Direct Functionalization of Nanodiamond Particles Using Dopamine

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Direct Functionalization of Nanodiamond Particles Using Dopamine Derivatives Alexandre Barras,† Jo€el Lyskawa,‡ Sabine Szunerits,† Patrice Woisel,‡ and Rabah Boukherroub*,† †

Institut de Recherche Interdisciplinaire (IRI, USR CNRS 3078), Universite Lille 1, Parc de la Haute Borne, 50 Avenue de Halley, BP 70478, 59658 Villeneuve d’Ascq, France ‡ Unite Materiaux et Transformations (UMET, UMR CNRS 8207), Equipe Ingenierie des Systemes Polymeres (ISP), Universite Lille 1, 59655 Villeneuve d’Ascq, France

bS Supporting Information ABSTRACT: The article reports on the strong linking of dopamine derivatives as a simple and a versatile strategy for the surface functionalization of hydroxyl-terminated nanodiamond (ND OH) particles. Azide- (ND N3) or poly-N-isopropylacrylamide-terminated (ND PNIPAM) particles were obtained from ND OH particles through the reaction with the corresponding dopamine derivatives. The azide-terminated ND particles were further derivatized with a fluorescent probe, alkynyl-pyrene, via copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition. The modified ND particles were characterized using transmission Fourier transform infrared (FTIR) spectroscopy, UV vis spectroscopy, electrochemical measurements, thermogravimetric analysis (TGA), and particle size measurements. The surface loading of ND particles with dopamine was estimated from TGA and UV vis spectroscopy and was found to be around 0.27 mmol g 1. Because of its simple, gentle nature and versatility, the chemistry developed in this work can be used as an avenue for the preparation of functional nanodiamond particles for various applications.

1. INTRODUCTION Nanodiamond (ND) particles have emerged in the last years as an attractive alternative carbon-based material next to carbon nanotubes, fullerenes, and carbon nanoparticles for biomedical applications.1,2 Properties such as optical transparency, high surface area, and chemical inertness, together with proven biocompatibility,3 have made ND particles a competitive alternative to other nanoparticles. A requirement in any application driven by ND particles is the integration of specific surface functions in a simple and specific manner.4 Various strategies for the functionalization of ND particles have thus been developed. The silanization reaction5,6 has been reported next to Williamson etherification7 or the direct reaction with aryldiazonium salts8,9 as strategies to link functional groups covalently onto ND particles. ND particles carrying alkyl, amino, and amino acid groups were prepared by the nucleophilic displacement of fluorine on fluorinated ND particles, which were previously incorporated using an elemental fluorine/hydrogen mixture at temperatures varying from 150 to 470 °C. 10 The surface graphitization of ND at 1200 °C, followed by ultrasonication and microwave-initiated free radical copolymerization, resulted in the surface grafting of oligomers with various functionalities, including C(dO)OCH3, COOH, NH2, and aliphatic moieties.11 The reaction of hydrogen-/deuterium-terminated ND particles with neat di-tertamyl peroxide (DTAP) at 120 °C was successfully used for the incorporation of fragments of di-tert-amyl peroxide through ether r 2011 American Chemical Society

linkages. Multilayers of DTAP were also prepared by repeated exposure of the substrate to this reagent.12 In the research for simple and versatile strategies to functionalize ND particles and encouraged by the successful demonstration of “click” chemistry to bind alkyne-terminated compounds covalently to azide-terminated, boron-doped diamond,13 15 we have recently used “click” chemistry to attach acetylene-bearing molecules covalently to azide-terminated ND particles.16,17 ND particles functionalized with terminal azido groups were prepared by a simple coupling reaction between amine-terminated ND particles and 4-azidobenzoic acid in a single step. The copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition between the azide terminal groups on the ND particles and 1-alkynes was then used as a facile, efficient way to link various functional molecules and polymers17 covalently onto the ND surface. In an attempt to broaden the scope of ND particles functionalization, we report here a simple and versatile strategy for the surface derivatization of hydroxyl-terminated nanodiamond (ND OH) particles using dopamine (DA) derivatives bearing terminal azide groups (DA N3) or poly-N-isopropylacrylamide (DA PNIPAM), a thermally responsive polymer. Dopamine (DA), chemically known as 4-(2-aminoethyl)benzene-1,2-diol, is one of the crucial catecholamine neutrotransmitters Received: July 7, 2011 Revised: September 2, 2011 Published: September 02, 2011 12451

