Talanta 85 (2011) 1566–1574 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Highly selectively monitoring heavy and transition metal ions by a fluorescent sensor based on dipeptide Lok Nath Neupane a , Ponnaboina Thirupathi a , Sujung Jang a , Min Jung Jang b , Jung Hwa Kim b , Keun-Hyeung Lee a,∗ a Bioorganic Chemistry Lab., Department of Chemistry, Inha University, 253 Yonghyun-Dong, Nam-Gu, Inchon-City 402-751, Republic of Korea b Department of Biological Science, Inha University, 253 Yonghyun-Dong, Nam-Gu, Inchon-City 402-751, Republic of Korea article info Article history: Received 18 March 2011 Received in revised form 17 June 2011 Accepted 17 June 2011 Available online 24 June 2011 Keywords: Peptide Ratiometric Fluorescent Sensor Hg(II) Ag(I) abstract Fluorescent sensor (DMH) based on dipeptide was efficiently synthesized in solid phase synthesis. The dipeptide sensor shows sensitive response to Ag(I), Hg(II), and Cu(II) among 14 metal ions in 100% aqueous solution. The fluorescent sensor differentiates three heavy metal ions by response type; turn on response to Ag(I), ratiometric response to Hg(II), and turn off detection of Cu(II). The detection limits of the sensor for Ag(I) and Cu(II) were much lower than the EPA’s drinking water maximum contaminant levels (MCL). Specially, DMH penetrated live cells and detected intracellular Ag + by turn on response. We described the fluorescent change, binding affinity, detection limit for the metal ions. The study of a heavy metal- responsive sensor based on dipeptide demonstrates its potential utility in the environment field. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Detection and quantification of a low contamination of heavy and transition metal ions (HTM) in waters have become signifi- cant due to the toxicity of these metal ions to living organisms and humans. Specially, the use of silver and silver compounds has increased in electrical industry. Recently, bioaccumulation and potential toxicity of Ag(I) to fishes, invertebrates, and bacteria in waters have been reported [1–5]. Hg(II) has been regarded as the most toxic metal ions among HTM [6,7]. Thus, the development of fluorescence chemical sensors for Ag(I) and Hg(II) ions has received attention because fluorescence is a most powerful optical way for detecting low concentration of metal ions in waters. However, most of fluorescent chemical sensors for Ag(I) and Hg(II) ions displayed one of the following drawbacks such as low sensitivity, low selec- tivity, turn off response, or low water solubility [8–18]. Since Ag(I) and Hg(II) ions induced quenching of fluorescence emission inten- sity [19,20], chemical sensors that detect them by turn on response or ratiometric response are highly demanded. Furthermore, syn- thesis of fluorescent chemical sensors that differentiate Ag(I) and Hg(II) ions is highly challenging because both ions have similar size and belong to soft ions. ∗ Corresponding author. Tel.: +82 32 860 7674; fax: +82 32 867 5604. E-mail address: leekh@inha.ac.kr (K.-H. Lee). The receptor part of fluorescent chemical sensors mainly decides which kind of analysts can be detected. The selectiv- ity and sensitivity of chemical sensors are mostly determined by recognition ability of the receptor part. The receptor part also contributes to converting a recognition event into a fluo- rescent signal. Generally, macrocyclic compounds such as crown ether and calixarene have been used as a receptor part in vari- ous fluorescent chemical sensors [14,15,19]. However, macrocyclic compounds are usually available only through tedious syntheses with low yield and frequently show poor solubility in 100% aque- ous solution. Thus, we focus on dipeptide as a receptor because amino acid and peptide are highly water soluble and environ- mentally compatible and amino acid and peptide can be easily conjugated into fluorophores in solid phase synthesis with high yield. Several research groups including us reported amino acid based fluorescent sensors for HTMs [21–25]. In comparison to the chem- ical sensors, amino acid based sensors were highly water soluble and showed sensitive response to specific metal ions in 100% aque- ous solution. The selectivity of the sensors based on amino acids strongly depends on metal chelating ability of the amino acid of the sensors. For example, fluorescent sensors based on Trp, Met, or Asp acid showed an exclusive response to Hg(II) ions in aque- ous solution [21–25] because the amino acids were regarded as an effective chelator for Hg(II) ions. Fluorescent sensor based on Cys amino acid showed response to several HTMs such as Hg(II), Pb(II), 0039-9140/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2011.06.052