Fast Assembling of Magnetic Iron Oxide Nanoparticles byMicrowave-Assisted Copper(I) Catalyzed Alkyne−AzideCycloaddition (CuAAC)Delphine Toulemon,† Benoît P. Pichon,*,† Cedric Leuvrey,† Spyridon Zafeiratos,‡ Vasiliki Papaefthimiou,‡

Xavier Cattoen,§,∥ and Sylvie Begin-Colin†

†Institut de Physique et Chimie des Materiaux de Strasbourg, UMR 7504 (CNRS−UdS), 23, rue du Loess, BP 43, 67034 StrasbourgCedex 2, France‡Institut de Chimie et Procedes pour l’Energie, l’Environnement et la Sante, UMR 7515 (CNRS−UdS), 25 rue Becquerel, 67087Strasbourg Cedex 2, France§Institut Charles Gerhardt Montpellier, UMR 5253 (CNRS−UM2−ENSCM−UM1), 8 Rue de l’Ecole Normale, 34296 MontpellierCedex 5, France

*S Supporting Information

ABSTRACT: Two dimensional (2D) nanoparticles (NP)assemblies have become very attractive due to their originalcollective properties, which can be modulated as a function ofthe nanostructure. Beyond precise control on nanostructureand easy way to perform, fast assembling processes are highlydesirable to develop efficient and popular strategies to preparesystems with tunable collective properties. In this article, wereport on the highly efficient and fast 2D assembling of ironoxide nanoparticles on a self-assembled monolayer (SAM) oforganic molecules by the microwave (MW)-assisted copper(I)catalyzed alkyne−azide cycloaddition (CuAAC) click reaction.Microwave irradiation favors a dramatic enhancement of the assembling reaction, which was completed with maximum density inNPs within one hour, much faster than the conventional CuAAC click reactions that require up to 48 h. Moreover, the MW-assisted click reaction presents the great advantage to preserve specific reactions between alkyne and azide groups at SAM andNP surfaces, respectively, and also to avoid undesired reactions. To the best of our knowledge, this is the first time this approachis performed to nanoparticles assembled on surfaces.

KEYWORDS: nanoparticle, assembly, click chemistry, CuAAC, microwave, magnetism, iron oxide

■ INTRODUCTION

Owing to their great ability to modulate their physicalproperties as a function of their nanostructure, 2D nanoparticle(NP) assemblies have become a highly attractive field ofresearch for the development of new applications such asbiosensors for molecule detection, high density magneticstorage, or magneto-resistive media.1−4 Indeed, collectiveproperties are ruled by the fine control on the preparation ofmono- and multilayer assemblies on surfaces.5−8 For instance,assemblies with well-defined interparticle distances enable tomodulate the dipolar interactions between magnetic NPs andthus the overall magnetic properties.9−11 Patterned NPsassemblies on surfaces have been obtained in a very efficientway by functionalizing substrates using self-assembled mono-layers (SAMs) of organic molecules.12−17 Because of theincreasing interest for the assembly of NPs and their originalcollective properties, easy-to-process methods are now requiredto develop device miniaturization. Among current assemblingtechniques, deposition of NPs driven by specific interactions

between terminal functional groups on both NPs and SAMssurfaces meets most of these objectives. A crucial point is thatthe assembling reaction has to proceed with high yield and highrates.Over the past years, the copper(I) catalyzed azide−alkyne

cycloaddition (CuAAC) click reaction,18−21 which wasdeveloped initially for small-molecule organic synthesis, hasproved to be a very simple and efficient method for surfacemodification of substrates22,23 and nanoparticles.24 Veryrecently, this approach has been reported by Kinge et al.25

and our group26 as a very useful tool to address the assemblingof magnetic NPs on SAMs by the irreversible covalentformation of triazole linkages. Such a strategy strongly preventsthe formation of unspecifc NP assemblies, which may be drivenby dipolar interactions.26 Depending on the reaction time, we