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Langmuir that is widely distributed in mammalian brain tissues.18 Like adrenaline, it serves as a chemical messenger and plays a pivotal role in the functions of the cardiovascular, hormonal, renal, and central nervous systems. Indeed, abnormal levels of DA have been linked to Parkinson’s disease and schizophrenia.19 In addition, the biomimetic dopamine has sparked great interest as an anchor for the functionalization of metal oxide surfaces because of the stability and strength of the resultant fivemembered metallocycle chelate. This property was exploited for the introduction of functional groups onto metal oxide surfaces such as TiO2, SiO2, and Nb2O5.20 24 Several studies have also been conducted on the surface functionalization of ZnO and Fe2O3 nanoparticles with dopamine derivatives. Colloidal ZnO nanoparticles were successfully modified with catechol anchoring group containing dye molecules and used for photochemical studies.25 Water-soluble and dispersible Fe2O3 nanoparticles were prepared by functionalization with PEGdopamine derivatives as high-affinity anchor groups26 or through the dopamine ligand-exchange process.27 Goldmann et al.28 reported a versatile strategy for the preparation of fluorescent, water-soluble Fe2O3 nanoparticles using an alkyne-modified dopamine anchor and a “click” chemistry approach with fluorescent azide derivatives. A multifunctional polymer based on dopamine was linked to the surfaces of Fe2O3 nanoparticles by Shukoor et al.29 This polymer contained functional nitrilotriacetic acid (NTA) groups allowing the immobilization of a Histagged enzyme. In a similar way, the NTA-terminated DA anchor was immobilized onto magnetic nanoparticles and used for protein separation and purification.30,31 In this article, we demonstrate that dopamine derivatives bearing an azide or a thermally responsive polymer (PNIPAM) moiety can be covalently linked to hydroxyl-terminated nanodiamond particles in a simple manner. The modified particles with dopamine bearing an azide functional group were further used for “clicking” alkynyl-terminated molecules. The modified ND particles were characterized using Fourier transform infrared (FTIR) spectroscopy, UV vis spectroscopy, cyclic voltammetry, thermogravimetric analysis (TGA), and dynamic light scattering (DLS).

2. EXPERIMENTAL SECTION 2.1. Materials. Acetonitrile (99.8%, CH3CN), dichloromethane (g99.8%, CH2Cl2), dimethylsulfoxide (DMSO), copper(I) iodide (CuI), absolute ethanol (g99.8%, EtOH), tetrabutylammonium hexafluorophosphate (TBAPF6), and triethylamine (g99.5%, TEA) were obtained from Sigma-Aldrich. All reagents and solvents were used without further purification. N-Isopropylacrylamide (NIPAM, 99% Acros Organics) was recrystallized from hexane. Milli-Q water (18 MΩ) was used for all experiments. Hydroxyl-terminated nanodiamond (ND OH) particles were purchased from International Technology Center (Raleigh, NC, USA) and display a primary average particle size of 4.0 nm. N-Propargyl1-pyrenecarboxamide was synthesized as reported by Barras et al.16 DA N3 and well-defined DA PNIPAM (Mn(RMN) = 12 500, PDI = 1.27) were synthesized according to refs 24 and 32. 2.2. Functionalization of Nanodiamond Particles. 2.2.1. Pretreatment of Nanodiamond Particles. As-received ND OH particles were treated by the bead-assisted sonic disintegration process (BASD) to break down the persistent particle agglomerates.5 Briefly, the reactor was charged with 40 g of zirconia beads (Tosoh Co., YTZ Grinding Media, 0.05 mm), 200 mg of ND OH particles, and 20 mL of DMSO. An ultrasonicator equipped with a horn-type sonotrode

