ARTICLE pubs.acs.org/JPCC
Self-Assembly Change by Gold Nanoparticle Growth Sungsook Ahn,† Sung Yong Jung,‡ and Sang Joon Lee*,†,‡,§ †
Center for Biofluid and Biomimic Research, ‡Department of Mechanical Engineering, and §Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 790-784, Korea
bS Supporting Information ABSTRACT: Inorganic nanoparticles in the self-assembled organic/biological templates are of great interest in nanoparticle-mediated therapy, biosafety, and hybrid functional material design for photonic devices. The gold nanoparticles (AuNPs) grown in situ in the aqueous solutions/hydrogels of amphiphilic polymers significantly influence the radius of gyration (Rg), correlation length (ζ), fractal dimension (α), and structure-dependent specific sizes. As a result of selective wetting by gold ion aqueous solution, the grown AuNPs are expected to locate in the hydrophilic domain of the self-assembly structures, which leads to the prominent changes in the size and the structures accordingly. The increase in the surfactant number (Ns) of the self-assembled template is suggested to decrease the effective surface area (As) (i.e., decrease in the mean curvature) on which smaller AuNPs are preferably formed. There is a strong correlation between the self-assembled template structure and the formed nanoparticles.
A
cell membrane is a self-assembly system composed of amphiphilic lipid bilayers with a hydrophilic charged outer layer and a hydrophobic lipidic inner layer, including embedded proteins.1 Recently, nanoparticlecell interactions have become one of the key issues in the areas of drug delivery,2 cancer treatment,3 and imaging agent transport,4 etc. The disruption of membrane structure by nanoparticle introduction is one of the main reasons by which cells lose their destined functions, cytotoxicity.5 On the other hand, nanoparticle-introduced organic/inorganic hybrid materials are useful in the applications such as light-emitter/absorber, photovoltaics, nonlinear-optics, sensors, and energy harvest/storage.68 Nevertheless, most studies have focused on the nanoparticle control usually in the form of dried thin films or polymer melts.912 Block copolymers have been reported as excellent templates for nanoparticle formation,1315 usually emphasizing the sizes and the spatial arrangements of the nanoparticles in the polymeric composites.9,10 Mixed with a solvent, a block copolymer self-assembles into unique structures dominated by the degree of repulsion, length and selectivity of the blocks, and the environmental conditions such as pH, ion, temperature, and polarity of the solvent, etc.1621 By applying external forces such as electric fields, the curvature and the direction of copolymer films can be controlled.22,23 However, the changes in the self-assembled structures of polymeric templates affected by the nanoparticle incorporations are seldom emphasized, especially in the form of aqueous solutions/hydrogels. The dynamics of polymer chains are significantly influenced by the strength of the polymer chainparticle interactions, morphology, particle dispersion, and interparticle distances.24,25 Nonetheless, nanoparticle effects on the physical properties of polymers are still controversial and mainly focused on the size of r 2011 American Chemical Society
