- Email: [email protected]
Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection
Accepted Manuscript Title: Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection Authors: Shuang Li, Te Wei, Guojuan Ren, Fang Chai, Hongbo Wu, Fengyu Qu PII: DOI: Reference:
S0927-7757(17)30848-8 http://dx.doi.org/10.1016/j.colsurfa.2017.09.028 COLSUA 21931
To appear in:
Colloids and Surfaces A: Physicochem. Eng. Aspects
Received date: Revised date: Accepted date:
3-7-2017 11-9-2017 15-9-2017
Please cite this article as: Shuang Li, Te Wei, Guojuan Ren, Fang Chai, Hongbo Wu, Fengyu Qu, Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection, Colloids and Surfaces A: Physicochemical and Engineering Aspectshttp://dx.doi.org/10.1016/j.colsurfa.2017.09.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection Shuang Li, Te Wei, Guojuan Ren, Fang Chai*, Hongbo Wu*, and Fengyu Qu * Key Laboratory of Design and Synthesis of Functional Materials and Green Catalysis, Colleges of Heilongjiang Province, College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, P. R. China. * Corresponding author. E-mail: [email protected], [email protected], [email protected]
Graphical Abstract
Highlights
The sodium hyaluronate protected AuNPs were synthesized through a simple process.
The SH-AuNPs can be used for colorimetric detection of Cr3+ and Cr6+ synchronously.
The SH-AuNPs can be applied to detecting for chromium ions in real lake water samples with strong anti-interference ability.
1
Abstract A simple and highly practical colorimetric method has been proposed for detection of chromium ions (Cr3+ and Cr6+) synchronously by sodium hyaluronate functionalized gold nanoparticles (SH-AuNPs). The SH-AuNPs were synthesized and characterized by UV-vis spectra and transmission electron microscopy (TEM). The colorimetric response of Cr3+ and Cr6+ can be performed simultaneously by the same probe SH-AuNPs, based on the property of special localized surface plasmon resonance (LSPR). The interaction between chromium ions and sodium hyaluronate causes rapid aggregation of the SH–AuNPs conjugates and a concurrent color conversion from wine red to blue gray which is clearly detectable by the naked eye. By using SH-AuNPs as colorimetric probe, the color change with 3 µM Cr3+, 1 µM Cr6+, or 10 µM mixed chromium ions can be recognized easily by naked eye with highly selectivity. The detection limit calculated by the linear relationship of LSPR were at 0.78 nM (for Cr3+), 2.90 nM (Cr6+) and 0.69 nM (mixed chromium ions) respectively, which were all below the guideline value set by World Health Organization (0.962 µM). The practical applicability of the SH-AuNPs was also verified by the detection of chromium ions in natural lake water samples.
Keywords: gold nanoparticles; sodium hyaluronate; colorimetric detection; chromium ions
2
1 Introduction Chromium is one of the most toxic heavy metals which is mainly exists in the form of Cr3+ and Cr6+ [1]. Cr3+ is a component part of the glucose tolerance factor, thus, Cr3+ can affect the body lipid metabolism, lower cholesterol and triglyceride levels in the blood. More seriously, excessive Cr3+ can cause mutations and malignant cells, which endangers human health [2]. Nevertheless, Cr6+ is ca. 100 times more toxic than Cr3+, which is carcinogenic and mutagenic due to its high oxidation potential and it has ability to penetrate biological membranes [3-7]. Unfortunately, Cr6+ is widely distributed in wastewater all over the world, which was a persistent great threat to the environment and human health [5-7]. The World Health Organization (WHO) stipulates that the maximum amount of chromium acceptable to the drinking water is 0.962 µM [8, 9]. Thus, there is a pressing need to explore an accurate and reliable method for the detection and monitor of chromium ions. At present, the determination of chromium ions has been performed by a variety of traditional techniques, including atomic absorption spectrometry [10], inductively coupled plasma-atomic emission spectrometry [11], electrothermal atomic absorption spectrometry [12] and so on. In comparison, some nanotechnology such as colorimetry, fluorimetry and electrochemical techniques have been obtained more attention and exhibited great potential application [13-17]. Among them, the AuNPs based colorimetric method is an ideal choice, which can overcome some drawbacks, such as the time-consuming, relied on large instrument and need pretreatment. The AuNPs exhibit distinct localized surface plasmon resonance (LSPR), which causes the 3
AuNPs are highly sensitive to the size, shape, capping agent and the state of AuNPs [18]. LSPR-based detection methods offer some significant advantages such as low cost, speedy and ease of readout [11, 19, 20]. A number of research pay close attention to the application of LSPR of AuNPs for the detection of various analytes [21-23]. For example, the modified AuNPs have been widely used in colorimetric probes to determinate heavy metal ions. Recently, Jiang and co-workers reported a recyclable colorimetric detection of trivalent cations (Cr 3+, Fe3+, Al3+) in using zwitterionic AuNPs, and the aggregated AuNPs could be regenerated and recycled by removing M3+, which was a cost-effective method [24]. Wu et al. designed a gallic acid capped AuNPs as colorimetric probe to detect Cr3+ and Cr6+ with high selectivity [25]. Ha and coworkers developed a simple method for detecting Cr3+ based on AuNPs functionalized with xanthoceras sorbifolia tannin as a colorimetric probe [26]. Li’s group designed a gold nanorods based colorimetric probe which could be applied for Cr3+ detection in real lake water sample with the limit of 8.8×10 –8 M [27]. More recently, Lin and co-workers reported the determination of Cr6+ using AuNPs modified with the reagent 1,5-diphenylcarbazide with highly selective for Cr6+ with 0.3 μM concentration of detection [28]. The chromium ions determinate by functionalized AuNPs have been widely researched by using the property of LSPR of AuNPs [7, 29]. Colorimetric method based on LSPR of AuNPs is convenient, speedy and can be easily monitored by the naked eyes [30-32]. And the AuNPs probe had been expanded to the paper based sensor by Huo and Yang, which developed the AuNPs based colorimetric probe to a portable sensor for Cr6+ with limit of 280 nM 4
[33]. However, among these methods, the Cr3+ and Cr6+ could not be detected simultaneously by the same probe (as shown in Table S1), sometimes, detection of Cr6+ can be realized by reducing Cr6+ to Cr3+ readily in the process of detection. So, a probe which can detect both Cr3+ and Cr6+ will be urgently needed. In this research, we synthesized gold nanoparticles using sodium hyaluronate as protect reagent and exploited a SH-AuNPs based colorimetric probe for detecting Cr3+ and Cr6+ simultaneously. The SH-AuNPs possess a favorable capability on recognizing Cr3+ and Cr6+ over other metal ions. Upon addition of Cr3+ or Cr6+ to the SH-AuNPs solution, the color conversion occurred from wine red to blue grey which can be easily readout. The color change or aggregation process can be quantitatively analyzed by detecting the LSPR of SH-AuNPs using a standard spectrophotometer.
2 Experimental Section 2.1 Materials All chemicals used were commercially purchased and used without any further treatment. The ascorbic acid and hydrogen tetrachloroaurate (III) trihydrate (HAuCl4·3H2O, 99.9%) were obtained from Aladdin. The used metal salts Cr(NO3)3·9H2O, K2Cr2O7 and other metal salts were purchased from Beijing Chemical Reagent Company (Beijing, China). 2.2 Apparatuses The morphologies of the SH-AuNPs were characterized by TEM with a Hitachi H-7650 electron at an acceleration voltage of 120 KV with a CCD camera. The 5
UV-vis absorption spectra were recorded with a UV-2600 spectrophotometer (Shimadzu, Japan). 2.3 Preparation of AuNPs coated with sodium hyaluronate In this experiment, a sodium hyaluronate solution (4 mL, 3.6 mM) was mixed with aqueous a HAuCl4 solution (6.4 mL, 2 mM) under the strong magnetic stirring at 70℃. After incubated for 2 min, the ascorbic acid solution (0.2 mL, 0.1 M) was introduced quickly and continued stirring. During the reaction sustained at 70℃, the color of the solution changed from light yellow to wine red within 30 min, the final products SH-AuNPs was cooled naturally at room temperature and stored at 4℃ before use. 2.4 Colorimetric detection of chromium ions The as-prepared SH-AuNPs used as a colorimetric probe to detect chromium ions. Various concentrations (0.001-20.0 μΜ) of chromium ions were prepared by serial dilutions of the Cr(NO3)3·9H2O and K2Cr2O7 stock solution to evaluate the lowest detectable concentration. The colorimetric detection of aqueous Cr3+ and Cr6+ was performed by mixing the SH-AuNPs probe and the samples of metal ions with volume ratio 1:1 at room temperature. Then the UV-vis spectra of all samples were recorded and compared with the blank. The selectivity was investigated by performing detection of other relevant metal ions, including Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+. In order to further study the interference of the other ions, the SH-AuNPs solutions with mixtures containing chromium ions (20 μM) and possible interference ions (20 μM) were also tested. The 6
practical application of the probe was performed at same condition just using the real water samples in the detection, and the detailed illustration of experiments was listed in the supporting information [34].
