Biomediated Silver Nanoparticles for the Highly Selective Copper(II) Ion Sensor Applications C. Joseph Kirubaharan, † D. Kalpana, ‡ Yang Soo Lee, ‡ A. R. Kim, § Don Jin Yoo, § Kee Suk Nahm,* ,§ and G. Gnana Kumar* ,† † Department of Physical Chemistry, Madurai Kamaraj University, Madurai-625 021, Tamilnadu, India ‡ Department of Forest Science and Technology, Institute of Agricultural Science and Technology, Chonbuk National University, Jeonju 561-756, South Korea § Department of Hydrogen and Fuel Cells Engineering, Specialized Graduate School, Chonbuk National University, Jeonju 561-756, South Korea * S Supporting Information ABSTRACT: Nanoparticles synthesis is an evergreen research field of 21st century in which the connotation of the biomediated experimental process is highly imperative. Biomediated silver nanoparticles were synthesized with the aid of an eco-friendly biomaterial, namely, aqueous Azadirachta indica extract. The effect of pH and temperature on the formation of silver nanoparticles was analyzed. Formation of the silver nanoparticles was verified by surface plasmon spectra using a UV-vis spectrophotometer. Morphology and crystalline structure of the prepared silver nanoparticles were characterized by TEM and XRD techniques, respectively. Furthermore, the biomediated silver nanoparticles without any surface modification were used for the heavy metal ion sensors in aqueous media. The prepared silver nanoparticles were successful in detecting even the minimal amount of heavy metal copper(II) ion and exhibited excellent specific metal ion selectivity. 1. INTRODUCTION Nanoscience is one of the most vibrant growing fields ever known and continues to rigorously reach its branches into various modern technologies such as hydrogen storage, photocatalysis, green energy devices, sensors, biomedical implants, and photovoltaics. 1-4 Though chemical synthesis has been widely adopted for the preparation of a variety of nanostructures, their cost effectiveness, need of sophisticated equipments, environments, stabilizing and capping agents, and environmental hitches fade not only the applications of nanoparticles but also the dream of a green world. 5 For the emphasis of biological protocol applications of nanoparticles, there is also an immense need for synthesizing nanoparticles with a greater biocompatibility. 6 Hence, there is an alarming demand for finding cheaper and environmentally friendly nanoparticles synthesis. In recent years, biomediated synthesis has been considered as an enthralling method for the synthesis of nanoparticles by bridging the two major criteria, satisfying the green chemistry principles and stabilizing the formed nanoparticles with not much more than the bioextract itself. 5 The state of the art biomediated nanoparticles synthesis satisfies all of the necessary requirements, especially the mentionable dual nature of the biomass as a reducing as well as a stabilizing agent. 7 The detection and quantification of heavy metal ions is a rapid subject of enrollment in recent days which influences their significant applications in environmental monitoring, waste management, and clinical toxicology fields. 8 Specifically, the detection of heavy metal copper is vital due to the existence of copper(II) ions in wastewater originated from the electro- plating plants and other metal manufacturing industries and corrosion of copper pipes. 9 An increase in the Cu 2+ level in the biological cells leads to kidney related and neurodegenerative diseases, 10 and the free Cu 2+ elicits toxicity to cells as they generate hydroxyl radicals, causing apoptosis. 10 Cu 2+ binds with the histidine-rich regions of the Prion Protein, which results in misfolding and protein fibrilization. 11 Therefore, on-site and real-time detection of Cu 2+ ions is important to avoid its toxic effects. For the successive detection of heavy metal copper ions, copper(II) sensitive optical sensors have been reported using immobilized Lucifer Yellow fluorophore, 12 copper chelators such as Zincon, 13 fast sulphon black F (FSBF), 14 urease enzyme, 15 and PAN and PAR indicators. 16 However, the mentioned reports exhibited major limitations such as complex preparation, expensive, high time consumption, and sample pretreatment and analyte preconcentration steps which limit the sensor applications at a large scale. It urges the identification and development of a copper sensor to satisfy the simple, rapid, inexpensive, selective, and sensitive character- istics. Nanoparticles find extensive application in bio- and eco- sensors, especially for the detection of heavy metal ions. Though few nanoparticles have been reported for heavy metal ion sensors, all of the nanoparticles have been synthesized via chemical routes and are to be stabilized with the aid of external chemical stabilizers in which most of them were toxic. 17 An objective of the sensors is to detect pollutants in the effluents, Received: February 6, 2012 Revised: May 7, 2012 Accepted: May 8, 2012 Published: May 17, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 7441 dx.doi.org/10.1021/ie3003232 | Ind. Eng. Chem. Res. 2012, 51, 7441-7446