Elsevier

Carbohydrate Polymers

Volume 83, Issue 2, 10 January 2011, Pages 883-890
Carbohydrate Polymers

Silver nanoparticles encapsulated in glycogen biopolymer: Morphology, optical and antimicrobial properties

https://doi.org/10.1016/j.carbpol.2010.08.070Get rights and content

Abstract

The glycogen biopolymer from the bovine liver has been used as stabilization agent for the growth of silver nanoparticles. The samples with various contents of silver were prepared by two different procedures that include fast (using microwave radiation) and slow (conventional) heating of the reaction mixtures. The TEM images of the two nanocomposites showed the presence of nanoparticles with average diameter of 9.7 and 10.4 nm, respectively. The results also revealed that the optical properties of the obtained nanocomposite samples strongly depend on the method of preparation. The samples prepared using microwave radiation exhibited narrower surface plasmon resonance peaks, while the silver nanoparticles induced quenching of the photoluminescence of glycogen in all of the tested samples. Antimicrobial activity tests were carried out against Staphylococcus aureus, Escherichia coli and Candida albicans pathogens and showed that the microbial growth was gradually reduced as the concentration of the silver increased. Also, after 2 h of exposure to the nanocomposites the number of cells was significantly reduced (>99%) for all the strains tested.

Introduction

Research on integration of polysaccharide biopolymers and inorganic nanoparticles into hybrid systems is witnessing a dramatic activity in current bio-nanoscience. Characteristic macromolecular and supramolecular properties of these biopolymers make them good controlled environments for growth of metallic and semiconductor nanocrystals. Due to a large number of OH groups, polysaccharide chains complexate well with metallic ions in solution, while supramolecular nanostructures formed by inter- and intra-chain hydrogen bonding act as template for nanoparticle growth (Raveendran, Fu, & Wallen, 2003). To date, starch is the most extensively used biopolymer for the stabilization of the growth of metallic (Božanić et al., 2007, Djoković et al., 2009, Raveendran et al., 2003, Sarma and Chattopadhyay, 2004) and semiconductor (Božanić et al., 2007, Božanić et al., 2009, Radhakrishnan et al., 2007Rodriguez et al., 2008, Vigneshwaran et al., 2006) nanoparticles. The other polysaccharide biopolymers such as chitosan (Murugadoss and Chattopadhyay, 2008, Sun et al., 2008, Wei and Qian, 2008), alginate (Pal et al., 2005, Brayner et al., 2007), gum Arabic (Kattumuri et al., 2007) or cellulose (Pirkkalainen et al., 2008) also proved to be good stabilization agents. It is also important to mention that nanoparticles synthesized within the biopolymer are biocompatible and hydrophilic, which could be important for their application in biology and medicine. On the other hand, the number of studies in which polysaccharide biopolymers of animal origin were used in preparation of inorganic nanoparticles is limited. In the present study we prepared silver nanoparticles in the presence of a glycogen biopolymer.

Glycogen, the main carbohydrate-storage in animals and microorganisms, is a polysaccharide that consists of highly branched (1  4)(1  6)-linked α-d-glucoses (Manners, 1991). It is produced primarily by the liver and the muscles, but can also be made by glycogenesis within the brain, thymus and skin (Brown, 2004). Glycogen has a high molecular weight (106–109) and its molecules are packed into spherical granules (β-particles), 20–40 nm in size, which often group together into much larger α-particles. The highly branched, actually fractal (Melendez, Melendez-Hevia, & Canela, 1999), structure of the glycogen enables a very easy pathway of synthesis and degradation as well as simplicity in the regulation mechanism. However, we believe that this dendrimeric structure is also an ideal environment for the controlled synthesis of metallic nanoparticles. The preparation of metal–glycogen hybrid nanostructures could be important from a practical point of view, due to their possible application as probe materials for glucan–biomolecule interactions. Li and co-workers (Xiang, Xu, Liu, Li, & Li, 2009) found, after mixing previously prepared gold nanoparticles and glycogen, that interactions between glycogen and biomacromolecules can alter the aggregation status of gold nanoparticles, which produced intensity changes in plasmon resonance light-scattering.

Antimicrobial activity is an important property of silver nanoparticles and/or silver–polymer nanocomposites. A number of studies emerged lately on this subject (Dror-Ehre, Mamane, Belenkova, Markovich, & Adin, 2009Jain et al., 2009, Kvitek et al., 2008, Lok et al., 2007, Morones et al., 2005, Panacek et al., 2006, Sharma et al., 2009), reporting on the influence of different factors, such as the nanoparticle concentration, size and capping agents involved on the inhibition of the antimicrobial growth. It is believed that the antimicrobial activity of silver nanoparticles originates from the formation of Ag+ active species (Lok et al., 2007), since they exhibit strong affinity towards sulphur and phosphor containing functional groups from the membrane-bound enzymes (McDonnell & Russell, 1999). The accumulation of the nanoparticles in the cells might also be a source of bactericidal activity (Morones et al., 2005). Given that glycogen is a biocompatible polymer of animal origin and that, to our best knowledge, it was not used so far as a stabilization agent for the growth of silver nanoparticles, we considered that it would be interesting from a fundamental as well as from a practical point of view to investigate the antimicrobial effects of this material. The present study is divided into two parts. In the first part, the structure and the optical properties of the silver–glycogen nanocomposites prepared by two different synthetic procedures were investigated. In the second part the antimicrobial activity of the nanocomposite films was tested against the Staphylococcus aureus, Escherichia coli and Candida albicans pathogens.

Section snippets

Materials

Glycogen from bovine liver, ammonium hydroxide (NH4OH), d-glucose and silver nitrate (AgNO3) were purchased from Sigma–Aldrich and used as received. High purity water (specific resistance ∼1018 Ω m) was used in all synthetic procedures.

Synthesis of Ag–glycogen nanocomposites

Two different green chemical procedures for the preparation of the nanocomposites were employed:

  • 1.

    In the first procedure, a modified Tollens method for the preparation of silver nanoparticles was used (Panacek et al., 2006). The silver nanoparticles were synthesized

Characterization of the nanocomposites

The morphology and dispersion of the Ag nanoparticles in the glycogen matrix were investigated by transmission electron microscopy (Philips CM100 instrument) at a 80 kV operating voltage. A water dispersion of the nanocomposite was deposited on carbon coated (MW3 sample) and formvar coated (HP3 sample) copper grids using a fine pipette. The samples were left to dry in air before they were transferred to the TEM chamber. The distribution of particle sizes was determined by measuring the diameters

Morphology and structure

Fig. 1 shows the SEM micrographs of the as received glycogen powder and the two nanocomposite films. The image of the neat glycogen in Fig. 1a depicts spherical α-particles with sizes in the range from several hundred nanometers to approximately 1 μm. After casting of the glycogen–Ag solution into films, the morphology changed. The images in Fig. 1b and c, show that the film surfaces are rough but no particle-like structures were observed. On the other hand, the morphology of the pure glycogen

Conclusions

The presented results show that glycogen can be regarded as a good stabilization agent for the preparation of silver nanoparticles. At the same time, glycogen can take the role of the matrix of the solid nanocomposite films. The physical properties of the silver–glycogen nanocomposites depended on the mode of preparation. The average sizes of the nanoparticles obtained by MW and HP methods were found to be 9.7 and 10.4 nm, respectively. The samples prepared using microwave radiation showed more

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