Supporting Information. Role of Tris on the colorimetric recognition of anions with

Transcription

1 Supporting Information Role of Tris on the colorimetric recognition of anions with melamine-modified gold nanoparticle probe and the visual detection of sulfite and hypochlorite Jia Zhang, Xiaowen Xu, and Xiurong Yang* *Correspondence 1. Experimental section 1.1. Reagents and apparatus Hydrogen tetrachloroaurate(iii) trihydrate, melamine and sodium hypochlorite were purchased from Sigma-Aldrich chemical company, Inc. (USA). Trisodium citrate dihydrate, sodium sulfite, and other inorganic chemicals were obtained from Beijing Chemical Reagent Company (China). They were all used without additional purification. Ultrapure water (18.2 M cm) was used throughout the experiment. The room temperature at which the experiment was conducted was o C. To avoid the oxidation of sulfite at lower concentrations, the working solutions of sulfite were freshly prepared by diluting the stock solution (0.1 M) with water. The hypochlorite stock solution was prepared by spiking 10 μl concentrated NaOCl solution to 2 ml NaOH solution (ph = 12). The working hypochlorite solution was freshly prepared by water-dilution of the stock solution whose concentration was determined by the UV absorbance at 292 nm using the molar absorptivity equal to 350 M -1 cm -1. Both the stock solutions of sulfite and hypochlorite were stored at 4 o C. UV/vis absorption spectra were recorded with a Cary 50 UV/vis spectrophotometer (Varian). Photographs were taken with a commercial digital camera. S1

2 1.2. Synthesis of citrate-capped gold nanoparticle The citrate-capped gold nanoparticle of an average 13 nm diameter was synthesized by the Natan s method. s1 The final concentration of the gold colloid solution was determined to be 5.86 nm by UV/vis spectroscopy, based on an extinction coefficient of M -1 cm -1 at λ = 520 nm for 13 nm Au NP. s The procedure for sulfite detection 50 μl of as-prepared gold colloid solution was mixed with 2.35 μl of 10 μm melamine (melamine/au molar ratio = 80) for 5 min. Then 1 mm of carbonate and different concentrations of sulfite were spiked, followed by the addition of 50 μl of buffer (10 mm Tris-HCl, ph = 7.0). After homogeneous mixing, it was incubated for 5 min before the absorbance recording The procedure for hypochlorite detection 50 μl of buffer (10 mm Tris-HCl, ph = 7.0) was spiked with 1 mm of carbonate, 0.5 μm of sulfite, and different concentrations of hypochlorite. After several minutes, μl of melamine-modified gold nanoparticle (melamine/au molar ratio = 80) was added and mixed. 5 min was allowed before the absorbance recording Sulfite assay of real samples Three commodities, i.e. red wine, fresh beer, and fruit juice, were subject to no other pretreatment than being diluted by different fold with buffer and then centrifuged in special centrifugation tubes filled with a 3 kda cut-off polymer membrane for 5 min. After this, it was spiked to the sensor solution (melamine/au molar ratio = 80; 10 mm Tris-HCl buffer, ph = 7.0; 50 μl Au + 50 μl buffer; [CO 2-3 ] = 1 mm) and 5 min was allowed for the colorimetric response. To identify the credibility of the assay, standard addition was employed by adding known amounts of sulfite to each sample before the dilution. Percent recovery was then measured. S2

3 1.6. Hypochlorite assay of tap water Household tap water samples were collected from two different places and stored at 4 o C. They were analyzed within 24 h without other pretreatment. Typically, 4 μl of sample was spiked to 50 μl of buffer (10 mm Tris-HCl, ph = 7.0) containing 1 mm of carbonate and 0.5 μm of sulfite. After several minutes, μl of melamine-modified gold nanoparticle was added and mixed. 5 min was allowed before the absorbance recording. 2. Supplementary figures Fig. S1 The absorption spectra of the melamine-modified gold nanoparticle in the presence of anions. Melamine/Au molar ratio = 80, 10 mm Tris-HCl (ph = 7.0), 1 mm for all anions. S3

4 Fig. S2 Selectivity test by the addition of another ion to the sulfite sensor solution. SO 3 2- : 0.5 μm, other anions: 0.1 mm, Ca 2+ : 0.1 mm, and other cations: 10 μm. Fig. S3 The absorption spectra of the melamine-modified gold nanoparticle probe containing 1 mm CO 3 2- and 0.5 μm SO 3 2- after the addition of 1 mm H 2 O 2 for 5 min. S4

5 Table S1 Determination of sulfite in practical samples by three replicate measurements. Table S2 Determination of hypochlorite in household tap water samples by three replicate measurements. 3. References S1 K. G. Grabar, R. G. Freeman, M. B. Hommer and M. J. Natan, Anal. Chem., 1995, 67, 735. S2 W. Zhao, M. M. Ali, Aguirre S. D., M. A. Brook and Y. Li, Anal. Chem., 2008, 80, S5