- Nano Express
- Open Access
Facile synthesis and optical properties of polymer-laced ZnO-Au hybrid nanoparticles
© Wang et al.; licensee Springer. 2014
- Received: 30 December 2013
- Accepted: 27 February 2014
- Published: 7 March 2014
Bi-phase dispersible ZnO-Au hybrid nanoparticles were synthesized via one-pot non-aqueous nanoemulsion using the triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. The characterization shows that the polymer-laced ZnO-Au nanoparticles are monosized and of high crystallinity and demonstrate excellent dispersibility and optical performance in both organic and aqueous medium, revealing the effects of quantum confinement and medium. The findings show two well-behaved absorption bands locating at approximately 360 nm from ZnO and between 520 and 550 nm from the surface plasmon resonance of the nanosized Au and multiple visible fingerprint photoluminescent emissions. Consequently, the wide optical absorbance and fluorescent activity in different solvents could be promising for biosensing, photocatalysis, photodegradation, and optoelectronic devices.
- ZnO-Au nanoparticles
- Optical properties
Multi-constituent nanomaterials with diverse compositions and tailorable morphology exhibit multiple functionalities and novel properties, showing prospective potentials in biological detection and sensing, drug delivery, hyperthermia, cell separation, magnetic data storage, strong catalysis, photoelectric conversion, and many other areas [1–3]. Syntheses of such nanoparticles and investigating their properties are hence of general interest. On one hand, gold nanoparticles as a typical noble metal product, because of their chemical stability, original biocompatibility, and prevailing effects of surface plasmon resonance in the visible region, offer excellent, versatile opportunities in immunoassay, biosensing, and optimal catalysis [4–8]. On the other hand, ZnO nanoparticles with a wide energy bandgap are an excellent, well-studied semiconductor, accompanied by shifting of the intrinsic band due to quantum confinement [3, 9–11]. Strong, tunable absorption and emission bands revealed in ZnO nanostructure, characterized by the particle size and the surrounding medium, have found uses in biosensing technology, electronics, photoelectronics, catalysis, and chemical degradation.
By nanoengineering these two materials into a single entity, the ensuing nanostructure would not only exercise the unique properties of gold and the semiconductor, but also generate novel collective phenomena based on the interaction between Au and ZnO [12–15]. Such a structural nanoassembly can have the extra advantages of biocompatibility and low toxicity and afford an easy, effective contact between biological tissue and the nanoparticles, anticipated to be benign for biological detection, photocatalysis, and dye-sensitized solar cells. Ranking in a variety of interesting structural forms, the synthesis of ZnO-Au nanoparticles has been performed for various purposes [16–21]. In addition, the natural coating of nanoparticle surfaces by an ultrathin film of biocompatible molecules is highly desirable for future biomedical applications, especially if done in situ during the synthesis process of the nanoparticles [3, 17]. We here report the preparation of ZnO-Au hybrid nanoparticles by one-pot non-aqueous nanoemulsion with the triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO) as the surfactant. The copolymer has proved many distinctive merits, such as aqueous solubility, biocompatibility, non-charging, and non-toxicity, and is often used in a number of fields [22–26]. In nanoemulsion processes, the PEO-PPO-PEO molecules principally participate in the reactions as a surfactant, playing a role in stabilizing the nanoparticles formed and even acting as a reducing agent, as attested in our reports on long-term stable, highly crystalline, monosized Fe3O4/Ca3(PO4)2, Fe3O4/ZnO, Fe3O4/Au, and FeAu nanoparticles [3, 8, 27, 28]. In this work, the ZnO-Au nanoparticles prepared without a secondary surface modification were bi-phase dispersible. The characterization shows that such polymer-laced ZnO-Au nanoparticles are monosized and of high crystallinity and possess excellent dispersibility and optical performance in both organic and aqueous medium.
