Fluoro- and Chromogenic Chemodosimeters for Heavy Metal Ion Detection in Solution and Biospecimens

Abstract

Heavy metal ions are of great concern, not only among the scientific community, especially chemists, biologists, and environmentalists, but increasingly among the general population, who are aware of the some of the disadvantages associated with them. In spite of the fact that some heavy metal ions play important roles in living systems, they are very toxic and hence capable of causing serious environmental and health problems.1-6 Some heavy metal ions, such as Fe(III), Zn(II), Cu(II), Co(II), Mn(II), and Mo(VI), are essential for the maintenance of human metabolism. However, high concentrations of these ions can lead to many adverse health effects.1,2,7-20 It is also a fact that others such as Hg(II), Cd(II), Pb(II), and As(III) are among the most toxic ions known that lack any vital or beneficial effects. Accumulation of these over time in the bodies of humans and animals can lead to serious debilitating illnesses.2,21-30 Therefore, the development of increasingly selective and sensitive methods for the determination of heavy metal ions is currently receiving considerable attention.7,23,31-36 Several methods, including atomic absorption spectroscopy, inductively coupled plasma atomic emission spectrometry, electrochemical sensoring, and the use of piezoelectric quartz crystals make it possible to detect low limits.37-40 However, these methods require expensive equipment and involve time-consuming and laborious procedures that can be carried out only by trained professionals. Alternatively, analytical techniques based on fluorescence detection are very popular because fluorescence measurements are usually very sensitive (parts per billion/trillion), easy to perform, and inexpensive.23,37,41-45 Furthermore, the photophysical properties of a fluorophore can be easily tuned using a range of routes: charge transfer, electron transfer, energy transfer, the influence of the heavy metal ions, and the destabilization of nonemissive n-π* excited states.5 Consequently, a large number of papers involving fluorescent chemosensors (see definition in section 2) have been published. In general to date, fluorescent chemosensors for anions and cations have proven popular, but those for many heavy metal ions such as Hg(II), Pb(II), Cu(II), Fe(III), and Ag(I) present challenges because these ions often act as fluorescence quenchers. Cu(II) is a typical ion that causes the chemosensor to decrease fluorescent emissions due to quenching of the fluorescence by mechanisms inherent to the paramagnetic species.46-48 Such decreased emissions are impractical for analytical purposes because of their low signal outputs upon complexation. In addition, temporal separation of spectrally similar complexes by time-resolved fluorimetry is subsequently prevented.49 Compared to the relatively well-developed fluorescent chemosensors, fluorescent chemodosimeters (see definition in section 2) have recently emerged as a research area of * Corresponding author. E-mail: jongskim@korea.ac.kr. † Hue University. ‡ Korea University. Duong Tuan Quang was born in 1970 in Thanhhoa, Vietnam, and graduated from Hue University in 1992, where he obtained his M.S. degree two years later and began his career as a lecturer in Chemistry soon afterwards. He received his Ph.D. degree in 2003 from Institute of Chemistry, Vietnamese Academy of Science and Technology. In 2006, he worked as a postdoctoral fellow in Professor Jong Seung Kim’s laboratory, Dankook University, Seoul, Korea. He was promoted as an associate professor in 2009 and went to Korea University as a research professor in 2010. His main task involved the development of chromogenic and fluorogenic molecular sensors to detect specific cations and anions. Chem. Rev. 2010, 110, 6280–6301 6280