect alone on the aforementioned species, but it could improve the antifungal effect, adhesion, and stability of CNFs on the banknote surfaces. This study suggested a new approach to decrease the infection spreads through banknotes.

Introduction

Paper currency is a public health risk when associated with the simultaneous handling of food, leading to spread of nosocomial infections. The previous research reported that the banknotes were contaminated with either bacteria or fungi (Honua, 2017). In order to decrease the public health risk, various additives such as antibacterial and antifungal agents could be added to the banknote papers. Nanotechnology is an approach that can be used to produce antimicrobial coatings on the papers. The nanomaterials, not only improve specific mechanical, physical, and chemical properties, but also serve as carriers for some active substances, such as antioxidants and antimicrobial agents (Yien, Zin, Sarwar, & Katas, 2012). Adding these nano-size additives could also increase the durability of the final products. In the recent years, inorganic nanomaterials have been used as antifungal agents, but concerns regarding their negative effects on human health restrict their applications as antimicrobial agents (Ahamed, AlSalhi, & Siddiqui, 2010; Gopalan, Osman, Amani, De Matas, & Anderson, 2009).

Chitosan is considered as an antibacterial and antifungal agent. Due to its similar structure to the cellulose, the applications of chitosan have been received attention in the paper making industry. In a dilute acidic solution, −NH₂ groups of chitosan transforms into a polycation, leading to better absorption to an anionic pulp by electrostatic interactions. This characteristic makes chitosan an ideal wet-end functional additive in paper making (Tsigos et al., 2000). There has been a growing interest in using chitosan as a coating material for various applications, because of its remarkable film-forming (Aider, 2010). Antifungal activity is one of the most important bioactivities of chitosan, and earlier studies have reported that chitosan films can be used for preservation of foods in packaging and reducing microbial numbers on health care (Hamed, Özogul, & Regenstein, 2016; Roller & Covill, 1999). The antifungal effect can be offered to the paper by the immobilization of CNFs on cellulose fibers before paper forming or by the incorporation into surface coating films. The positive charges in chitosan enhance the permeability of the membrane and leakage of cellular contents through interaction with negatively charged phospholipids of fungal membrane. The other mechanisms through which chitosan acts as antifungal agent are related to its binding to trace nutrients and inhibition of DNA synthesis (Kong, Chen, Xing, & Park, 2010; Rabea, Badawy, Steurbaut, & Stevens, 2009). Studies reported that chitosan based nanoparticles has antifungal activity in some fungi such as A. brassicicola, A. solani, A. flavus, A. niger and etc. (Kashyap, Xiang, & Heiden, 2015; Saharan et al., 2013). It has been reported that the chitosan nanofibers (CNFs) showed more effective antimicrobial activity compared with chitosan, may be due to their high surface to volume ratio and higher affinity with the cells, which produce a quantum-size effect (Jayakumar, Prabaharan, Nair, & Tamura, 2010).

Previous research showed that combination of chitosan and cellulose nanocrystals (CNCs) can produce coating films with superior properties (Naseri, Mathew, Girandon, Fröhlich, & Oksman, 2015). CNCs are crystalline nanometer sized rod-like particles. It has been demonstrated that antimicrobial activity can be affected by conjugation of CNCs with different antimicrobial agents such as metal nanoparticles, organic compounds, etc. (Abouhmad, Dishisha, Amin, & Hatti-Kaul, 2017). We hypothesize that using CNCs could reinforce films produced from CNFs and therefore enhance its stability and even its functionality. To this end, an attempt was made here to produce antifungal coatings for banknotes through roller coating of CNFs and CNCs mixture with the highest noncytotoxic doses. Moreover, the fungal frequency on a common currency note of lower denominations was identified. Then, the efficiency of antifungal activity of coating was assessed against the most abundant fungal species on the banknotes.