3 Results and Discussion 3.1 Sensing process Scheme 1 depicted the sensing process for detection of chromium ions by the SH-AuNPs. Sodium hyaluronate was used as the stabilizer in the synthesis of the gold nanoparticles. The molecule of sodium hyaluronate had more than one free –OH groups and one –COOH group, which provided a hydrophilic interface and a handle for further reaction with heavy metal ions. When Cr3+ (3d3) or Cr6+ (3d0) was exposed to the SH-AuNPs probe, it could be bound onto the surface of AuNPs through the hyaluronate ions. Thereby, the SH-AuNPs produced a substantial shift in the plasmon band energy to longer wavelengths and a wine red to blue gray color change, which can be observed by UV-vis absorption spectroscopy or just visualized by the naked eye. 3.2 Characterization The morphology and size of the SH-AuNPs were investigated by TEM. As indicated in Fig. 1a, the as prepared SH-AuNPs were spherical and exhibited well monodispersed state. The inset of Fig. 1a showed the size distribution of SH-AuNPs, which indicated that the size of the nanoparticles was in a scale of 17-21 nm, and the average diameter was 19.5 nm. The corresponding LSPR of SH-AuNPs reflected by 7
UV-vis absorbance spectrum had a characteristic peak at about 525 nm (Fig. 2), which exactly equivalent the wine red color solution of as prepared SH-AuNPs. The UV-vis absorbance spectra were recorded to manifest the LSPR of SH-AuNPs in the absence and presence of chromium ions, and the inset showed the corresponding digital images. The characteristic LSPR of the as prepared SH-AuNPs at about 525 nm indicated that SH-AuNPs exhibited well monodispersed state. When in the presence of 20 μM of chromium ions, the SH-AuNPs solution occured a dramatic color change from wine red to blue gray immediately. The corresponding TEM images (Fig. 1b, 1c and 1d) showed the serious aggregation of the SH-AuNPs with chromium ions, which led to a colorimetric response from wine red to blue gray (inset of Fig. 2). As can be depicted from the LSPR spectra of the SH-AuNPs, the intensity of the LSPR of SH-AuNPs at 525 nm decreased, meanwhile another longerabsorbance at about 650 nm or 695 nm appeared, which were corresponded to the aggregated Au NPs. This would be reflected change of LSPR for chromium reaction system monitored by UV-vis spectroscopy. 3.3 Sensitivity of the detection system for chromium ions To evaluate the detectable minimum concentration of chromium ions by colorimetric response, the samples with various concentrations of chromium ions reacted with the SH-AuNPs were recorded by UV-vis spectra. As depicted from the LSPR absorption of the SH-AuNPs with various concentrations of Cr3+ (Fig. 3a), the intensity of LSPR decreased gradually with an increase in Cr 3+ concentration due to the addition of Cr3+ exacerbated the aggregation of the SH-AuNPs further. When the 8
concentration of Cr3+ increased from 10 μM to 20 μM, the intensity of the LSPR peak of SH-AuNPs at 525 nm decreased seriously, and another plasmon band at about 650 nm appeared (Fig. 3a), which implied the aggregation of AuNPs in presence of Cr3+. The significant and distinguishable color changes were observed within 1 min, which allowed high speed detecting and monitoring. And the corresponding color transformed from wine red to blue gray accompanied as a bathochromic shift in the UV-vis spectra (Fig. 3a and 3c). As indicated in the Fig. 3c, when exposed to 3 μM of Cr3+, the color of the SH-AuNPs has transformed evidently, and the 5 μM of Cr3+ discolored distinctly which can be perceived by naked eyes clearly. The blue gray color can be noticed at the high concentration over 10 μM of Cr3+ was related to the high intensity at the longitudinal LSPR around 650 nm. The lowest detectable concentration of Cr3+ by eye vision was 3 μM. Similarly, the detection for Cr6+ could be achieved by the colorimetric response and the LSPR of the SH-AuNPs. As illustrated in the Fig. 4a, the intensity of LSPR at 525 nm was decreased with the addition of the concentration of Cr6+. When the concentration of Cr6+ was added up to 10 μM, the second absorption peak of the SH-AuNPs was emerged at around 650 nm (Fig. 4a), which reflected the extent of aggregation of the SH-AuNPs related to the concentrations of Cr6+. As can be seen in Fig. 4c, when exposed to 1 μM of Cr6+, the SH-AuNPs discolored though the process of response was delayed to 15 min. If the concentration of Cr6+ was added up to 5 μM, the color of the SH-AuNPs turned immediately. Thus, the lowest detectable concentration of Cr6+ by eye vision was defined to 1 μM. 9
The above results indicated that the transformation of the observed spectra was related to the concentrations of Cr3+ or Cr6+ closely. The increased absorbance intensity at around 650 nm and the decrease at 525 nm were concentration-dependent, which could be an indicator of the formation of aggregation of the SH-AuNPs with Cr3+ or Cr6+. In order to quantitatively analyze the colorimetric response, the ratio of the intensity of two LSPR peaks (A650/A525) was calculated and used as a criterion representing the extent of aggregation. There was a good linear relationship between the value of A650/A525 and the concentration of Cr3+ in the range 0.001–0.020 μM. And a calibration curve of y=0.028+0.193x with a correlation coefficient of 0.9939 for the detection Cr3+ was obtained (Fig. 3b). The lowest detectable concentration was then calculated to be of 0.78 nM for a signal-to-noise (S/N) ration of 3. The detection for Cr6+ was also existed a linear relationship (R2=0.9864) between the A650/A525 value and the concentration of Cr6+ in the range 0.005–1.0 μM (Fig. 4b), the lowest detectable concentration was 2.90 nM. Due to the conversion between Cr3+ and Cr6+ existed commonly, the detection of the mixed chromium ions was also investigated. The colorimetric response and UV-vis spectra were used to further evaluate the sensitivity of the detection system for mixed chromium ions (the volume ratio of Cr3+ and Cr6+ was 1:1). UV-vis spectra of the detection system with the various concentrations of mixed chromium ions were shown in Fig. 5a. It was found that the decrease in the intensity of the absorbance at 525 nm and an increase at 695 nm with increasing of concentrations of mixed chromium ions. Fig. 5b showed a good linear relationship (R2=0.9944) between 10
A695/A525 and the concentrations of mixed chromium ions ranged from 0.001–0.01 μM with the lowest detectable concentration of 0.69 nM. With the increase of the concentrations of mixed chromium ions from 0.001 to 20 μM, the color transformation of the SH-AuNPs (from wine red to blue gray) could be easily visualized in Fig. 5c. The lowest detectable concentration of mixed chromium ions was determined at 5 μM by naked eyes. The lowest detectable concentrations of Cr3+, Cr6+ and mixed chromium ions were 0.78 nM, 2.90 nM and 0.69 nM, which was much lower than the maximal permitted level in drinking water (0.962 µM) as regulated by the World Health Organization and Chinese Ministry of Environmental Protection (GB 7466-87) [8, 35]. And, compared with those of other optical chromium ions sensors reported previously, the detection sensitivity of the proposed method was much higher [36-39]. More importance, the Cr6+ could be detected with Cr3+ simultaneously by using SH-AuNPs. 3.4 Selectivity of the detection system To estimate the selectivity of the SH-AuNPs for chromium ions, the detection of a variety of environmentally relevant metal ions (including Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+) were performed at the same conditions. As can be observed from Fig. 6a, there is no obvious change in the LSPR with other ions, however, in presence of chromium ions, the LSPR absorption peaks occurred significant shift. The corresponding colorimetric images indicated that the SH-AuNPs showed evidently colorimetric response with chromium ions, from wine red to blue gray, however, with other ions, the SH-AuNPs seemed almost no change 11
(Fig. 6c). To determine the selectivity quantitatively, the ratio of A650/A525 of all samples were provided in Fig. 6b, the value of chromium ions were exceeded 4 fold higher than other metal ions, which proved that the SH-AuNPs exhibited evident selectivity toward chromium ions. The corresponding images indicated that SH-AuNPs have no transition of color in presence of other metal ions (Fig. 6c). The results indicated that this system exhibited a good selectivity for chromium ions over other 13 kinds of metal ions. To test the specifity for chromium ions, the interference of other ions in detection was also investigated, since heavy metal ions are mixed with other ions in many cases. The relevant metal ions were acted as disturbing ions, and the response of the proposed probe SH-AuNPs to the mixed solution were tested under same conditions. Fig. 7a indicated that the SH-AuNPs remained dispersed states when exposed to the relevant metal ions suggesting that there was no aggregation occurred, and in presence of Cr3+ or Cr6+ induce the aggregation of AuNPs, which led to the color conversion from wine red to blue gray (Fig. 7b and 7c). The selectivity of the SH-AuNPs towards various metal ions was further quantified by comparing the extinction intensity ratio, as obseved from Fig. 8a and 8b, the Cr3+ and Cr6+ induced value of A650/A525 were over 4 fold larger than that of other metal ions. These results indicate that SH-AuNPs can be employed to detecting chromium ions without interference from other metal ions in environmental samples.
