Letter pubs.acs.org/NanoLett
Hair Fiber as a Nanoreactor in Controlled Synthesis of Fluorescent Gold Nanoparticles Shrutisagar D. Haveli,†,‡ Philippe Walter,*,‡ Gilles Patriarche,§ Jeanne Ayache,∥ Jacques Castaing,‡ Elsa Van Elslande,‡ Georges Tsoucaris,‡ Ping-An Wang,†,‡ and Henri B. Kagan† †
Institut de Chimie Moléculaire et des Matériaux d’Orsay, ICMMO, CNRS UMR 8182, Université Paris-Sud, 15, rue Georges Clemenceau, 91405 Orsay cedex, France ‡ Laboratoire d’archéologie moléculaire et structurale, LAMS, CNRS UMR 8220, Université Pierre et Marie Curie, 3 rue Galilée, 94200 Ivry-sur-Seine, Paris, France § Laboratoire de Photonique et Nanostructures, CNRS UPR 20, route de Nozay, 91460 Marcoussis, France ∥ Institut Gustave Roussy, CNRS UMR 8126 Signalisation, Noyaux et Innovations en Cancérologie, 114 rue Edouard Vaillant, 94800 Villejuif, France S Supporting Information *
ABSTRACT: The synthesis and detailed characterization of gold nanoparticles (AuNPs) inside human hair has been achieved by treatment of hair with HAuCl4 in alkaline medium. The AuNPs, which show a strong red fluorescence under blue light, are generated inside the fiber and are arranged in the cortex in a remarkably regular pattern of whorls based on concentric circles, like a fingerprint. It opens an area of genuine nanocomposites with novel properties due to AuNPs inside the hair shaft. KEYWORDS: Gold nanoparticles, nanoreactor, fluorescence, exocuticle, macrofibril, keratin
S
many other applications.31−33 Recently gold nanoparticles were used as colorant for the merino wool,34 but until now there are no reports for the use of AuNPs for the dyeing of human hair. Human hair appears like a thin elongated cylinder with a diameter of 30−120 μm.35,36 The hair shaft is mainly composed of three regions. The outermost region is the cuticle which is a thick sheath of several cell-like scales. The cuticle tightly protects the cortex which contains components as lipids, keratins, and melanin (which provides color to the hair). The third part is the medulla, which is close to the center of hair. In human hair, the medulla is either completely absent or if present, there are various cells piled up leaving large empty spaces. Sulfur-containing amino acids like cysteine, cystine, cysteic acid, and methionine are some of the major components of keratin inside the hair (about 1400−1500 μmol of amino acid residues per gram of dry hair). One can anticipate that these sulfur-containing amino acids could be binding sites for the AuNPs due to the chemical affinity of gold for sulfur.37 Since Greco-Roman times lead minerals were used to dye human hair. An ancient recipe using a paste made of litharge (PbO), slaked lime (Ca(OH)2), and water was used to blacken hair: the change of color was due to the synthesis of PbS quantum dots within the hair shaft.38 The caustic solution
ince the Roman period, gold was used in the staining of glasses. Only recently these materials have been ascribed to the formation of gold nanoparticles (AuNPs).1 In these glasses different shades from yellow to purple have been made by changing the concentration and size of the AuNPs. For example, the Lycurgus cup, produced during the fourth century, shows dichroic effects due to use of Au−Ag alloy nanoparticles (50−100 nm in diameter) as colorants in the glass,2 later called the Gold ruby glass and used for luxury perfume bottles. Medieval artists used gold nanoparticles to get a bright red color on church stained glass. The main origin of this color is the excitation of surface plasmon modes in metal nanoparticles. This phenomenon was unclear for long time: Faraday was the first to show the correlation between particle size and the color phenomenon and to prepare diluted colloidal gold solution.3 Subsequently, various methods have been developed to synthesize AuNPs like the pioneering Turkevich method,4 then more recently the Burst method5 and the Perrault method.6 After the discovery of some unusual properties of gold nanoparticles compared to bulk gold, many scientists were attracted to this field.7,8 There are various reports of use of AuNPs for biology9−12 as drug delivery in diseases like Alzheimer's disease9 and cancer.13−19 AuNPs are also used in many electrochemical applications20−25 like the preparation of gold deposited hair as a microelectrode.22 In organic synthesis, they provide efficient catalysts.26−30 AuNPs are also involved in © 2012 American Chemical Society
Received: August 21, 2012 Revised: October 16, 2012 Published: November 2, 2012 6212