Bi-phase dispersible polymer-laced ZnO-Au nanoparticles were prepared by one-pot non-aqueous nanoemulsion, using gold acetate and zinc acetylacetonate as the precursors, the triblock copolymer PEO-PPO-PEO as the surfactant, and 1,2-hexadecanediol as the reduction agent. Typically, 0.25 mmol of gold acetate, 0.25 mmol of zinc acetylacetonate, 0.1358 mmol of PEO-PPO-PEO, and 2.5 mmol of 1,2-hexadecanediol were mingled in 10 ml octyl ether in a 250-ml flask under vigorous stirring. The reaction mixture was first slowly heated to 125°C within 2 h and homogenized at this temperature for 1 h under vigorous stirring, then rapidly heated to 280°C within 15 min and refluxed at the temperature for 1 h. After cooling down to room temperature, ethanol was added to the reacted solution to precipitate the PEO-PPO-PEO-laced ZnO-Au nanoparticles by centrifugation. The precipitated product was washed with ethanol/hexane (2:1) several times. The resultant nanoparticles prepared in such a process can be re-dispersed in hexane, ethanol, and distilled water directly, without a secondary surface modification which is usually required . For comparison, Au and ZnO nanoparticles were prepared similarly using only gold acetate or zinc acetylacetonate as the precursor.
The morphology of the ZnO-Au nanoparticles was analyzed by transmission electron microscopy (TEM, JEM-100CX), whereas the structure was characterized by X-ray diffractometry (XRD, X'Pert Pro, PANalytical B.V., Almelo, The Netherlands; λ = 1.54056 Å) using Cu Kα radiation. An Avatar 360 Fourier transform infrared spectroscopy (FTIR) spectrometer (Nicolet Company, Madison, WI, USA) was applied to perform the Fourier transform infrared spectroscopy investigation. In the FTIR studies, the washed ZnO-Au nanoparticles and the pure PEO-PPO-PEO polymer employed in the preparation were crushed with a pestle in an agate mortar, the individually crushed material was mixed with potassium bromide (IR spectroscopy grade) (Merck, Darmstadt, Germany) in about 1:100 proportion. The mixture was then compressed into a 2-mm semitransparent disk by applying a force of 10 t for 2 min. The FTIR spectra were recorded at the wavelength range of 400 to 4,000 cm-1. Moreover, the optical properties of the ZnO-Au nanoparticles separately dispersed in hexane, ethanol, and water, together with the Au and ZnO nanoparticles in hexane, were characterized by an UV-visible spectrophotometer (UV-vis near IR spectrophotometer, Hitachi U4100; Hitachi, Shanghai, China) and a photoluminescence (PL) spectrophotometer (Hitachi F7000, Japan).
where and ϵ = ϵ2/ϵ1.
In the expression, Eg(R) and Eg(bulk) represent the bandgap energies of the nanoparticles of radius R and the bulk material with a dielectric constant ϵ2 surrounded in a medium of dielectric constant ϵ1. The parameters me and mh indicate the effective masses of the electron and the hole of the exciton, whereas e is the electron charge and ħ the Planck constant divided by 2π. The bracket <> means average over a wave function of position r. In addition to the change observed in the band positions from the ZnO nanoparticles to the Au-ZnO nanoparticles, comparing the shapes of the bandgap absorption in Figure 4a,e further sheds light on the impact of Au on ZnO, in which the Au-ZnO nanoparticles show increased absorption intensity with the decreasing wavelength against the almost flat absorption of the ZnO nanoparticles. As revealed in the multiple domain nanostructure from the TEM analysis above, moreover, the Au nanocrystallites in the hybrid nanoparticles produce more surface and interface defects, i.e., imperfect lattices and oxygen vacancies that are expected to generate a defect level in the energy band, resulting in likely contributions of more induced excitons and increased exciton density to the moderate enhancement in the absorption intensity in the UV range. Furthermore, the SPR action induced by the Au nanocrystallites, which is to be addressed below, offers additional channels to absorb the incident electromagnetic waves and thus probably augment the UV absorption of the hybrid nanoparticles.
