Journal of Colloid and Interface Science 358 (2011) 73–80

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Journal of Colloid and Interface Science

www.elsevier .com/locate / jc is

Preparation of quantum dots encoded microspheres by electrosprayfor the detection of biomolecules

Lei Sun a, Xiaofang Yu a, Mingda Sun a, Hengguo Wang a, Shufei Xu a, John D. Dixon c, Y. Andrew Wang c,Yaoxian Li a, Qingbiao Yang a,⇑, Xiaoyi Xu b,⇑a Department of Chemistry, Jilin University, Changchun 130021, People’s Republic of Chinab Cancer Center, The First Hospital, Jilin University, Changchun 130021, People’s Republic of Chinac Ocean NanoTech, LLC 2143 Worth Lane, Springdale, AR 72764, United States

a r t i c l e i n f o

Article history:Received 15 December 2010Accepted 17 February 2011Available online 22 February 2011

Keywords:Electrospray techniqueQD-encoded microspheresImmunofluorescence

0021-9797/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.jcis.2011.02.047

⇑ Corresponding authors. Fax: +86 431 88499845.E-mail address: yangqb@jlu.edu.cn (Q. Yang).

a b s t r a c t

In this paper, a novel method based on the electrospray technique has been developed for preparation ofquantum dot (QD)-encoded microspheres for the fist time. By electrospraying the mixture of polymersolution and quantum dots solution (single-color QDs or multi-color QDs), it is accessible to obtain a ser-ies of composite microspheres containing the functional nanoparticle. Poly(styrene–acrylate) was uti-lized as the electrospray polymer materials in order to obtain the microsphere modified with carboxylgroup on the surface. Moreover, to test the performance of the QD-encoded microsphere in bioapplica-tion, it is carried out that immunofluorescence analysis between antigens of mouse IgG immobilizedon the functional microsphere and FITC labeled antibodies of goat–anti-mouse IgG in experiment. Tothe best of our knowledge, this is the first report of QD-encoded microspheres prepared by electrospraytechnology. This technology can carry out the one-pot preparation of different color QD-encoded micro-spheres with multiple intensities. This technology could be also suitable for encapsulating other opticalnanocrystals and magnetic nanoparticles for obtaining multifunctional microspheres. All of the results inthis paper show that the fluorescence beads made by electrospray technique can be well applied in mul-tiplex analysis. These works provide a good foundation to accelerate application of preparing micro-spheres by electrospray technique in practice.

� 2011 Elsevier Inc. All rights reserved.

1. Introduction overcome some of the functional limitations encountered by or-

In recent years, the fluorescence-encoded bead-based multiplextechnology has attracted considerable attention in bioassays, med-ical diagnostics, drug screening and cancer imaging [1–6]. So far,both organic [7,8] and inorganic [9,10] fluorophores have beenused to optically encode microspheres. However, the applicationof organic fluorophores in multicolor analysis is limited to prob-lems including narrow excitation bands and broad emission spec-tra, which can make detection of multiple light emitting probesdifficult due to spectral overlap and photodegradation [11].

The use of colloidal II–VI semiconductor nanocrystals, known asquantum dots (QDs), as luminescence probes has become an areaof intense research focus over the past few years. Compared withtraditional organic fluorophores, quantum dots have superior opti-cal properties, particularly in multicolor analysis, such as tunableemission from visible to infrared wavelengths, symmetric emissionspectrum, broadband excitation spectra, photostability, high quan-tum yield of fluorescence, and good chemical stability. These un-ique optical properties make quantum dots have the potential to

ll rights reserved.

ganic dyes. The QDs have been shown to be ideal for use as fluores-cent probes in bioanalysis and bioimaging [12–19]. The ability toconjugate QDs to biomolecules was first performed by Bruchezand Nie in 1998. They applied QDs to label biomolecules as fluores-cent probes [20,21]. In 2001, Nie and his co-workers extended theirstudy, and firstly applied QDs-tagged microspheres in multiplexedoptical coding of DNA hybridization, which initiated a new applica-tion field of QD-encoded microbeads in life science [9]. They did asignificant try in the multicolor encoding and the application of en-coded microbeads in multiplex analysis. To date, multicolor optical‘‘bar codes’’ have been studied widely by embedding different-colored quantum dots with different intensities into microspheres(such as polymeric, silicon or glass microspheres) at precisely con-trolled ratios [22–25].

