Elsevier

Applied Surface Science

Volume 355, 15 November 2015, Pages 446-452
Applied Surface Science

Developing of a novel antibacterial agent by functionalization of graphene oxide with guanidine polymer with enhanced antibacterial activity

https://doi.org/10.1016/j.apsusc.2015.07.148Get rights and content

Highlights

  • A novel antibacterial material, polyethylene glycol (PEG) and polyhexamethylene guanidine hydrochloride (PHGC) dual-polymer-functionalized graphene oxide (GO) (GO-PEG-PHGC), was synthesized.

  • GO-PEG-PHGC had excellent antibacterial activity against E. coli and S. aureus.

  • GO-PEG-PHGC shows enhanced antibacterial activity when compared to GO, GO-PEG or GO-PHGC alone, which was described to be related to a better dispersion of GO-PEG-PHGC in the presence of PEG.

Abstract

New materials with excellent antibacterial activity attract numerous research interests. Herein, a facile synthetic method of polyethylene glycol (PEG) and polyhexamethylene guanidine hydrochloride (PHGC) dual-polymer-functionalized graphene oxide (GO) (GO-PEG-PHGC), a novel antibacterial material, was reported. The as-prepared products were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), X-ray pattern (XRD) and elemental analysis. The antibacterial effect on the bacterial strain was investigated by incubating both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). The results show that GO-PEG-PHGC has enhanced antibacterial activity when compared to GO, GO-PEG or GO-PHGC alone. The improved antibacterial activity was described to be related to a better dispersion of GO-PEG-PHGC in the presence of PEG. This better dispersion leads to a greater contact between the bacteria membrane and nanomaterials, therefore leading to greater cell damage. Not only Gram-negative bacteria but also Gram-positive bacteria are greatly inhibited by this antibacterial agent. With the powerful antibacterial activity as well as its low cost and facile preparation, the GO-PEG-PHGC as a novel antibacterial agent can find potential application in the areas of healthcare and environmental engineering.

Introduction

Infection control is of utmost importance in various fields. As a consequence, antibacterial materials that can effectively inhibit the growth of microorganisms with limited cytotoxicity have aroused considerable research interests. Antimicrobials, for instance quaternary ammonium salts [1], quaternary phosphonium salts [2], N-halamines [3], metal ions [4], and polyguanidine [5] have been underlined by their broad applications in the filed of biomedicine, food packaging and sterilization of hygienic areas. Guanidine polymer synthesized by the polycondensation of guanidinium and diamine has a wide spectrum antimicrobial activity, excellent biocide efficiency and nontoxicity [6]. However, Guanidine polymer-based antibacterial agents also have the undeniable congenital defects, as a result of its well water soluble, it is difficult to recycle, as a result cause secondary contamination. If the water soluble guanidine polymer is used as additives for industrial goods, the final products are deficient in antibacterial fastness [7]. So developing guanidine polymer composite materials with excellent antibacterial properties and strong antibacterial fastness under various conditions is still a critical need.

Graphene, a single-atom-thick 2-dimensional (2D) graphitic carbon material, has already gained great attention since its discovery [8]. Due to their impressive physical and chemical properties, graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), have been extensively studied for application in diverse fields, including water purification, molecule sensing, composite materials, energy research, catalysis, and even antibacterial activity [9], [10], [11], [12], [13], [14], [15]. Among all graphene derivatives, graphene oxide (GO), which has a graphene sheet with carboxylic groups at its edge and phenol hydroxyl and epoxide groups on its basal plane, is the most popular one [16]. These abundant oxygen functional groups of GO served as active sites have been used to build new composites. GO can be modified through different types of covalent and non-covalent functionalization approaches, which make it a popular target for functional application. Furthermore, GO can be easily synthesized at a large scale and low cost, from graphite flakes according to the modified Hummers’ method [17], [18].