the nanoparticles;68 ceramic materials with cluster sizes less than 15 nm are reported to change from brittle to ductile, reflecting a typical viscosity increase of a Brownian particle suspension where the viscosity is a function of the particle volume fraction and the viscosity of the suspending liquid.26,27 However, a viscosity decrease is observed with a 0.35 nm silicate cluster blended in linear polymers, suggesting an unusual effect exclusively occurring in a nanoscale process.28,29 Poly(ethylene oxide-block-propylene oxide-block-ethylene oxide) triblock copolymer [Pluronic (EO)x(PO)y(EO)x] was reported to reduce gold ions selectively into gold nanoparticles (AuNPs) especially dominated by ethylene oxide (EO) segment.3035 Gold nanoparticle formation in the Pluronics has been studied by Sakai et al.2935 In this study, series of Pluronics having various EO and PO units are employed to reduce chloroauric acid solution into gold nanoparticle (AuNP), and the changes in the self-assembled structures at an isothermal condition (20 °C) are observed using small-angle X-ray scattering (SAXS) systematically. It is suggested that, in addition to the size, the compatibility and the location of the formed nanoparticles in the self-assembled template are important to determine the physical properties of the nanoparticle-incorporated hybrid system. The formed AuNPs in this study range from several nanometers to hundreds of nanometers. Using SAXS, the AuNP-incorporated aqueous solutions/hydrogels designed in this study can be observed in situ without drying into thin films or adding additional dye chemicals that might distort the structural analysis. The Pluronics L61, L62, F68, L92, and P104 (BASF Korea, Seoul, Korea) employed in this study are diversified according to the Received: September 5, 2011 Revised: October 7, 2011 Published: October 10, 2011 22301
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Table 1. Size Changes in the Self-Assembled Structures by AuNP Incorporation: Radius of Gyration (Rg), Correlation Length (ζ), and Fractal Dimension (α) Evaluation without AuNP
L61
L62 F68 L92
P104
a
ϕ
Rg
L1
19.5
0.20
1.0
Lα
N/A
0.05
2.3
L2 L1
21.2 23
0.04 0.20
2.1 0.2
Lα
N/A
0.17
L1
25.7
0.33
H1
N/A
H1
ζ
α
with AuNP ϕ
Rg
2.13
L1
23.4
0.63
1.2
2.04
3.9
0.43
0.2
0.09
10.44
Lα
N/A
0.55
2.5
10.44
N/A
0.5
0.2
0
1.16 N/A
L2 L1
21.9 24.2
0.40 1.07
3.4 1.3
1.37 N/A
0.7 1.2
0.36 0.87
1.3 1.1
+0.21 N/A
6.1
7.55
Lα
N/A
1.02
5.4
7.93
N/A
0.8
0.5
+0.38
1.2
N/A
L1
25.7
1.03
0.1
N/A
0
0.7
1.1
N/A
0.10
3.2
11.52
H1
N/A
0.26
4.6
11.70
N/A
0.16
1.4
+0.18
N/A
0.10
0.8
12.73
H1
N/A
0.71
0.6
12.96
N/A
0.61
0.2
+0.23
Lα
N/A
0.12
1.6
10.10
Lα
N/A
0.89
1.9
10.27
N/A
0.77
0.3
+0.17
H2
N/A
0.20
0.1
12.51
Lα
N/A
0.88
2.5
9.35
N/A
0.78
2.4
N/A
I1 H1
23.7 N/A
0.37 0.41
0.9 1.0
1.89 8.53
I1 H1
24.2 N/A
1.04 1.16
2.1 2.7
2.00 8.85
0.5 N/A
0.67 0.75
1.2 1.7
+0.11 +0.32
L
N/A
0.39
2.5
10.10
L
N/A
1.15
3.1
10.26
N/A
0.76
0.6
+0.16
q*-based size
a
ζ
α
q*-based size a
α α √ Sizes of 1/q* for L and I, 4π/ 3q* for H, and 2π/q* for Lα are applied, respectively.
number of EO and PO unit, molecular weight, and hydrophiliclipophilic balance (HLB) (Supporting Information, Table S1). L61, L62, and F68 have similar number of PO units of 30 but different number of EO units, which are expected to be critical to AuNP formation. L92 and P104 have similar EO/PO with L62, but the absolute number of the unit is different. Gold chloride(III) trihydrate (HAuCl4 3 3H2O) is dissolved in deionized (DI) Milli-Q water at 1.0 103 mol/L. Each Pluronic was mixed with chloroauric acid stock solution at the designed volume concentration (cp) from 0.1 to 0.9, followed by centrifuging up-and-down several times (3000 rpm) and stabilizing at 20 °C for a week for an equilibration. The structural changes observed by SAXS at 20 °C are summarized (Table S1). According to the increase in the hydrophobicity of a system (and cp), the structural changes follow a typical sequence; the structures are identified as micellar solution (L1) f micellar cubic (I1) f hexagonal (H1) f bicontinuous cubic (V1) f lamellar (Lα) structures followed by the inverted structures from bicontinuous cubic (V2) f hexagonal (H2) f micellar cubic (I2) f micellar solution (L2). Between the specific structures, phase-separated state (2ϕ) is designated as observed. From the SAXS profiles, the changes in the main peak position q* are detected to determine the structure and the size (Supporting Information). In addition, at dilute condition with isotropic samples, the relation 1 is applied regardless of the particle shape:36 IðqÞ ¼ Ið0Þ exp½ q2 R g 2 =3
