Ratiometric Ultrasensitive Fluorometric Detection of Ascorbic Acid Using a Dually Emitting

ElectronicSupportingMaterialontheMicrochimicaActapublicationentitled:

Ratiometric ultrasensitive fluorometric detection of ascorbic acid using a dually emitting CdSe@SiO2@CdTe quantum dot hybrid

Jing Wangab[*], Xiao Penga, DaquanLia, XiaochunJiangb, ZaifaPana, Aimin Chena, Liang Huanga, Jun Hua[*]

aCollege of Chemical Engineering, Zhejiang University of Technology. Hangzhou310014, PR China.

bHubei Key Laboratory of Processing and Application of Catalytic materials, Huanggang Normal University, Huangzhou 438000, PR China.

Experimental detail

Synthesis of red-emitting GSH-stabilizedCdTe QDs

Water-soluble GSH-stabilizedCdTe QDs(termed as GSH-CdTe) were prepared according to previous literature[1]. Fora typical synthesis, 0.80 mL of CdCl2 solution (0.20 M) wasadded to a three-necked flaskcontaining 24 mL of H2O, and then 0.1 g of trisodiumcitrate were introducedto the solution under magnetic stirring. After that, the solution was added with 0.05 g of GSH, 0.5 mL of Na2TeO3 (0.020 M) and 0.05 g of NaBH4. Thefinalmixture was refluxed at 90 °C for 8 h to obtain the red-emitting CdTe QDs. The obtained crude products werepurified by centrifugation after adding the same volume of ethanol. The purified CdTeQDs were finally redispersed in ultrapure waterand put it at 4 °C for further use.

Synthesis of green-emitting dual-stabilizers-capped CdSe QDs

Dual-stabilizers capped CdSe QDs were prepared according to a reported method [2]. For a typical synthesis, 0.80 mL of CdCl2 solution (0.20 M) was added to a three-necked flask containing 50 mL of H2O, and then SHMP (72.5 mg) and MPA (34.60 μL) were injected into the solution under magnetic stirring. After the pH of solution was adjusted to 9.0 with 1.0 M NaOH, 1.60 mL of Na2SeO3 solution (0.010 M) was added to the above solution. After the resulting mixture was refluxed at 100 °C for 10 min, 3.67 mL of N2H4·H2O was introduced into the above solution, and then the final mixed solution was refluxed under open-air conditions for about 9 h to obtain the green-emitting CdSe QDs. The obtained crude products were purified by centrifugation after adding the same volume of ethanol. The purified CdSe QDs were finally redispersed in ultrapure water and stocked at 4 °C for further use.

Synthesis of amino group functionalized CdSe@SiO2composite

Amino capped CdSe@SiO2 core-shell structured fluorescentsilica NPs were synthesized by a modified StÖbermethod[3]. Briefly, ethanol (40 mL) and 10 mL of green-emittingdual-stabilizerscappedQD solution(from 10 mL of stock CdSe solution)were added into a single-necked flaskunder magnetic stirringfor 10 min. Then,NH3·H2O(0.5 mL, 25wt%) and TEOS (0.5 mL) were introduced into the above solutionunder magnetic stirringfor 12h. To obtainamino-functionalized CdSe@SiO2 NPs (termed as CdSe@SiO2–NH2),100μLof APTES were added to the above solution system andstirred for another 12 h. The precipitate was collected by centrifugationand washed withethanol and water insequence until the supernatant no fluorescence, and then dispersed in ultrapure water for future use.

Synthesis of CdSe@SiO2@CdTe nanohybrid

The red-emitting GSH-stabilizedCdTe QDs(termed as GSH-CdTe QDs)were covalentlylinked to the CdSe@SiO2nanoparticle surface according to a reportedmethod[4]. Briefly, EDC (24 mg) was added to the 2 mL of CdTe solution (from 1.2 mL of stockCdTe solution) under magnetic stirring for 20 min. Then the above solution was mixed withCdSe@SiO2–NH2NPs (9 mg). The reaction mixture was then stirred for 10 h at room temperaturein the dark. The resulting dually emitting silica NPswere isolated by centrifugation and washed with ultrapurewater three times to remove the excess CdTe QDs. The purifiedCdSe@SiO2@CdTe nanohybrids were finally redispersedin ultrapure water and stocked at 4 °C for further use.

Results

Fig. S1. FTIR spectra of CdTe, CdSe@SiO2-NH2 and CdSe@SiO2@CdTe NPs.

Fig. S2. PL spectra of the CdSe@SiO2@CdTe nanohybrid (50 µg mL-1) upon the exposure to different concentrations of KMnO4. The concentrations of KMnO4 from top to bottom are 0,0.2,0.4,0.8,1.2, 1.6,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0, and 10.0 µM, respectively.

Fig. S3. UV-Vis spectra of the CdSe@SiO2@CdTe nanohybrid (2 mg mL-1) in the absence of KMnO4, in the presence of KMnO4 (270 μM), and in the presence of KMnO4 (270 μM) and AA (270 μM).

Fig.S4. XPS of (A) Cd 3d, (B) Te 3d, and (C) S 2p peaks of the CdSe@SiO2@CdTe nanohybrid, (a) original CdSe@SiO2@CdTe nanohybrid, (b) after addition of 5.0 µM KMnO4 to (a), (c) after addition of 5.0 µM AA to (b).

Fig. S5. Influence of AA on the PL of CdSe@SiO2@CdTe nanohybrid(50 µgmL-1).

Fig. S6. Time-dependent PL quenching efficiency (A) of the outer CdTe QDs in nanohybrid (CdSe@SiO2@CdTe,50 µg mL-1) to KMnO4 (7.0 µM) and subsequent PL restoration efficiency (B) by AA2+ (7.0μM).

Fig. S7. Stability of the PL intensity ratios of the nanohybrid (CdSe@SiO2@CdTe) at 522 nmversus that at 616 nm.

Fig. S8. Digital photos of detection of AA in lemon juice and orange juice by thenanohybrid.

Reference

[1] Wang QS,Fang TT,Liu P,Deng BH,Min XM, Li X (2012) Direct synthesis of high-quality water-soluble CdTe:Zn2+quantumdots. InorgChem51:9208−9213

[2]Liu SF, Zhang X, Yu YM, Zou GZ (2014)Bandgap engineered and high monochromatic electrochemiluminescence from dual-stabilizers-capped CdSe nanocrystals with practical application potential.BiosensBioelectron55:203–208

[3] ZhangK, ZhouHB, MeiQS, WangSH, GuanGJ, LiuRY, ZhangJ, ZhangZP (2011) Instant visual detection of trinitrotoluene particulates on various surfaces by ratiometric fluorescence of dual-emission quantum dots hybrid. JAm Chem Soc 133:8424–8427

[4] WuCL, ZhengJS, HuangCB, LaiJP, LiSY, ChenC, ZhaoYB (2007)Hybrid silica–nanocrystal–organic dye superstructures as post-encoding fluorescent probes.AngewChem119:5489–5492

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