Controlled Assembly of Polymer-Tethered Gold Nanorods via a

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Letter

Controlled Assembly of Polymer-Tethered Gold Nanorods via a RayleighInstability-Driven Transformation: Implications for Biomedical Applications Tang-Yao Chiu, Ming-Hsiang Cheng, Chun-Wei Chang, Hao-Wen Ko, and Jiun-Tai Chen ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.9b00423 • Publication Date (Web): 16 Apr 2019 Downloaded from http://pubs.acs.org on April 17, 2019

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ACS Applied Nano Materials

Controlled Assembly of Polymer-Tethered Gold Nanorods via a Rayleigh-Instability-Driven Transformation: Implications for Biomedical Applications Tang-Yao Chiu,1 Ming-Hsiang Cheng,1 Chun-Wei Chang,1 Hao-Wen Ko,1 and Jiun-Tai Chen1,2* 1

Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan 30010

2

Center for Emergent Functional Matter Science, National Chiao Tung University, Hsinchu, Taiwan

30010

*To whom correspondence should be addressed. Email: [email protected]. Tel: 886-3-5731631

Abstract We study the assembly and morphology transformation of gold nanorods tethered with polystyrene ligands (AuNRs@PS). The AuNRs@PS nanotubes are first fabricated in the nanopores of anodic aluminum oxide (AAO) templates by the solution wetting method. When the samples are thermally annealed, the Rayleigh-instability-driven transformations of the nanostructures are triggered by the 1

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decrease of the interfacial energies between the nanotubes and the inner air cylinders. Four different morphologies are identified: nanotubes (I), undulated structures (II), Rayleigh-instability-induced structures (III), and nanorods (IV). The morphology diagrams of the AuNRs@PS structures using different thermal annealing temperatures and times are also made, showing that the morphology transformation rates are higher at increased annealing temperatures. This work has implications to be applied in different fields such as biomedical applications.

KEYWORDS: gold nanorods, hybrid nanostructures, Rayleigh instability, template method, thermal annealing

Introduction Owing to the unique surface plasmon resonance properties, gold nanorods (AuNRs) have been extensively studied in several research fields including bioimaging, drug delivery, photothermal therapy, and devices for sensing.1-6 AuNRs can be modified with inorganic materials such as silica or organic molecules such as alkylamines, alkanethiols, thiol-terminated polymers to offer better stability and versatility. The applications of modified AuNRs can be further extended by controlling the assembled structures.7-9 For instance, Kumacheva et al. not only fabricated AuNRs tethered with polystyrene ligands at both ends but also studied the self-assembly behavior of these pom-pom structures in the DMF/H2O mixture.10 Two independent variables were discussed; one is the molecular weight of the polystyrene and the other is the fraction of water in the DMF/H2O system. Under various conditions, the pom-pom structures can be triggered to form bundles, bundled chains, and chains structures.10 In 2


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addition, Zhu et al. introduced AuNRs@PS into cylindrical nanochannels of anodic aluminum oxide (AAO) membranes and fabricated AuNRs@PS hybrid nanostructures, of which the orientations of the AuNRs can be further controlled by applying electric fields.11 The experimental results demonstrated that AuNRs@PS can assemble into ordered structures by controlling the orientations of the electric field, molecular weights of the PS, and pore sizes of the AAO templates. Despite these works, the morphology transformation processes of modified AuNRs upon posttreatments, such as thermal annealing or solvent vapor annealing, are still not clear. In this study, we examine the morphology transformations of AuNRs@PS hybrid nanostructures restricted in the nanopores of AAO membrane via thermal annealing. The AuNRs@PS hybrid nanotubes are first made using a solution wetting method. Upon thermal annealing, the nanotubes change to undulated structures, Rayleigh-instability-induced structures, and nanorods, driven by the reduction of the interfacial energies between the nanotubes and the inner air cylinders. Morphology diagrams using different thermal annealing temperatures and times are also plotted to clarify the Rayleigh-instability-driven morphology transformation process. The results obtained in this work are related to the Rayleigh-instability-driven morphology transformation of polymer nanostructures restricted in nanochannels. Previously, Russell et al. examined the morphology transformation of poly(methyl methacrylate) (PMMA) nanostructures confined in the nanochannels of AAO membranes by thermal annealing.12 The surfaces of the PMMA nanotubes start to undulate for reducing the interfacial energies between the PMMA nanotubes and air. As the amplitudes of the surface undulation grow over time, the nanotubes undergo morphology transformation and eventually form PMMA nanorods with periodic encapsulated holes. Previously, we also studied the morphology transformation of PS nanotubes by thermal annealing.13 PS with higher molecular weights 3