12
3.5 Detection of real samples Inspired by the successful and extensive application of AuNPs in detection, the SH-AuNPs have a great potential to be extended into the environmental assay. Thus, the SH-AuNPs were further applied to determinate chromium ions in real water samples [25]. The real samples came from our campus Mengxi lake and a natural Chagan lake, the sample of lake water was first tested by ICP-AES to determine the actual contents of metal ions or element (Table S2 and S3), respectively. There was almost no Cr3+ or Cr6+ in the lake water according the ICP data. To test the applicable performance of SH-AuNPs in real water sample, a simulated detection in lake water was carried out. A series of different spiked concentrations of chromium ions with lake water samples were formulated by the same volume according to the literature [19, 29], and the other ions of lake water samples were also prepared by the same method. The detection of the sensitivity of Mengxi lake samples was performed in Fig. 9 (A: Cr3+, B: Cr6+ and C: mixed chromium ions). The intensity of LSPR peaks was decreased with the addition of the different concentrations of chromium ions (Fig. 9a). When the concentrations of Cr3+, Cr6+ and mixed chromium ions were raised to 5 μM, 1 μM and 10 μM respectively, the corresponding LSPR began to emerge a second peak at about 650 nm, indicated the aggregation of the SH-AuNPs. These results illustrated that the SH-AuNPs detecting for Cr3+, Cr6+ and mixed chromium ions did not affected by other unknown components of the campus Mengxi lake water. The corresponding colorimetric images were shown in Fig. 9b, which were in line with the 13
analysis of LSPR. The selectivity was also studied by comparison in other ions of Mengxi lake water samples. As presented in Fig. 10a and corresponding images (Fig. 10b), the other ions of Mengxi lake water samples could not trigger the aggregation of the SH-AuNPs under the same conditions. While chromium ions caused the colorimetric conversion of the SH-AuNPs, the corresponding LSPR of the SH-AuNPs emerged a second peak due to the aggregation (Fig. 10a). The results indicated that SH-AuNPs could be used as an excellent colorimetric probe towards chromium ions with strong anti-interference ability in campus lake water. As a natural lake, Chagan lake can represent the natural complex environment, so, the detection and application of simulation was performed in Chagan lake water samples obtained straight from Chagan lake. The detection was first carried out, and the result was consistent with the data of ICP (Table S3). Then the spiked concentrations of chromium ions with Chagan lake water samples were precisely prepared, and the selectivity and sensitivity of detection was tested respectively. The Fig. 11 revealed the detection selectivity of the probe SH-AuNPs for chromium ions over other metal ions. The chromium ions samples were exclusive metal ions to induce the aggregation of AuNPs, which proved the excellent specificity of the SH-AuNPs for chromium ions. The sensitivity detection in natural Chagan lake water was displayed in Fig. 12. A group of convincing data was obtained, including the characteristic LSPR of SH-AuNPs in presence of chromium ions, the corresponding 14
colorimetric conversion of samples and the ratio of A650/A525. As can be seen from the Fig. 12a, in presence of Cr3+ (Fig. 12A), Cr6+ (Fig. 12B) or mixed chromium ions (Fig. 12C), the intensity of the LSPR peak at 525 nm significantly decreased and a new peak located at 650 nm was observed, which indicated the aggregation of SH-AuNPs. And the similar linear relationship between the ratio (A650/A525) and the concentration of metal ions existence in the three detection results (inset of Fig. 12a), indicated that the good sensitivity of detection in Chagan lake samples. Fig. 12b showed that the corresponding photographic images of SH-AuNPs with Chagan lake water samples. All above results proved that the SH-AuNPs can be used as a colorimetric probe in complex natural environment. 3.6 Effect of pH value Furthermore, the evaluation of effect of pH value of detection was carried out due to the pH value was found to be essential to detection especially in practical application. The resistance adaptability of the concussion from the alkali was important for this probe. The pH value of as-prepared SH-AuNPs was about 3. To investigate effect of the pH, the detection was examined in the various pH value (Fig. S1). The final pH of the detective probe was adjusted by a neutralization reaction with a high-concentration NaOH solution (0.5 M, Table S4). These results indicated that the SH-AuNPs were stable in the pH range of 3-6, and upon exposure to the acidic conditions, the LSPR with aggregation degree of SH-AuNPs would not be affected, which illustrated the SH-AuNPs can resist the strong base. The influence of pH for 15
detection of the chromium ions with the aggregation of SH-AuNPs was manifested by the value of A650/A525 shown in Fig. S2. The performance of the probe could be maintained as long as the final pH of the mixed solution was less than 5. However, when the pH was rose to 6 (Fig. S1c), the SH-AuNPs still remained dispersed after exposed to the chromium ions. The results manifested the sensitivity and selectivity of the detection decreased accompanied the rise of pH value, which may be owing to the deprotonation on carboxylic group from hyaluronate occurring under alkaline conditions [9]. Thus, the detection using as-prepared SH-AuNPs was selected as the optimal pH condition for all experiments. 3.7 Principle for the chromium sensing The mechanism of recognition for detection of chromiun ions by SH-AuNPs could be illustrated from the coordination between the carboxylic ions and metal ions basically [9, 29]. The recognition of chromium ions by SH-AuNPs was attributed to the coordination between the carboxylic ions and metal ions due to the carboxyl group and available carboxyl group at pH value of 3. The chromium ions can induce the aggregation of SH-AuNPs which may be attributed to the Cr3+(Cr6+) coordination with amide group and carboxyl groups of the molecule of hyaluronate to form a stable complexation species accompanied with the intramolecular charge transfer [9, 13-17]. Owing to the outermost electron configuration of the Cr3+ and Cr6+, they were strong receptor of electrons to half-fill and unoccupied d orbitals. In accordance with the general coordination, a specific and strong interaction between the detection probes and chromium ions existed due to the strong binding energies [34, 40] of chromium 16
ions with Au ions. Chromium ions had a higher effective charge, smaller radius, and stronger coordination ability than the other transition metal ions, which made this method highly sensitive and selective. As a result, the LSPR absorption decreased dramatically and allowed the quantitation of chromium ions in aqueous solution.
4 Conclusions In conclusion, a simple, rapid and cost-effective SH-AuNPs based colorimetric sensor was synthesized and used for selective detection of Cr 3+ and Cr6+ simultaneously. The selectivity of the SH-AuNPs-based detection system by the naked eye and UV-vis spectra was excellent for chromium ions compared with other ions. The lowest detectable concentrations of Cr3+, Cr6+ and mixed chromium ions were 0.78 nM, 2.90 nM and 0.69 nM, respectively. In addition, the AuNPs-based detection system was applicable for rapid colorimetric detection of chromium ions in complicated real lake water samples with excellent stability and capability.
Acknowledgements The authors gratefully acknowledge financial support from the 863 Program (2013AA032204), the NSF of China (21205024), the project of Harbin Science and Technology bureau (2014RFQXJ151), the National Science Foundation for Post-doctoral Scientists of China (2012M520659, 2013T60307).
References 1.
L.B. Zhang, E.K. Wang, Metal nanoclusters: new fluorescent probes for sensors and bioimaging, Nano Today 9 (2014) 132-157. 17
2.
A.D. Dayan, A.J. Paine, Mechanisms of chromium toxicity, carcinogenicity and allergenicity: Review of the literature from 1985 to 2000, Hum. Exp. Toxicol 20 (2001) 439-451.
3.
D.Y. Li, J. Li, X.F. Jia, Y. Xia, X.W. Zhang, E.K. Wang, A novel Au-Ag-Pt three-electrode microchip sensing platform for chromium (VI) determination, Anal. Chim. Acta 804 (2013) 98-103.
4.
S.H.
Liu,
F.
Lu,
J.J.
Zhu,
Highly
fluorescent
Ag
nanoclusters:
microwave-assisted green synthesis and Cr3+ sensing, Chem. Commun 47 (2011) 2661-2663. 5.
Y. Gong, X.L. Liu, L. Huang, W.Y. Chen, Stabilization of chromium: an alternative to make safe leathers, J. Hazard. Mater 179 (2010) 540-544.
6.
N. Shevchenko, V. Zaitsev, A. Walcarius, Bifunctionalized mesoporous silicas for Cr(VI) reduction and concomitant Cr(III) immobilization, Environ. Sci. Technol 42 (2008) 6922-6928.
7.
M.V. Dozzi, A. Saccomanni, E. Selli, Cr(VI) photocatalytic reduction: effects of simultaneous organics oxidation and of gold nanoparticles photodeposition on TiO2, J. Hazard. Mater 211 (2012) 188-195.
8.
World Health Organization (WHO), Chromium in drinking water. Guidelines for drinking-water quality. 2nd ed. World Health Organization (2004) Geneva Vol. 2.
9.
Y.M. Yu, Y. Hong, Y.Q. Wang, X.Y. Sun, B. Liu, Mecaptosuccinic acid modified gold nanoparticles as colorimetric sensor for fast detection and simultaneous identification of Cr3+, Sensor. Actuat. B-Chem 239 (2017) 865-873. 18
10. M.R. Moghadam, S. Dadfarnia, A.M.H. Shabani, Speciation and determination of ultra trace amounts of chromium by solidified floating organic drop microextraction
(SFODME)
and
graphite
furnace
atomic
absorption
spectrometry, J. Hazard. Mater 186 (2011) 169-174. 11. F. Seby, S. Charles, M. Gagean, H. Garraud, O.F.X. Donard, Chromium speciation by hyphenation of high-performance liquid chromatography to inductively coupled plasma-mass spectrometry-study of the influence of interfering ions, J. Anal. Atom. Spectrom 18 (2003) 1386-1390. 12. Y.J. Ye, H.L. Liu, L.B. Yang, J.H. Liu, Sensitive and selective SERS probe for trivalent chromium detection using citrate attached gold nanoparticles, Nanoscale 4 (2012) 6442-6448. 13
Q.T. Meng, W.P. Su, X.M. Hang, X.Z. Li, C. He, C.Y. Duan, Dye-functional mesoporous silica material for fluorimetric detection of Cr(III) in aqueous solution and biological imaging in living systems, Talanta 86 (2011) 408-414.
14
S. Goswami, K. Aich, S. Das, A.K. Das, D. Sarkar, S. Panja, T.K. Mondal and S.K. Mukhopadhyay, A red fluorescence ‘off–on’ molecular switch for selective detection of Al3+, Fe3+ and Cr3+: experimental and theoretical studies along with living cell imaging, Chem. Commun 49 (2013) 10739-10741.
15
J.F. Wang, Y.B. Li, N.G. Patel, G. Zhang, D.M. Zhou and Y. Pang, A single molecular probe for multi-analyte (Cr3+, Al3+ and Fe3+) detection in aqueous medium and its biological application, Chem. Commun 50 (2014) 12258-12261.
16
S. Guha, S. Lohar, A. Banerjee, A. Sahana, I. Hauli, S.K. Mukherjee, J.S. 19
Matalobos, D. Das, Thiophene anchored coumarin derivative as a turn-on fluorescent probe for Cr3+: Cell imaging and speciation studies, Talanta 91 (2012) 18-25. 17
C.Y. Li, X.F. Kong, Y.F. Li, C. Weng, J.L. Tang, D. Liu, W.G. Zhu, Ratiometric near-infrared chemosensor for trivalent chromium ion based on tricarboyanine in living cells, Anal. Chim. Acta 824 (2014) 71-77.