Received: April 22, 2013Revised: June 20, 2013Published: June 20, 2013

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have been able to tune the average interparticle distance so asto produce either assemblies of quasi noninteracting NPs orhigh density assemblies of NPs, which display collectiveproperties.26 Although this approach represents an importantstep toward the assembling of NPs on SAMs in a controlledfashion through specific interactions, it suffers from very slowkinetics. Indeed, reaction times are longer (up to 48 h) than theones of reactions between alkyne and azide molecularderivatives in solution and require large amounts of catalysts(up to 10 times as much as the molar amount of azide andalkyne groups). The assembling kinetics of NPs on SAMsstrongly depend on the probability that nanoparticles reach thecorresponding functional groups at the SAM surface. Severalparameters may slow down the kinetics of the reaction: (i) theBrownian motion that rules the mobility of nanoparticles insolution, (ii) the number of functional groups that are availableat the SAM surface, and (iii) the intermolecular interactionsbetween these groups that are favored by the tight packing ofmolecules and thus reduce their reactivity. Although densemonolayers of NPs can be obtained by specific interactionsusing the CuAAC reaction, the assembly of NPs has beenreported to occur much faster by using other types ofSAMs.12,15,27 Therefore, a general and versatile strategy thatenables fast assembling of NPs on SAM surfaces still representsan unfilled goal.Recently, microwave (MW)-assisted synthesis has been

developed for CuAAC reactions. This approach is highlyappealing because of its major advantages such as decrease ofreaction time from hours to minutes, improved reaction yields,absence of side products, and reproducibility. Originallyreported for molecular synthesis,21,28,29 MW-assisted CuAACreactions have very recently emerged for surface functionaliza-tion. Gold29 and iron oxide30 NPs and SAMs on siliconwafers31−33 have been functionalized by this method. All thesestudies have demonstrated the acceleration of the CuAACreaction under exposure to MW irradiations from hours tominutes. This has been established for relatively low power(40−100 W), which resulted in mild to elevated temperatures(70−150 °C). In all cases, these reactions featured a fast-moving molecular derivative reacting with an immobilesubstrate or a particle in slow-motion. It is worth noting thatthese studies have been exclusively performed by using theSharpless conditions in the presence of Cu(II) catalyst and areducing agent (ascorbic acid) in aqueous and polar organicsolvent mixtures. Nevertheless, the alternative approach in thepresence of Cu(I) and triethylamine34 is much more suited forNPs coated with hydrophobic molecules since such NPs formunstable suspensions of aggregates in hydrophilic media.Herein, we report on the development of a new way to

accelerate the assembling of slow-motion magnetic iron oxideNPs on immobile SAMs by using the MW-assisted CuAACclick reaction. The reaction proceeds under hydrophobicconditions,29,30 and results in dramatically faster kineticscompared to conventional heating, with an easy control ofsurface coverage. This approach could be applied to theassembly of a wide range of functionalized nanoparticles andnano-objects. To the best of our knowledge, the benefits ofMW-assisted CuAAC click reaction has never been reported forNPs assembling addressed by SAMs.

■ EXPERIMENTAL SECTIONChemicals. Tetrahydrofurane (THF), methanol, and ethanol were

purchased from Carlo Erba and used as received. Iron stearate was

purchased from Strem Chemicals. Oleic acid, methanesulfonylchloride, and 11-undec-1-ynol were purchased from Alfa Aesar.Triethylamine was obtained from Fluka and docosene from Aldrich.

Synthesis of diethyl (12-bromododecyl)phosphonate. In around-bottomed flask equipped with a short distillation apparatus, amixture of 1,12-dibromododecane (65.6 g, 0.20 mol) andtriethylphosphite (5.7 mL, 33 mmol) was heated at 160 °C for 4 h.The excess dibromododecane was then distilled off under vacuum,then the crude product was purified by column chromatography onsilica gel (cyclohexane/ethyl acetate 3:1 to 1:1). Yield: 75%. 1H NMR(CDCl3, 400 MHz): 4.09 (m, 4H); 3.40 (t, J = 7.0 Hz, 2H); 1.84 (m,2H); 1.78−1.66 (m, 2H); 1.64−1.52 (m, 2H); 1.44−1.23 (m, 22H).

Synthesis of Diethyl (12-Azidododecyl)phosphonate. Amixture of diethyl (12-bromododecyl)phosphonate (1.83 g, 4.7mmol) and sodium azide (1.54 g, 23.8 mmol) in ethanol (96%, 10mL) was refluxed for 40 h. After evaporation of the solvent, water wasadded, and then, the mixture was extracted three times withdichloromethane. The combined organic fractions were washed withwater then brine, and finally concentrated to afford diethyl (12-azidododecyl)phosphonate (1.60 g, 97%). 1H NMR (CDCl3, 400MHz): 4.09 (m, 4H); 3.25 (t, J = 7.0 Hz, 2H); 1.80−1.46 (m, 6H);1.44−1.18 (m, 22H).