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The red fluorescence can be accounted on the basis of surface plasmon resonance phenomena or optical properties of AuNPs.40−45 To confirm the correlation between the presence of AuNPs and the observed fluorescence we followed the hair dyeing at different intervals of time (Figure 2 C−E). This progressive radial development of fluorescence throughout the hair cross-section clearly indicates a direct correlation with formation of AuNPs. This will be closely examined below with STEM and EDS techniques. Large nanoparticules (50−100 nm) are also formed and stuck at the surface of the hair shaft as observed in scanning electron microscopy (Figure 3 a,b). Elemental analysis shows the presence of gold everywhere on the surface but mainly aggregated at the edge of the layers. In STEM analysis (sample with 16 days of treatment), an important uptake of gold is visible in the cuticle and in the cortex. The clear zones correspond to organic matter enriched with gold (Figure 3c). Each layer of the cuticle corresponding to flattened cuticle cells is decorated by gold (Figure 3d). These cells have a laminar structure with an outer layer, 110nm-thick, termed the A-layer (Figure 3d), which is rich in halfcystine content (approximately one-half-cystine in every 2.7 amino acid residues). It contains a higher density of AuNPs due to which the strongest contrast is observed by HAADF (Figure 3e). The area below A-layer is termed as an exocuticle (“Ex” in Figure 3d), which is followed by an endocuticule (“En” in Figure 3d). The exocuticle is a keratin-based material without any regular fine structure but is resistant to many chemical and enzymatic treatments, as it contains a high concentration of cystine, whereas the endocuticle consists mainly of nonkeratinous cellular debris.46 The A-layer and the exocuticle were stained intensively by gold. At a higher magnification (Figure 3e) AuNPs are visible. They are shown in Figure 3f to be crystalline AuNPs. The diameter of the AuNPs is 2.6 nm (±0.5 nm standard deviation for about 50 AuNPs), and the Au concentration measured by STEM-EDX in the exocuticle is about 1.2 at. %. In the cortex, AuNPs are located up to the center of the shaft after 16 days of treatment and are staining the structure of the cortex. There are several microfibrils packed together in a single macrofibril unit (Figure 4a). The cortex is constituted of an array of dead cells, lacking DNA and held together by a lipiddominated cement. No gold seems to be present in the intermacrofibrillar matrix (“IMM” in Figure 4a), which is mainly composed of lipids. AuNPs are concentrated in the
produced by the dissolution of Ca(OH)2 in the paste degrades the cysteine residues from the keratin proteins to release the sulfur which reacts with the lead ions available from the lead oxide component of the dye. Interestingly hair keratin organization seems to control or limit the growth of PbS nanoparticles inside the fiber, acting as a nanoreactor. Similar reactions have been recently used to form HgS nanoparticles in the hairs.39 In continuation of these works, we report here the direct synthesis of gold nanoparticles inside human white hair by using an alkaline solution of HAuCl4. The white hair fibers were treated with HAuCl4 in basic medium (pH = 12.5). It was observed that the hair starts changing color within 7 h, and with the progress of the treatment it further darkens. It gave different color shades from pale yellow to brown (Figure 1), and finally after 16 days, it turned into a deep brown color. We will show the color is due to the formation of AuNPs.
Figure 1. Hairs after different time intervals of dyeing.
To understand the process going on inside the hair during the dyeing, we performed chemical treatments with increasing duration, from 7 h to 16 days. Various 3-μm-thick cross sections of the treated fibers were analyzed by optical microscopy and Raman spectroscopy; 70-nm-thin sections were prepared for scanning transmission electron microscope (STEM) imaging and for measuring the gold uptake in the shaft by energy-dispersive X-ray spectroscopy (EDS). An optical microscope image under the normal light clearly showed the change of color inside the shaft (Figure. 2 A, F). Under the blue light (510 nm), an intense red fluorescence (Figure 2 E) was observed instead of the light green fluorescence of hair without treatment WT (Figure 2 B).
Figure 2. Observation of cross sections of treated hair by optical microscopy: under white light (A: hair without treatment, F: hair after a treatment during 16 days) and under blue light filter (B: hair without treatment, C, D, E: hair after a treatment during 7 h, 1 day, and 16 days, respectively). 6213
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Figure 3. Observations of the hair cuticle after 16 days of treatment with SEM (a−b) and STEM (c−f). (a−b) Surface topography of the cuticle cells preserved after the treatment. (c,d) STEM, Au-rich zone in the five cuticle layers, being clear in a high angle annular dark field (HAADF) and (e) bright field image showing the “A”-layer and “I”-inner layer as well as the CMCcell membrane complex). (f) Observation in bright field at the atomic resolution of the AuNPs in the cuticle.