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(Branson, Ultrasonic-Homogenizer Sonifier II W-450 with a 4.8 mm microtip) was used for BASD (2  60 min; amplitude, 70%; pulse on/ off, 0.3 s/0.2 s). During BASD, the slurry in the vial was cooled with ice. Zirconia beads were then removed by centrifugation at 10 000 rpm. Finally, the ND OH particles were purified by consecutive washing/ centrifugation cycles in CH3CN and oven dried at 50 °C for 24 h. The drying step was performed prior to FTIR and UV vis analysis. 2.2.2. Surface Functionalization of Nanodiamond Particles with Dopamine Derivatives. A dopamine derivative (16.8 mg) bearing an azide moiety, DA N3, was added to a suspension of ND OH particles (5 mg mL 1) in CH3CN (8 mL). The resulting suspension was sonicated in an ice bath with an ultrasonicator equipped with a horn-type sonotrode (amplitude, 70%; continuous mode) for three 10 min periods and then stirred at room temperature for 24 h. The functionalized ND particles were separated by centrifugation at 10 000 rpm, purified through four consecutive washing/centrifugation cycles at 10 000 rpm with CH3CN, and finally oven dried at 50 °C for 24 h. Similarly, 27.5 mg of a dopamine derivative bearing a polymer moiety, DA PNIPAM (Mn(RMN) = 12 500, PDI = 1.27) was added to a suspension of ND OH particles (2.5 mg mL 1) in CH3CN (8 mL). The resulting suspension was sonicated in an ice bath with an ultrasonicator equipped with a horn-type sonotrode (amplitude, 70%; pulse on/off, 0.3 s/0.2 s) for 10 min and then stirred at room temperature for 24 h. The functionalized ND particles were separated by centrifugation at 10 000 rpm, purified through four consecutive washing/centrifugation cycles at 10 000 rpm with CH3CN, and finally oven dried at 50 °C for 24 h. 2.2.3. Reaction of Nanodiamond Particles with Benzyl-PNIPAM. In a control experiment, 27.5 mg of Bz-PNIPAM (Mn(RMN) = 12 750, PDI = 1.10), a polymer without a catechol anchor, was added to a suspension of ND OH particles (2.5 mg mL 1) in CH3CN (8 mL). The resulting suspension was sonicated in an ice bath with an ultrasonicator equipped with a horn-type sonotrode (amplitude, 70%; pulse on/off, 0.3 s/0.2 s) for 10 min and then stirred at room temperature for 24 h. The functionalized ND particles were separated by centrifugation at 10 000 rpm, purified through four consecutive washing/centrifugation cycles at 10 000 rpm with CH3CN, and finally oven dried at 50 °C for 24 h. 2.2.4. “Click” Reaction on Azide-Terminated Nanodiamond Particles. The azide-terminated (ND N3) particles (10 mg) were dispersed in anhydrous CH3CN (10 mL) and sonicated for 30 min. The “click” reaction was performed by the addition of N-propargyl-1-pyrenecarboxamide (2 mM), CuI (3 mM), and TEA (40 mM) to the ND N3 particles and subsequent stirring for 24 h at room temperature. The resulting particles were separated by centrifugation at 10 000 rpm, purified through three consecutive washing/centrifugation cycles at 10 000 rpm with CH3CN and CH2Cl2, and finally oven dried at 50 °C for 24 h. The traces of copper remaining on the nanoparticles after “click” chemistry can be easily removed by rinsing with a 1 mM aqueous solution of EDTA.

3. INSTRUMENTATION 3.1. Fourier Transform Infrared Spectroscopy. Fourier transform infrared (FTIR) spectra were recorded using a PerkinElmer Spectrum One FTIR spectrometer with a resolution of 4 cm 1. Dried ND powder (1 mg) was mixed with KBr powder (100 mg) in an agate mortar. The mixture was pressed into a pellet under a 10 ton load for 2 4 min, and the spectrum was recorded immediately. Sixteen accumulative scans were collected. The signal from a pure KBr pellet was subtracted as the background. 3.2. UV Vis Spectroscopy. UV vis measurements were carried out on a Perkin-Elmer Lambda 950 dual-beam spectrophotometer 12452

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Scheme 1. Illustration of ND OH Particle Functionalization Using DA N3, DA PNIPAM, and Subsequent “Clicking” of the Alkynyl Pyrene onto the Azide-Terminated ND Particles

operating at a resolution of 1 nm in the region of 250 800 nm. Functionalized ND particles were dispersed in CH 3 CN (20 μg mL 1 ). Unmodified ND OH particles were used as the background. 3.3. Fluorescence Measurements. The fluorescence emission spectrum of the fresh solution of ND Py particles (20 μg mL 1 in CH3CN) was collected from a Leica TCS SP5 X MP confocal microscope system (excitation at 405 nm). 3.4. Cyclic Voltammetry. Cyclic voltammetry (CV) measurements were performed using an Autolab potentiostat 20 (Eco Chemie, Utrecht, The Netherlands) in a classical three-electrode configuration. The ITO working electrode (A ≈ 0.12 cm2) was sealed against the bottom of a single-compartment electrochemical cell by means of a rubber O-ring. Electrical contact was made to a copper plate through the bottom of the ITO coated with an adhesive silver tape. Platinum and saturated calomel (SCE) electrodes were used as counter and reference electrodes, respectively. CVs were recorded in CH3CN/TBAPF6 (0.1 M) solution and after the addition of 200 μL of nanodiamond particles suspended in CH3CN (2 mg mL 1) at a scan rate of 50 mV s 1. 3.5. Thermogravimetric Analysis. Thermogravimetric analysis (TGA) measurements were carried out in Al2O3 crucibles in