The second well-defined absorption between 520 and 550 nm features the optical property of surface plasmon resonance in consequence of Au nanostructuring [27, 28, 33, 34]. Dependent on the solvent, the peak position of the plasmon band in the solution of the Au-ZnO nanoparticles varies from approximately 533 nm in hexane, approximately 550 nm in water, to approximately 542 nm in ethanol, in comparison to the Au nanoparticles in hexane which has an absorption peaking at approximately 525 nm. Nominally, the peak position and band shape of the plasmon resonance may be subject to factors of composition, dimension, nanostructure shape, dielectric medium, and nanostructuring of the nanoparticle system [33–35]. The distinctly broadening and red-shifting of the surface plasmon spectra of the ZnO-Au hybrid nanoparticles could be due to the fact that the strong interfacial coupling between Au and ZnO results in electron transfer from Au to ZnO taking account of the formation of ZnO-Au nanocomposites [12, 33, 34]. It is useful to point out that the Au atoms sitting on the surface of the ZnO-Au nanoparticles covered by PEO-PPO-PEO, which is observed as a result of the plasmon resonance addressed above and tested in the experiment, enable thiolation linkage to other molecules .
In summary, we have synthesized the amphiphilic ZnO-Au hybrid nanoparticles by the one-pot non-aqueous nanoemulsion process adopting the biocompatible and non-toxicity triblock copolymer PEO-PPO-PEO as the surfactant. The FTIR assessment substantiates the lacing of the PEO-PPO-PEO macromolecules onto the surface of the nanoparticles. The morphology and structural analyses show the narrow particle size distribution and high crystallinity of the polymer-laced nanoparticles. Moreover, the optical measurements present the well-defined absorption band of the nanoparticles dispersed in different polar and non-polar solvents, manifesting both the ZnO bandgap absorption and the surface plasmon resonance of the nanosized Au, whereas the fluorescent properties reveal multiple fingerprint emissions. Such bi-phase dispersible ZnO-Au nanoparticles could be applicable in biological detection, solar cells, and photocatalysis.
This work was supported partly by the Scientific and Technological Development Projects, Science and Technology Department of Henan Province, China (No. 112300410011), the National Natural Science Foundation of China (No. 51172064), Research Center Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology, South Korea (No. 2009-0081506) and the Industrial Core Technology Development Program funded by the Ministry of Knowledge Economy, South Korea (No. 10033183).
- Ronny C, Aaron ES, Uri B: Colloidal hybrid nanostructures: a new type of functional materials metal–semiconductor. Angew Chem Int Ed 2010, 49: 4878–4897. 10.1002/anie.200906010View ArticleGoogle Scholar
- Wang DS, Li YD: One-pot protocol for Au-based hybrid magnetic nanostructures via a noble-metal-induced reduction process. J Am Chem Soc 2010, 132: 6280–6281. 10.1021/ja100845vView ArticleGoogle Scholar
- Cho NH, Cheong TH, Min JH, Wu JH, Lee SJ, Kim D, Yang JS, Kim S, Kim YK, Seong SY: A multifunctional core–shell nanoparticle for dendritic cell-based cancer immunotherapy. Nature Nanotechnology 2011, 6: 675–682. 10.1038/nnano.2011.149View ArticleGoogle Scholar
- Tom RT, Samal AK, Sreeprasad TS, Pradeep T: Hemoprotein bioconjugates of gold and silver nanoparticles and gold nanorods: structure function correlations. Langmuir 2007, 23: 1320–1325. 10.1021/la061150bView ArticleGoogle Scholar
- Haruta M: When gold is not noble: catalysis by nanoparticles. Chem Rec 2003, 3: 75–87. 10.1002/tcr.10053View ArticleGoogle Scholar