Figure 4. In the cortex (a,b,c: HAADF) the macrofibril (MF) boundaries are decorated by gold that is also present in the MF bulk. (d) Fourier transform of the image identified by the red square in image (c), showing a ring at a position between 11 and 12 nm. (e) Observation in bright field at the atomic resolution of the AuNPs in the cortex. (f) Model of the AuNPs distribution in the cortex according to the hexagonal paracrystal model of the intermediate filaments (beige circles) arrangement and the location of the AuNPs from e represented by blue circles.
hair.47 It could be distinguished in Figure 4b−c, but only locally. Lower AuNP densities are visible in the cortex (Figure 4e) compared to the cuticle (Figure 3f), as shown by STEM HAADF, giving contrast for Au atoms even in the case of isolated atom or small aggregates. Their sizes are going from one atom to clusters of 1 or 2 nm. Our observations suggest that many of the aggregates are near the size of Schmid’s clusters48 Au55 with a size of 1.4−1.5 nm. It is difficult here to determine a statistical distribution of their size with STEM.
limits between the macrofibrils (MF), but AuNPs are also inside them. Each MF consists in turn of highly organized socalled intermediate filaments (IFs), mainly constituted by αhelix keratins, embedded in an amorphous sulfur-rich proteinaceous matrix. We see in Figure 4b that the AuNPs are arranged in a remarkably regular pattern of whorls based on concentric circles or spirals. The nanoparticles are decorating the postulated IFs, known to be arranged in a pseudohexagonal array with a periodicity of about 10 nm in wool18 and human 6214
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A rough estimation of the repeat distances in the structure, performed by Fourier transforming of images such as Figure 4c, gives values between 11 and 12 nm (Figure 4d), equivalent to the characteristic distance of the IFs pseudohexagonal organization. This supports the relation between the abovementioned hair structure and the AuNP nucleation: nanoparticles are localized between the IFs or inside them, to display similar organization/pattern. To impose this local order, a strong modulation of the probability of AuNPs nucleation and growth is needed. The IFs are constituted by a compact arrangement of protofibrils (2.5 nm large, 47 nm long), that is, two coiled coils of α-helix keratin molecules associated together to form a tetramer where nucleation of AuNPs can occur only with difficulty. We verified by X-ray diffraction that the α-helix characteristics of the keratin molecules from the protofibrils are well-preserved (with a pitch of 0.515 nm and a lateral packing of 0.98 nm). Therefore, AuNPs are unlikely to form inside the IFs. All of these elements show that the AuNPs were formed more likely around the IFs, in the amorphous matrix rich in cystine-containing peptides. This relationship between the matrix and the growth of the nanoparticles can be highlighted by overlapping the experimental pattern of Figure 4e (in bright field)reproducing the AuNP positions with blue circleswith a hexagonal model of the intermediate filaments (Figure 4f). This hexagonal model is schematic and too restrictive because of the natural disorder in the biological matter: it cannot be applicable at long distances. Moreover, the STEM observation of a longitudinal section of the hair treated during 16 days shows a distribution of nanoparticles in lines (Figure 5) that respects the geometry of
Figure 6. STEM HAADF observations of the hair cuticle after 16 days of treatments. Relative concentration of gold along a section of the hair shaft, from the cuticle (at left, the surface is estimated at x = 0.6 μm) to the cortex (at right) according to the contrast profile in the STEM HAADF micrograph. (The STEM HAADF images for shorter intervals of treatment are given in the Supporting Information.)
inside the cortex. After 24 h, gold has diffused throughout all the six layers of cuticle cells but not in the cortex. The synthesis of gold nanoparticles requires the reduction of HAuCl4 to gold. Usually, sodium citrate or ascorbic acid is used. In our case, many reagents can be considered as reducing agents. As we have observed that the AuNPs are mainly formed in the keratin-rich area of the hair shaft, we can first assume that different amino acids participate to the reduction process. But we observe also that the distribution of the AuNPs is clearly correlated to the cystine content as the distribution of cystine also shows a similar pattern. In Table 1, we have compared the Table 1. Correlation between AuNPs Density with the Cystine Content, at Different Histological Levels of Hair after a 16 days Treatment. The AuNPs Density Is Given for the Whole Thin Cross-Section of the Hair Shaft
Figure 5. STEM observation of the longitudinal cross-section of 16 days-treated hair. In the inset, a Fourier transform of the image.
