Inorganic Chemistry Communications 63 (2016) 93–95 Contents lists available at ScienceDirect Inorganic Chemistry Communications j ourna l homepage: www.e lsev ie r .com/ locate / inoche Short communication A new luminescent silver-based probe for on/off sulfide determination Daniel Fonseca Segura a,b,⁎, João Flávio da Silveira Petruci a,⁎⁎, Arnaldo Alves Cardoso a, Regina Célia Galvão Frem a, Adelino Vieirade de Godoy Netto a, Neil R. Champness b a Institute of Chemistry, UNESP - Universidade Estadual Paulista, Araraquara, São Paulo, Brazil b School of Chemistry, University of Nottingham, Nottingham, United Kingdom ⁎ Correspondence to: D.F. Segura, Depto de Química G Química, UNESP, Rua Francisco Degni 55, Araraquara, São ⁎⁎ Correspondence to: J. F. S. Petruci, Depto de Química UNESP, Rua Francisco Degni 55, Araraquara, São Paulo ZIP E-mail addresses: danielfsegura@outlook.com (D.F. Se (J.F.S. Petruci). http://dx.doi.org/10.1016/j.inoche.2015.11.019 1387-7003/© 2015 Elsevier B.V. All rights reserved. a b s t r a c t a r t i c l e i n f o Article history: Received 17 July 2015 Received in revised form 21 October 2015 Accepted 29 November 2015 Available online 1 December 2015 The sulfide anion is a corrosive, toxic and harmful compound found in a wide range of anoxic environments. Metal-based complexes have been used as luminescent probes for sulfide determination. However, their synthesis usually involves laborious procedures and the use of toxic reagents. In this paper, we describe the synthesis, characterization and application of a new, sensitive and selective silver complex probe for sulfide detection. The process of sulfide determination is based on rapid reaction in aqueous/methanolic media between the silver (I) complex and sulfide leading to an increase in fluorescence intensity. Analytical performance has been studied in the concentration range of 190 to 950 nmol L−1 of sulfide with suitable linearity, and the limit of detection was calculated to be (3σ/S) to 20 nmol L−1. The probe's selec- tivity to S2− was evaluated over other competing anions showing excellent results and its reversibility was demonstrated upon addition of AgCF3SO3. © 2015 Elsevier B.V. All rights reserved. Keywords: Luminescent probes Silver complex Sulfide detection Sulfides have been found in anoxic environments including natu- ral water, wastewater, crude petroleum, natural gas and volcanic gases [1]. Water containing sulfide does not usually pose a health risk, but it can give water an unpleasant “rotten egg” smell and taste [2]. Determination of sulfide concentration is an important pa- rameter to guarantee drinking water quality. Controlling sulfides is an important issue in wastewater since sulfide solutions can attack metals, concrete and cause corrosion on pipe walls, resulting in sig- nificant economic damage. In the human body, mercaptans are read- ily oxidized to their respective sulfides and, consequently, sulfide can be founded in animal halite. Animals showing signs of liver cirrhosis produce more sulfides in their bloodstream and halite. Thus, deter- mination of sulfide could be used as a marker of liver diseases [3]. Environmental sulfide concentration has been usually found in concentrations of μmol L−1. For example, the recognition threshold range which hydrogen sulfide odor can be detected by humans is 0.30–90 μmol L−1 [4]. Thus, the determination of sulfide is essential in a variety of different human activities, but continues to present challenges due to the complexity of samples, and the necessity to determine low concentrations of sulfide. eral e Inorgânica, Instituto de Paulo ZIP 14801-970, Brazil. Analitica, Instituto de Química, 14801-970, Brazil. gura), jfpetruci@gmail.com Fluorescence is an appealing technique for determination of sulfide because of its high sensitivity and potential for selectivity. Indeed, mo- lecular fluorescent probes can offer