- Yeh YC, Creran B, Rotello VM: Gold nanoparticles: preparation, properties, and applications in bionanotechnology. Nanoscale 2012, 4: 1871–1880. 10.1039/c1nr11188dView ArticleGoogle Scholar
- Lee S, Chon H, Yoon SY, Lee EK, Chang SI, Lim DW, Choo J: Fabrication of SERS-fluorescence dual modal nanoprobes and application to multiplex cancer cell imaging. Nanoscale 2012, 4: 124–129. 10.1039/c1nr11243kView ArticleGoogle Scholar
- Liu HL, Sonn CH, Wu JH, Lee KM, Kim YK: Synthesis of streptavidin-FITC-conjugated core–shell Fe3O4-Au nanocrystals and their application for the purification of CD4+ lymphocytes. Biomaterials 2008, 29: 4003–4011. 10.1016/j.biomaterials.2008.06.031View ArticleGoogle Scholar
- Arakelova E, Khachatryan A, Avjyan K, Farmazyan Z, Mirzoyan A, Savchenko L, Ghazaryan S, Arsenyan F: Zinc oxide nanocomposites with antitumor activity. Natural Science 2010, 2: 1341–1348. 10.4236/ns.2010.212163View ArticleGoogle Scholar
- Brus LE: Electron–electron and electron–hole interactions in small semiconductor crystallites: the size dependence of the lowest excited electronic state. J Chem Phys 1984, 80: 4403–4409. 10.1063/1.447218View ArticleGoogle Scholar
- Maciel AV, Mussel WDN, Pasa VMD: A novel synthesis of nanostructured ZnO via thermal oxidation of Zn nanowires obtained by a green route. Materials Sciences and Applications 2010, 1: 279–284. 10.4236/msa.2010.15041View ArticleGoogle Scholar
- Wang LY, Wang J, Zhang SL, Sun Y, Zhu XN, Cao YB, Wang XH, Zhang HQ, Song DQ: Surface plasmon resonance biosensor based on water-soluble ZnO–Au nanocomposites. Analytica Chimica Acta 2009, 653: 109–115. 10.1016/j.aca.2009.09.001View ArticleGoogle Scholar
- Campos LC, Tonezzer M, Ferlauto AS, Grillo V, Magalhães-Paniago R, Oliveira S, Ladeira LO, Lacerda RG: Vapor-solid-solid growth mechanism driven by an epitaxial match between solid AuZn alloy catalyst particle and ZnO nanowire at low temperature. Adv Mater 2008, 20: 1499–1504. 10.1002/adma.200701612View ArticleGoogle Scholar
- Bora T, Kyaw HH, Sarkar S, Pa SK, Dutta J: Highly efficient ZnO/Au Schottky barrier dye-sensitized solar cells: role of gold nanoparticles on the charge-transfer process. Beilstein J Nanotechnol 2011, 2: 681–690.View ArticleGoogle Scholar
- Shan GY, Wang S, Fei XF, Liu YC, Yang GL: Heterostructured ZnO/Au nanoparticles-based resonant Raman scattering for protein detection. J Phys Chem B 2009, 113: 1468–1472. 10.1021/jp8046032View ArticleGoogle Scholar
- Yu H, Ming H, Gong JJ, Li HT, Huang H, Pan K, Liu Y, Kang ZH, Wei J, Wang DT: Facile synthesis of Au/ZnO nanoparticles and their enhanced photocatalytic activity for hydroxylation of benzene. Bull Mater Sci 2013, 36: 367–372. 10.1007/s12034-013-0491-yView ArticleGoogle Scholar
- Wang X, Kong XG, Yu Y, Zhang H: Synthesis and characterization of water-soluble and bifunctional ZnO-Au nanocomposites. J Phys Chem C 2007, 111: 3836–3841.View ArticleGoogle Scholar
- Li P, Wei Z, Wu T, Qing P, Peng Q, Li YD: Au-ZnO hybrid nanopyramids and their photocatalytic properties. J Am Chem Soc 2011, 133: 5660–5663. 10.1021/ja111102uView ArticleGoogle Scholar
- Herring NP, AbouZeid K, Mohamed MB, Pinsk J, El-Shall MS: Formation mechanisms of gold-zinc oxide hexagonal nanopyramids by heterogeneous nucleation using microwave synthesis. Langmuir 2011, 27: 15146–15154. 10.1021/la201698kView ArticleGoogle Scholar
- Schaefer ZL, Vaughn DD II, Schaak RE: Solution chemistry synthesis, morphology studies, and optical properties of five distinct nanocrystalline Au–Zn intermetallic compounds. J Alloys Compounds 2010, 490: 98–102. 10.1016/j.jallcom.2009.10.137View ArticleGoogle Scholar