Synthesis of (12-Azidododecyl)phosphonic Acid. Trimethyl-silyl bromide (1.97 g, 12.9 mmol) was added to a solution of diethyl(12-azidododecyl)phosphonate (1.50 g, 4.7 mmol) in anhydrousdichloromethane (8 mL) under argon. The solution was stirredovernight at room temperature, and subsequently, the solvent wasremoved by rotary evaporation. Water (10 mL) was then added, andthe mixture was stirred for two hours. The white solid was filtered offand air-dried. (12-Azidododecyl)phosphonic acid (1.17 g, 93%) wasobtained as a white solid. 1H NMR (CDCl3, 400 MHz): 9.32 (br, 2H);3.26 (t, J = 6.8 Hz, 2H); 1.80−1.67 (m, 2H); 1.65−1.52 (m, 4H);1.40−1.22 (m, 16H). 13C NMR (CDCl3, 100 MHz): 51.4 (C−N3);29.5−28.8; 26.7. 31P NMR (CDCl3, 400 MHz): 36.9.

Synthesis of (11-Undec-1-ynyl)thiol. (11-Undec-1-ynyl)thiolwas synthesized from (11-undec-1-ynyl)thioacetate, which has beensynthesized following the synthesis pathway we have reportedpreviously.26 Then, 300 mg of (11-undec-1-ynyl)thioacetate weredissolved in 20 mL of methanol. The solution was degassedthoroughly and backfilled with N2. One milliliter of concentratedHCl was added dropwise, and the entire mixture was refluxed underN2 atm for 5 h. The reaction was then stopped by adding 20 mL of icecold water. The product was extracted twice with diethyl ether (20mL), and the organic phase was washed twice with water (20 mL) anddried over MgSO4. Rotary evaporation yielded a yellow oil. 1H NMR(CDCl3, 400 MHz): 2.52 (q, J = 7.3 Hz, 2H); 2.18 (dt, J = 6.8 and 2.6Hz, 2H); 1.94 (t, J = 2.6 Hz, 1H); 1.61 (m, 4H); 1.22−1.41 (m, 11H).13C NMR (CDCl3, 100 MHz): 85.6 (C terminal C−H); 67.9 (Calkyne); 39.1 (CH2−SH); 30.2−28.4 (6 CH2); 22.6 (CH2); 18.3(CH2); 14.0 (CH2).

Synthesis of Azide-Terminated Iron Oxide Nanoparticles(NP@N3). Iron stearate (Fe(stearate)2) (1.38 g, 2.2 × 10−3 mol) wasdissolved in docosene (20 mL) in the presence of oleic acid (1.24 g,3.3 × 10−3 mol). The mixture was kept at 110 °C for at least 4 h toavoid water residues and to completely dissolve the reactants. Thetemperature was then carefully raised to reflux with a heating rate of 5°C·min−1 and kept under reflux without stirring for 120 min under air.After cooling to room temperature, the black suspension was washed12 times with a mixture of hexane and acetone (v:v, 1:4) andcentrifuged (14 000 rpm, 10 min). The obtained nanoparticles coatedwith oleic acid (NP@OA) were easily suspended in (THF) at aconcentration of 1.67 mg/mL. Oleic acid was subsequently replaced by(12-azidododecyl)phosphonic acid (AP12N3) following direct ex-change. A solution of AP12N3 (15 mg) in THF (10 mL) was added to10 mL of the NP@OA suspension and stirred for 48 h at roomtemperature. Free molecules were removed by ultrafiltration (using a30 kD membrane, Millipore) in 60 mL of THF.

Preparation of Alkyne-Terminated Self-Assembled Mono-layer (SAM-CC). Ion sputtered gold substrates were cleaned underO2/H2 plasma for 2 min and were soaked in a 10 mM ethanolic

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solution of 11-(undec-1-ynyl)thiol at room temperature for 24 h. TheSAM was then rinsed with copious amounts of pure ethanol and useddirectly after drying under air.Nanoparticles Assembling. The assembling of nanoparticles by

microwave-assisted CuAAC click reaction was performed using anAnton Paar microwave device (Monowave 300) with a 10 mL vial byimmersing SAM-CC (5 × 5 mm2) in 5 mL of a solution of NP@N3 inTHF (0.67 mg/mL). Then, 0.5 mL (3.70 mmol) of triethylamine and6.5 mg (6.7.10−3 mmol) of CuBr(PPh3)3 were added. The MWCuAAC reaction was performed under a maximum temperature of 100°C, which was controlled by an infrared sensor, while the reaction vialwas cooled by compressed air flow. A maximum power of 50 W at afrequency of 2.45 GHz was applied to the reaction medium. Thereaction time was varied from 2 min to 1 h. The power, temperature,and pressure were recorded during the assembling reaction.Characterization Techniques. Transmission electron microscopy