ð1Þ
where the radius of gyration (Rg) is obtained at small q region (q < 1/Rg). The SAXS profile is produced by the OrnsteinZernike (OZ) type scattering function: IðqÞ ¼ Ið0Þ=½1 þ q2 ζ2
ð2Þ
where ζ is the thermal correlation length for the fluctuation and I(0) is the forward scattering intensity. The ζ is obtained at low q condition (qζ < 1). ζ reflects the specific sizes corresponding to the distances between the separated particles/polymer globules or junction points in the interconnected networks. According to the relation expressed in eq 2, q2 versus 1/I(q) are plotted in each system at low q condition (q2 < 0.02 nm1, therefore q < 1/Rg is
ΔRg
Δζ
Δα
Δq*-based size
satisfied), where the slope indicates the square of the correlation length (ζ) of the Pluronic structures with and without AuNPs. On the other hand, for the length scales where the qζ > 1 is satisfied, I(q) obeys the power law:36 IðqÞ≈qα
ð3Þ
The power law expresses the density of the objects as a fractal dimension. The fractal dimension α is evaluated by the average slope of the graph at high q region (q > 0.5 nm1 or q > q*). The observed structures and their size of each Pluronics with and without AuNPs are summarized in Table 1. Detailed SAXS profiles for each Pluronics are displayed in the Supporting Information (Figure S2). The representative SAXS profiles of L61 and L92 are shown in Figure 1A. Both L61 and L92 display the structural changes from the normal phase L1 to the inverted phase L2 (Table S1). For hydrophobic L61 (HLB = 3), the normal oil-in-water structure (L1) formation is relatively weak (the peaks are not so sharp). Nonetheless, the characteristic size indicated by q* becomes smaller, the same, and larger by AuNP incorporation at normal phase L1, planar Lα, and inverted phase L2, respectively. However, the ζ, Rg, and α become higher by AuNP incorporation in all of the cases (Table 1). In Scheme 1, the size change for normal (O/W) phase, planar, and inverted (W/O) phase is suggested. By AuNP incorporation, the normal phase might shrink due to the AuNPs encircling the outer layer, while the inverted phase increases the size due to AuNP incorporation and further swelling of the hydrophilic inner side of the structure. Nonetheless, the planar structure might have a negligible effect by AuNP incorporation. As compared to L61, L92 (HLB = 5.5) exhibits more diverse structural changes between L1 and L2 (Table S1). L92 generates a slightly large size (q*) at normal H1 and Lα by AuNP incorporation. Yet, the change is more significant at the inverted phase; the inverted hexagonal (H2) becomes lamellar (Lα) structure. The AuNP incorporation to L92 changes the system more hydrophilic indicated by the structural modification to the hydrophilic direction (H2 f Lα). This also supports that the AuNPs grown in the self-assembled structures are located in the hydrophilic domain, under which the inverted phases can be 22302
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Figure 1. (A) Representative SAXS profiles of Pluronics L61 and L92 with and without AuNP incorporation at the selected structures. (B) The changes in the sizes by AuNP incorporation. Radius of gyration (Rg), correlation length (ζ), and fractal dimension (α) evaluation by %, [Δ size by AuNP incorporation/size without AuNP] 100 (%). Structural changes are observed according to the Pluronic concentration (cp) by SAXS at 20 °C.
