Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 102 (2015) 273 – 277 The 7th World Congress on Particle Technology (WCPT7) Near Infrared Emission of Ag2S Quantum Dots and their Fluorescence Quenched by Gold Nanoparticles Xiulan Wu1, Lei Liao2, Weilin Du1, Aimiao Qin1* 1Key Lab New Processing Technology for Nonferrous Metals & Materials Ministry of Education, College of Materials science & engineering, Guilin University of Technology, Guilin, China College of Environmental science & engineering, Guilin University of Technology, Guilin, China Abstract The near-infrared emitting Ag2S quantum dots (QDs) coated with L-cysteine were prepared by one-pot aqueous synthesis at room temperature Several characterization methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), fluorescence spectrophotometer (PL) and ultraviolet -visible spectrophotometer (UV-vis) were used to characterize the structure, morphology and optical properties of the samples The effects of gold nanoparticles on the fluorescence of Ag2S QDs were systematically investigated, it was found that gold nanoparticles could enhance or quench the fluorescence intensity of Ag2S QDs in some situation Within a certain range, the fluorescence intensity of Ag2S QDs shows a linear quenching proportional to the colloidal gold concentration Under the optimized experimental conditions, the linear range was obtained for colloidal gold concentration from 5.93 - 27.09 ×10-6mol/l (r2 = 0.9956) The determined detection limit (LOD) was about 5.08×10-6 mol/l The quenching mechanism of Ag2S QDs is discussed Gold nanoparticles also have similar effects on Ag2Te QDs A new method for the quantitative detection of inorganic nanoparticles was established, and it provides a new way for the bio-analytical applications © 2015 2014The TheAuthors Authors Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license © Published by Elsevier Ltd This (http://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Chinese Society of Particuology, Institute of Process Engineering, Chinese Selection under responsibility of Chinese Society of Particuology, Institute of Process Engineering, Chinese Academy Academyand ofpeer-review Sciences (CAS) of Sciences (CAS) Keywords: Ag2S; Quantum dots; fluorescence quenching * Corresponding author Tel.: +086-773-5893252; fax: +086-773-5896672 E-mail address: miaoaiqin@aliyun.com 1877-7058 © 2015 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of Chinese Society of Particuology, Institute of Process Engineering, Chinese Academy of Sciences (CAS) doi:10.1016/j.proeng.2015.01.143 274 Xiulan Wu et al / Procedia Engineering 102 (2015) 273 – 277 Introduction In recent years, quantum dots (semiconductor nanocrystals) aroused widespread interest from researchers, and its research involves physics, chemistry, material science and electronics engineering and many other disciplines Initially, the quantum dots were used in microelectronics and optoelectronic materials[1, 2], then quantum dots were applied in biological and medical aspects[3, 4] due to their visible area unique and excellent fluorescence properties With the deepening research of quantum dots, quantum dots have been extended to quantitative analysis of heavy metal ions, small organic molecules and drugs[5, 6] Currently most research is mainly concentrated on CdX (X = S, Se, Te) or CdX as the core, the rest of the semiconductor material for the shell of the core-shell quantum dots So far, quantitative detection based on Ag2S QDs fluorescence quenching effect has not been reported in the literature Similar to the traditional fluorescent probe analysis, the proposed methodology was based on the enhancement or quenching effect induced by the physics process, chemical action between the analyte and quantum dots, and then the content determination of inorganic/organic molecules content could be obtained Cai et al [7] synthesized a watersoluble CdS quantum dots coated with L-cysteine, and the CdS QDs were used as fluorescence probes for Hg2+ detection Under optimal conditions, the method shows a high sensitivity, and the limit of detection was 2.4nmol·L-1 Wang et al[8]used pH-sensitive CdTe quantum dots as proton probes to detect tiopronin The determination was established based on fluorescence quenching method The limit of detection wa †s 0.15mg·L-1 The method was used to determine tiopronin in tablets successfully Cao[9]established a sensitive, rapid, simple and economical turn-on fluorescent detection assay for melamine using the inner filter effect of AuNPs on L-Cys-capped CdS QDs, a detection limit was as low as 0.017 mg·L-1 In this work, an analytical approach involving the use of aqueous infrared Ag 2S QDs was