Very recently, the incorporation of QDs into different monodis-perse polymer microspheres has been gaining increasing attentionfor multiplex analysis. Different techniques have been reported toincorporate QDs into polymer microspheres, such as swellingmethod [9], solvent extraction/evaporation method [26],suspension polymerization method [27] and emulsion polymeriza-tion method [28]. In our work, the electrospray technique has beenused to produce QD-encoded microspheres for the first time.

74 L. Sun et al. / Journal of Colloid and Interface Science 358 (2011) 73–80

Comparing with above methods, electrospray technology is morefast and effective. This technology can carry out the one-pot prep-aration of different color QD-encoded microspheres with multipleintensities.

This technique, applied to polymer solutions above a critical va-lue, bears nanofibres, and the process is called electrospinning.Electrospinning is an effective and simple method for preparingvarious composite nanofibres. The electrospinning technique hasbeen developed since 1934 for the synthesis of nanofibres [29]. Itis a process which uses a strong electrostatic force by a high staticvoltage applied to a polymer solution placed into a container thathas a millimeter diameter nozzle. Under applied electrical force,the polymer solution is ejected from the nozzle. After the solventsare evaporated during the course of jet spraying, the nanofibres ornanoparticles are collected on a grounded collector [30–32]. Thestructure and the morphology of the electrospun polymer materi-als, be it fibers or particles, are determined by a synergetic effect ofsolution parameters and electrostatic forces.

Electrospinning is usually used for making various compositenanofibres for a variety of applications [33–42]. However, electros-pinning at relatively low polymer concentrations results in parti-cles rather than fibers, which is observed in early but regainedgreat attention in recent years. This particle-formation processcan be termed as electrospray [43,44]. Kim et al. [45] fabricatedpoly(methyl methacrylate) (PMMA) particles of decreasing sizewith increasing voltage. Rietveld et al. [46] prepared poly(vinyli-dene fluoride) (PVDF) particles and found that the droplet size iscontrolled by the conductivity and flow rate of the solution. Fantiniet al. [47] produced the polystyrene (PS) micro- and nanospheresby electrospray and investigated the effect of PS molecular weighton beads morphology and the fundamental role of concentration.Liu et al. [48] electrospun PMMA particles with different morphol-ogies and discussed a qualitative relationship between thedifferent solvent properties and the particle morphologies. Unfor-tunately, almost all reports have paid their attention to the bettermorphologies of electrospun particles rather than the function andapplication. Therefore, it is a new and active field that preparingthe functional composite microspheres by electrospray techniqueand developing their application.

To the best of our knowledge, few have reported the prepara-tion of QD-encoded microspheres by electrospray yet. As shownin Scheme 1, we reported a novel and effective approach for prep-aration of polystyrene microspheres containing CdSe–ZnS QDs byelectrospray for the first time and then we applied the QD-encodedmicrosphere in detection of biomolecules. By using electrospraymethod, we easily obtain encoded polystyrene microspheres withluminescent QDs of single color or various colors. The encapsula-tion of QDs also solves problems associated with QDs such as bio-compatibility, cytotoxicity and stability. Compared to otherapproaches, electrospray is one of the most efficient methods forfabricating microspheres with QDs. Moreover, to test the perfor-mance of the QD-encoded microsphere in bioapplication, antibodyconjugation fluoroimmunoassays are carried out on QD-encodedmicrospheres in experiment. This technology could be also suitablefor encapsulating other optical nanocrystals and magnetic nano-particles for obtaining multifunctional microspheres. All of the re-sults in this paper show that the fluorescence microspheres madeby electrospray can be applied in multiplex analysis.

2. Experimental details

2.1. Materials

Poly(styrene–acrylate) (Mw = 78,657 g mol�1) were synthe-sized in our laboratory using cyclohexane as a solvent and benzoyl

peroxide as an initiator; the molecular weights were all deter-mined by means of gel permeation chromatography (GPC). N-hydroxysuccinimide (NHS), dimethyl sulfoxide (DMSO, 99.9%),chloroform (99%), Tris(hydroxymethyl)aminomethane (Tris), N,N-dimethylformamide (DMF) and N-(3-Dimethylaminopropyl)-N0-ethylcarbodiimide hydrochloride (EDC) were obtained fromShanghai Chemical Reagent Company. 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and Dulbecco’smodified eagle medium (DMEM) were obtained from InvitrogenCorp. Mouse IgG and FITC-goat–anti-mouse IgG were ordered fromSigma (USA). Three kinds of hydrophobic CdSe/ZnS nanocrystals(CdSeS QDs) with central photoluminescence peaks at 620 nm,589 nm, and 530 nm, capped with octadecylamine (ODA) ligands,were provided by Dr. Y. Andrew Wang, Principle Scientist of OceanNanotech, USA (quantum yield, QY: 42% in hexane versus Rhoda-mine 640). In the experiment, all other chemicals were analyticalgrade and all reagents were used as received without any furtherpurification.