histological area A-layer exocuticle endocuticle cortex at 0.1 μm
IFs. A Fourier transform of the image indicates a distance between the lines of about 11 nm, a value similar to the apparent diameter of the IFs observed in the transversal crosssection. The kinetics of the Au diffusion has been observed by STEM-EDX measurements. Micrographs of the cuticle (Figure 6) showed a rapid penetration of gold near the surface. Concentration profiles can be taken by plotting the HAADF contrast versus distance. The strong peaks at the interfaces between the cuticle layers represent the gold accumulation (0.08 at. % after 7 h in the exocuticule of the first cell and up to about 1.2 at. % after 16 days in the same area of the cuticle) according to direct EDX measurements. The content of Au then slightly decreases in the cortex down to the center of the shaft (0.45% of non-hydrogen atoms (at. %) at 0.1 μm from the cuticle/cortex interface, 0.3 at. % at 0.4 μm and 0.15 at. % at 10 μm for a 16 days treatment). After 7 h, the first layer of dead cell shows an important uptake of gold, but no AuNP is visible
half-cystine49 (mol %)a Au (at. %)b AuNPs densityc 37 20 3 14
2 1.2 1 0.45
100 000 50 000 15 000 14 000
a mol % of amino acids. bNonhydrogen at. %. cμm−2 in 70-nm thin section.
measured concentration of gold after 16 days, the number of AuNPs per μm2 in the 70-nm thin section of hair and the halfcystine content in the different histological areas. An interesting correlation is observed between the half-cystine concentration and the density of AuNPs in the layers where diffusion brings large amounts of gold. The half-cystine residues are likely playing an important role in the reduction of gold ions. To confirm this role, the cortex region of the hair fibers was analyzed by Raman spectroscopy. The Raman spectra of untreated hair and hair treated during 7 h are almost identical except the strong decease of the disulfide peak at 508 cm−1 (Figure 7). 6215
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which we anticipate some novel properties resulting from mechanical characteristics arising from the hair shaft, whereas chemical and physical properties are given by the AuNPs. The red fluorescence produced by AuNPs inside the hair can be useful in biological applications. The use of hair fibers with fluorescent AuNPs as microsensors for various metal salts is under investigation. This biomineralization of human hair with gold may have also applications in the hair dyeing industry. Methods. Dyeing Procedure. The dyeing procedure was initiated by adding 4 mg of HAuCl4 + 8 mg of human white hairs + Ca(OH)2 until pH = 12.5. A sample of 8 mg of white hair fibers was taken in a vial containing a solution of 4 mg of HAuCl4 in 2 mL of distilled water. The solution was made alkaline (pH = 12.5) by adding Ca(OH)2. The vial was closed and left aside. After different intervals of time the hair was taken out. The hairs were rinsed with distilled water three times, dried gently over tissue paper, and dried in vacuum for a short time. Thin Foil Preparation and Electron Microscopy. Thin foils for transmission electron microscopy were performed by ultramicrotomy with the DIATOME LEICA of the IGR CNRS UMR 8126 laboratory. The hair fibers were embedded in flat epoxy resin blocks (Epon) to orientate the cut perpendicularly to the fiber axis.53 The TEM foil thickness, ranging between 50 to 70 nm according to the microtome knife displacement for each cut, were performed using a speed rate of 4−5 mm/s. The thin foils were deposited on collodion/carbon film grids (300 and 200 mesh size). They were examined first by conventional TEM imaging using a 120 kV Zeiss 912 microscope and a 80 kV Zeiss 902 microscope equipped with a ZEISS energy filter (IGR-CNRS 8126). Specimen TEM imaging was performed using the zero loss elastic energy peak. They were secondly examined at the atomic resolution with the JEM 2200 FS STEM (scanning TEM) of the LPN (CNRS UPR 20) equipped with an energy dispersive X-ray spectrometry (EDS) for chemical analysis. The observations were performed in Z-contrast imaging generated by high angle annular detection (HAADF) that collects electrons deflected by nuclear interactions at angle between 100 and 170 mrad. Bright field images are also obtained with electrons scattered at a low angle (less than 10 mrad) from the incident beam. UV-Fluorescence Observation. Sample preparation for optical microscopy and Raman spectroscopy were performed at the Institut de Chimie des Substances Naturelles, CNRS UPR 2301, Gif-sur-Yvette, France. Cross sections (4 μm thick) were cut at −20 °C with a CM3050-S cryostat (Leica Microsystems SA, Rueil-Malmaison, France). The hair fibers were embedded with OCT glue, and the cross sections were deposited on glass slides. Optical images were recorded with a Nikon-Labophot 2 microscope equipped with lenses ×5 to ×50 and a Nikon DS-Fi1 (5-megapixel CCD), monitored by NISElements. The microscope is equipped for epi-fluorescence microscopy (Xenon lamp, B-2A filter; excitation, 450−490 nm; barrier, 520 nm; dichroic mirror, 505 nm). Raman Spectroscopy. Raman measurements were performed at SMIS beamline at SOLEIL, Gif-sur-Yvette, France. Spectra were recorded using a DXR Raman microscope (ThermoNicolet, Montigny-le-Bretonneux, France) equipped with a 532 nm ThermoNicolet laser providing 7 mW of power on sample, edge filters, a charge coupled device detector, and a 100 × /0.9 numerical aperture objective giving a spot size of 0.9 μm at 780 nm. The spectra were recorded with five accumulations of 60 s from 50 to 3400 cm −1 . The microspectrometer was operated in nonconfocal mode with a
Figure 7. Raman spectrum of untreated hair and hair treated with and without HAuCl4 in alkaline medium (pH = 12.5).