- Zamiri R, Zakaria A, Jorfi R, Zamiri G, Mojdehi MS, Ahangar HA, Zak AK: Laser assisted fabrication of ZnO/Ag and ZnO/Au core/shell nanocomposites. Appl. Phys. A 2013, 111: 487–493. 10.1007/s00339-012-7517-yView ArticleGoogle Scholar
- Jain TK, Foy SP, Erokwu B, Dimitrijevic S, Flask CA, Labhasetwar V: Magnetic resonance imaging of multifunctional pluronic stabilized iron-oxide nanoparticles in tumor-bearing mice. Biomaterials 2009, 30: 6748–6756. 10.1016/j.biomaterials.2009.08.042View ArticleGoogle Scholar
- Herve K, Douziech-Eyrolles L, Munnier E, Cohen-Jonathan S, Souce M, Marchais H, Limelette P, Warmont F, Saboungi ML, Dubois P, Chourpa I: The development of stable aqueous suspensions of PEGylated SPIONs for biomedical applications. Nanotechnology 2008, 19: 1–7.View ArticleGoogle Scholar
- Yang JP, Zhai YP, Deng YH, Gu D, Li Q, Wu QL, Huang Y, Tu B, Zhao DY: Direct triblock-copolymer-templating synthesis of ordered nitrogen-containing mesoporous polymers. J Colloid Interface Sci 2010, 342: 579–585. 10.1016/j.jcis.2009.10.037View ArticleGoogle Scholar
- Alexis F, Pridgen E, Molnar LK, Farokhzad OC: Factors affecting the clearance and biodistribution of polymeric nanoparticles. Mol Pharm 2008, 5: 505–515. 10.1021/mp800051mView ArticleGoogle Scholar
- Chen S, Li Y, Guo C, Wang J, Ma JH, Liang XF, Yang LR, Liu HZ: Temperature-responsive magnetite/PEO-PPO-PEO block copolymer nanoparticles for controlled drug targeting delivery. Langmuir 2007, 23: 12669–12676. 10.1021/la702049dView ArticleGoogle Scholar
- Liu HL, Hou P, Zhang WX, Kim YK, Wu JH: The synthesis and characterization of polymer-coated FeAu multifunctional nanoparticles. Nanotechnology 2010, 21: 1–9.Google Scholar
- Liu HL, Wu JH, Min JH, Hou P, Song AY, Kim YK: Non-aqueous synthesis of water-dispersible Fe3O4–Ca3(PO4)2 core–shell nanoparticles. Nanotechnology 2011, 22: 1–7.View ArticleGoogle Scholar
- Strunk J, Kahler K, Xia XY, Comotti M, Schuth F, Reinecke T, Muhler M: Au/ZnO as catalyst for methanol synthesis: the role of oxygen vacancies. Appl Catal A: Gen 2009, 359: 121–128. 10.1016/j.apcata.2009.02.030View ArticleGoogle Scholar
- Cullity BD, Stock SR: Elements of X-ray Diffraction. New Jersey: Englewood Cliffs; 2001:167–171.Google Scholar
- Music S, Saric A, Popovic S: Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate. Ceramics International 2010, 36: 1117–1123. 10.1016/j.ceramint.2009.12.008View ArticleGoogle Scholar
- Singh AK, Viswanath V, Janu VC: Synthesis, effect of capping agents, structural, optical and photoluminescence properties of ZnO nanoparticles. J Lumin 2009, 129: 874–878. 10.1016/j.jlumin.2009.03.027View ArticleGoogle Scholar
- Daniel MC, Astruc D: Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology. Chem Rev 2004, 104: 293–346. 10.1021/cr030698+View ArticleGoogle Scholar
- Scaffardi LB, Pellegri N, Sanctis OD, Tocho JO: Sizing gold nanoparticles by optical extinction spectroscopy. Nanotechnology 2005, 16: 158–163. 10.1088/0957-4484/16/1/030View ArticleGoogle Scholar
- Pawinrat P, Mekasuwandumrong O, Panpranot J: Synthesis of Au–ZnO and Pt–ZnO nanocomposites by one-step flame spray pyrolysis and its application for photocatalytic degradation of dyes. Catalysis Communications 2009, 10: 1380–1385. 10.1016/j.catcom.2009.03.002View ArticleGoogle Scholar
- Tong YH, Liu YC, Lu SX, Dong L, Chen SJ, Xiao ZY: The optical properties of ZnO nanoparticles capped with polyvinyl butyral. J Sol–Gel . Sci Technol 2004, 30: 157–161.Google Scholar
- Nikesh VV, Mahamuni S: Highly photoluminescent ZnSe/ZnS quantum dots. Semiconductor Science Technology 2001, 16: 687–690. 10.1088/0268-1242/16/8/309View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.