high sensitivity, real-time imaging, high spatiotemporal resolution and have excellent potential as useful tools [5–9]. Luminescent metal-based complexes have previously been described as sulfide recognition and determination probes [10–15]. Mercury-complexing agents, such as alkaline fluorescein mercuric ace- tate (FMA), havemainly been employed to sulfhydryl groupdetermina- tion [10]. This well-known and sensitive reaction results in quenching of FMA fluorescence. However, the drawback of this reaction is the use of a toxic metal which generates residues which require expensive disposal procedures. Zinc, ruthenium, copper and palladium have also been used as luminescent probes, but usually involve laborious and time-consuming synthesis, high cost, and often a low yield of the desired product. Environmentally friendly metals with high affinity to sulfides could be a promising alternative research path. Ag(I) ions rap- idly react with sulfide forming a slightly water soluble compound (Ksp = 1.48 × 10−51) [16], and has been used in several analytical methods for sulfide determination [17] but has not been exploited previously as a luminescent metal-based probe. Herein we describe, for the first time, the synthesis of the new silver(I) complex bearing 1,10- phenanthroline-5,6-[pteridine-2,4-diamine] (phenpte), and its use as a sensitive on/off luminescent probe for sulfide determination. The silver (I) complex was prepared by a two step route. Firstly, ligand 1,10-phenanthroline-5,6-[pteridine-2,4-diamine] (phenpte) was synthesized by the reaction of a 1:1 mixture of 1,10- mailto:jfpetruci@gmail.com Journal logo http://dx.doi.org/10.1016/j.inoche.2015.11.019 Unlabelled image www.elsevier.com/locate/inoche http://crossmark.crossref.org/dialog/?doi=10.1016/j.inoche.2015.11.019&domain=pdf Fig. 1. Synthesis scheme of 1,10-phenanthroline-5,6-[pteridine-2,4-diamine] (phenpte) and the new silver(I) complex [Ag(phenpte)]CF3SO3. 94 D.F. Segura et al. / Inorganic Chemistry Communications 63 (2016) 93–95 phenanthroline-5,6-dione and 2,4,5,6-tetraminepyrimidine in refluxing methanol for 2 h [18,19]. Subsequently, separate methanol solutions of phenpte and AgCF3SO3 (1:1 ratio) were mixed with stir- ring and exclusion of ambient light. After 30 min a yellow precipitate had formed, was filtered, washed with cold methanol, chloroform, diethyl ether, and dried in a vacuum. Elemental (C,H,N) analysis results indicate formation of the complex [Ag(phenpte)]CF3SO3 as the product. Spectroscopic data indicates that the phenpte ligand coordinates in two different modes, the phenanthrolinemoiety chelates to the silver ion as a bidentate ligand and the amino group coordinates to a different silver ion as a monodentate ligand [21]. Fig. 1 shows the synthesis of phenpte (I) and [Ag(phenpte)]CF3SO3 (II), and suggests a possible extended structure of [Ag(phenpte)]CF3SO3 as a coordination polymer. Preliminary luminescent studies of phenpte, in methanol, show a strong emission peak centered at 492 nm when the ligand is ex- cited at 376 nm. Upon addition of AgCF3SO3, ligand fluorescence is strongly quenched as shown in Fig. 2. Moreover, phenpte lumi- nescence is suppressed when an equivalent of Ag(I) is added to a solution of phenpte, corroborating the proposed 1:1 metal–ligand stoichiometry. Importantly the addition of metal ions such as Pb2+, Al3+, Fe3+, Cd2+, Ni2+ and Pd2+ (1:1 ratio) had no significant effect on phenpte fluorescence intensity. However, the addition of Cu+ and Cu2+ showed similar effects to Ag+ on phenpte luminescence (Table 1). Fig. 2. Effect on intensity of phenpte fluorescence upon the addition of AgCF3SO3. Concen- tration of AgCF3SO3 solution: 0.2 mmol L−1. Volume of AgCF3SO3 added: 10, 20, 30, 40, 60 and 80 μL. Upon addition of sulfide [20], the quenching effect (sensormode off) of the Ag(I) cation is reduced by strong interaction between Ag(I) and S2− (Ksp = 