more significantly affected by the AuNP incorporation rather than normal phases as illustrated in Scheme 1. At L1, α becomes smaller by AuNP incorporation, but it becomes larger at Lα and inverted H2. ζ becomes higher by AuNP incorporation in all of the cases. For L62 (HLB = 7) having increased hydrophilicity as compared to that L61, the lamellar structure becomes prominent with increased cp, where the repeat distance becomes larger by
AuNP incorporation. The ζ and Rg of L62 increase by AuNP incorporation, but α decreases at Lα. More hydrophilic F68 (HLB = 29) forms a structure at low cp, and the size of the structure (q*) becomes slightly larger by AuNP incorporation. The α decreases at L1, but the ζ becomes higher by AuNP incorporation in all conditions. P104 (HLB = 13) also shows an increased size by AuNP incorporation without changes in the structures detected by the q*. The α and the ζ become higher by 22303
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Scheme 1. Size Changes in the Self-Assembly by Gold Nanoparticle (AuNP) Introduction in Normal (O/W), Planar, and Inverted (W/O) Phases
Scheme 2. Self-Assembled Structures According to the Surfactant Number (Ns)a
AuNP incorporation. Overall, some normal phases and unstable lamellar (Lα) structure display the decreases in the density of the system (α). However, the radius of gyration (Rg) and the correlation length (ζ) become higher by AuNP growth in most of the cases. Scheme 2 suggests the changes in the self-assembled structures generated by amphiphilic force balance based on the dimensionless surfactant number (Ns):17
a
N s ¼ v=ao lc
ð4Þ
where v and lc are the volume and the length of the hydrophobic portion of the amphiphilic molecule, and ao is the effective area per headgroup. Kinetic processes of the block copolymer solutions involve a combination of the fast intramicellar process generating interfacial curvature in an isolated micelle and the slow intermicellar process for micelle fusion or fission.16,17 Gold ions introduced in the Pluronic aqueous solutions are expected to affect both kinetic procedures leading to a characteristic AuNPincorporated Pluronic system. The detailed time-dependent dynamic processes are out the scope of this study, and only the fully equilibrated final states are concerned. The resulting selfassembled Pluronic structures are affected by the AuNP growth depending on the changes in the modified hydrophiliclipophilic force balance. Under the conditions that the formed AuNPs are concentrated at the hydrophilic EO domain of the selfassembly, the hydrophilic portion is expected to increase as a result of the AuNP formation, which would mainly change the ao in the relation 4. In Figure 1B, the size changes by AuNP incorporation are evaluated according to the surfactant number (Ns). The changes in Rg and ζ for large-scale size, α for small-scale size, as well as the characteristic size detected by the main peak position q* are expressed in %, [Δ size by AuNP incorporation/size without AuNP] 100 (%). The Δ size (q*) is decreasing (P104, LHB = 13), almost similar (L92, HLB = 5.5), or increasing (L61, HLB = 3) until Ns = 1. Therefore, at least at the normal phase, there is no specific structure that AuNP incorporation preferably modifies. Nonetheless, it seems that the formed AuNPs more effectively increase the size of the low Ns structure formed by hydrophilic amphiphiles (high HLB),
The AuNP-incorporated structures are suggested considering the AuNPs grown in the hydrophilic domain of the self-assembled structures. Effective surface area (A s ) is suggested for each structure where gold ions grow into AuNPs. On a fixed projected area of 2R 2R, A s is diversified depending on the self-assembled structures and the morphological men curvature. With the increase in N s , the A s becomes smaller, thus generating smaller size AuNPs.
while they increase the high Ns structure formed by hydrophobic amphiphiles (low HLB). The structure-independent Rg is determined only at dilute isotropic condition; thus limited data are obtained. Nonetheless, the Rg increases by AuNP incorporation in all of the detected cases. From L61 two data points are generated where the inverted phase shows far lower ΔRg than the normal phase. At a fixed Ns (=0.33), the ΔRg of the lower HLB Pluronics is larger than that of the higher. On the other hand, Δζ becomes slightly higher until Ns = 1, and then decreases at Ns > 1 overall. Δα for elongated structure (Ns = 0.5) is slightly higher than that of isotropic structure (Ns = 0.33). Also, it becomes lower at the planar structure (Ns = 1) and increases again at Ns > 1 overall. The formed AuNPs can generate network structure due to multiple anchoring sites emanating from a single AuNP. This might lead to an effective increase in the density of AuNPincorporated Pluronic solutions/hydrogels overall, in addition to the addition of metal elements of high density. An interesting point is that for the density change of the solutions/hydrogels, the location of the incorporated AuNPs in the self-assembly is important. Figure 1B exhibits that most of the Δ sizes in each system exhibit consistent tendency according to the Ns. The changes in the physical properties of the nanoparticle-incorporated hybrid systems are strongly dependent on the structures of the templates represented by the Ns. One of the blocks in the copolymer is selectively wetted by the metals (or metal ion solutions), which can result in the metal nanoparticles located in the corresponding self-assembly domains.37,38 Nonetheless, the nanoparticles of designed sizes and shapes molded by the self-assembled polymeric structures are hardly observed; even with highly elongated self-assembled 22304
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Figure 2. (A) Representative TEM images of L92 at L1, H1, Lα, and H2 structures. The scale bar is 0.2 μm. (B) Observed absorption wavelength (left) and size of the formed AuNPs (right) at different Ns condition. The line on the right graph indicates the error range. (C) UVvis spectrum and the pictures of the AuNP-incorporated Pluronic solutions. (D) Summarized UVvis absorption spectra shown in Figure 1A.