2.2. Preparation of electrospray solution

The electrospray polymer solution containing QDs were pre-pared as follows: Poly(styrene–acrylate) (0.1 g) was dissolved inDMF (0.75 g) solution at room temperature, with vigorous stirringfor 24 h. Then 0.15 g of QDs nanoparticles in chloroform solutionwas added to the solution. By changing the molar ratio of QDs inchloroform solution, the resulting electrospray solution with cer-tain fluorescence intensity ratio was obtained.

2.3. Preparation of QD-encoded microspheres by electrospray

The above each composite solution was loaded into a 1 ml glasssyringe with a plastic needle being used as the nozzle. The needlewas connected to a high-voltage generator, an aluminum foilserved as the counter electrode. In the electrospray process, thefollowing parameters were used: voltage 18 kV, distance from nee-dle to collecting plate 15 cm, and polymer solution flux 0.6 ml h�1.Finally, the particles were separated from the aluminum foil intowater solution by ultrasound. The particles powder was obtainedby lyophilization.

2.4. Cytotoxicity of the QD-encoded microspheres

The in vitro cytotoxicity was measured by using the MTT assayin Hela cells. Cells (1 � 105 well�1) were inoculated into a 96-wellcell-culture plate and then incubated at 37 �C in a 5% CO2-humidified incubator for 24 h. 10 ll of QD-encoded microsphereswith different concentrations (10–100 lg ml�1, diluted in DMEM)were added to the well, separately. After incubation for 24 h at37 �C under 5% CO2, the supernatant was removed, and the cellswere washed with PBS for three times. Subsequently, MTT (10 ll,5 mg ml�1) solved in DMEM (90 ll) were added and the plateswere incubated at 37 �C for another 4 h. Then supernatant wasremoved before DMSO was added to each well to dissolve the for-mazan. The absorbance at 490 nm was detected with spectropho-tometric microplate reader (BioRad Model 550). Each data pointwas collected by averaging that of six wells, and the untreated cellswere used as controls.

2.5. Immunofluorescence assay

Ten milligrams of the single color (620 nm) QD-encoded micro-spheres were firstly washed with PBS (0.01 M, pH = 7.4) solutionfor three times. Then microspheres were dispersed in 400 ll ofPBS solution in centrifugal tube, 20 ll of EDC (220 mg/ml) wasadded in and stirred for 10 min, after that, 100 ll of NHS

Scheme 1. Schematic illustration for preparation of QD-encoded microspheres by electrospray for fluoroimmunoassays between antigens of the mouse IgG and FITC labeledantibodies of the goat–anti-mouse IgG.

L. Sun et al. / Journal of Colloid and Interface Science 358 (2011) 73–80 75

(0.20 mg/ml) was added in and stirred for another 20 min. Then100 ll of mouse IgG (0.2 mg/ml) was added and incubated for3 h with stirring at room temperature, and then 50 ll of Tris(50 mg/ml) was added and stirred for 20 min. Washed with PBSafter all the solvent was removed, then the microspheres were dis-persed in 500 ll solution containing 400 ll of PBS and 100 ll ofFITC (�520 nm) tagged goat anti-human IgG (0.2 mg/ml), and incu-bated for 1 h at 37 �C. Finally, the microspheres were washed withPBS several times. Similar protocols were used for immunoreactionof the multicolor QD-encoded microspheres.

2.6. Characterization

The structure and component of QD-encoded microsphereswere characterized by field-emission scanning electron micros-copy (FESEM; FEI XL30), transmission electron microscopy (TEM;Hitachi S-570), and energy dispersive X-ray analysis (EDX, FEIXL30). The photoluminescent emission spectra of the QD-encodedmicrosphere and immunofluorescence assay were recorded at

room temperature with a Hitachi F-4500 spectrophotometerequipped with a continuous 150 W Xe-arc lamp. The carboxylgroup on the surface of microspheres was determined by the mea-surements of the X-ray photoelectron spectra (XPS) which per-formed by using a VG-Scientific ESCALAB 250 spectrometer witha monochromatic Al Ka X-ray source at 1486.6 eV.