a nitrogen atmosphere at a heating rate of 10 °C min 1 using a TA Instruments Q50 thermogravimetric analyzer. 3.6. Particle Size Measurements. ND suspensions (20 μg mL 1) in water were sonicated in cold or hot water for 30 min. Then the particle size of the ND suspensions was measured at different temperatures (20 or 50 °C) with an equilibration time of 15 min using a Zetasizer Nano ZS (Malvern Instruments S.A., Worcestershire, U.K.) in 173° scattering geometry.

4. RESULTS AND DISCUSSION The agglomeration of ND particles in aqueous solutions is a commonly encountered phenomenon. Deagglomeration of the as-received hydroxyl-terminated ND (ND OH) particles, produced via detonation synthesis, can be achieved through a beadassisted sonic disintegration process (BASD) as reported by Liang et al.5 The resulting ND OH particles are 94 ( 7 nm in size. The covalent linking of azide- and PNIPAM-terminated dopamine derivatives (DA N3 and DA PNIPAM) was achieved by mixing a solution of the dopamine derivative and ND particles in CH3CN, sonication with a horn-type sonotrode for short time periods, and then stirring at room temperature for 24 h (Scheme 1). FTIR spectra of the ND OH particles before and after chemical modification with dopamine derivatives are displayed 12453

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Figure 1. Transmission FTIR spectra of ND OH before and after functionalization with DA N3 and DA PNIPAM.

in Figure 1. The transmission FTIR spectrum of the starting ND OH particles is dominated by two broad peaks at 3400 and 1627 cm 1. The broad band between 3000 and 3600 cm 1 is assigned to the vibration of hydroxyl groups or/and adsorbed water molecules on the surfaces of the particles, and the large peak at 1627 cm 1 is most likely due to OH deformation modes of hydroxyl groups and adsorbed water. After the reaction of ND OH particles with DA N3 in CH3CN, additional peaks appear at 2100 and 1718 cm 1, consistent with the main vibrational modes of DA N3 (Supporting Information, Figure S1). Other peaks in the region of the C H vibration at 2938 cm 1 are also present in the FTIR spectrum. The presence of intense peaks at 2100 and 1718 cm 1, characteristic of νas(N3) and ν(CdOester) stretching modes, respectively, suggests the success of the grafting reaction. The bands at 1650 and 1555 cm 1 associated with amide(I) and amide(II) vibrations, respectively, overlap with the peak of the starting ND OH at 1627 cm 1. From the comparison of the relative intensity of the band at 2100 cm 1, associated with the azido group, the coupling reaction appears to be more effective when the reaction is performed in acetonitrile rather than in methanol or dimethylformamide. Particle size measurements indicate a slight increase in the particle agglomerate size to 122 nm after the modification of ND OH with DA N3. After the reaction of ND OH particles with DA PNIPAM in CH3CN, additional peaks are found in the regions between 2800 cm 1 and 3000 and 1450 1650 cm 1 (Figure 1), consistent with the main vibrational modes of DA PNIPAM (Supporting Information, Figure S2). The FTIR transmission spectrum of ND PNIPAM exhibits absorption peaks characteristic of PNIPAM at 3291 (N H stretching), 2974 ( CH3 asymmetric stretching), 2935, 2876 ( CH2 stretching modes), 1639 and 1545 (CdO and CNH vibrations of the amide, respectively), and 1460 cm 1 (methylene bending mode). The presence of these peaks suggests the chemical grafting of the PNIPAM moiety on the ND OH surface. Even though FTIR spectroscopy strongly suggests the presence of the dopamine derivatives on the ND OH particles, the nature of the bonding (chemical vs physical) is not clear. To exclude the eventual physisorption of DA PNIPAM polymer on

