Ion recognition properties of self-assembled monolayers (SAMs) Sheng Zhang, b Claudia M. Cardona a and Luis Echegoyen* a Received (in Cambridge, UK) 8th June 2006, Accepted 19th July 2006 First published as an Advance Article on the web 6th September 2006 DOI: 10.1039/b608146k In the search for new sensors, self-assembled monolayers (SAMs) have gained intensive interest due to their nanometre size, highly-ordered structures, and molecular recognition properties. This article presents an overview of ion recognition at SAM-modified surface/solution interfaces, and brings up to date the most notable examples for the sensing of cations and anions. Sensing is achieved with SAMs containing redox active and inactive receptors using techniques such as fluorescence spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Introduction The first ‘‘self-assembled monolayers’’ (SAMs) were reported twenty years ago, and since then, these structures have become an important component in the field of materials science. 1 SAMs are highly ordered two-dimensional assemblies that form spontaneously on a variety of surfaces by the adsorption of organic molecules from solution or gas phases. 1 Well- studied self-assembling systems include silanes on silicon surfaces, 2 sulfur-containing molecules on gold 3a and other metallic surfaces, 3b,c and carboxylic acids on metal oxides. 4 Organosulfur SAMs on gold are generally formed by the adsorption of thiol, thioether, disulfide, or thioctic ester derivatives. These types of SAMs are particularly useful because of their high degree of structural order, ease of preparation, and the diversity of terminal functionalities that can be placed at the monolayer surface. These properties, in conjunction with the nanometre scale of these organic thin- film materials, make them great candidates for a wide range of potential applications in nano-science and nano-technology. Therefore, SAMs have become one of the best systems for studying the effect of molecular structure and composition on the macroscopic properties of materials, and they serve as a tool to design ultra thin materials with different physical and chemical characteristics. To date, there are a number of reviews on SAMs which illustrate their formation, structure, and characterization using electrochemical and scanning tunneling microscopy (STM) techniques. 5 More recently, interest in SAMs has shifted from the fundamental research a Department of Chemistry, Clemson University, Clemson, SC, USA. E-mail: luis@clemson.edu; Fax: +1 (864) 656 6613; Tel: +1 (864) 656 0778 b Department of Chemistry, North Carolina State University, Raleigh, NC, USA Dr Sheng Zhang was born in 1972, and obtained his PhD in 2001 from Peking University, China, under the supervision of Prof. Liangbing Gan and Prof. Chunhui Huang. He joined Prof. Jean- Franc ¸ois Nierengarten’s group at the University of Louis Pasteur (France) after he got his PhD. In 2002, he moved to Clemson University to work as a postdoctoral fellow with Prof. Luis Echegoyen and currently he is a research associate at the North Carolina State University with Prof. Christopher Gorman. His main research interests include monolayer sensing, nanoparticle assembly, fullerene chemistry, and electrochemical and photo- electrochemical materials. Dr Claudia M. Cardona was born in Colombia, South America, in 1960. She obtained her PhD in 1999 from the University of Miami (UM), Coral Gables, under the supervision of Prof. Angel Kaifer. After three years postdoctoral work for Prof. Robert E. Gawley at NIEHS Marine and Freshwater Biomedical Sciences Center, UM, with an institutional NRSA NIH Postdoctoral Traineeship (2000–2001) and an individual NRSA NIH Postdoctoral Fellowship (2001–2003), she joined Prof. Luis Echegoyen’s group (Clemson University) in 2004, initially as a postdoctoral associate, and most recently as an Assistant Research Professor. Her main research interests include the design of supramolecular receptors, the chemistry of endohedral metallofullerene and fullerene species, and the fabrication of electrochemical and photovoltaic materials. Prof. Luis Echegoyen was born in La Habana, Cuba, in 1951. He obtained both his BSc and PhD degrees from the University of Puerto Rico in Rio Piedras in 1971 and 1974, respectively. After a one-year postdoctoral stay at the University of Wisconsin- Madison, subsequent appointments have included Chemist I, Nuclear Magnetic Resonance Spectroscopist at Union Carbide Corporation, Bound Brook, New Jersey, (1975–1977); Assistant Professor at the University of Puerto Rico, (1977–1980); Associate Professor at the University of Puerto Rico, (1980– 1982); Adjunct Associate Professor at the University of Maryland, College Park, Maryland, (1982–1983); Program Officer, Chemical Dynamics Program, National Science Foundation, Washington, D.C., (1982–1983); Associate Professor at the University of Miami, Coral Gables, Florida, (1983–1987); Member of the Chemistry Advisory Committee- NSF (1986–1989); and Professor at the University of Miami, Coral Gables, Florida (1987–2001). In 2002 he was appointed to serve as Chair of the Department of Chemistry at Clemson University, in South Carolina. His research interests include fullerene chemistry, electrochemistry and supramolecular chem- istry, with special emphasis on molecular electronics and endohedral fullerenes. He is the author or co-author of over 270 research articles. FEATURE ARTICLE www.rsc.org/chemcomm | ChemComm This journal is ß The Royal Society of Chemistry 2006 Chem. Commun., 2006, 4461–4473 | 4461 Published on 06 September 2006. Downloaded by Université Claude Bernard Lyon on 10/10/2013 11:38:58. View Article Online / Journal Homepage / Table of Contents for this issue