An Evaluation of Acute Toxicity of Colloidal Silver Nanoparticles

Engineered nanoparticles (NP) are defined as materials produced within the nanoscale range of 1–100 nm in length or diameter that exhibit unique novel properties of the structural integrity as well as physical and chemical properties
[26]. Over the past few decades, nanomaterials have had a great impact and gained enormous attention in science, technology and business because of their potential for achieving specific processes and selectivity. Although the applications and benefits of these engineered nanomaterials are extensively and currently being widely used in modern technology and many commercial and medical sectors, there is still limited information concerning human health and environmental impacts. Several studies expected that nanoparticles could lead to unexpected health or environmental hazards because of their unique properties such as extremely high surface area and increased reactivity [7].

Silver nanoparticles (AgNPs), one of the most commonly used metal-nanoparticles, have been known to have a wide range of applications including solar energy absorption coatings, chemical catalysts and especially antimicrobial agents. AgNPs have potentials for inhibitory and bactericidal effects as well as retarding the growth of mold, harmful spores and germs [5]. Compared to bulk silver metal, AgNPs are expected to have higher antimicrobial activity due to their high specific surface area and high fraction of surface atoms. Because of these properties, AgNPs are added to numerous consumer products including textiles, home appliances, paints, food supplements and even health applications. Despite the varied uses of these AgNPs in many commercial products that launched into the market recently, there is a lack of information on the basic toxicity of silver nanoparticles regarding the health implications, occupational risks and hazards. Thus, the objective of this study was to investigate the acute toxicity of AgNPs by in vivo experiments. Tests for acute oral toxicity, eye irritation, corrosion and dermal toxicity were conducted using the recommended Organization for Economic Cooperation and Development (OECD) guidelines for the testing of chemicals for safety evaluation. Furthermore, lethal Dose 50 (LD50) in acute oral toxicity test was evaluated.

Materials and Methods

Preparation and characterization of AgNPs: High concentration of colloidal AgNPs solution was synthesized via chemical reduction process according to the method previously described with same minor modifications [14, 23]. Briefly, a 0.094 M aqueous solution of silver nitrate (AgNO3; Merck) was prepared with soluble starch (Merck) as a stabilizer. An aqueous solution of 0.07 M sodium borohydride (NaBH4; Merck) reducing agent with the soluble starch solution as a solvent were equentially prepared. By mixing both solutions, the AgNO3 solution was added dropwise to the NaBH4 solution under a vigorous stirring. A dark cloud appeared and turned to yellowish brown within a few seconds. When all reactants were completely added, the solution turned dark brown.

The purification of the AgNPs was precipitated using the centrifugation. Then, the purified AgNPs were washed three times with DI water and adjusted to the same volume before dilution. The percentage purity of the AgNPs was measured from free Ag ion concentration in the original AgNPs solution (10,000 ppm) using the macro- and microelectrode [15]. The results showed that the Ag ion concentration was contented at 3.77 ± 0.2 and 3.61 ± 0.2 ppm with the macro- and microelectrode, respectively. Therefore, AgNPs in this study was very pure (99.96%) and Ag ions were very low concentrated (less than 0.04%). The AgNPs solutions were diluted with distilled water to obtain various concentrations of AgNPs prior to use. The particle morphology of AgNPs was observed using JEOL JEM-2010 analytical transmission electron microscope (Fig. 1). The AgNPs had a spherical configuration which had a primary particle diameter of 10– 20 nm. The plasmon extinction of AgNPs was measured by Ocean Optics Portable UV-Visible spectrometer (USB 4000-UV VIS detector) shown in Fig. 2. The maximum of extinction spectrum (λmax) of AgNPs was at 395 nm with a narrow full width at half height (FWHH) about 45 nm. This result indicated that the size distribution of AgNPs was narrow.