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were observed to have slower kinetics in the morphology transformation processes. In another work, we further investigated the effect of the wall thickness on the morphology transformation of PS nanotubes confined in nanopores by thermal annealing; we demonstrated that the transformation kinetics of the PS nanostructures are not affected by the film thicknesses.14 Although many studies have been conducted, it is questionable whether the Rayleigh transformation can be applied to polymer metal hybrid nanomaterials concerning the optical properties and potential applications of hybrid nanomaterials, such as bioimaging, drug delivery, and photothermal therapy. Compared with the previous studies, this work using AuNRs@PS hybrid nanostructures not only extends the Rayleigh-instability-driven transformation to polymer metal hybrid nanomaterials but also offers new possibilities in controlling the morphologies of hybrid functional nanomaterials. This work also has implications to be applied in different fields. For example, Weissleder et al. proposed a therapeutic window, the wavelength ranges from 800 to 1200 nm, for bioimaging.15 In the region, there are several advantages such as fewer absorptions of hemoglobin and water. Gold nanorods, with tunable longitudinal surface plasmon resonance (LSPR) bands may meet the need of the window by adjusting their aspect ratios and become the promising materials for biological applications.16

Results and Discussion

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Figure 1. Schematic illustration of (a) modification and (b) fabrication processes of AuNRs@PS hybrid nanostructures.

Figure 1 shows the experimental processes to prepare the AuNRs@PS hybrid nanostructures. First, we adopt the modified seed-mediated method to synthesize the AuNRs stabilized by CTAB (CTABAuNRs). The modified seed-mediated method was proposed by Vigderman et al. using hydroquinone instead of ascorbic acid as the reducing agent to obtain highly monodisperse AuNRs.17 Compared with the traditional seed mediated method developed by Nikoobakht and El-Sayed et al, the modified method exhibits several advantages such as high gold conversion rates, low quantities of sphere-like byproducts, and tunable parameters for the longitudinal surface plasmon resonance (LSPR) band.18 After the preparation of the CTAB-AuNRs, two-step ligand exchange procedures are utilized to functionalize the AuNRs with PS of different molecular weights.

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AAO membranes with nanopores are commonly used as templates to prepare nanomaterials because the pore lengths, pore to pore distances, and pore diameters can be finely tuned.19-22 For infiltrating polymer chains into the nanopores of AAO templates to fabricate polymer nanostructures, four main wetting-based methods have been developed, which are the solution wetting method, the microwave annealing wetting method, the melt wetting method, and the solvent vapor annealing wetting method.23-27 In this work, AAO templates with an average pore diameter of ~237 nm and an average pore length of ~60 μm (Fig S1) are used to fabricate the AuNRs@PS hybrid nanostructures.28 The nanopores of the AAO membranes are filled by AuNRs@PS solutions by applying the solution wetting method. Through capillary force, the AuNRs@PS are infiltrated into the nanopores in the form of solution. Upon the evaporation of the solvents, the AuNRs@PS deposit on the walls of the nanopores. Empty spaces are formed because of the removal of the solvents. As a result, nanotubes instead of nanorods are generated. The hybrid nanotubes can then be isolated by selectively removing the AAO templates using 5 wt % NaOH(aq).

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Figure 2. (a) UV-Vis spectra and (a’) corresponding summary table of AuNRs with different modifications in the solution state. (b) Self-assembled monolayer of [email protected] k. (c) Graphical illustration, (d) SEM, and (e) TEM images of hierarchical hybrid nanotubes for [email protected] k. (b’) Self-assembled monolayer of AuNRs@PS53 k. (c’) Graphical illustration, (d’) SEM, and (e’) TEM images of hierarchical hybrid nanotubes for AuNRs@PS53 k.

