Colloids and Surfaces A: Physicochem. Eng. Aspects 389 (2011) 134–137 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journa l h omepa g e: www.elsevier.com/locate/colsurfa Green synthesis of stable silver nanoparticles using Euphorbia milii latex Ricardo Almeida de Matos a , Thiago da Silva Cordeiro b , Ricardo Elgul Samad b , Nilson Dias Vieira Jr. b , Lilia Coronato Courrol a,b,* a Universidade Federal de São Paulo, UNIFESP, São Paulo, Brazil b Instituto de Pesquisas Energéticas e Nucleares, IPEN-CNEN/SP, São Paulo, Brazil a r t i c l e i n f o Article history: Received 7 April 2011 Received in revised form 28 July 2011 Accepted 28 August 2011 Available online 3 September 2011 Keywords: Silver Green synthesis Nanoparticles Euphorbia milli Femtosecond laser a b s t r a c t We report a simple method to create silver nanoparticles that consists in the irradiation of a silver nitrate and Euphorbia milii solution by light from a xenon lamp followed by ultrashort laser pulses. The formation of silver nanoparticles has been confirmed with UV–visible and TEM microscopy, and no additives, such as solvents, surfactants or reducing agents, were used in the procedure. Nanoparticles are present after the xenon lamp illumination, and after the laser irradiation the silver nanoparticles sizes are reduced drastically to the range of 10–50 nm. A concentration variation study of silver nitrate and aqueous latex extract was carried out, as well as with the laser irradiation energy and time. The size reduction can be explained by a multiphoton process that promotes the photoexcitation of the surface plasmon band, breaking the particles due to charge accumulation. The utilization of environmentally friendly solvents is one of the key issues that merits important consideration in a green synthesis strategy. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Nanotechnology comprises the science and technology at dimensions below one hundred of nanometers. At this scale the properties of materials are different from those found in larger scales and bulk materials due to quantum effects [1], and the union of nanotechnology and biology can revolutionize the field of health and medicine [2–4]. Within this context, silver nanopar- ticles exhibit optical properties that depend on its size [5,6], present a strong bactericidal effect and are known as powerful antibiotics [7,8], besides being used in anticancer [9] and antiviral [10–13] therapies. Silver nanoparticles are mainly produced by chemical processes involving the use of highly toxic chemical polymers [14], and as a consequence, the development of new “green” techniques is of the highest importance [15]. Silver nanoparticles present strong surface plasmon resonances (SPR), which are collective oscillations of free electrons on the metallic particle surface [5]. These resonances are a consequence of the electrons oscillations in the potential well defined by the parti- cle size, and define a specific wavelength range of absorption in the visible spectrum. As a nanoparticle size grows, the potential well dimensions increase, and its absorption is red-shifted [16,17]. * Corresponding author at: Instituto de Ciências Ambientais, Químicas e Farma- cêuticas (ICAQF) Departamento de Ciências Exatas e da Terra (DCET) Universidade Federal de São Paulo (UNIFESP)-Campus Diadema Rua Prof. Artur Riedel, 275 CEP 09972-270-Diadema, SP, Brazil. Tel.: +55 11 95811307; fax: +55 11 4043-6428. E-mail address: lcourrol@gmail.com (L.C. Courrol). Nanoparticles can be created by chemical synthesis followed by irradiation with blue or UV light [18], and the subsequent irradia- tion with a high intensity laser is known to decrease the particles size [18]. The laser incidence causes the ejection of electrons from the nanoparticles, resulting in charge accumulation on the surface. This means that the larger silver clusters become charged with elec- trons at their surface, intraparticle changes occur and this leads to surface rupture due to Coulombic explosion, and as a consequence, the particles sizes are reduced [19]. This process is also known as laser photolysis [20] and is an alternative to chemical processes for the reduction of ionic silver into metallic silver (which comprises the nanoparticle). In this work a new technique for synthesizing silver nanopar- ticles is reported, which instead of using toxic chemical polymers, uses a natural polymer extracted from the Euphorbia milli plant, and light irradiation to create the nanoparticles. E. milli is a very common ornamental plant in Brazil and other tropical regions, popularly known as Crown of Thorns or Christ Plant. The E. milli plant is a spiny, climbing succulent shrub member of the fam- ily Euphorbiaceae (Spurge family) that exude a milky white latex from any cut surface. Latexes are complex emulsions in which pro- teins, alkaloids, starches, sugars, oils, tannins, resins and gums are found [21]. The Euphorbia milii latex is found in special branch- ing tubes called latex tubes [22,23], and has been the subject of interest due to its biological activities as antibacterial [24], antiherpetics [25] and anticarcinogenic agent [26]. Additionally, Euphorbian latexes are commonly used as molluscicides, and the Euphorbia milii latex was reported as the most powerful mol- luscicidal agent [27]. Studies on the chemical composition of 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.08.040