As previously described for the PbS nanoparticle formation in hair,38 the alkali treatment has liberated sulfur species able to reduce the Au species that have diffused in the cortex. This supports the relationship between AuNPs formation and disulfide bond modifications from half-cystine residues inside the cortex and cuticle. In the treatment Ca(OH)2 was used as a base to adjust the pH at 12.5. It is known that the disulfide part of cystine also undergoes cleavage by alkali treatment.50,51 To check this, we compared the above result with a hair treated with only Ca(OH)2 at pH = 12.5 for 3 days. The disulfide peak at 508 cm−1 was indeed reduced but only by 40%, a result similar to the one obtained by ion exchange chromatography analysis of the amino acids.38 With the presence of gold salt in the alkaline medium, only 7 h are needed for a decrease of about 80−90%. This indicates the strong acceleration of the breaking of disulfide linkage in the presence of gold. To verify that AuNPs are formed in situ in the hair and have not diffused from the solution as AuNPs, white hairs were treated with a premade gold nanoparticle solution (standard Turkevich method52 with Na3(citrate) and HAuCl4). It was observed that the hair turned into deep purple color after 2 days. Optical microscopic image of the cross section did not show any red fluorescence under blue light. STEM observations of the cross section and EDS analyses of the different parts of the hair also did not show the presence of any gold particles. The AuNPs are located only at the surface of the fiber. From this data, it is clear that premade gold particles cannot penetrate inside the hair and just dye the surface. In conclusion, using an alkaline solution of HAuCl4, the synthesis of AuNPs inside the human hair has been achieved for the first time. Various experiments established that the AuNPs are not formed outside the hair but are generated in situ with the homogeneous control by hair at some levels like cuticle Alayer (AuNPs size = 2−3 nm) or cortex (AuNPS with a diameter less than 2 nm). Furthermore, we have verified that multiple washings of treated hairs did not affect the color of the hair as the colored AuNPs are buried and stabilized inside the hair by the keratin structure. It highlights the possible use of these chemical conditions to produce gold nanoparticles from Au(III) salts in a one-pot nucleation, growth, morphogenesis, and passivation of extremely small AuNPs. We have not only shown the discrete location of AuNPs at different levels of hair but also its chemical interaction with cystine residues in the beneath of cortex. Hair is both a biological entity and a remarkably sophisticated composite solid-state material linked to the supramolecular organization of the keratin molecules, which are playing a remarkable role in the formation of AuNPs. We see the emergence of a genuine composite material for 6216
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pinhole of 50 μm and a 400 lines/mm grating, giving a spectral resolution varying from 10.1 to 18.5 cm−1.