structures of the polymers, elongated metal nanoparticles are hardly formed due to a strong metalmetal interaction, which usually overcomes the metalpolymer interaction. Some studies have been done to control the gold nanoparticle shape by changing the metalpolymer interactions.35,3941 Gold ions grow into spherically shaped AuNPs to minimize the surface tension, even
though the geometry of the template structures is important to determine the size of the resulting AuNPs. A projected area of 2R 2R is suggested as illustrated in Scheme 1, on which the maximum surface area (As) of diverse mean curvature is formed. With a sphere of radius R placed on the projected area, the As becomes 2πR2. With a cylinder of radius R, 22305
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Scheme 3. Radius of Gyration (Rg) Increase (A) and Thermal Correlation Length (ζ) Increase by (B) Gold Nanoparticle Incorporations
the As leads to 2πR2. With a flexible bilayer, it is between 2πR2 and 4R2. With a lamellar, As results in 4R2. The As of an inverted phase becomes smaller than that of the lamellar (Lα), unless there is a swelling of the hydrophilic domain. Thus, for an inverted sphere, it turns to be 2πR0 2, where R0 < R. The mean curvature becomes smaller with the increase in Ns, leading to a decrease in As. Typical transmission electron microscopy (TEM) images of the AuNPs formed by L92 at L1, H1, Lα, and H2 structures are displayed in Figure 2A. The size of the AuNPs decreases along with the increase in the cp corresponding to the Ns of normal (water-in-oil) (Ns < 1), lamellar (Ns = 1), and inverted (oil-inwater) (Ns > 1) structure. The relation between the AuNP growth and the As is suggested in Scheme 2. Under the Ns e 1 condition, the AuNPs become smaller along with Ns, where the As and the morphological mean curvature become smaller. At the Ns > 1 condition, the AuNP size can be conceptually smaller, but the observed AuNPs are larger than that of Lα. This can be caused from effective swelling of the hydrophilic domain by the AuNP introduction as suggested in Scheme 2. The observed size of the formed AuNPs and the UVvis results are strongly related based on the structures expressed by Ns. In Figure 2B, each structure expressed by the surfactant number (Ns) is plotted against the absorption wavelength observed by UVvis spectroscopy (left) and the average size of the AuNPs observed by TEM (right). Because of high hydrophobicity, the normal oil-in-water phase of L61 is not stable (Supporting Information, Figure S1). Except L61, the increase in the Ns leads to the decrease in the wavelength of the absorption as well as the size of AuNPs until Ns = 1, and they increase at Ns > 1. This result supports the aforementioned relation on the self-assembled structureAuNP formation summarized in Scheme 1. The originally colorless Au-incorporated Pluronics change their unique colors as a result of the equilibration for a week (Supporting Information, Figure S1). The physical properties of the grown AuNPs in the self-assembled structures are
investigated in terms of the surface Plasmon resonances in conjunction with the physical sizes. Figure 2C shows typical surface plasmon resonances and the solution pictures of the AuNP-incorporated Pluronics represented by F68 and P104 from cp = 0.10.9 (v/v). The maximum and minimum wavelength of the surface plasmons and their differences from cp = 0.1 to 0.9 for each system are summarized in Figure 2D. The intensity of the surface Plasmon shows either an increase (v) or a decrease (V) from cp = 0.1 to 0.9. The detailed information for each system is available in Supporting Information, Figure 2S. The physical properties of the formed AuNPs are characterized by UVvis spectroscopy where the surface plasmon absorption is detected. As summarized in Figure 2D, the surface plasmon of the hydrophobic L61 (HLB = 3, Table S1) slightly changes from 665 to 675 nm with the increased intensity from cp = 0.1 to cp = 0.9 (v), indicating an increase in the size and the concentration of the AuNPs by that order. At cp = 0.1, L61 does not show any detectable peak reflecting no AuNP formation. Meanwhile, at cp = 0.2, L61 shows bimodal peaks at 665 and 880 nm, indicating mixed AuNP formation with different physical property. Relatively homogeneous AuNP is formed only at higher cp possibly because of proper EO domain formation. The hydrophobic L61 hardly generates discrete self-assembled structure at low cp, but as the cp becomes higher the reverse phase forms prominent structures where a hydrophilic core can contain formed AuNPs displaying a narrow surface plasmon difference (Δ 10 nm). Similar to L61, lower concentration cp = 0.1 of L62 shows bimodal peaks at 560 and 630 nm due to heterogeneous AuNP formation. Nonetheless, with increased hydrophilicity, AuNP formation of L62 is more effective than that of L61 due to effective EO domain formation. As cp increases, L62 forms a prominent lamellar structure (Lα) after the normal solution (L1). From cp = 0.1 to cp = 0.9, the AuNP-incorporated L62 solutions/ hydrogels show distinguished colors from red via green to purple, and UVvis spectroscopy results display the wavelength change from 560 to 525 nm (Δ 35 nm) with increased intensity (v). Highly hydrophilic F68 shows a more prominent color change 22306