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the ND particles, a control experiment consisting of the reaction of ND OH particles with well-defined benzyl-PNIPAM (Mn(RMN) = 12 750, PDI = 1.10), under the same conditions as with DA PNIPAM, was performed. After the usual rinsing steps, FTIR spectroscopy indicates the absence of vibrational peaks in the region between 1450 and 1650 cm 1 (Supporting Information, Figure S3), a region characteristic of the main vibrational modes of PNIPAM. The result is consistent with the formation of strong bonds between the ND OH particles and the dopamine derivatives with a negligible contribution from physisorption. The DA N3-modified ND particles were further reacted with a fluorescent molecule bearing an alkynyl group, N-propargyl-1pyrenecarboxamide, in a “click” chemistry approach using the copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (Scheme 1). The presence of a pyrene moiety on the diamond particle surface was first monitored by transmission FTIR spectroscopy. The cycloaddition of N-propargyl-1-pyrenecarboxamide to the azide terminal groups is evidenced by the complete disappearance of the νas(N3) stretching mode at 2100 cm 1 (Figure 2A). The FTIR transmission spectrum of ND Py exhibits absorption peaks characteristic of pyrene at 3045, 1515, 843, and 711 cm 1. The peak at 843 cm 1 is most likely due to the pyrene ring deformation mode, and the broad band at 3045 cm 1 is attributed to the aromatic C H stretching vibration. In addition, the successful incorporation of pyrene moieties on the ND N3 particles was further confirmed by UV vis spectroscopy and fluorescence measurements. Figure 2B shows the UV vis absorption spectrum of pyrene-terminated ND dispersed in CH3CN (20 μg mL 1). It displays absorption features at 276 and 342 nm, in accordance with the absorption peaks recorded on free N-propargyl-1-pyrenecarboxamide in CH3CN (inset in Figure 2B). Therefore, in using the calibration curve (Supporting Information, Figure S4), the surface loading of functionalized ND with the pyrene moiety was estimated to be Γ ≈ 0.27 mmol g 1 (Supporting Information). Furthermore, the pyrene monomer is a well-known fluorescent probe that emits light at around 400 nm. When two pyrene molecules are in close proximity, they form an excimer (excitedstate dimer) with a characteristic emission band at around 480 nm. The fluorescence emission spectrum of a fresh solution of nanodiamond particles (20 μg mL 1 in CH3CN) derivatized with the pyrene fluorescent probe showed strong fluorescence emission at 480 nm upon excitation at 405 nm (Figure 2C). This emission peak is most likely due to the formation of the pyrene excimer. The formation of pyrene excimers was also suggested with pyrene-functionalized gold and ruthenium nanoparticles.33,34 For example, Wang et al.33 synthesized gold nanoparticles capped with pyrene-terminated long-chain alkanethiols (10-(1-pyrenyl)-6-oxo-decanethiol and 17-(1-pyrenyl)-13oxo-heptadecanethiol) and found that the intensity of the excimer fluorescence increased with the increasing concentration of the gold nanoparticles (from 3  10 5 to 1.5  10 2 mg/mL in CH2Cl2). This was accounted for by the increasingly close proximity of pyrene moieties between neighboring gold nanoparticles that favored the formation of pyrene excimers. All of these observations along with the absence of a residual signal from azido groups in the FTIR spectra clearly confirm the efficient ligation between azido groups on ND particles and alkyne-containing compounds using “click” chemistry. The ND OH particles derivatized with DA N3 were further characterized using cyclic voltammetry. Dopamine can be readily 12454

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Figure 2. (A) Transmission FTIR spectra of ND N3 before and after “clicking” alkynyl-pyrene. (B) UV vis spectrum of ND Py particles in CH3CN. (Inset) UV vis spectrum of N-propargyl-1-pyrenecarboxamide in CH3CN at 50 μM. (C) Fluorescence emission spectrum of ND Py particles upon excitation at 405 nm.

Figure 3. (A) Cyclic voltammogram of an ITO electrode immersed in CH3CN/TBAPF6 (0.1 M)/10 mM DA N3. (B) Cyclic voltammogram of an ITO electrode immersed in CH3CN/TBAPF6 (0.1 M) in the presence of 200 μL of a suspension of 2 mg mL 1 ND N3 at a scan rate of 50 mV s 1.

oxidized electrochemically, and this process has been largely used in the literature for the analytical detection of dopamine in solution.35 37 Although its electro-oxidation seems to be complicated, cyclic voltammetry can nevertheless be used to characterize dopamine-modified ND nanoparticles.38,39 Figure 3A shows the cyclic voltammogram of a CH3CN solution containing

0.1 M TBAPF6 and 10 mM of the starting material, DA N3, recorded on an indium tin oxide (ITO) electrode. The dopamine derivative shows an irreversible oxidation wave with an anodic peak potential at Ep,ox = 1.46 V vs SCE (DA N3). This oxidation peak corresponds to the two-electron oxidation of dopamine to dopaquinone, which is reduced in part back to dopamine at 12455