(TEM), high resolution TEM (HRTEM), and electron diffraction(ED) were performed with a TOPCON model 002B TEM, operatingat 200 kV, with a point-to-point resolution of 0.18 nm. The sizedistribution was calculated from the size measurement of more than100 nanoparticles by using the Image J software. Granulometrymeasurements were performed on a nanosize MALVERN (nano ZS)apparatus for each NP suspension. Fourier transform infrared (FTIR)spectroscopy was performed using Digilab Excalibur 3000 spectropho-tometer (CsI beamsplitter) in the energy range 4000−400 cm−1.Scanning electron microscopy (SEM) was performed using a JEOL6700 microscope equipped with a field emission gun (SEM-FEG)operating at an accelerating voltage of 3 kV. Atomic Force Microscopy(AFM) was performed in the tapping mode using a Digital Instrument3100 microscope coupled to a Nanoscope IIIa recorder. Collected datawere analyzed with Nanotec WSXM software.35 Polarizationmodulation infrared reflection−absorption spectroscopy (PM-IRRAS) was performed on gold substrates after being immersed inthiol solution, using a IF66S Bruker spectrometer with a liquidnitrogen-cooled mercury cadmium telluride (MCT) detector. The X-ray photoelectron spectroscopy (XPS) measurements were carried outin an ultrahigh vacuum (UHV) setup equipped with a VSW ClassWAhemispherical electron analyzer (150 mm radius) with a multi-channeltron detector. A monochromated AlKα X-ray source (1486.6eV; anode operating at 240 W) was used as incident radiation. Thebase pressure in the measurement chamber was ∼1 × 10−9 mbar. XPspectra were recorded in the fixed transmission mode using passenergy of 22 eV resulting in an overall energy resolution better than0.4 eV. Prior to individual elemental scans, a survey scan was taken forall the samples to detect all of the elements present. The CASA XPSprogram with a Gaussian−Lorentzian mix function and Shirleybackground subtraction was employed to deconvolute the XP spectra.Magnetic curves were recorded at 300 and 5 K by applying a magneticfield in the plane of the substrate by using a superconducting quantuminterference device (SQUID) magnetometer (Quantum DesignMPMS SQUID-VSM dc magnetometer).

■ RESULTS AND DISCUSSIONThe assembling process operating by click chemistry wasconducted between azide-terminated NPs (NP@N3) andalkyne-terminated SAM (SAM-CC) (Figure 1). Iron oxideNPs coated with oleic acid were prepared by the thermaldecomposition of iron stearate in docosene (bp 365 °C) andwere further functionalized by (12-azidododecyl)phosphonicacid (AP12) following a ligand exchange procedure.9,26 NPsexhibiting a narrow size distribution centered at 19.8 ± 1.6 nmwere obtained and formed a highly stable suspension intetrahydrofurane (THF) according to TEM micrographs andgranulometry measurement, respectively. Prior to the assem-bling reaction, the alkyne terminated SAM was prepared by theadsorption of (11-mercaptoun)dec-1-yne in ethanol on a goldsubstrate after plasma cleaning. This molecule was synthesizedby performing the acidic deprotection of the corresponding

thioacetate derivative.26 The assembling of thiol molecules as aSAM was confirmed by the thickness measured by ellipsometry(1.1 ± 0.1 nm) and also by PM-IRRAS spectroscopy and XPS.In contrast to the very few studies that report only on surfacefunctionalization by microwave-assisted CuAAC reaction fromCu(II) catalyst associated to a reducing agent (ascorbicacid),31−33 the assembling of NPs was performed by dippingthe SAM-CC in a mixture of the NP@N3 suspension in THF,triethylamine, and the CuBr(PPh3)3 catalyst, which enable thereaction to proceed in nonaqueous, aprotic solvents.34 TheCuAAC reaction was carried out in a sealed tube undermicrowave irradiations with a maximum power of 50 W withthe aim not to exceed 100 °C. More details related to thesyntheses and assembling processes are available in theexperimental section of the Supporting Information.The assembling of NP@N3 on SAM-CC was characterized

by scanning electron microscopy (SEM) (Figure 2a).