3. Results and discussion

Our group has reported that micro- and nanostructures ofpoly(methyl methacrylate) (PMMA) with different morphologies(fibers, spheres, cup-like, and ring-like) could be produced by afacile electrospinning/electrospray method [49]. The morphologyof electrospray product has shown a great dependence on the con-centration of solution and the strength of electric field [50,51]. Inthis experiment, it is obvious that the jet of polymer solutionsfrom the tip of a capillary begins to break up into droplets atconcentration below 13 wt.%. At a concentration of 10 wt.%, thefibers disappear and the complete microspheres take place. The

Fig. 1. FESEM images of microspheres encoded with different color QDs: 530 nm (a), 620 nm (b), 530 nm/589 nm/620 nm (c) and 530 nm/620 nm (d).

76 L. Sun et al. / Journal of Colloid and Interface Science 358 (2011) 73–80

concentration of the solution is set as high as possible but not toproduce any fiber. In order to obtain uniform diameter the regularmorphology of the microspheres, we further investigate the effectof the voltage. At proper voltages, the solutions are elongated tothe direction of electric field and break up into uniform-sizedmicrospheres due to the Rayleigh instability. This is called thecone-jet mode which is appropriate for the preparation of micro-spheres. However, too high voltage can create multiple jets be-cause it destabilizes the electric field at the nozzle tip. Thosemultiple jets are uncontrollable and they produce particles withlarge size distribution. Preparation of uniform-sized particles isachievable when the liquid jet from the cone is long enough to al-low break of the jet in a regular wavelength [52]. Herein, we usedlow polymer concentrations to prepare microspheres at the propervoltage. By using single-color QDs, we systematically investigatedthe electrospray conditions for preparing the composite micro-spheres and obtained the better morphology. Different from earlyreports, we firstly prepared functional composite microspheres byelectrospray. The morphology of composite microspheres can be

Fig. 2. EDX results (A) and TEM images

confirmed directly by field-emission scanning electron microscopy(FESEM). The FESEM imaging are presented in Fig. 1a–d whichshows diameters of microspheres are in the range of 500 nm to1 lm. From the FESEM images, it can be seen that the micro-spheres have a narrow size distribution. In order to prove the suc-cessful assembly of QDs into the polymer microspheres, theenergy-dispersive X-ray (EDX) characterization is carried out. Asshown in Fig. 2A, EDX microanalysis pattern shows the presenceof C, O, Se, S, Cd and Zn in the samples of microspheres, whicheffectively proves that CdSe/ZnS QDs are successfully coated bypolymer. The distribution of CdSeS QDs in the microsphere com-posites are further investigated by transmission electron micros-copy (TEM). From the TEM images of QDs-loaded microspheresin Fig. 2B, well-formed microspheres encapsulated can be clearlyseen. The QDs (seen as dark spots) are successfully encapsulatedin the polymer microspheres. TEM images are consistent withthe EDX observation, which is proved that the electrospun tech-nology can be successfully applied in preparing QD-encodedmicrospheres.

(B) of QD-encoded microspheres.

Fig. 3. Fluorescence spectra of microspheres with a series of different intensities of single-color QDs: 530 nm (a), 589 nm (b) and 620 nm (c). The concentration of QDs in theelectrospray solution is 8 wt.%, 5 wt.%, 3 wt.%, and 2 wt.%, respectively.

Fig. 4. Fluorescence spectra of microspheres with a series of different intensities of multi-color QDs: 530 nm/620 nm (a) and 530 nm/589 nm/620 nm (b). The totalconcentration of QDs (530 nm and 620 nm) in the electrospray solution (a) is 10 wt.%, 8 wt.%, 5 wt.%, 3 wt.% and 2 wt.%, respectively. The total concentration of QDs (530 nm,589 nm and 620 nm) in (b) is 10 wt.%, 8 wt.% and 5 wt.% respectively.