18. R. Elghanian, J.J. Storhoff, R.C. Mucic, R.L. Letsinger, C.A. Mirkin, Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles, Science 277 (1997) 1078-1081. 19. X. Liu, J.J. Xiang, Y. Tang, X.L. Zhang, Q.Q. Fu, J.H. Zou, Y.H. Lin, Colloidal gold nanoparticle probe-based immunochromatographic assay for the rapid detection of chromium ions in water and serum samples, Anal. Chim. Acta 745 (2012) 99-105. 20. J.J. Du, L. Jiang, Q. Shao, X.G. Liu, R.S. Marks, J. Ma, X.D. Chen, Colorimetric detection of mercury ions based on plasmonic nanoparticles, Small 9 (2013) 1467-1481. 21. K. Saha, S.S. Agasti, C. Kim, X. Li, V.M. Rotello, Gold nanoparticles in chemical and biological sensing, Chem. Rev 112 (2012) 2739-2779. 22. K.E. Sapsford, W.R. Algar, K.B. Gemmill, B.J. Casey, E. Oh, M.H. Stewart, I.L. Medintz, Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology, Chem. Rev 113 (2013) 1904-2074. 23. Y. Zhang, I.D. McKelvie, R.W. Cattrall, S.D. Kolev, Colorimetric detection 20
based on localised surface plasmon resonance of gold nanoparticles: Merits, inherent shortcomings and future prospects, Talanta 152 (2016) 410-422. 24. W.S. Zheng, H. Li, W.W. Chen, J. Ji, X.Y. Jiang, Recyclable colorimetric detection of trivalent cations in aqueous media using zwitterionic gold nanoparticles, Anal. Chem 88 (2016) 4140-4146. 25. C. Dong, G.H. Wu, Z.Q. Wang, W.Z. Ren, Y.J. Zhang, Z.Y. Shen, T.H. Li, A.G. Wu, Selective colorimetric detection of Cr(III) and Cr(VI) using gallic acid capped gold nanoparticles, Dalton. Trans 45 (2016) 8347-8354. 26. W. Ha, J. Yu, R. Wang, J. Chen, Y.P. Shi, “Green” colorimetric assay for the selective detection of trivalent chromium based on xanthoceras sorbifolia tannin attached to gold nanoparticles, Anal. Methods 65 (2014) 720-5726. 27. F.M. Li, J.M. Liu, X.X. Wang, L.P. Lin, W.L. Cai, X. Lin, Y.N. Zeng, Z.M. Li, S.Q. Lin, Non-aggregation based label free colorimetric sensor for the detection of Cr(VI) based on selective etching of gold nanorods, Sensor. Actuat. B-Chem 155 (2011) 817-822. 28. L. Liu, Y.M. Leng, H.W. Lin, Photometric and visual detection of Cr(VI) using gold nanoparticles modified with 1,5-diphenylcarbazide, Microchim. Acta 183 (2016) 1367-1373. 29. X. Yang, S.S. Fu, G.J. Ren, F. Chai, F.Y. Qu, Facile preparation of 2,6-Pyridinedicarboxylic acid protected gold nanoparticles with sensitive chromium-ion sensing and efficient catalysis, Eur. J. Inorg. Chem 32 (2015) 5411-5418. 21
30. Y.J. Song, W.L. Wei, X.G. Qu, Colorimetric biosensing using smart materials, Adv. Mater 23 (2011) 4215-4236. 31. J.
Tang,
P.
Wu,
X.D.
Hou,
K.L.
Xu,
Modification-free
and
N-acetyl-L-cysteine-induced colorimetric response of AuNPs: a mechanistic study and sensitive Hg(2+) detection, Talanta 159 (2016) 87-92. 32. H.Y. Kim, I. Choi, Ultrafast colorimetric determination of predominant protein structure evolution with gold nanoplasmonic particles, Nanoscale 8 (2015) 1952-1959. 33. J.F. Guo, D.Q. Huo, M. Yang, C.J. Hou, J.J. Li, H.B. Fa, H.B. Luo, P. Yang, Colorimetric detection of Cr(VI) based on the leaching of gold nanoparticles using a paper-based sensor, Talanta 161 (2016) 819-825. 34. C.A. Rusinek, A. Bange, I. Papautsky, W.R. Heineman, Cloud point extraction for electroanalysis: anodic stripping voltammetry of cadmium, Anal. Chem 87 (2015) 6133-6140. 35. Chinese
Ministry
of
Environmental
Protection
(CMEP),
Water
quality-Determination of total chromium, GB (1987) 7466-87. 36. Y.
Mikata,
A.
Kizu,
H.
Konno,
(2-quinolylmethyl)-1,2-phenylenediamine)
TQPHEN derivatives
(N,N,N′,N′-tetrakis as
highly
selective
fluorescent probes for Cd2+, Dalton. Trans 44 (2015) 104-109. 37. P.S. Yao, Z.H. Liu, J.Z. Ge, Y. Chen, Q.Y. Cao, A novel polynorbornene-based chemosensor for the fluorescence sensing of Zn2+ and Cd2+ and subsequent detection of pyrophosphate in aqueous solutions, Dalton. Trans 44 (2015) 22
7470-7476. 38. S. Goswami, K. Aich, S. Das, C.D. Mukhopadhyay, D. Sarkar, T.K. Mondal, A new visible-light-excitable ICT-CHEF-mediated fluorescence ‘turn-on’ probe for the selective detection of Cd2+ in a mixed aqueous system with live-cell imaging, Dalton. Trans 44 (2015) 5763-5770. 39. P.P.P. Kumar, C.H. Suresh, V. Haridas, A supramolecular approach to metal ion sensing: cystine-based designer systems for Cu2+, Hg2+, Cd2+ and Pb2+ sensing, RSC. Adv 5 (2015) 7842-7847. 40. L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P.V. Duyne, J.T. Hupp, Metal-organic framework materials as chemical sensors, Chem. Rev 112 (2012) 1105-1125.
23
5 Figure Captions Scheme. 1 View of the preparation process and strategy for the detection of chromium ions with SH-AuNPs. Fig. 1 (a) TEM images of the SH-AuNPs, the inset shows the size distribution of the SH-AuNPs. (b) TEM images after the addition of 20 μM of Cr3+. (c) TEM image after the addition of 20 μM of Cr6+. (d) TEM images after the addition of 20 μM of mixed chromium ions. Fig. 2 The UV-vis absorbance spectra of the SH-AuNPs before and after the addition of 20 μM of chromium ions, the inset shows the corresponding digital images. Fig. 3 (a) UV-vis spectra of the SH-AuNPs after the addition of different concentrations of Cr 3+ (0.001, 0.003, 0.005, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10, 15 and 20 μM). (b) Plot of A650/A525 versus the concentrations of Cr3+ in the range 0.001–0.02 μM (the error bars represent the standard deviations of three independent measurements). (c) Photograph of the SH-AuNPs in the presence of different concentrations of Cr3+. Fig. 4 (a) UV-vis spectra of the SH-AuNPs after the addition of different concentrations of Cr 6+ (0.001, 0.003, 0.005, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10, 15 and 20 μM). (b) Plot of A650/A525 versus the concentrations of Cr6+ in the range 0.005–1.0 μM (the error bars represent the standard deviations of three independent measurements). (c) Photograph of the SH-AuNPs in the presence of different concentrations of Cr6+. Fig. 5 (a) UV-vis spectra of the SH-AuNPs in presence of different concentrations of mixed chromium ions (0.001, 0.005, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 5, 10, 15 and 20 μM). (b) Plot of A695/A525 versus the concentrations of mixed chromium ions in the range 0.001–0.01 μM (the error bars represent the standard deviations of three independent measurements). (c) Photograph of the SH-AuNPs in the presence of different concentrations of mixed chromium ions. Fig. 6 (a) The LSPR spectra of the SH-AuNPs with different metal ions (20 μM). (b) The A650/A525 value of the SH-AuNPs solution with various metal ions. (c) Corresponding colorimetric images. Fig. 7 (a) Photograph of the SH-AuNPs solutions in the presence of different metal ions. (b) Photograph of the SH-AuNPs solutions in the presence of Cr 3+ mixing with relevant metal ions. (c)
24
Photograph of the SH-AuNPs solutions in the presence of Cr6+ mixing with relevant metal ions. Fig. 8 The absorbance ratio (A650/A525) of the SH-AuNPs in the presence of all kinds of metal ions and mixing metal ions with (a) Cr3+ (Cr3+ and other metal ions are all 20 μM), and the mixing metal ions with (b) Cr6+ (Cr6+ and other metal ions are all 20 μM). Fig. 9 (a) The LSPR of the SH-AuNPs in presence of Mengxi lake water samples with different concentrations of (A: Cr3+ B: Cr6+ C: mixed chromium ions). (b) Photograph of the SH-AuNPs in the presence of different concentrations of (A: Cr3+ B: Cr6+ C: mixed chromium ions). Fig. 10 (a) UV-vis absorption spectra of SH-AuNPs after the addition of Mengxi lake water samples, the concentrations of all metal ions are 20 μM. (b) Images of Mengxi lake water samples with SH-AuNPs in the presence of various metal ions. Fig. 11 (a) UV-vis absorption spectra of the SH-AuNPs in presence of Chagan lake water samples (the concentrations of metal ions are 20 μM). (b) Corresponding photographic images of SH-AuNPs with Chagan lake water samples. Fig. 12 (a) UV-vis absorption spectra of the SH-AuNPs in presence of Chagan lake water samples with different concentrations of (A: Cr 3+ B: Cr6+ C: mixed chromium ions). Inset: plot of A650/A525 value of the SH-AuNPs versus the concentration of (A: Cr 3+ B: Cr 6+ C: mixed chromium ions). (b) Corresponding photographic images of the SH-AuNPs system with different concentrations of Chagan lake water samples (A: Cr3+ B: Cr6+ C: mixed chromium ions).