1.48 × 10−51 [16]), forming Ag2S and leading to the libera- tion of the free ligand. As a result, an increase of fluorescence intensity (sensor mode on) has been observed (see Fig. 3), and reached a plateau in less than 2 min, after which no further increase was observed (up to at least 2 h). Among common potential interfering species, anions such as NO3 −, NO2 −, SCN−, SO4 2−, Cl− and CO3 2− were evaluated and did not increase fluorescence intensity (Table 2). Hence, excellent sul- fide recognition has been demonstrated for this new silver (I) complex. Reversibility is a fundamental issue in probe design. The reversibility of the [Ag(phenpte)]CF3SO3 probe inmethanolic solutionwas evaluated by adding a further equivalent of AgCF3SO3, in methanol solution, fol- lowing previous reaction between [Ag(phenpte)]CF3SO3 and sulfide. The fluorescence signal shows a reversible cycle upon alternating addition of sulfide and Ag(I) ions. Fig. 4 shows that fluorescence intensity versus time (seconds) demonstrates the return of the fluorescence signal to original values upon the addition of AgCF3SO3, confirming the ability to rejuvenate the probe complex, [Ag(phenpte)]CF3SO3. Furthermore, an analytical curve of fluorescence intensity (λexc = 376 nm, λem = 492 nm) versus sulfide concentration has been established for quantitative data evaluation. For each concentration, measurements were performed in triplicate over a range of 0.19 to 0.95 μmol L−1. The curve linearity was evaluated over the same concen- tration range, with a linearity factor of r N 0.99. The probe's limit of de- tection (LD) has been determined as 0.02 μmol L−1. Repeatability was evaluated by measuring the fluorescence intensity of ten repeat addi- tions of 0.50 μmol L−1 of sulfide, achieving excellent results (4% R.S.D). In conclusion, a new on/off luminescent probe has been developed for sulfide determination. The new probe is based on a Table 1 Effect of addition of one equivalent of metal cations on phenpte fluorescence intensity comparing to Ag+ (factor of 1.00). Metal Effect factor Ag+ 1.00 Al3+ 0.02 Cd2+ 0.04 Fe3+ 0.02 Ni2+ 0.02 Pb2+ 0.02 Cu+ 0.70 Cu2+ 0.90 Image of Fig. 1 Image of Fig. 2 Fig. 3. Luminescence response mechanism of [Ag(phenpte)]CF3SO3 towards H2S. Table 2 Effect of interfering ions upon sulfide determination. In each instance a ratio of 100:1 of interferent sulfide was used. Interferent [ion]/[sulfide] Interference NO3 − 100 −1.7% NO2 − 100 −2.7% SCN− 100 −3.6% SO4 2− 100 −1.9% Cl− 100 3.6% CO3 2− 100 1.4% 95D.F. Segura et al. / Inorganic Chemistry Communications 63 (2016) 93–95 silver complex synthesized by mixing a luminescent dye (1,10- phenanthroline-5,6-[pteridine-2,4-diamine]) and AgCF3SO3. The probe fluorescence intensity increases proportionally upon sulfide addition. Analytical performance of the probe shows excellent re- sults competitive with other probes in the literature [10,13,19]. Moreover, the use of a non-toxic metal, ease of preparation and reversibility of the probe represent a valuable contribution in Fig. 4. Test for sensing capabilities of [Ag(phenpte)]CF3SO3 complex. Variation of the fluo- rescence signal intensity at 492 nm, alternating additions of sulfide ions (signal intensity increases) andAg+ ions (signal intensity decreases). Experimental conditions: Concentra- tion and volume of the complex solution: 0.1 mmol L−1 and 3.0 mL; concentration and volume of sulfide solution added: 10 μmol L−1 and 10 μL; concentration and volume of AgCF3SO3 added: 0.2 mmol L−1 and 15 μL. the development of metal-based luminescent probes for sulfide determination. Acknowledgments This research was supported by CNPq (487092/2012-0), FAPESP (2013/22995-4) and CAPES (12707/12-0). NRC gratefully acknowl- edges receipt of a Royal Society Wolfson Merit Award. Appendix A. Supplementary material Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.inoche.2015.11.019. References [1] N.S. Lawrence, J. Davis, R.G. Compton, Talanta 52 (2000) 771–784. [2] M.E.A.G. Oprime, O. Garcia, A.A. Cardoso, Process Biochem. 