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The Journal of Physical Chemistry C from a red to a purple. The surface plasmon changes from 550 to 535 nm as cp increases from 0.1 to 0.9. Different from other Pluronics employed in this study, the intensity of the main AuNP surface plasmon peak decreases (V) according to the cp, while a new surface plasmon band develops in the near-infrared region. From the peak decrease (V), it is suggested that the more EO units (80 2 in F68) does not guarantee proliferate AuNP formation. L92 shows the surface plasmon change from 560 to 535 nm, and the observed solution colors turn from a red to a green from cp = 0.1 to cp = 0.6. However, from cp = 0.7 to cp = 0.9, the purple color turns back to a red, and the wavelength becomes longer from 535 to 550 nm. L92 exhibits diverse structural changes from normal to reverse when the surface plasmon resonance of incorporated AuNPs becomes shorter and then longer along with cp, where the turning point is the lamellar (Lα). P104 displays the most diverse structural changes in the normal phase and changes its solution color from red to purple monotonously as cp increases. P104 exhibits the surface plasmon changes from 590 to 550 nm where the observed difference (Δ 40 nm) is the maximum. Overall, the AuNPs grown and embedded in the Pluronic selfassembly emit the lights at the corresponding wavelength of the absorbed lights (i.e., energy conservation); the red color solutions more effectively absorb longer wavelength light, while purple solutions absorb shorter wavelength. Nonetheless, the physical properties of the grown AuNPs strongly depend on the surfactant number (Ns), thus the self-assembled structures. Normal and inverted structures generate the turning point of the surface plasmon for the formed AuNPs (observed by L92). The most diverse structural changes within the normal O/W phase exhibit the most broad absorption wavelength of the surface plasmon of the formed AuNPs (observed by P104). The structure of the self-assembled polymer is determinant for the physical properties of the grown AuNPs than are the molecular weight, HLB, EO/PO ratio, or absolute number of EO units of the amphphile template. In conclusion, cooperative interactions between the incorporated nanoparticle and self-assembled templates are investigated. The nanoparticle-introduced aqueous solution/hydrogel of amphiphilic polymer exhibits systematic changes in the size and the morphology of the self-assembled structures as well as the size and surface plasmon resonance of the incorporated AuNPs. Grown from the aqueous gold ion solution, the formed AuNPs contribute to the hydrophilicity of the aqueous polymer solutions/hydrogels possibly due to selective wetting of the hydrophilic block of the amphiphilic copolymer. Effective surface area (As) for AuNP formation in the organicinorganic hybrid selfassembly structures is evaluated according to the surfactant number (Ns); at the normal O/W phases, the size of the AuNPs becomes smaller as Ns increases because the effective As and the mean morphological curvature decrease, while the size of AuNP become larger again at the inverted (water-in-oil) phases due to effective swelling of the hydrophilic domain. Thermodynamically equilibrated AuNP growth increases the radius of gyration (Rg) and correlation length (ζ), as illustrated in Scheme 3. In addition, the increase in the density (α) of the solution/hydrogel state of the self-assembled system is especially effective in the reverse W/O phase possibly because the AuNP introduction increases the volume of the hydrophilic discontinuous domain. In addition to the size of the nanoparticle, the template structure and the location of the formed AuNPs are significantly important for the physical properties of the nanoparticle-incorporated hybrid
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system. The formula of the polymer has been considered as one of the important factors to control the AuNP formation because the reduction rate of gold ions also affects the final particle size and shape.3035 We find in this study that the different polymer formula is important because it also decides the self-assembly structure. The results obtained in this study would contribute to the basic understanding of the nanoparticle-incorporated hybrid system and would be broadly valuable to the biomedical applications as well as organicinorganic hybrid functional material developments.