25
Scheme 1
26
27
28
29
30
31
32
33
34
35
36
37
38
S0927-7757(17)30848-8 http://dx.doi.org/10.1016/j.colsurfa.2017.09.028 COLSUA 21931
To appear in:
Colloids and Surfaces A: Physicochem. Eng. Aspects
Received date: Revised date: Accepted date:
3-7-2017 11-9-2017 15-9-2017
Please cite this article as: Shuang Li, Te Wei, Guojuan Ren, Fang Chai, Hongbo Wu, Fengyu Qu, Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection, Colloids and Surfaces A: Physicochemical and Engineering Aspectshttp://dx.doi.org/10.1016/j.colsurfa.2017.09.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gold nanoparticles based colorimetric probe for Cr(III) and Cr(VI) detection Shuang Li, Te Wei, Guojuan Ren, Fang Chai*, Hongbo Wu*, and Fengyu Qu * Key Laboratory of Design and Synthesis of Functional Materials and Green Catalysis, Colleges of Heilongjiang Province, College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, P. R. China. * Corresponding author. E-mail: [email protected], [email protected], [email protected]
Graphical Abstract
Highlights
The sodium hyaluronate protected AuNPs were synthesized through a simple process.
The SH-AuNPs can be used for colorimetric detection of Cr3+ and Cr6+ synchronously.
The SH-AuNPs can be applied to detecting for chromium ions in real lake water samples with strong anti-interference ability.
1
Abstract A simple and highly practical colorimetric method has been proposed for detection of chromium ions (Cr3+ and Cr6+) synchronously by sodium hyaluronate functionalized gold nanoparticles (SH-AuNPs). The SH-AuNPs were synthesized and characterized by UV-vis spectra and transmission electron microscopy (TEM). The colorimetric response of Cr3+ and Cr6+ can be performed simultaneously by the same probe SH-AuNPs, based on the property of special localized surface plasmon resonance (LSPR). The interaction between chromium ions and sodium hyaluronate causes rapid aggregation of the SH–AuNPs conjugates and a concurrent color conversion from wine red to blue gray which is clearly detectable by the naked eye. By using SH-AuNPs as colorimetric probe, the color change with 3 µM Cr3+, 1 µM Cr6+, or 10 µM mixed chromium ions can be recognized easily by naked eye with highly selectivity. The detection limit calculated by the linear relationship of LSPR were at 0.78 nM (for Cr3+), 2.90 nM (Cr6+) and 0.69 nM (mixed chromium ions) respectively, which were all below the guideline value set by World Health Organization (0.962 µM). The practical applicability of the SH-AuNPs was also verified by the detection of chromium ions in natural lake water samples.
Keywords: gold nanoparticles; sodium hyaluronate; colorimetric detection; chromium ions
2
1 Introduction Chromium is one of the most toxic heavy metals which is mainly exists in the form of Cr3+ and Cr6+ [1]. Cr3+ is a component part of the glucose tolerance factor, thus, Cr3+ can affect the body lipid metabolism, lower cholesterol and triglyceride levels in the blood. More seriously, excessive Cr3+ can cause mutations and malignant cells, which endangers human health [2]. Nevertheless, Cr6+ is ca. 100 times more toxic than Cr3+, which is carcinogenic and mutagenic due to its high oxidation potential and it has ability to penetrate biological membranes [3-7]. Unfortunately, Cr6+ is widely distributed in wastewater all over the world, which was a persistent great threat to the environment and human health [5-7]. The World Health Organization (WHO) stipulates that the maximum amount of chromium acceptable to the drinking water is 0.962 µM [8, 9]. Thus, there is a pressing need to explore an accurate and reliable method for the detection and monitor of chromium ions. At present, the determination of chromium ions has been performed by a variety of traditional techniques, including atomic absorption spectrometry [10], inductively coupled plasma-atomic emission spectrometry [11], electrothermal atomic absorption spectrometry [12] and so on. In comparison, some nanotechnology such as colorimetry, fluorimetry and electrochemical techniques have been obtained more attention and exhibited great potential application [13-17]. Among them, the AuNPs based colorimetric method is an ideal choice, which can overcome some drawbacks, such as the time-consuming, relied on large instrument and need pretreatment. The AuNPs exhibit distinct localized surface plasmon resonance (LSPR), which causes the 3
AuNPs are highly sensitive to the size, shape, capping agent and the state of AuNPs [18]. LSPR-based detection methods offer some significant advantages such as low cost, speedy and ease of readout [11, 19, 20]. A number of research pay close attention to the application of LSPR of AuNPs for the detection of various analytes [21-23]. For example, the modified AuNPs have been widely used in colorimetric probes to determinate heavy metal ions. Recently, Jiang and co-workers reported a recyclable colorimetric detection of trivalent cations (Cr 3+, Fe3+, Al3+) in using zwitterionic AuNPs, and the aggregated AuNPs could be regenerated and recycled by removing M3+, which was a cost-effective method [24]. Wu et al. designed a gallic acid capped AuNPs as colorimetric probe to detect Cr3+ and Cr6+ with high selectivity [25]. Ha and coworkers developed a simple method for detecting Cr3+ based on AuNPs functionalized with xanthoceras sorbifolia tannin as a colorimetric probe [26]. Li’s group designed a gold nanorods based colorimetric probe which could be applied for Cr3+ detection in real lake water sample with the limit of 8.8×10 –8 M [27]. More recently, Lin and co-workers reported the determination of Cr6+ using AuNPs modified with the reagent 1,5-diphenylcarbazide with highly selective for Cr6+ with 0.3 μM concentration of detection [28]. The chromium ions determinate by functionalized AuNPs have been widely researched by using the property of LSPR of AuNPs [7, 29]. Colorimetric method based on LSPR of AuNPs is convenient, speedy and can be easily monitored by the naked eyes [30-32]. And the AuNPs probe had been expanded to the paper based sensor by Huo and Yang, which developed the AuNPs based colorimetric probe to a portable sensor for Cr6+ with limit of 280 nM 4
[33]. However, among these methods, the Cr3+ and Cr6+ could not be detected simultaneously by the same probe (as shown in Table S1), sometimes, detection of Cr6+ can be realized by reducing Cr6+ to Cr3+ readily in the process of detection. So, a probe which can detect both Cr3+ and Cr6+ will be urgently needed. In this research, we synthesized gold nanoparticles using sodium hyaluronate as protect reagent and exploited a SH-AuNPs based colorimetric probe for detecting Cr3+ and Cr6+ simultaneously. The SH-AuNPs possess a favorable capability on recognizing Cr3+ and Cr6+ over other metal ions. Upon addition of Cr3+ or Cr6+ to the SH-AuNPs solution, the color conversion occurred from wine red to blue grey which can be easily readout. The color change or aggregation process can be quantitatively analyzed by detecting the LSPR of SH-AuNPs using a standard spectrophotometer.
2 Experimental Section 2.1 Materials All chemicals used were commercially purchased and used without any further treatment. The ascorbic acid and hydrogen tetrachloroaurate (III) trihydrate (HAuCl4·3H2O, 99.9%) were obtained from Aladdin. The used metal salts Cr(NO3)3·9H2O, K2Cr2O7 and other metal salts were purchased from Beijing Chemical Reagent Company (Beijing, China). 2.2 Apparatuses The morphologies of the SH-AuNPs were characterized by TEM with a Hitachi H-7650 electron at an acceleration voltage of 120 KV with a CCD camera. The 5
UV-vis absorption spectra were recorded with a UV-2600 spectrophotometer (Shimadzu, Japan). 2.3 Preparation of AuNPs coated with sodium hyaluronate In this experiment, a sodium hyaluronate solution (4 mL, 3.6 mM) was mixed with aqueous a HAuCl4 solution (6.4 mL, 2 mM) under the strong magnetic stirring at 70℃. After incubated for 2 min, the ascorbic acid solution (0.2 mL, 0.1 M) was introduced quickly and continued stirring. During the reaction sustained at 70℃, the color of the solution changed from light yellow to wine red within 30 min, the final products SH-AuNPs was cooled naturally at room temperature and stored at 4℃ before use. 2.4 Colorimetric detection of chromium ions The as-prepared SH-AuNPs used as a colorimetric probe to detect chromium ions. Various concentrations (0.001-20.0 μΜ) of chromium ions were prepared by serial dilutions of the Cr(NO3)3·9H2O and K2Cr2O7 stock solution to evaluate the lowest detectable concentration. The colorimetric detection of aqueous Cr3+ and Cr6+ was performed by mixing the SH-AuNPs probe and the samples of metal ions with volume ratio 1:1 at room temperature. Then the UV-vis spectra of all samples were recorded and compared with the blank. The selectivity was investigated by performing detection of other relevant metal ions, including Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+. In order to further study the interference of the other ions, the SH-AuNPs solutions with mixtures containing chromium ions (20 μM) and possible interference ions (20 μM) were also tested. The 6
practical application of the probe was performed at same condition just using the real water samples in the detection, and the detailed illustration of experiments was listed in the supporting information [34].