for the first time applied, to our knowledge, in the determination of colloidal gold The proposed methodology was based on the quenching effect by colloidal gold on L-cysteine-capped Ag2S QDs fluorescence signal Experiment All chemical reagents were analytical grade without further purification Distilled water was used throughout this experimental study Water-soluble Ag2S QDs were prepared as follows In a typical synthesis process, 0.1g L-Cysteine was dissolved in 100mL distilled water and then 4mL of 0.1mM AgNO3 was added under stirring Subsequently, the solution was adjusted to pH 11 with 1M NaOH Later, 1mL of 0.1mM freshly prepared Na2S solution was injected into the reaction solution while the mixture continued to stir constant The solution rapidly changed to red brown For the spectrofluorometric detection of AuNPs, 1.8 mL of 1.0×10-3mol/L Ag2S QDs solution was transfered into the calibrated test tube and was diluted to 3ml with 0.05mol/L PBS buffer solution(pH = 8.04), then certain amounts of Au NPs solution was added into the mixture with a microsyringe The fluorescence intensity was measured with the following settings of the spectrofluo-photometer (excitation wavelength (_ex) 520 nm; excitation slit 10.0 nm; emission slit 10.0 nm) The X-ray powder diffraction (XRD) patterns of the products were measured on an X’Pert PRO X-ray powder diffractometer with Cu Kα radiation (λ=1.5418Å) for 2θ ranging from 20° to 70° The morphology, size and chemical composition of the products were observed by using Hitachi S-4800 field emission scanning electron microscope (FE-SEM) and FE-2000 transmission electron microscope (TEM) The zeta potential was measured on a nano particle analyzer(Malvern Nano ZS) Results and discussions 2.1 XRD and TEM of Ag2S QDs Xiulan Wu et al / Procedia Engineering 102 (2015) 273 – 277 ˄˅ The crystal phase of the as-obtained Ag2S QDs was confirmed by the XRD patterns, which are shown in Fig And the characteristic peaks of the samples are identified as monoclinic Ag2S (JCPDS no.14-0072) In addition, several peaks are broadened due to the smaller size of nanoparticles Fig 2a shows a typical TEM image of Ag2S QDs It presents a spherical morphology and well dispersion of Ag2S QDs with an average diameter of 4.993±0.732nm which obtained by measuring the diameter of several hundred particles in the TEM image It is noted that some Ag2S QDs arrange in chains and the edges are not clear It is speculated that the redundant coordinating groups in the capped agent of L-cysteine make the nanoparticles bind together The morphology of Ag2S QDs in the present of colloidal gold is shown in Fig 2b, it shows that the shape and the size of the nanoparticles of Ag2S are similar to that of Ag2S QDs in the absence of colloidal gold, but the chain-shaped particles disappear and the crystallization of the nanopartilces seems better This maybe due to the competition effect of gold nanoparticles which are capped by the dissociative L-cysteine molecules JCPDS 14-0072 Ag2S 20 25 30 35 40 45 50 55 60 65 70 7KHWD>e@ Fig XRD pattern of Ag2S QDs Fig (a) TEM of Ag2S QDs (b)TEM of Ag2S QDs contained colloidal gold 2.2 Spectral characteristic Fig shows the UV-vis, fluorescence emission spectra of Ag2S QDs and Ag2S QDs in the present of colloidal gold The UV-vis spectra (Fig3 1a) shows that characteristic peaks are not found in the absorbance curves of Ag2S QDs, but the absorbance of Ag2S QDs declined when Au colloid was added, which maybe be due to the plasmonic effect of Au nanoparticles The undetected of the characteristic absorbance peak of Au colloid is due to the minute amounts of Au colloid The fluorescence emission spectra (Fig 1b) show that the L-cysteine-capped-Ag2S QDs have a strong fluorescence in the near infrared range with a maximum emission at 750 nm When Au colloid was added into Ag2S QDs solution, the fluorescence intensity of L-cysteine-capped-Ag2S QDs was found to be enhanced 275 276 Xiulan Wu et al / Procedia Engineering 102 (2015) 273 – 277 and then significantly quenched with the increase of Au colloid concentration Fig 3.2a displays the quenching of the fluorescence intensity of Ag2S QDs induced by Au colloid Under the optimal conditions, a liner between the quenched fluorescence intensity of Ag2S QDs and concentration of Au colloid was observed in the range of 5.9327.09×10-6mol/l with a correlation coefficient (r2) of 0.9956, the linear regression equation is ႤF =470.88-3.81C (×10-6mol/l), and the direction limit is 5.08×10-6 mol/l Similarly, a liner between the quenched fluorescence intensity of Ag2Te QDs and the concentration of Au colloid was also observed in the range of 3.39-16.93×10-6mol/l with a correlation coefficient (r2) of 0.9865, the linear regression equation is ႤF =469.86-3.19C (×10-6mol/l), and the direction limit is 2.54×10-6 mol/l, as shown in Fig 2b a1 a2 400 300 0.6 200 0.4 0.0 400 500 600 700 800 900 a b y=469.86-3.19x, R=-0.99321 100 0.2 ˄˅ 450 Intensity(a.u.) Abs(a.u.) 475 b1 b2 b3 ˄˅ 0.8 Intensity(a.u.) 1.0 425 400 y=470.88-3.81x, R=-0.99779 375 350 1000 10 15 20 25 30 ConcentrationO *10 mol/lP -6 Wavelength(nm) Fig (1) UV-vis (a) and fluorescence spectra (b) of Ag2S QDs and Ag2S QDs in the present of Au colloid; (2) the liner relation between the quenched fluorescence of Ag2S QDs with various concentration of Au colloid(a); the liner relation between the fluorescence quenched of Ag2Te QDs and the various concentration of Au colloid(b) The quenching mechanism of Ag2S QDs induced by Au colloid can be explained with the electrostatic theory Zeta potential measurement results show that Au colloid carries positive charges while Ag 2S QDs solution does negative charges, shown in Fig The fluorescence intensity of Ag2S QDs was quenched for the electrostatic interaction between Ag2S QDs and Au colloid This theory is also useful for the revealing the fluorescence quenched of Ag2Te QDs with negative charges induced by Au colloid with positive charges (Fig 2) 800000 ˄˅ Au Ag2S 600000 ˄˅ 500000 400000 300000 Au Ag2Te 500000 Total Counts Total Counts 700000 Ag2Te+Au 400000 300000 200000 200000 100000 100000 -200 -100 100 Zeta Potential(mV) 200 -200 -100 100 200 Zeta Potential(mV) Fig (1) Zeta potential of Ag2S QDs, Au colloid; (2) Zeta potential of Ag2Te QDs, Ag2Te QDs + Au colloid, Au colloid Conclusions Based on the L-cysteine-capped Ag2S QDs fluorescence quenching effect induced by colloidal gold (Au), a simple, rapid, highly selective determination of colloidal gold was established The way to determination of Xiulan Wu et al / Procedia Engineering 102 (2015) 273 – 277 colloidal gold is also appropriate for the similar type QDs, such as, Ag2Te, Ag2Se QDs, and etc In our work, a new method for the quantitative detection of inorganic nanoparticles was established, and it provides a new way for the bio-analytical applications Acknowledgements This work was supported by the National Science Foundation of China (under Grant Numbers: 21063005, 50968005, 21264005 and 51163003), and by the National Science Foundation of Guangxi Province(under Grant Number: 2010GXNSFC013007 and 2014GXNSFAA118331) References [1] A.E Rider, K Ostrikov, The path to stoichiometric composition of III-V binary quantum dots through plasma/ion-assisted self-assembly, Surf Sci 603 (2009) 359-368 [2] W Feng, C.Q Qin, Y.T Shen, A layer-nanostructured assembly of PbS quantum dot / multiwalled carbon nanotube for a high-performance photoswitch, Sci Rep (2014) 1-7 [3] B.H Dong, C.Y Li, G.C Chen, Facile Synthesis of Highly Photoluminescent Ag 2Se Quantum Dots as a New Fluorescent Probe in the Second Near-Infrared Window for in Vivo Imaging, Chem Mater 25 (2013) 2503-2509 [4] Y.P Gu, R Cui, Z.L Zhang, Ultrasmall near-infrared Ag2Se quantum dots with tunable fluorescence for in vivo imaging, J Am Chem Soc 134 (2012) 79-82 [5] A.H Gore, M.B Kale, P.V Anbhule, A novel FRET probe for selective and sensitive determination of vitamin B 12 by functionalized CdS QDs in aqueous media: applications to pharmaceutical and biomedical analysis, RSC Adv (2014) 683-692 [6] J Zhang, S.Q Zhao, K Zhang, Cd-doped ZnO quantum dots-based immunoassay for the quantitative determination of bisphenol A, Chemosphere 95 (2014) 105-110 [7] Z.X Cai, H Yang, Y Zhang, Preparation, characterization and evaluation of water-soluble L-cysteine-capped-CdS nanoparticles as fluorescence probe for detection of Hg(II) in aqueous solution, Anal Chim Acta 559 (2006) 234-239 [8] Y Q Wang, C Ye, Z.H Zhu, Cadmium telluride quantum dots as pH-sensitive probes for tiopronin determination, Anal Chim Acta 610 (2008) 50-56 [9] X.Y Cao, F Shen, M.W Zhang, Efficient inner filter effect of gold nanoparticles on the fluorescence of CdS quantum dots for sensitive detection of melamine in raw milk, Food Control 34 (2013) 221-229 277 ... morphology of Ag2S QDs in the present of colloidal gold is shown in Fig 2b, it shows that the shape and the size of the nanoparticles of Ag2S are similar to that of Ag2S QDs in the absence of colloidal... UV-vis (a) and fluorescence spectra (b) of Ag2S QDs and Ag2S QDs in the present of Au colloid; (2) the liner relation between the quenched fluorescence of Ag2S QDs with various concentration of Au... between the quenched fluorescence intensity of Ag2S QDs and concentration of Au colloid was observed in the range of 5.9327.09×10-6mol/l with a correlation coefficient (r2) of 0.9956, the linear regression