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(23) Xu, J.; Hu, C.; Ji, Y.; Hu, S. Electrochem. Commun. 2009, 11, 764−767. (24) Sharon, M.; Moncy, V. J.; Andersen, J. D.; Russell, A. J. Biosens. Bioelectron. 2011, 26, 2981. (25) Saha, K.; Agasti, S. S.; Kim, C.; Li, X.; Rotello, V. M. Chem. Rev. 2012, 112, 2739−2779. (26) Astruc, D.; Lu, F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44, 7852. (27) Soule, J. F.; Miyamura, H.; Kobayashi, S. J. Am. Chem. Soc. 2011, 133, 18550. (28) Zhang, Y.; Cui, X.; Shi, F.; Deng, Y. Chem. Rev. 2012, 112, 2467. (29) Della Pina, C.; Falletta, E.; Rossi, M. Chem. Soc. Rev. 2012, 41, 350. (30) Stratakis, M.; Garcia, H. Chem. Rev. 2012, 112, 4469−4506. (31) Chen, P. C.; Mwakwari, S. C.; Oyelere, A. K. Nanotechnol. Sci. Appl. 2008, 1, 45−66. (32) An, X.; Zhang, F.; Zhu, Y.; Shen, W. Chem. Commun. 2010, 46, 7202−7204. (33) Pissuwan, D.; Niidome, T.; Cortie, M. B. J. Controlled Release 2011, 149, 65. (34) Johnston, J. H.; Lucas, K. A. Gold Bull. 2011, 44, 85. (35) Bouillon, C.; Wilkinson, J. The Science of Hair Care, 2nd ed.; Taylor & Francis: Boca Raton, FL, 2005. (36) Morel, O. J. X.; Christie, R. M. Chem. Rev. 2011, 111, 2537− 2561. (37) Nath, S.; Ghosh, S. K.; Kundu, S.; Praharaj, S.; Panigrahi, S.; Pal, T. J. Nano. Res. 2006, 8, 111−116. (38) Walter, P.; Welcomme, E.; Hallégot, P.; Zaluzec, N. J.; Deeb, C.; Castaing, J.; Veyssière, P.; Bréniaux, R.; Lévêque, J.-L.; Tsoucaris, G. Nano Lett. 2006, 6 (10), 2215−2219. (39) Patriarche, G.; Walter, P.; Van Elslande, E.; Ayache, J.; Castaing, J. Philos. Mag. 2012, DOI: 10.1080/14786435.2012.674225. (40) Negishi, Y.; Nobusada, K.; Tsukuda, T. J. Am. Chem. Soc. 2005, 127, 5261−5270. (41) Huang, C. C.; Yang, Z.; Lee, K. H.; Chang, H. T. Angew. Chem., Int. Ed. 2007, 46, 6824−6828. (42) He, H.; Xie, C.; Ren, J. Anal. Chem. 2008, 80, 5951−5957. (43) Lin, C. Y.; Liu, C. H.; Tseng, W. L. Anal. Methods 2010, 2, 1810−1815. (44) Guo, Y.; Wang, Z.; Shao, H.; Jiang, X. Analyst 2012, 137, 301− 304. (45) Zheng, J.; Zhou, C.; Yu, M.; Liu, J. Nanoscale 2012, 4, 4073. (46) Fraser, R. D. B.; MacRae, T. P.; Rogers, G. E. Keratins, their Composition, Structure and Biosynthesis; Charles C. Thomas Publisher: Springfield, IL, 1972. (47) Briki, F.; Busson, B.; Doucet, J. Biochim. Biophys. Acta 1998, 1429, 57−68. (48) Schmid, G. Chem. Rev. 1992, 92, 1709. (49) Robbins, C. R. Chemical and Physical Behavior of Human Hair, 4th ed.; Springer: New York, 2001. (50) Galande, A. K.; Spatola, A. F. Lett. Peptide Sci. 2002, 8, 247−251. (51) Galande, A. K.; Trent, J. O.; Spatola, A. F. Biopolymers 2003, 71, 534−551. (52) McFarland, A. D.; Haynes, C. L.; Mirkin, C. A.; Van Duyne, R. P.; Godwin, H. A. J. Chem. Educ. 2004, 81, 544A. (53) Ayache, J.; Beaunier, L.; Boumendil, J.; Ehret, G.; Laub, D. Sample Preparation Handbook for Transmission Electron Microscopy; Springer: Berlin, 2010.
ASSOCIATED CONTENT
S Supporting Information *
STEM HAADF observations of the hair at different time intervals of treatment and Au concentrations (as measured by EDS in the STEM) at various points from the hair surface. This material is available free of charge via the Internet at http:// pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Phone: +33 1 44 27 82 22. Fax: +33 1 44 27 82 98. Author Contributions
These authors contributed equally. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was partially funded by the Agence Nationale de la Recherche (ANR); NANOCHEOPS project, ANR-08NANO-019-01). We would like to thank P. Dumas, Synchrotron SOLEIL, for Raman spectroscopy measurements.
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