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All of these thermogravimetric analyses suggest a strong link between the catechol anchor derivatives and the ND OH surface. Finally, we have investigated the solution-phase properties of the ND PNIPAM particles. Indeed, PNIPAM, a thermoresponsive polymer, has a low critical solution temperature (LCST) in aqueous solution of around 32 °C.40 This polymer is hydrophilic below the LCST but becomes hydrophobic above that temperature. Figure 5 shows the particle size distribution of thermoresponsive ND PNIPAM particles at 20 °C (distribution 1) and 50 °C (distribution 2). Interestingly, below 35 °C the ND PNIPAM particles exhibit good dispersion in water and form small aggregates with a particle size of ∼90 nm. Above 35 °C (T > LCST), the particle size increases abruptly to ∼340 nm because of the aggregation of the hydrophobic ND particles. Figure 4. Thermogravimetric analysis (TGA) of (a) ND OH, (b) ND N3, (c) ND Pyr, and (d) DA N3.

Figure 5. Particle size distribution of ND PNIPAM as a function of the temperature cycle (20 50 and 50 20 °C) measured in water by DLS: 1 and 2 correspond to particle size distributions recorded after a first cooling/heating cycle at 20 and 50 °C; 3 and 4 correspond to particle size distributions recorded after a second heating/cooling cycle at 20 and 50 °C; and 5 is the particle size distribution measured after cooling back to 20 °C.

Ep,red = 0.3 V vs SCE (DA N3). In the case of ND modified with the same dopamine ligand (Figure 3B), the peak potential is shifted to more negative values (Ep,ox = 1.31 V vs SCE). To gain more insight on how the dopamine derivatives are linked to the ND OH surface or the strength of the bonding, thermogravimetric (TGA) analysis of the ND particles before and after derivatization was carried out (Figure 4). The TGA thermogram of the as-received ND OH particles indicates that they are stable up to 600 °C without any apparent mass loss. Thermogravimetric analysis of the modified ND particles with DA N3 and then by “click” chemistry shows their decomposition at temperatures above 250 °C. At this temperature, more than 50% of DA N3 was decomposed. The weight loss of ND N3 between 200 and 500 °C corresponding to the removal of organic groups is around ∼6.1%. Therefore, the surface loading of functionalized ND with azide groups was found to be Γ ≈ 0.15 mmol g 1. This value is slightly lower than that obtained from the UV vis measurements and comparable to that reported for ND functionalized with oxyhexanol groups (0.13 mmol g 1).7

5. CONCLUSIONS The chemical functionalization of nanodiamond particles with catechol anchor derivatives has been successfully achieved. The technique reported in this work is straightforward and allows the introduction of various functional groups on the ND surface in a single step. Although the exact nature of the bonding is not clear, thermogravimetric analysis supports a very strong linking of the dopamine derivatives to the ND particles surface. From UV vis measurements, a surface loading of 0.27 mmol g 1 was estimated. This is comparable to the reported data on ND particles derivatization using different routes. Because of the versatility of the catechol anchor and the ease of synthesis of dopamine derivatives bearing different functional groups, the strategy proposed in this work can be used as a general platform for the preparation of functional ND nanoparticles for various applications. ’ ASSOCIATED CONTENT

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Supporting Information. Transmission FTIR spectra of DA N3, ND N3, DA PNIPAM, ND PNIPAM, ND OH, and ND PNIPAM. Calibration curve of N-propargyl1-pyrenecarboxamide in CH3CN. Estimation of pyrene loading on pyrene-terminated ND particles from UV vis measurements. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Tel: +33 3 62 53 17 24. Fax: +33 3 62 53 17 01.

’ ACKNOWLEDGMENT We thank Dr. Frederic Cazaux (Universite de Lille 1, Unite Materiaux et Transformations, UMR CNRS 8207) and Dr. Laurent Heliot and Dr. Corentin Spriet (Institut de Recherche Interdisciplinaire, Plate-forme d’Imagerie et Biophotonique Cellulaire Fonctionnelle, USR CNRS 3078) for technical support with TGA and fluorescence measurements, respectively. The Centre National de Recherche Scientifique (CNRS) and the Nord Pas de Calais region are acknowledged for financial support. 12456

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dx.doi.org/10.1021/la202571d |Langmuir 2011, 27, 12451–12457