ORIGINAL PAPER Simple optical determination of silver ion in aqueous solutions using benzo crown-ether modified gold nanoparticles Nahid Haghnazari & Abdolhamid Alizadeh & Changiz Karami & Zohreh Hamidi Received: 7 August 2012 / Accepted: 7 December 2012 / Published online: 21 December 2012 # Springer-Verlag Wien 2012 Abstract We describe a method for the modification of gold nanoparticles (Au-NPs) with benzo-15-crown-5 that led to the development of a colorimetric assay for Ag(I) ion. The brown color of a solution of the modified Au- NPs turns to purple on addition of Ag(I) ion. The ratio of the UV–vis absorption at 600 nm and 525 nm is proportional to the concentration of Ag(I) ions in the range from 20 to 950 nM, and the detection limit is 12.5 nM. Other metal ions do not interfere if present in up to millimolar concentrations. The method enables a rapid determination of Ag(I) in lake and drinking water and is amenable to bare-eye readout. Keywords Nano sensors . Gold nanoparticles . Benzo-15- crown-5 . Colorimetric sensing . Heavy metals . Silver sensor Introduction The combination of nanotechnology with chemistry, biology, physics, and medicine for the development of ultrasensitive detection and imaging methods in the analytical or biological sciences is becoming increasingly important in modern sci- ence [1]. In particular, the design and synthesis of gold nano- particles (AuNPs) functionalized with targeted functional molecules, owning to their unique optical properties (i.e. surface plasma resonance absorption and resonance light scat- tering), have been attracted much attention, and they have been extensively used as modern ultrasensitive detection and imaging probes for bioreorganizing events [2–4]. The design of functional nanomaterials is of current interest because of a variety of potential applications ranging from chemistry to biological sciences. Metal and semiconductor nanoparticles exhibit interesting size- and shape-dependent properties [5]. Generally, the optical properties of metal nanoparticles such as Au and Ag, are dominated by collective oscillation of elec- trons at surfaces (known as surface plasmon resonance) [6] and since nanoparticles have a high surface area to volume ratio, the plasmon frequency is exquisitely sensitive to the dielectric (refractive index) nature of its interface with the local medium. Any change to the environment of nanopar- ticles (surface modification, aggregation, medium refractive index, etc) leads to colorimetric changes of the dispersions and this fact nicely explains the visual sensing ability of these nanoparticles. Because of this unique optical property, func- tionalized nanoparticles have been extensively explored as probes for sensing/imaging a wide range of analytes/targets, such as alkali metal ions [7], heavy metal ions [8], mercury(II) [9], lead (II) [10, 11], and lectine [12]. Gold nanoparticle- based colorimetric assay does not utilize light sensitive dye molecules, lengthy protocols or sophisticated instrumentation and thereby their employment as sensor, helps to overcoming some of the limitations of more conventional methods. Electronic supplementary material The online version of this article (doi:10.1007/s00604-012-0928-9) contains supplementary material, which is available to authorized users. N. Haghnazari Department of Biochemistry, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran A. Alizadeh (*) Department of Chemistry and Nanoscience & Nanotechnology Research Center (NNRC), Razi University, Kermanshah 67149, Iran e-mail: ahalizadeh2@hotmail.com C. Karami (*) Department of Chemistry, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran e-mail: Changiz.Karmi@gmail.com Z. Hamidi Young Researchers Club, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran Microchim Acta (2013) 180:287–294 DOI 10.1007/s00604-012-0928-9