3 Results and Discussion 3.1 Sensing process Scheme 1 depicted the sensing process for detection of chromium ions by the SH-AuNPs. Sodium hyaluronate was used as the stabilizer in the synthesis of the gold nanoparticles. The molecule of sodium hyaluronate had more than one free –OH groups and one –COOH group, which provided a hydrophilic interface and a handle for further reaction with heavy metal ions. When Cr3+ (3d3) or Cr6+ (3d0) was exposed to the SH-AuNPs probe, it could be bound onto the surface of AuNPs through the hyaluronate ions. Thereby, the SH-AuNPs produced a substantial shift in the plasmon band energy to longer wavelengths and a wine red to blue gray color change, which can be observed by UV-vis absorption spectroscopy or just visualized by the naked eye. 3.2 Characterization The morphology and size of the SH-AuNPs were investigated by TEM. As indicated in Fig. 1a, the as prepared SH-AuNPs were spherical and exhibited well monodispersed state. The inset of Fig. 1a showed the size distribution of SH-AuNPs, which indicated that the size of the nanoparticles was in a scale of 17-21 nm, and the average diameter was 19.5 nm. The corresponding LSPR of SH-AuNPs reflected by 7
UV-vis absorbance spectrum had a characteristic peak at about 525 nm (Fig. 2), which exactly equivalent the wine red color solution of as prepared SH-AuNPs. The UV-vis absorbance spectra were recorded to manifest the LSPR of SH-AuNPs in the absence and presence of chromium ions, and the inset showed the corresponding digital images. The characteristic LSPR of the as prepared SH-AuNPs at about 525 nm indicated that SH-AuNPs exhibited well monodispersed state. When in the presence of 20 μM of chromium ions, the SH-AuNPs solution occured a dramatic color change from wine red to blue gray immediately. The corresponding TEM images (Fig. 1b, 1c and 1d) showed the serious aggregation of the SH-AuNPs with chromium ions, which led to a colorimetric response from wine red to blue gray (inset of Fig. 2). As can be depicted from the LSPR spectra of the SH-AuNPs, the intensity of the LSPR of SH-AuNPs at 525 nm decreased, meanwhile another longerabsorbance at about 650 nm or 695 nm appeared, which were corresponded to the aggregated Au NPs. This would be reflected change of LSPR for chromium reaction system monitored by UV-vis spectroscopy. 3.3 Sensitivity of the detection system for chromium ions To evaluate the detectable minimum concentration of chromium ions by colorimetric response, the samples with various concentrations of chromium ions reacted with the SH-AuNPs were recorded by UV-vis spectra. As depicted from the LSPR absorption of the SH-AuNPs with various concentrations of Cr3+ (Fig. 3a), the intensity of LSPR decreased gradually with an increase in Cr 3+ concentration due to the addition of Cr3+ exacerbated the aggregation of the SH-AuNPs further. When the 8
concentration of Cr3+ increased from 10 μM to 20 μM, the intensity of the LSPR peak of SH-AuNPs at 525 nm decreased seriously, and another plasmon band at about 650 nm appeared (Fig. 3a), which implied the aggregation of AuNPs in presence of Cr3+. The significant and distinguishable color changes were observed within 1 min, which allowed high speed detecting and monitoring. And the corresponding color transformed from wine red to blue gray accompanied as a bathochromic shift in the UV-vis spectra (Fig. 3a and 3c). As indicated in the Fig. 3c, when exposed to 3 μM of Cr3+, the color of the SH-AuNPs has transformed evidently, and the 5 μM of Cr3+ discolored distinctly which can be perceived by naked eyes clearly. The blue gray color can be noticed at the high concentration over 10 μM of Cr3+ was related to the high intensity at the longitudinal LSPR around 650 nm. The lowest detectable concentration of Cr3+ by eye vision was 3 μM. Similarly, the detection for Cr6+ could be achieved by the colorimetric response and the LSPR of the SH-AuNPs. As illustrated in the Fig. 4a, the intensity of LSPR at 525 nm was decreased with the addition of the concentration of Cr6+. When the concentration of Cr6+ was added up to 10 μM, the second absorption peak of the SH-AuNPs was emerged at around 650 nm (Fig. 4a), which reflected the extent of aggregation of the SH-AuNPs related to the concentrations of Cr6+. As can be seen in Fig. 4c, when exposed to 1 μM of Cr6+, the SH-AuNPs discolored though the process of response was delayed to 15 min. If the concentration of Cr6+ was added up to 5 μM, the color of the SH-AuNPs turned immediately. Thus, the lowest detectable concentration of Cr6+ by eye vision was defined to 1 μM. 9
The above results indicated that the transformation of the observed spectra was related to the concentrations of Cr3+ or Cr6+ closely. The increased absorbance intensity at around 650 nm and the decrease at 525 nm were concentration-dependent, which could be an indicator of the formation of aggregation of the SH-AuNPs with Cr3+ or Cr6+. In order to quantitatively analyze the colorimetric response, the ratio of the intensity of two LSPR peaks (A650/A525) was calculated and used as a criterion representing the extent of aggregation. There was a good linear relationship between the value of A650/A525 and the concentration of Cr3+ in the range 0.001–0.020 μM. And a calibration curve of y=0.028+0.193x with a correlation coefficient of 0.9939 for the detection Cr3+ was obtained (Fig. 3b). The lowest detectable concentration was then calculated to be of 0.78 nM for a signal-to-noise (S/N) ration of 3. The detection for Cr6+ was also existed a linear relationship (R2=0.9864) between the A650/A525 value and the concentration of Cr6+ in the range 0.005–1.0 μM (Fig. 4b), the lowest detectable concentration was 2.90 nM. Due to the conversion between Cr3+ and Cr6+ existed commonly, the detection of the mixed chromium ions was also investigated. The colorimetric response and UV-vis spectra were used to further evaluate the sensitivity of the detection system for mixed chromium ions (the volume ratio of Cr3+ and Cr6+ was 1:1). UV-vis spectra of the detection system with the various concentrations of mixed chromium ions were shown in Fig. 5a. It was found that the decrease in the intensity of the absorbance at 525 nm and an increase at 695 nm with increasing of concentrations of mixed chromium ions. Fig. 5b showed a good linear relationship (R2=0.9944) between 10
A695/A525 and the concentrations of mixed chromium ions ranged from 0.001–0.01 μM with the lowest detectable concentration of 0.69 nM. With the increase of the concentrations of mixed chromium ions from 0.001 to 20 μM, the color transformation of the SH-AuNPs (from wine red to blue gray) could be easily visualized in Fig. 5c. The lowest detectable concentration of mixed chromium ions was determined at 5 μM by naked eyes. The lowest detectable concentrations of Cr3+, Cr6+ and mixed chromium ions were 0.78 nM, 2.90 nM and 0.69 nM, which was much lower than the maximal permitted level in drinking water (0.962 µM) as regulated by the World Health Organization and Chinese Ministry of Environmental Protection (GB 7466-87) [8, 35]. And, compared with those of other optical chromium ions sensors reported previously, the detection sensitivity of the proposed method was much higher [36-39]. More importance, the Cr6+ could be detected with Cr3+ simultaneously by using SH-AuNPs. 3.4 Selectivity of the detection system To estimate the selectivity of the SH-AuNPs for chromium ions, the detection of a variety of environmentally relevant metal ions (including Ag+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+) were performed at the same conditions. As can be observed from Fig. 6a, there is no obvious change in the LSPR with other ions, however, in presence of chromium ions, the LSPR absorption peaks occurred significant shift. The corresponding colorimetric images indicated that the SH-AuNPs showed evidently colorimetric response with chromium ions, from wine red to blue gray, however, with other ions, the SH-AuNPs seemed almost no change 11
(Fig. 6c). To determine the selectivity quantitatively, the ratio of A650/A525 of all samples were provided in Fig. 6b, the value of chromium ions were exceeded 4 fold higher than other metal ions, which proved that the SH-AuNPs exhibited evident selectivity toward chromium ions. The corresponding images indicated that SH-AuNPs have no transition of color in presence of other metal ions (Fig. 6c). The results indicated that this system exhibited a good selectivity for chromium ions over other 13 kinds of metal ions. To test the specifity for chromium ions, the interference of other ions in detection was also investigated, since heavy metal ions are mixed with other ions in many cases. The relevant metal ions were acted as disturbing ions, and the response of the proposed probe SH-AuNPs to the mixed solution were tested under same conditions. Fig. 7a indicated that the SH-AuNPs remained dispersed states when exposed to the relevant metal ions suggesting that there was no aggregation occurred, and in presence of Cr3+ or Cr6+ induce the aggregation of AuNPs, which led to the color conversion from wine red to blue gray (Fig. 7b and 7c). The selectivity of the SH-AuNPs towards various metal ions was further quantified by comparing the extinction intensity ratio, as obseved from Fig. 8a and 8b, the Cr3+ and Cr6+ induced value of A650/A525 were over 4 fold larger than that of other metal ions. These results indicate that SH-AuNPs can be employed to detecting chromium ions without interference from other metal ions in environmental samples.