L. Sun et al. / Journal of Colloid and Interface Science 358 (2011) 73–80 77

Evidence for the formation of QDs/microsphere polymer com-posite is also provided by fluorescence spectroscopy. By using theelectrospray technology, we easily obtain various single-color QD-encoded microspheres with different fluorescence intensities viachanging the concentration of the QDs solution. Fig. 3a–c showsthe fluorescence emission spectra of the single-color QD-encodedmicrospheres. Multiple intensities and multiple wavelengths havebeen widely recognized as the important technology of multi-plexed coding. In this experiment, green (520 nm), yellow(589 nm) and red (620 nm) QDs are used to quantitatively investi-gate the multicolor encoding of microspheres and multicolor codedmicrospheres with different intensities are prepared by electro-spray. Fig. 4a and b shows the fluorescence emission spectra of

the multiple wavelengths QD-encoded microspheres with multipleintensities. As shown in Fig. 4a, by controlling the molar ratio ofthe green and red QDs in chloroform solution and mixing theQDs solution with the polymer solution, we obtain the multiplecolor QD-encoded microspheres with multiple intensities by elec-trospray technology. Electrospinning at relatively low polymerconcentrations results in particles. The formation process of beadsis observed but their presence has been considered to be an avoid-able fiber imperfection. The electrospun particle has regained greatattention in recent years.

However, much effort has been usually focused their minds onpreparing the better morphologies of electrospun particle. In thispaper an attempt has been made to development of the function

Fig. 6. The XPS O1s spectra for the microspheres prepared by electrospray.

78 L. Sun et al. / Journal of Colloid and Interface Science 358 (2011) 73–80

and application of electrospun particles. Previous studies of theencapsulation of different-sized quantum dots in polymer beadsusually are devoted on swelling method. In that work, the embed-ding process involved swelling the particles in a suitable solventmixture containing the QDs. Comparing with swelling method,electrospray technology is more fast and effective. This technologycan carry out the one-pot preparation of different color QD-encoded microspheres with multiple intensities. For multicolordoping, different color quantum dots solution are premixedthoroughly in precisely controlled ratios.

The potential applications of quantum dots in biology and med-icine are usually limited due to the toxic effects of semiconductorQDs. The CdSe/ZnS QDs were highly toxic for the cell in culture dueto the released Cd2+ ions, which were caused by surface oxidationof QDs [53–57], and that the surface oxidation was repressed bycoating with appropriate shells, which decreased the cytotoxicityof QDs. Thus, they must be encapsulated or surface modified to re-duce the cytotoxicity and make them biocompatible. To prove theQD-encoded microspheres prepared by the electrospray techniquecan be applied in biomedical researches, we further evaluate thecytotoxicity of the microspheres, where the cultured Hela cell linesare used by the MTT method. The results show that cell viability isgreater than 70% at concentration of QD (620 nm)-encoded micro-spheres up to 500 lg ml�1 after 24 h of incubation (Fig 5) and thesimilar results are obtained in cytotoxicity studies of multicolorencoding of microspheres as shown in Figs. S1 and S2, which indi-cates that the electrospray technique can solve the cytotoxicityproblem associated with QDs. By changing the concentration ofQDs in the electrospray solution, we obtained a serious of QD-encoded microspheres with multiple intensities by electrospraytechnology. We also study the cytotoxicity of the microsphereswith different content of QDs by the MTT method (Fig. S3). The re-sults indicate that cell viability is slightly declined but greater than78% at QDs concentration up to 20 wt.%. Therefore, these data showthat the QDs/microspheres composites can be applied in biomedi-cal researches and considered to possess low cytotoxicity.

In order to investigate the applicability of QD-encoded micro-spheres prepared by the electrospray technology in biologicalapplications, antigens conjugations are carried out on the micro-spheres which are encoded with single-color and multi-colorQDs. In this paper, poly(styrene–acrylate) is used as the electro-spray polymer materials for the purpose of obtaining the micro-spheres with the carboxyl group on the surface. The surface

Fig. 5. In vitro cell viability of Hela cells incubated with the QD (620 nm)-encodedmicrospheres at different concentrations for 24 h. The concentration of QDs in theelectrospray solution is 5 wt.%.