In recent years, it has been reported that graphene and graphene-based composites present powerful antibacterial effect [13], [19], [20], [21], [22], [23], [24], [25], [26]. Antibacterial activity of graphene and graphene-based composites is found to assign to membrane puncture [22]. By direct contact, the sharp edges of graphene nanosheets can induce membrane stress, which may result in physical damage on cell membranes, leading to the loss of bacterial membrane integrity and the leakage of RNA [22]. Several GO-based composites, such as GO-Ag [20], [23], [24], [25] and GO-ZnO [26] are fabricated as antibacterial products. Those GO-based composites demonstrate markedly enhanced antibacterial effects. Although tremendous explorations have been achieved, a facile synthesis of cost-effective and powerful antibacterial agent is still highly desirable.

Therefore, conjugation of guanidine polymer with GO sheets which act as substrates may give new life to a common antibacterial agent. Yet GO will aggregate in saline solution [27]. Guanidine polymer is usually obtained as a salt, which may cause the aggregation of GO. The aggregation of GO sheets makes them have fewer chances to interact with bacteria for membrane puncture than that of disperse GO sheets [19]. Poly(ethylene glycol) is a very useful reagent for its minimal toxicity, biocompatibility and good solubility in water or other common solvents [28]. The combination of GO with poly(ethylene glycol) can effectively improve its colloidal stability in saline solution [29]. In this paper, the as-prepared GO was functionalized with poly-(ethylene glykol) methylether (PEG) to render higher aqueous solubility and stability in saline solution. Then guanidine polymer was bond to PEGylation of GO sheets without any aggregation.

In this work, polyhexamethylene guanidine hydrochloride (PHGC, as guanidine polymer) was prepared by polycondensation of guanidine hydrochloride with hexamethylenediamine. Then GO-PEG-PHGC consisting of GO sheets with covalently conjugated PEG and PHGC was synthesized. PEG was employed as a stabilizer for conjugating PHGC to GO sheets. Escherichia coli (typical Gram negative bacteria) and S. aureus (typical Gram positive bacteria) were used as model in this experiment. The antibacterial activity of the GO-PEG-PHGC composite was evaluated qualitatively by a biocidal kinetic test. For comparison, the antibacterial activity of GO, GO-PEG and GO-PHGC were discussed by the same method.

Section snippets

Material

Nature graphite powder was purchased from Tianjin Guangfu Fine Chemical Research Institute. Poly-(ethylenglykol) methylether (PEG, Mn = 2000) was purchased from Sigma–Aldrich and used without further purification. Guanidine hydrochloride and hexamethylenediamine were provided from Sinopharm Chemical Reagent Co., Ltd. Concentrated H2SO4, sodium nitrate potassium permanganate and H2O2 (30%) were obtained from Beijing Chemical Company. 1-(3-Dimethylaminopropyl)-3-ehylcarbodiimide hydrochloride (EDC)

Synthesis and Characterization of GO-PEG-PHGC

The modified Hummer's method was employed to prepare GO using natural graphite powder as starting material [17], [18]. GO sheet with carboxylic groups at its edge and phenol hydroxyl and epoxide groups on its basal plane [8] is usually applied as the staring functional precursor. These oxygen-containing groups, acting as anchor sites, enable the in situ functionalization and hybridization with other materials, such as the esterification of carboxyls or ring opening reaction of epoxy groups [30]

Conclusions

In this study, the dual-polymer-functionalized GO (GO-PEG-PHGC) was synthesized by covalently conjugating PEG and PHGC to the surface of GO sheets. GO-PEG-PHGC demonstrates superior antibacterial property against both Gram negative bacteria E. coli and Gram positive bacteria S. aureus. The improved antibacterial activity was described to be related to a better dispersion of GO-PEG-PHGC in the presence of PEG. Furthermore, PHGC obtains strong antibacterial fastness under various conditions,

Acknowledgement

This research was supported by the National Nature Science Foundation of Jilin Province (201115011).

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