’ ASSOCIATED CONTENT
bS
Supporting Information. Additional table and figures, and experimental procedures. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Tel.: +82-54-279-2169. Fax: +82-54-279-3199. E-mail: sjlee@ postech.ac.kr.
’ ACKNOWLEDGMENT This work was supported by the Creative Research Initiatives (Diagnosis of Biofluid Flow Phenomena and Biomimic Research) of the Ministry of Education, Science, and Technology (MEST) and the National Science Foundation (NSF) of Korea. This research was jointly supported by the World Class University program funded by the Ministry of Education, Science, and Technology (MEST) (R31-2008-000-10105-0). We are grateful for the valuable help with the small-angle X-ray scattering experiments performed at the 4C1 beamlines of the Pohang Accelerator Laboratory (PAL) (Pohang, Korea). ’ REFERENCES (1) Goodman, S. R. Medical Cell Biology, 3rd ed.; Academic Press: New York, 2007. (2) Chen, Y.; Bathula, S. R.; Yang, Q.; Huang, L. J. Invest. Dermatol. 2010, 130, 2790–2798. (3) Kukowska-Latallo, J. F.; Candido, K. A.; Cao, Z.; Nigavekar, S. S.; Istvan, J.; Majoros, I. J.; Thomas, T. P.; Balogh, L. P.; Khan, M. K.; Baker, J. R., Jr. Cancer Res. 2005, 65, 5317–5324. (4) Ahn, S.; Jung, S. Y.; Seo, E.; Lee, S. J. Biomaterials 2011, 32, 7191–7199. (5) Stephan, M. T.; Moon, J. J.; Um, S. H.; Bershteyn, A.; Irvine, D. J. Nat. Med. 2010, 16, 1035–1041. (6) Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.; Holmes, A. B. Chem. Rev. 2009, 109, 897–1091. (7) Schmid, G. Nanoparticles; Wiley-VCH: Weinheim, 2004. (8) Milliron, D. J.; Gur, I.; Alivasatos, A. P. MRS Bull. 2005, 30, 41–41. (9) Winkler, P. M.; Steiner, G.; Vrtala, A.; Vehkam€aki, H.; Noppel, M.; Lehtinen, K. E. J.; Reischl, G. P.; Wagner, P. E.; Kulmala, M. Science 2008, 319, 1374–1377. (10) Zhao, Y.; Thorkelsson, K.; Mastroianni, A. J.; Schilling, T.; Luther, J. M.; Rancatore, B. J.; Matsunaga, K.; Jinnai, H.; Wu, Y.; Poulsen, D.; et al. Nat. Mater. 2009, 8, 979–985. (11) Nie, Z.; Petukhova, A.; Kumacheva, E. Nat. Nanotechnol. 2009, 5, 15–25. (12) Lin, Y.; B€oker, A.; He, J.; Sill, K.; Xiang, H.; Abetz, C.; Li, X.; Wang, J.; Emrick, T.; Long, S.; Wang, Q.; Balazs, A.; Russell, T. P. Nature 2005, 434, 55–59. 22307
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