A highly selective fluorescent probe for pyrophosphate detection in aqueous solutions M. R. Ganjali a *, M. Hosseini b , F. Aboufazeli a , F. Faridbod c , H. Goldooz d and A. R. Badiei d ABSTRACT: A novel and simple fluorescence enhancement method is introduced for selective pyrophosphate (PPi) sensing in an aqueous solution. The method is based on a 1:1 metal complex formation between tris(8‐hydroxyquinoline‐5‐sulphonate) thulium(III) [Tm(QS) 3 ] and PPi ion. The linear response covers a concentration range of 1.6 × 10 -7 –1.0 × 10 -5 mol/L PPi and the detection limit is 2.3 × 10 -8 mol/L. The association constant of Tm(QS) 3 –PPi complex was calculated as 2.6 × 10 5 mol/L. Tm(QS) 3 shows a selective and sensitive fluorescence enhancement toward PPi ion in comparion with I 3 - , NO 3 - , CN - , CO 3 2- , Br - , Cl - ,F - ,H 2 PO 4 - and SO 4 2- , which is attributed to higher stability of the inorganic complex between pyrophosphate ion and Tm(QS) 3 . Copyright © 2011 John Wiley & Sons, Ltd. Keywords: fluorescence enhancement; sensor; pyrophosphate; Tm(QS) 3 Introduction Anions are generally larger than cations such as metal ions, therefore anions are more subject to solvation than cations. In organic solvents, it is not difficult to capture and detect anions because the solvation energy is relatively small and electrostatic interactions can operate effectively. It is very difficult to rec- ognize anions in aqueous solvents, which are relevant to bio- logical applications, because of their strong hydration. To date, only a few anion fluorescent sensors that work in aqueous solution have been developed, while many anion fluorescent sensors are known for organic environments (1). An anion fluorescent sensor for use in aqueous solution should have two requirements; one is a sufficiently strong affinity for anions, and the other is the ability to convert an anion recognition signal into a fluorescent signal. It is difficult to satisfy both requirements simultaneously. Most known anion sensors do not have a sufficiently strong affinity for anions in water, while they satisfy the latter requirement. Although some anion hosts can capture anions in aqueous solvent, they are only host molecules, not sensor molecules (1). Metal‐based sensing systems use metal–ligand interactions for the recognition of target anions, and thus result in high selectivity, a large binding constant and good solubility in aqueous solution (2,3). We have recently reported a number of highly selective and sensitive anion sensors based on metal complexes (4–7). Since many organic and inorganic anions play important roles in living organisms, there is now an increasing interest in anion recognition and anion sensing (8–17). Among the various anionic analytes, pyrophosphate (PPi) is a biologically important target because it is produced in ATP hydrolysis in cellular conditions (18). PPi also plays an important role in energy transduction in organisms and could control metabolic processes by participating in enzymatic reactions (19). Until now, some examples of selective PPi fluorescent sensors have been reported but only a few display turn‐on in emission spectra (20–22). Here, we present a novel fluorescent turn‐on PPi sensor using Tm(QS) 3 possessing three 8‐hydroxyquinoline (Scheme 1). Experimental Reagents All Chemicals were of the reagent grade from Fluka and Merck chemical companies. The fluorogenic reagent bis(8‐hydroxyquinoline‐ 5‐sulphonate) thulium(III) chloride [Tm(QS) 3 ] was prepared as follows (23). An ethanolic solution of TmCl 3 was added to an ethanolic solution of HQS under stirring with the molar ratio of Tm 3+ :HQS being 1:2. Then the pH of the solution was adjusted to 7.0 by adding an ammonium hydroxide solution (2 mol/L) and an appropriate amount of water was added and the mixture was stirred at room temperature for 10 h. The obtained yellow precipitates were collected by filtration and washed with water and cold ethanol three times. 1 H‐NMR (DMSO, 500 MHz): σ H 6.16 (m, 1 H), 7.8 (m, 3 H), 8.6 (m, 1 H), 9.19 (m, 1 H). IR data: ν max (KBr pellets)/cm -1 3175 (C‐H str.), 1323, 1370, 1402, 1460 (C–C, C–N, CO str. and C–H bend.) 1498, 1577, 1604 (C–C str.) 754 (Al–N str.). * Correspondence to: M. R. Ganjali, Centre of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran, Tehran, Iran. E‐mail: ganjali@ khayam.ut.ac.ir a Centre of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran, Iran b Department of Chemistry, Islamic Azad University, Savadkooh, Iran c Endocrinology and Metabolism Research Centre, Tehran University of Medical Sciences, Iran d School of Chemistry, University College of Science, University of Tehran, Iran Luminescence 2012; 27: 20–23 Copyright © 2011 John Wiley & Sons, Ltd. Research article Received: 13 October 2010, Revised: 06 February 2011, Accepted: 08 April 2011, Published online in Wiley Online Library: 7 July 2011 (wileyonlinelibrary.com) DOI 10.1002/bio.1316 20