Fig. 7. Fluorescence spectrum of the single-color QD-encoded microspheres(620 nm) without any reaction (a), florescence microspheres + FITC labeled goat–anti-mouse IgG (b) and florescence microspheres + antigens of mouse IgG + FITClabeled goat–anti-mouse IgG (c). Excitation wavelength is 445 nm. The concentra-tions of microspheres are 1 mg/ml. The concentrations of mouse IgG and FITClabeled antibody are 0.2 mg/ml.

chemical composition of the microspheres was determined byXPS. The existence of the carboxyl group on the surface of micro-spheres prepared by this technology is proved via O 1s signals

Fig. 8. Fluorescence spectra of the microspheres encoded with 589 nm and 620 nmQDs before (A) and after (B) immunoreaction between mouse IgG on themicrosphere surface and FITC labeled goat–anti-mouse IgG. Excitation wavelengthis 445 nm.

L. Sun et al. / Journal of Colloid and Interface Science 358 (2011) 73–80 79

(Fig. 6). The carboxyl group on the microspheres is conjugated withthe amine group on the antigens of mouse IgG by EDC and NHSchemical strategy and then the microsphere is incubated withthe FITC tagged goat anti-mouse IgG. According to the emissionwavelength of the dye (FITC) labeled on antibodies, the QDs withappropriate emission wavelength are chosen to code the micro-spheres. In this experiment, 589 and 620 nm QDs are used to en-code the microsphere (single color microsphere: 620 nm andmulticolor microsphere: 589 nm/620 nm). The immunoreactionsbetween antigens immobilized on the functional fluorescentmicrospheres and FITC labeled antibodies can be confirmed in thisstudy. For this purpose, FITC labeled antibodies of goat–anti-mouseIgG were added to the systems of functional fluorescent micro-spheres with antigens of mouse IgG. If the immunoreactions be-tween antigens of the mouse IgG and FITC labeled antibodies ofthe goat–anti-mouse IgG occurred, the green emitting FITC peak(520 nm) can be detected by the fluorescence spectra. The fluores-cence spectra of the signal-color microsphere before and afterimmunoreactions are shown in Fig. 7. It can be seen that the FITCpeak of FITC labeled goat–anti-mouse IgG appears in the fluores-cence spectra of mouse IgG/single-color QDs(620 nm)-encodedmicrospheres obviously (Fig. 7c) in comparison with the spectrumof the QDs encoded microspheres before immunoreactions(Fig. 7a). However, the characteristic peak of FITC does not appearwhen the QD-encoded microsphere is directly incubated with FITClabeled antibodies without conjugation with the antigens (Fig. 7c)and it dose not also appear when the sheep IgG are used instead ofmouse IgG (Fig. S4). The fluorescence spectra of Fig. 7b and Fig. S4are used as the non-specific binding control and a negative control,respectively. The result indicates that the antigens of mouse IgGare covalently conjugated to the microspheres successfully andthe immunoreaction between QD-encoded microspheres/antigensand antibodies really occurred on the surface of the fluorescentmicrospheres in this study.

Furthermore, the multi-color QDs encoded microspheres arealso applied in immunoreaction. The results are shown in Fig. 8.There is a strong emission peak of FITC at approximately 520 nm(Fig. 8A) in the fluorescence spectrum of the multicolor QD-encoded microspheres after immunoreaction compared with thetwo peaks of QDs in spectrum B. The FITC labeled goat–anti-mouseIgG successfully coupled to the mouse IgG probe on the micro-sphere encoded with multi-color QDs (589 nm and 620 nm).

4. Conclusions

In conclusion, we have developed a simple and novel methodfor preparing QD-encoded microspheres, which could provide

enormous and reliable codes for multiplex detection. The QD-encoded fluorescent microspheres were prepared by the electro-spray technique for the first time in the present study. This methodis a novel and effective approach for the preparation of functionalcomposite microspheres and could be also suitable for encapsulat-ing other optical nanocrystals and magnetic nanoparticles for pre-paring multifunctional microspheres. This technology can carryout the one-pot preparation of different color QD-encodedmicrospheres with multiple intensities. Furthermore, we furtherevaluate the as prepared signal color QD-encoded and multicolorQD-encoded microspheres for biodetection. The in vitro immuno-fluorescence assay indicates that the QD-encoded microspheresprepared by electrospray technique can be effectively applied inbiological applications. These works provide a good foundation toaccelerate application of preparing microspheres by electrospraytechnique in practice.

Acknowledgments

The authors gratefully acknowledge the support of the NationalNatural Science Foundation of China (No. 20874033). We thank Mr.Y.A. Wang for providing the quantum dot samples with ODAligands.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.jcis.2011.02.047.

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