12
3.5 Detection of real samples Inspired by the successful and extensive application of AuNPs in detection, the SH-AuNPs have a great potential to be extended into the environmental assay. Thus, the SH-AuNPs were further applied to determinate chromium ions in real water samples [25]. The real samples came from our campus Mengxi lake and a natural Chagan lake, the sample of lake water was first tested by ICP-AES to determine the actual contents of metal ions or element (Table S2 and S3), respectively. There was almost no Cr3+ or Cr6+ in the lake water according the ICP data. To test the applicable performance of SH-AuNPs in real water sample, a simulated detection in lake water was carried out. A series of different spiked concentrations of chromium ions with lake water samples were formulated by the same volume according to the literature [19, 29], and the other ions of lake water samples were also prepared by the same method. The detection of the sensitivity of Mengxi lake samples was performed in Fig. 9 (A: Cr3+, B: Cr6+ and C: mixed chromium ions). The intensity of LSPR peaks was decreased with the addition of the different concentrations of chromium ions (Fig. 9a). When the concentrations of Cr3+, Cr6+ and mixed chromium ions were raised to 5 μM, 1 μM and 10 μM respectively, the corresponding LSPR began to emerge a second peak at about 650 nm, indicated the aggregation of the SH-AuNPs. These results illustrated that the SH-AuNPs detecting for Cr3+, Cr6+ and mixed chromium ions did not affected by other unknown components of the campus Mengxi lake water. The corresponding colorimetric images were shown in Fig. 9b, which were in line with the 13
analysis of LSPR. The selectivity was also studied by comparison in other ions of Mengxi lake water samples. As presented in Fig. 10a and corresponding images (Fig. 10b), the other ions of Mengxi lake water samples could not trigger the aggregation of the SH-AuNPs under the same conditions. While chromium ions caused the colorimetric conversion of the SH-AuNPs, the corresponding LSPR of the SH-AuNPs emerged a second peak due to the aggregation (Fig. 10a). The results indicated that SH-AuNPs could be used as an excellent colorimetric probe towards chromium ions with strong anti-interference ability in campus lake water. As a natural lake, Chagan lake can represent the natural complex environment, so, the detection and application of simulation was performed in Chagan lake water samples obtained straight from Chagan lake. The detection was first carried out, and the result was consistent with the data of ICP (Table S3). Then the spiked concentrations of chromium ions with Chagan lake water samples were precisely prepared, and the selectivity and sensitivity of detection was tested respectively. The Fig. 11 revealed the detection selectivity of the probe SH-AuNPs for chromium ions over other metal ions. The chromium ions samples were exclusive metal ions to induce the aggregation of AuNPs, which proved the excellent specificity of the SH-AuNPs for chromium ions. The sensitivity detection in natural Chagan lake water was displayed in Fig. 12. A group of convincing data was obtained, including the characteristic LSPR of SH-AuNPs in presence of chromium ions, the corresponding 14
colorimetric conversion of samples and the ratio of A650/A525. As can be seen from the Fig. 12a, in presence of Cr3+ (Fig. 12A), Cr6+ (Fig. 12B) or mixed chromium ions (Fig. 12C), the intensity of the LSPR peak at 525 nm significantly decreased and a new peak located at 650 nm was observed, which indicated the aggregation of SH-AuNPs. And the similar linear relationship between the ratio (A650/A525) and the concentration of metal ions existence in the three detection results (inset of Fig. 12a), indicated that the good sensitivity of detection in Chagan lake samples. Fig. 12b showed that the corresponding photographic images of SH-AuNPs with Chagan lake water samples. All above results proved that the SH-AuNPs can be used as a colorimetric probe in complex natural environment. 3.6 Effect of pH value Furthermore, the evaluation of effect of pH value of detection was carried out due to the pH value was found to be essential to detection especially in practical application. The resistance adaptability of the concussion from the alkali was important for this probe. The pH value of as-prepared SH-AuNPs was about 3. To investigate effect of the pH, the detection was examined in the various pH value (Fig. S1). The final pH of the detective probe was adjusted by a neutralization reaction with a high-concentration NaOH solution (0.5 M, Table S4). These results indicated that the SH-AuNPs were stable in the pH range of 3-6, and upon exposure to the acidic conditions, the LSPR with aggregation degree of SH-AuNPs would not be affected, which illustrated the SH-AuNPs can resist the strong base. The influence of pH for 15
detection of the chromium ions with the aggregation of SH-AuNPs was manifested by the value of A650/A525 shown in Fig. S2. The performance of the probe could be maintained as long as the final pH of the mixed solution was less than 5. However, when the pH was rose to 6 (Fig. S1c), the SH-AuNPs still remained dispersed after exposed to the chromium ions. The results manifested the sensitivity and selectivity of the detection decreased accompanied the rise of pH value, which may be owing to the deprotonation on carboxylic group from hyaluronate occurring under alkaline conditions [9]. Thus, the detection using as-prepared SH-AuNPs was selected as the optimal pH condition for all experiments. 3.7 Principle for the chromium sensing The mechanism of recognition for detection of chromiun ions by SH-AuNPs could be illustrated from the coordination between the carboxylic ions and metal ions basically [9, 29]. The recognition of chromium ions by SH-AuNPs was attributed to the coordination between the carboxylic ions and metal ions due to the carboxyl group and available carboxyl group at pH value of 3. The chromium ions can induce the aggregation of SH-AuNPs which may be attributed to the Cr3+(Cr6+) coordination with amide group and carboxyl groups of the molecule of hyaluronate to form a stable complexation species accompanied with the intramolecular charge transfer [9, 13-17]. Owing to the outermost electron configuration of the Cr3+ and Cr6+, they were strong receptor of electrons to half-fill and unoccupied d orbitals. In accordance with the general coordination, a specific and strong interaction between the detection probes and chromium ions existed due to the strong binding energies [34, 40] of chromium 16
ions with Au ions. Chromium ions had a higher effective charge, smaller radius, and stronger coordination ability than the other transition metal ions, which made this method highly sensitive and selective. As a result, the LSPR absorption decreased dramatically and allowed the quantitation of chromium ions in aqueous solution.
4 Conclusions In conclusion, a simple, rapid and cost-effective SH-AuNPs based colorimetric sensor was synthesized and used for selective detection of Cr 3+ and Cr6+ simultaneously. The selectivity of the SH-AuNPs-based detection system by the naked eye and UV-vis spectra was excellent for chromium ions compared with other ions. The lowest detectable concentrations of Cr3+, Cr6+ and mixed chromium ions were 0.78 nM, 2.90 nM and 0.69 nM, respectively. In addition, the AuNPs-based detection system was applicable for rapid colorimetric detection of chromium ions in complicated real lake water samples with excellent stability and capability.
Acknowledgements The authors gratefully acknowledge financial support from the 863 Program (2013AA032204), the NSF of China (21205024), the project of Harbin Science and Technology bureau (2014RFQXJ151), the National Science Foundation for Post-doctoral Scientists of China (2012M520659, 2013T60307).
References 1.
L.B. Zhang, E.K. Wang, Metal nanoclusters: new fluorescent probes for sensors and bioimaging, Nano Today 9 (2014) 132-157. 17
2.
A.D. Dayan, A.J. Paine, Mechanisms of chromium toxicity, carcinogenicity and allergenicity: Review of the literature from 1985 to 2000, Hum. Exp. Toxicol 20 (2001) 439-451.
3.
D.Y. Li, J. Li, X.F. Jia, Y. Xia, X.W. Zhang, E.K. Wang, A novel Au-Ag-Pt three-electrode microchip sensing platform for chromium (VI) determination, Anal. Chim. Acta 804 (2013) 98-103.
4.
S.H.
Liu,
F.
Lu,
J.J.
Zhu,
Highly
fluorescent
Ag
nanoclusters:
microwave-assisted green synthesis and Cr3+ sensing, Chem. Commun 47 (2011) 2661-2663. 5.
Y. Gong, X.L. Liu, L. Huang, W.Y. Chen, Stabilization of chromium: an alternative to make safe leathers, J. Hazard. Mater 179 (2010) 540-544.
6.
N. Shevchenko, V. Zaitsev, A. Walcarius, Bifunctionalized mesoporous silicas for Cr(VI) reduction and concomitant Cr(III) immobilization, Environ. Sci. Technol 42 (2008) 6922-6928.
7.
M.V. Dozzi, A. Saccomanni, E. Selli, Cr(VI) photocatalytic reduction: effects of simultaneous organics oxidation and of gold nanoparticles photodeposition on TiO2, J. Hazard. Mater 211 (2012) 188-195.
8.
World Health Organization (WHO), Chromium in drinking water. Guidelines for drinking-water quality. 2nd ed. World Health Organization (2004) Geneva Vol. 2.
9.
Y.M. Yu, Y. Hong, Y.Q. Wang, X.Y. Sun, B. Liu, Mecaptosuccinic acid modified gold nanoparticles as colorimetric sensor for fast detection and simultaneous identification of Cr3+, Sensor. Actuat. B-Chem 239 (2017) 865-873. 18
10. M.R. Moghadam, S. Dadfarnia, A.M.H. Shabani, Speciation and determination of ultra trace amounts of chromium by solidified floating organic drop microextraction
(SFODME)
and
graphite
furnace
atomic
absorption
spectrometry, J. Hazard. Mater 186 (2011) 169-174. 11. F. Seby, S. Charles, M. Gagean, H. Garraud, O.F.X. Donard, Chromium speciation by hyphenation of high-performance liquid chromatography to inductively coupled plasma-mass spectrometry-study of the influence of interfering ions, J. Anal. Atom. Spectrom 18 (2003) 1386-1390. 12. Y.J. Ye, H.L. Liu, L.B. Yang, J.H. Liu, Sensitive and selective SERS probe for trivalent chromium detection using citrate attached gold nanoparticles, Nanoscale 4 (2012) 6442-6448. 13
Q.T. Meng, W.P. Su, X.M. Hang, X.Z. Li, C. He, C.Y. Duan, Dye-functional mesoporous silica material for fluorimetric detection of Cr(III) in aqueous solution and biological imaging in living systems, Talanta 86 (2011) 408-414.
14
S. Goswami, K. Aich, S. Das, A.K. Das, D. Sarkar, S. Panja, T.K. Mondal and S.K. Mukhopadhyay, A red fluorescence ‘off–on’ molecular switch for selective detection of Al3+, Fe3+ and Cr3+: experimental and theoretical studies along with living cell imaging, Chem. Commun 49 (2013) 10739-10741.
15
J.F. Wang, Y.B. Li, N.G. Patel, G. Zhang, D.M. Zhou and Y. Pang, A single molecular probe for multi-analyte (Cr3+, Al3+ and Fe3+) detection in aqueous medium and its biological application, Chem. Commun 50 (2014) 12258-12261.
16
S. Guha, S. Lohar, A. Banerjee, A. Sahana, I. Hauli, S.K. Mukherjee, J.S. 19
Matalobos, D. Das, Thiophene anchored coumarin derivative as a turn-on fluorescent probe for Cr3+: Cell imaging and speciation studies, Talanta 91 (2012) 18-25. 17
C.Y. Li, X.F. Kong, Y.F. Li, C. Weng, J.L. Tang, D. Liu, W.G. Zhu, Ratiometric near-infrared chemosensor for trivalent chromium ion based on tricarboyanine in living cells, Anal. Chim. Acta 824 (2014) 71-77.