Representative micrographs recorded on different areas showthe high efficiency of the microwave-assisted CuAAC clickreaction. NPs cover the whole surface of the SAM with adensity of 1470 ± 14 NP/μm2 after 1 h of reaction, which,when taking into account the adsorption process, is rather closeto the maximum theoretical value (1820 NP/μm2) calculatedfor compact assemblies. These results were confirmed by AFMimages and the corresponding cross-sectional profile, which

Figure 1. Schematic representation of the MW-assisted CuAAC clickreaction between azido-terminated NPs and alkyne-terminated SAMs,which result in the formation of irreversible triazole linkages.

Figure 2. (a) SEM image of NPs assembled on SAM after 1 h of MW-assisted CuAAC click reaction. (b) Density in NPs assembled on SAMas a function of the reaction time. (c) Height AFM images and (d)cross-section profile corresponding to the line in panel c.

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shows that NPs were assembled in a well-defined and densemonolayer (Figure 2c,d). In addition, extensive washings withTHF and exposure to ultrasounds do not affect the structure ofthe NP assembly, which shows the irreversible formation ofhighly stable covalent triazole linkages between NPs and theSAM.Beyond the fact that NPs were assembled with a very high

density, a very important point is that the microwave-assistedassembling reaction is dramatically faster than using conven-tional heating conditions for which the maximum density wasobtained at 60 °C after 48 h.26 Because of the geometricconsiderations, unreacted alkyne and azide groups are expectedto remain at the surface of SAM and NPs, respectively, after theassembling reaction. Therefore, surface analysis methods suchas PM-IRRAS or XPS cannot reveal with certainty theoccurrence of the assembling reaction by CuAAC. With theaim to gain better insight on this point, we performedadditional counter experiments that indirectly prove theoccurrence of the cycloaddition reaction. First, the reactionwas performed identically as the main experiment withoutadding the Cu catalyst and resulted in the nondeposition ofNPs on SAM by SEM (see Supporting Information). Althoughthe microwave activation is highly efficient, it cannot overpassthe role of the Cu catalyst. Second, the reaction was performedin the presence of methyl-terminated SAM, which alsoprohibited the assembling of NPs. These two experimentsdemonstrate the requirement of both Cu catalyst and alkynegroups at SAM surface to assemble NP@N3 by the CuAACclick reaction.More details on the kinetics of the microwave-assisted

CuAAC reaction have been obtained by performing theexperiment for different durations. Reaction times shorterthan one hour resulted in lower NP densities (see SupportingInformation). Plotting the NP density as a function of timeshows the nonlinear increase of the kinetics (Figure 2b).Indeed, the NP assembling does not happen within the first fewminutes. A minimum incubation time is necessary for ironoxide NPs and gold surface to accumulate energy, whichinduces local increase in temperature. Between 2 and 5 min, theassembling reaction starts and the density increases faster toreach 50% of the maximum value after 10 min. These resultsare correlated to the increase in temperature, which reaches itsmaximum (100 °C) only after 5 min of irradiation (seeSupporting Information). Although 100 °C is necessary toobtain the maximum density in NPs after 1 h of reaction, theclick reaction can also occur at lower temperature. For longertimes, the kinetics decrease, which is related to the loweramount of empty space at the SAM surface that NPs canoccupy. More generally, NPs that are suspended in solution aresubmitted to the Brownian motion, which results on theirrather low mobility and statistic adsorption. Whatever theefficiency of the microwave-assisted CuAAC reaction, theprobability of azide terminated NPs to react with free alkynegroups at SAM surface decreases as long as the NP densityincreases on SAM. In addition, the time needed (1 h) to reach amaximum density is rather long in comparison to studies thatdeal with the reaction of molecules with functional groups atthe SAM surface by using the same reaction, which can beaccomplished within a couple of minutes.28 This findingsupports the argument of the low mobility of NPs in solution incomparison to molecules that are far smaller. Such an increaseof reaction time has been also noticed for increasing sterichindrance of molecules.31

Although the assembling of NPs on SAM clearlydemonstrates that organic functionalities are preserved uponthe MW-assisted CuAAC reaction, we investigated the structureof SAM and NPs before and after exposure to MW irradiation.The reaction was performed without Cu catalyst to maintainboth SAM and NPs under the same conditions. All spectrarelated to the following measurements can be seen in theSupporting Information. The composition of SAM wasanalyzed by XPS. Both C1s spectra exhibit a very similarmain peak at 284.6 eV with a slight asymmetry toward to thehigh binding energy side. The main peak is related to sp3

carbon atoms in alkylene chains,36 while the peak asymmetry iscaused by shake up satellite peaks and/or contribution of sp1