37 (2001) 111–114. [3] N. Marczin, M. Yacoub, Disease Markers in Exhaled Breath: Basic Mechanisms and Clinical Applications, 2002. [4] T.L. Guidotti, Int. J. Toxicol. 29 (2010) 569–581. [5] Z. Xu, J. Yoon, D.R. Spring, Chem. Soc. Rev. 39 (2010) 1996–2006. [6] T. Ueno, T. Nagano, Nat. Methods 8 (2011) 642–645. [7] N. Kumar, V. Bhalla, M. Kumar, Coord. Chem. Rev. 257 (2013) 2335–2347. [8] V.S. Lin, C.J. Chang, Curr. Opin. Chem. Biol. 16 (2012) 595–601. [9] A. Cardoso, H. Liu, P. Dasgupta, Talanta 44 (1997) 1099–1106. [10] H.D. Axelrod, J.H. Cary, J.E. Bonelli, J.P. Lodge, Anal. Chem. 41 (1969) 1856–1858. [11] E. Galardon, A. Tomas, P. Roussel, I. Artaud, Dalton Trans. (2009) 9126–9130. [12] R. Zhang, X. Yu, Y. Yin, Z. Ye, G. Wang, J. Yuan, Anal. Chim. Acta 691 (2011) 83–88. [13] J.F.D.S. Petruci, A.A. Cardoso, Microchem. J. 106 (2013) 368–372. [14] X. Lou, H. Mu, R. Gong, E. Fu, J. Qin, Z. Li, Analyst 136 (2011) 684–687. [15] L. Tang, P. Zhou, Q. Zhang, Z. Huang, J. Zhao, M. Cai, Inorg. Chem. Commun. 36 (2013) 100–104. [16] T.-M. Hseu, G.A. Rechnitz, Anal. Chem. 40 (1968) 1054–1060. [17] R. Chen, H.R. Morris, P.M. Whitmore, Sensors Actuators B Chem. 186 (2013) 431–438. [18] M.D. Stephenson, T.J. Prior, M.J. Hardie, Cryst. Growth Des. 8 (2008) 643–653. [19] S.R. Dalton, S. Glazier, B. Leung, S. Win, C. Megatulski, S.J.N. Burgmayer, J. Biol. Inorg. Chem. 13 (2008) 1133–1148. [20] A.D. Eaton, M.A.H. Franson, A.P.H. Association, A.W.W. Association, W.E. Federation, Standard Methods for the Examination of Water & Wastewater, American Public Health Association, 2005. [21] D.F. Segura, A.V.G. Netto, R.C.G. Frem, A.E. Mauro, P.B. da Silva, J.A. Fernandes, F.A.A. Paz, A.L.T. Dias, N.C. Silva, E.T. de Almeida, M.J. Marques, L. de Almeida, K.F. Alves, F.R. Pavan, P.C. de Souza, H.B. de Barros, C.Q.F. Leite, Polyhedron 79 (2014) 197–206. http://dx.doi.org/10.1016/j.inoche.2015.11.019 http://dx.doi.org/10.1016/j.inoche.2015.11.019 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0005 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0010 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0015 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0015 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0020 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0025 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0030 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0035 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0040 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0045 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0050 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0055 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0060 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0065 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0070 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0075 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0075 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0080 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0085 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0085 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0090 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0095 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0095 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0100 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0100 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0100 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0105 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0105 http://refhub.elsevier.com/S1387-7003(15)30147-7/rf0105 Image of &INS id= Image of Fig. 4 A new luminescent silver-�based probe for on/off sulfide determination Acknowledgments Appendix A. Supplementary material References