18. R. Elghanian, J.J. Storhoff, R.C. Mucic, R.L. Letsinger, C.A. Mirkin, Selective colorimetric detection of polynucleotides based on the distance-dependent optical properties of gold nanoparticles, Science 277 (1997) 1078-1081. 19. X. Liu, J.J. Xiang, Y. Tang, X.L. Zhang, Q.Q. Fu, J.H. Zou, Y.H. Lin, Colloidal gold nanoparticle probe-based immunochromatographic assay for the rapid detection of chromium ions in water and serum samples, Anal. Chim. Acta 745 (2012) 99-105. 20. J.J. Du, L. Jiang, Q. Shao, X.G. Liu, R.S. Marks, J. Ma, X.D. Chen, Colorimetric detection of mercury ions based on plasmonic nanoparticles, Small 9 (2013) 1467-1481. 21. K. Saha, S.S. Agasti, C. Kim, X. Li, V.M. Rotello, Gold nanoparticles in chemical and biological sensing, Chem. Rev 112 (2012) 2739-2779. 22. K.E. Sapsford, W.R. Algar, K.B. Gemmill, B.J. Casey, E. Oh, M.H. Stewart, I.L. Medintz, Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology, Chem. Rev 113 (2013) 1904-2074. 23. Y. Zhang, I.D. McKelvie, R.W. Cattrall, S.D. Kolev, Colorimetric detection 20
based on localised surface plasmon resonance of gold nanoparticles: Merits, inherent shortcomings and future prospects, Talanta 152 (2016) 410-422. 24. W.S. Zheng, H. Li, W.W. Chen, J. Ji, X.Y. Jiang, Recyclable colorimetric detection of trivalent cations in aqueous media using zwitterionic gold nanoparticles, Anal. Chem 88 (2016) 4140-4146. 25. C. Dong, G.H. Wu, Z.Q. Wang, W.Z. Ren, Y.J. Zhang, Z.Y. Shen, T.H. Li, A.G. Wu, Selective colorimetric detection of Cr(III) and Cr(VI) using gallic acid capped gold nanoparticles, Dalton. Trans 45 (2016) 8347-8354. 26. W. Ha, J. Yu, R. Wang, J. Chen, Y.P. Shi, “Green” colorimetric assay for the selective detection of trivalent chromium based on xanthoceras sorbifolia tannin attached to gold nanoparticles, Anal. Methods 65 (2014) 720-5726. 27. F.M. Li, J.M. Liu, X.X. Wang, L.P. Lin, W.L. Cai, X. Lin, Y.N. Zeng, Z.M. Li, S.Q. Lin, Non-aggregation based label free colorimetric sensor for the detection of Cr(VI) based on selective etching of gold nanorods, Sensor. Actuat. B-Chem 155 (2011) 817-822. 28. L. Liu, Y.M. Leng, H.W. Lin, Photometric and visual detection of Cr(VI) using gold nanoparticles modified with 1,5-diphenylcarbazide, Microchim. Acta 183 (2016) 1367-1373. 29. X. Yang, S.S. Fu, G.J. Ren, F. Chai, F.Y. Qu, Facile preparation of 2,6-Pyridinedicarboxylic acid protected gold nanoparticles with sensitive chromium-ion sensing and efficient catalysis, Eur. J. Inorg. Chem 32 (2015) 5411-5418. 21
30. Y.J. Song, W.L. Wei, X.G. Qu, Colorimetric biosensing using smart materials, Adv. Mater 23 (2011) 4215-4236. 31. J.
Tang,
P.
Wu,
X.D.
Hou,
K.L.
Xu,
Modification-free
and
N-acetyl-L-cysteine-induced colorimetric response of AuNPs: a mechanistic study and sensitive Hg(2+) detection, Talanta 159 (2016) 87-92. 32. H.Y. Kim, I. Choi, Ultrafast colorimetric determination of predominant protein structure evolution with gold nanoplasmonic particles, Nanoscale 8 (2015) 1952-1959. 33. J.F. Guo, D.Q. Huo, M. Yang, C.J. Hou, J.J. Li, H.B. Fa, H.B. Luo, P. Yang, Colorimetric detection of Cr(VI) based on the leaching of gold nanoparticles using a paper-based sensor, Talanta 161 (2016) 819-825. 34. C.A. Rusinek, A. Bange, I. Papautsky, W.R. Heineman, Cloud point extraction for electroanalysis: anodic stripping voltammetry of cadmium, Anal. Chem 87 (2015) 6133-6140. 35. Chinese
Ministry
of
Environmental
Protection
(CMEP),
Water
quality-Determination of total chromium, GB (1987) 7466-87. 36. Y.
Mikata,
A.
Kizu,
H.
Konno,
(2-quinolylmethyl)-1,2-phenylenediamine)
TQPHEN derivatives
(N,N,N′,N′-tetrakis as
highly
selective
fluorescent probes for Cd2+, Dalton. Trans 44 (2015) 104-109. 37. P.S. Yao, Z.H. Liu, J.Z. Ge, Y. Chen, Q.Y. Cao, A novel polynorbornene-based chemosensor for the fluorescence sensing of Zn2+ and Cd2+ and subsequent detection of pyrophosphate in aqueous solutions, Dalton. Trans 44 (2015) 22
7470-7476. 38. S. Goswami, K. Aich, S. Das, C.D. Mukhopadhyay, D. Sarkar, T.K. Mondal, A new visible-light-excitable ICT-CHEF-mediated fluorescence ‘turn-on’ probe for the selective detection of Cd2+ in a mixed aqueous system with live-cell imaging, Dalton. Trans 44 (2015) 5763-5770. 39. P.P.P. Kumar, C.H. Suresh, V. Haridas, A supramolecular approach to metal ion sensing: cystine-based designer systems for Cu2+, Hg2+, Cd2+ and Pb2+ sensing, RSC. Adv 5 (2015) 7842-7847. 40. L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P.V. Duyne, J.T. Hupp, Metal-organic framework materials as chemical sensors, Chem. Rev 112 (2012) 1105-1125.
23
5 Figure Captions Scheme. 1 View of the preparation process and strategy for the detection of chromium ions with SH-AuNPs. Fig. 1 (a) TEM images of the SH-AuNPs, the inset shows the size distribution of the SH-AuNPs. (b) TEM images after the addition of 20 μM of Cr3+. (c) TEM image after the addition of 20 μM of Cr6+. (d) TEM images after the addition of 20 μM of mixed chromium ions. Fig. 2 The UV-vis absorbance spectra of the SH-AuNPs before and after the addition of 20 μM of chromium ions, the inset shows the corresponding digital images. Fig. 3 (a) UV-vis spectra of the SH-AuNPs after the addition of different concentrations of Cr 3+ (0.001, 0.003, 0.005, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10, 15 and 20 μM). (b) Plot of A650/A525 versus the concentrations of Cr3+ in the range 0.001–0.02 μM (the error bars represent the standard deviations of three independent measurements). (c) Photograph of the SH-AuNPs in the presence of different concentrations of Cr3+. Fig. 4 (a) UV-vis spectra of the SH-AuNPs after the addition of different concentrations of Cr 6+ (0.001, 0.003, 0.005, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 3, 5, 10, 15 and 20 μM). (b) Plot of A650/A525 versus the concentrations of Cr6+ in the range 0.005–1.0 μM (the error bars represent the standard deviations of three independent measurements). (c) Photograph of the SH-AuNPs in the presence of different concentrations of Cr6+. Fig. 5 (a) UV-vis spectra of the SH-AuNPs in presence of different concentrations of mixed chromium ions (0.001, 0.005, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5, 1, 5, 10, 15 and 20 μM). (b) Plot of A695/A525 versus the concentrations of mixed chromium ions in the range 0.001–0.01 μM (the error bars represent the standard deviations of three independent measurements). (c) Photograph of the SH-AuNPs in the presence of different concentrations of mixed chromium ions. Fig. 6 (a) The LSPR spectra of the SH-AuNPs with different metal ions (20 μM). (b) The A650/A525 value of the SH-AuNPs solution with various metal ions. (c) Corresponding colorimetric images. Fig. 7 (a) Photograph of the SH-AuNPs solutions in the presence of different metal ions. (b) Photograph of the SH-AuNPs solutions in the presence of Cr 3+ mixing with relevant metal ions. (c)
24
Photograph of the SH-AuNPs solutions in the presence of Cr6+ mixing with relevant metal ions. Fig. 8 The absorbance ratio (A650/A525) of the SH-AuNPs in the presence of all kinds of metal ions and mixing metal ions with (a) Cr3+ (Cr3+ and other metal ions are all 20 μM), and the mixing metal ions with (b) Cr6+ (Cr6+ and other metal ions are all 20 μM). Fig. 9 (a) The LSPR of the SH-AuNPs in presence of Mengxi lake water samples with different concentrations of (A: Cr3+ B: Cr6+ C: mixed chromium ions). (b) Photograph of the SH-AuNPs in the presence of different concentrations of (A: Cr3+ B: Cr6+ C: mixed chromium ions). Fig. 10 (a) UV-vis absorption spectra of SH-AuNPs after the addition of Mengxi lake water samples, the concentrations of all metal ions are 20 μM. (b) Images of Mengxi lake water samples with SH-AuNPs in the presence of various metal ions. Fig. 11 (a) UV-vis absorption spectra of the SH-AuNPs in presence of Chagan lake water samples (the concentrations of metal ions are 20 μM). (b) Corresponding photographic images of SH-AuNPs with Chagan lake water samples. Fig. 12 (a) UV-vis absorption spectra of the SH-AuNPs in presence of Chagan lake water samples with different concentrations of (A: Cr 3+ B: Cr6+ C: mixed chromium ions). Inset: plot of A650/A525 value of the SH-AuNPs versus the concentration of (A: Cr 3+ B: Cr 6+ C: mixed chromium ions). (b) Corresponding photographic images of the SH-AuNPs system with different concentrations of Chagan lake water samples (A: Cr3+ B: Cr6+ C: mixed chromium ions).
25
Scheme 1
26
27
28
29
30
31
32
33
34
35
36
37
38