(alkyne) species36 and carbon connected to oxygen species.The S 2p spectra have been fitted by two S 2p3/2,1/2 doublets.For each S 2p doublet, a 1.3 eV spin orbit splitting and a 2:1intensity ratio between the 3/2 and 1/2 components wasused. The first doublet at a binding energy of 161.9 ± 0.1 eV(S 2p3/2) is related to thiol groups bound to the gold surface(S−Au).37 The second doublet at a higher BE of 163.6 ± 0.1eV is attributed to some free thiol groups (unbound species).37

Moreover, the S/Au and S/C intensity ratios were calculated0.09 ± 0.01 and 0.1 ± 0.01 and are practically unaffected by theMW process, indicating that microwave irradiation does notmodify the composition of SAM.The SAM structure was also investigated by PM IRRAS.

While νCC and νCC−H vibration modes33,36 corresponding toalkyne terminal groups were not observed as reportedearlier,38,39 the νCH2 vibration modes are centered to 2918and 2854 cm−1, which demonstrates that alkylene chains are inthe all-trans conformation and remain tightly packed.26

However, granulometry and FTIR spectroscopy have beenperformed on NPs before and after exposure to MWirradiation. Similar spectra proved the stability of azideterminated NPs in the reaction medium.Finally, magnetic measurements have been performed on the

assembly obtained after 1 h of MW-assisted CuAAC reaction.Magnetization was recorded against a magnetic field in the −7to +7 T range (Figure 3). Curves recorded at 300 and 5 Kdisplay hysteresis loops with coercive fields (HC) of 50 and 400Oe, respectively. These curves correspond to the ferrimagneticbehavior of spinel iron oxide NPs with sizes of 20 nm, whichare featured by a rather high magnetic anisotropy incomparison to smaller iron oxide NPs that are super-

Figure 3. Magnetization recorded at 300 and 5 K against an appliedfield for NPs assembled after 1 h of MW assisted CuAAC clickreaction. The inset depicts the full curves.

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paramagnetic.40 As a consequence, SEM shows NPs toassemble in 1D chains after 10 min of reaction (see SupportingInformation). This behavior may be correlated to strong andcollective dipolar interactions, which may participate in theassembling reaction. More generally, these results show that themagnetic properties of these NPs are similar to others reportedin the literature40 and do not seem to be affected by themicrowave irradiations, even when the reaction is prolonged forone hour.

■ CONCLUSIONSTo summarize, the major finding of this study is the unseen andvery fast assembling of NPs on SAMs by performing themicrowave-assisted CuAAC click reaction. Beyond the fact offormation of dense assemblies of NPs with a well-definedmonolayer structure, this process promotes the enhancement ofthe kinetics of the reaction, reducing the reaction time fromdays to minutes. While the elevation of temperature of thereaction media is rather low in comparison to conventionalexperimental conditions, the mechanism of the reaction isexpected to proceed through a local increase of the temperatureat the interface between iron oxide NPs and gold substrate.This point is currently under investigation. Fortunately,microwave irradiation does not affect the functionalities andstructures of both SAMs and NPs. Notably, the MW-assistedCuAAC click reaction was demonstrated to be carried out forthe first time in the presence of a Cu(I) catalyst and alkyne-thiolate SAMs on a gold surface, which enables this assemblingmethod to proceed for hydrophobic NPs as stable suspensions.Other advantages of this assembling method are the absence ofside-products and that no purification process is required. Itspotential adaptability to a wide range of nanoparticles andsurfaces also renders it very promising to be used as a generalassembling technique.

■ ASSOCIATED CONTENT*S Supporting InformationMolecule synthesis. Structural analysis of nanoparticles beforeand after exposure to microwave irradiation. SEM micrographs,FTIR, PM-IRRAS, and XPS spectra. Experimental data. Thismaterial is available free of charge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*(B.P.P.) E-mail: benoit.pichon@unistra.fr. Tel: 0033 (0)3 8810 71 33. Fax: 0033 (0)3 88 10 72 47.Present Address∥Institut Neel, UPR2940 CNRS/UJF, 25 rue des Martyrs,38042 Grenoble, France.Author ContributionsThe manuscript was written through contributions of allauthors. All authors have given approval to the final version ofthe manuscript.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSProf. Laurent Douce and Dr. Julien Fouchet for providing theaccess to the microwave reactor and fruitful discussions.Funding was provided by Direction generale de l’armement(DGA) and region Alsace.

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