Sensors and Actuators B 181 (2013) 288–293 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o me pa ge: www.elsevier.com/locate/snb A new rapid colorimetric detection method of Mn 2+ based on tripolyphosphate modified silver nanoparticles Yue-Xia Gao a,b , Jun-Wei Xin a , Zhe-Yu Shen a , Wei Pan b , Xing Li b , Ai-Guo Wu a,∗ a Key Laboratory of Magnetic Materials and Devices, and Division of Functional Materials and Nanodevices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China b The School of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, China a r t i c l e i n f o Article history: Received 11 November 2012 Received in revised form 24 January 2013 Accepted 28 January 2013 Available online xxx Keywords: Mn 2+ Rapid colorimetric detection method P3O10 5- –AgNPs Aqueous solution Linear detection a b s t r a c t A new facile and rapid colorimetric method is proposed for detection of manganese ion (Mn 2+ ) with high sensitivity and excellent selectivity using tripolyphosphate stabilized silver nanoparticles (P 3 O 10 5- –AgNPs). The silver nanoparticles (AgNPs) were prepared by reducing silver nitrate with sodium borohydride in the presence of sodium tripolyphosphate. Energy dispersive X-ray spectrum (EDS) and infrared spectra (IR) indicate that tripolyphosphates anions (P 3 O 10 5- ) are capped on the surfaces of AgNPs. The P 3 O 10 5- –AgNPs aggregate quickly in the presence of Mn 2+ , which leads to color change of the nanopar- ticle dispersion from yellow to reddish brown and decrease of the surface plasmon absorption intensity. The Mn 2+ can form a six-coordinated structure with P 3 O 10 5- coating on the AgNPs and leads to formation of large particles aggregation. The selectivity of P 3 O 10 5- –AgNPs detection system for Mn 2+ is excellent comparing with other ions and mixture of the above ions except Mn 2+ . Furthermore, this Mn 2+ detection method based on surface plasmon resonance (SPR) absorption by ultraviolet and visible spectropho- tometer (UV–vis) offers a wide linear detection range from 0.05 M to 20 M. The lowest detection concentration by the naked eyes is 0.1 M, which is also lower than the national table-water standard (1.8 M). The results of Mn 2+ detection in real water samples reinforce that our P 3 O 10 5- –AgNPs detection system is applicable for Mn 2+ detection in the real environmental water samples. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Manganese ion (Mn 2+ ) is one of the essential microelements in human body, which plays an important role in the bone and other tissues formations, normal reproductive functions, carbohydrate and lipid metabolism under the normal condition. Mn 2+ deficiency in human body is related to delayed blood coagulation and hyper- cholesterolaemia. However, uptake of high concentration of Mn 2+ is harmful. Signs of toxicity were manifested in the form of severe psy- chiatric abnormalities, including hyperirritability, violent acts and hallucinations. As the diseases progressed, there was a permanent crippling neurological disorder of the extrapyramidal system with morphological lesions similar to those of Parkinson disease [1]. It is well known that Mn 2+ can exist in water stably compared to other valence states of manganese. Therefore, much more attention has been attracted to develop methods for detecting Mn 2+ at low con- centrations in samples (such as foodstuffs, waters and beverages) with high sensitivity and excellent selectivity. ∗ Corresponding author. Tel.: +86 574 86685039; fax: +86 574 86685163. E-mail address: aiguo@nimte.ac.cn (A.-G. Wu). In recent years, various methods have been reported for Mn 2+ detection, including atomic absorption spectrometry (AAS) [2], inductively coupled plasma mass spectroscopy (ICP-MS) [3], and inductively coupled plasma-atomic emission spectrometry (ICP-AES) [4]. However, these methods need costly instruments or complicated procedures, making them inconvenient and time- consuming. Moreover, many dynamic methods have been reported for Mn 2+ determination based on its catalytic effect on the oxida- tion of organic compounds. Although some of these methods have extremely low detection limitation, most of them lack sufficient sensitivity for detecting Mn 2+ and are cockamamie or uneconom- ical [5–8]. Recently, many colorimetric assay methods have been reported for detection of heavy metal ions based on gold or silver nanoparticles due to their high extinction coefficient and strong surface plasmon resonance properties [9–12]. Large numbers of colorimetric sensors have been established for detection of metal ions (Co 2+ [13,14], Hg 2+ [15–17], Cr 3+ [18,19], Cu 2+ [20], Pb 2+ [21], and so on), proteins [22], oligonucleotides [23,24], organic molecules [25] and biological applications [26,27]. A small number of researchers have been starting to explore Mn 2+ detection method based on gold or silver nanoparticles [28]. However, some of them used organic reagents as the functional selective reagents, which are instability and easily oxidized. In this work, we propose 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.01.079