Carbohydrate Polymers 103 (2014) 456–465 Contents lists available at ScienceDirect Carbohydrate Polymers jo u r n al homep age: www.elsevier.com/locate/carbpol Preparation and characterization of bio-nanocomposite films of agar and silver nanoparticles: Laser ablation method Jong-Whan Rhim a,∗ , Long-Feng Wang a , Yonghoon Lee b , Seok-In Hong c a Department of Food Engineering and Bionanocomposite Research Institute, Mokpo National University, 61 Dorimri, Chungkyemyon, Muangun, 534-729 Jeonnam, Republic of Korea b Department of Chemistry, Mokpo National University, 61 Dorimri, Chungkyemyon, Muangun, 534-729 Jeonnam, Republic of Korea c Korea Food Research Institute, 516 Baekhyun-dong, Bundang-gu, Seongnam-si, 463-746 Gyonggi-do, Republic of Korea a r t i c l e i n f o Article history: Received 4 October 2013 Received in revised form 23 December 2013 Accepted 26 December 2013 Available online 5 January 2014 Keywords: Laser ablation Silver nanoparticles Agar Bio-nanocomposites Antimicrobial activity a b s t r a c t Silver nanoparticles (AgNPs) were prepared by a laser ablation method and composite films with the AgNPs and agar were prepared by solvent casting method. UV–vis absorbance test and transmission elec- tron microscopy (TEM) analysis results revealed that non-agglomerated spherical AgNPs were formed by the laser ablation method. The surface color of the resulting agar/AgNPs films exhibited the characteris- tic plasmonic effect of the AgNPs with the maximum absorption peaks of 400–407 nm. X-ray diffraction (XRD) test results also exhibited characteristic AgNPs crystals with diffraction peaks observed at 2 val- ues of 38.39 ◦ , 44.49 ◦ , and 64.45 ◦ , which were corresponding to (1 1 1), (2 0 0), and (2 2 0) crystallographic planes of face-centered cubic (fcc) silver crystals, respectively. Thermogravimetric analysis (TGA) results showed that thermal stability of the agar/AgNPs composite films was increased by the inclusion of metal- lic silver. Water vapor barrier properties and surface hydrophobicity of the agar/AgNPs films increased slightly with the increase in AgNPs content but they were not statistically significant (p > 0.05), while mechanical strength and stiffness of the composite films decreased slightly (p < 0.05). The agar/AgNPs films exhibited distinctive antimicrobial activity against both Gram-positive (Listeria monocytogenes) and Gram-negative (Escherichia coli O157:H7) bacterial pathogens. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Silver has long been recognized as an effective antimicrobial agent with a broad spectrum of antimicrobial activity against not only both Gram-positive and Gram-negative pathogenic bacte- ria but also viruses and other eukaryotic microorganisms (Russell & Hugo, 1994). Accordingly, with the advent of nanotechnol- ogy, silver nanoparticles (AgNPs) have been emerged in the development of an antibacterial, antifungal, antiviral, and anti- inflammatory agent (Rai, Yadav, & Gade, 2009; Vaidyanathan, Kalishwaralal, Gopalram, & Gurunathan, 2009). Especially, in food packaging sectors, AgNPs have been exploited for the preparation of antimicrobial active food packaging films due to their strong antimicrobial activity with high thermal stability (Llorens, Lloret, Picouet, Trbojevich, & Fernandez, 2012). The antimicrobial efficiency of AgNPs-included antimicrobial packaging films is greatly influenced by various factors such as particle size, and its distribution, degree of particle agglomera- tion, silver content, and interaction of silver surface with the base ∗ Corresponding author. Tel.: +82 61 450 2423; fax: +82 61 454 1521. E-mail addresses: jwrhim@mokpo.ac.kr, jwrhim@hanmail.net (J.-W. Rhim). polymer (Kim et al., 2007). Above all, AgNPs should be well dis- persed through polymer matrix without agglomeration. Therefore, it is essential to obtain AgNPs with proper dimensions and to choose proper polymeric materials for the preparation of efficient antimi- crobial packaging films with AgNPs. Conventionally, AgNPs have been produced by the reduction of silver nitrate (AgNO 3 ) using chemical reducing agents such as sodium borohydride, dimethyl formamide, triethanolamine, and hydrazine (Yoksan & Chirachanchai, 2010). However, such chem- ical reduction method is not recommended since the chemicals are highly reactive and known to pose a potential environ- mental hazard and biological risks. Instead, a variety of green technologies for the preparation of AgNPs have been developed (Habbalalu, Lalley, Nadagouda, & Varma, 2013). For example, bio- logical materials such as plant extracts, bacteria, fungi, and yeast have been used as mediators for the synthesis of AgNPs (Rhim, Wang, & Hong, 2013). Recently, another type of green technol- ogy has been tested using various carbohydrates such as glucose, sucrose, starch, chitosan, and marine polysaccharides. In these technologies, the biopolymers act as both reducing and stabiliz- ing agents and also as polymer matrix for carrying AgNPs (Rhim et al., 2013; Venkatpurwar & Pokharkar, 2011). Furthermore, these approaches using biopolymers are safe, biocompatible, nontoxic 0144-8617/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbpol.2013.12.075