The unique optical properties of AuNRs are owing to the localized surface plasmon resonance (SPR), the collective oscillation of conduction electrons within the metallic nanoparticle upon interaction with light, which can be observed simply by UV-Vis spectroscopy. Different from the isotropic gold nanospheres with only one SPR band, there are two SPR bands for AuNRs in the UV-Vis spectra because of the two disparate oscillation modes of the electrons; one near 500 nm is the transverse SPR (TSPR) band, and the other is the longitudinal SPR (LSPR) band. According to the theory proposed by Gans and the experimental results in recent studies, it is believed that the wavelengths of the LSPR bands can be tuned by adjusting the aspect ratios of the AuNRs.29-30 The optical properties of the synthesized AuNRs modified with CTAB and thiol-terminated polystyrene are measured by UV-Vis spectroscopy with a scanning range from 400 to 1200 nm, as shown in Figure 2a. From the summary table of the absorption bands (Figure 2a’), the TSPR bands for the CTAB-AuNRs solution, [email protected] k solution, and AuNRs@PS53 k solution show similar values at 513, 514, and 511 nm, respectively. The results agree with the previous studies that the TSPR bands are insensitive to the environment.30 On the other hand, the LSPR bands for the CTAB-AuNRs solution, [email protected] k solution, and AuNRs@PS53 k solution show distinct values at 828, 846, and 843 nm, respectively. The

7



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redshifted LSPR bands for the ligands changing from CTAB to PS can be attributed to the increased refractive index of the surrounding medium.31-34 To further understand the packing behaviors of the AuNRs tethered with PS of different molecular weights, self-assembled monolayers are prepared by dropping the AuNRs@PS solutions onto copper grids and drying the solvents.35 Figure 2b and 2b’ show the self-assembled monolayers of AuNRs tethered with PS5.8 k and PS53 k, where the interparticle distances are 3 and 26 nm, respectively. The TEM results indicate that the interparticle distances can be controlled by changing the molecular weights of the polymer ligands. After the characterization of the solutions and self-assembled monolayers of AuNRs@PS, the AuNRs@PS solution are introduced into the nanopores of the AAO templates using the solution wetting method.28 After the solvent evaporation process, the AuNRs@PS hybrid nanotubes then can be obtained by selectively removing the AAO templates with 5 wt % NaOH(aq). Figure 2c-e displays the graphical illustration, SEM, and TEM images of the [email protected]

k

nanotubes. The surface features of the

AuNRs can still be clearly observed in the SEM image (Figure 2d) because the AuNRs are covered by PS with lower molecular weights (PS5.8 k). The closer packing of the AuNRs with PS ligands of lower molecular weights in the nanotubes is also observed in the TEM image (Figure 2e). Figure 2c’-e’ displays the graphical illustration, SEM, and TEM images of AuNRs@PS53 k nanotubes. By comparison, the surface features of the AuNRs can barely be seen in the SEM image (Figure 2d’) because the AuNRs are covered by PS ligands with higher molecular weights (PS53 k). The larger interparticle distances in the nanotubes is also observed in the TEM image (Figure 2e’), which are caused by the PS ligands with higher molecular weights. It should be noted that the circular regions shown in the SEM images (Figure 2d and 2d’) are the holes of the polycarbonate filters (pore sizes ∼0.1 μm), which are used to conduct 8


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the filtration experiments for the polymer samples. The SEM image of a polycarbonate filter without any polymer sample is displayed in Figure S2.

Figure 3. (a) Rayleigh-instability-driven transformation of AuNRs@PS hybrid nanostructures restricted in the nanochannels of AAO membranes. SEM images of AuNRs@PS hybrid nanostructures with different morphologies: (b and c) nanotubes with different magnifications, (d) Rayleigh-instabilityinduced nanostructures, and (e) nanorods. The red arrows in (d) indicate the cavities. Inlets in Figure 3be are the corresponding illustrations of the AuNRs@PS hybrid nanostructures.

We then study the morphology transformation of the AuNRs@PS hybrid nanotubes restricted in the nanochannels of the AAO membranes upon thermal annealing. To trigger the morphology transformations of the AuNRs@PS hybrid nanotubes, it is critical to apply the appropriate annealing temperatures, which should be higher than the glass transition temperatures (Tg) of the polymers (polystyrene tethered with the AuNRs). The DSC measurements show that the Tg of PS-SH5.8 k and PS9



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SH53 k are 88 and 106 °C, respectively (Figure S3). Assuming that the thermal properties of PS-SH are similar to those of AuNRs@PS, we use 110 °C as the starting annealing temperature for the posttreatment experiments. For the samples annealed at different annealing temperatures and times, the released nanostructures are characterized mainly by SEM and the morphologies at different stages are determined. Based on the experimental results and literatures, we can divide the morphology transformation process into four stages during the annealing process.13 For the first stage (Stage I), the AuNRs@PS hybrid nanotubes are considered as the system of an air cylinder with a diameter of 2r surrounded by the polymer matrix. For the second stage (Stage II), the air cylinder starts to undulate with a wavelength of λ; the perturbations with λm = 8.89r possess the maximum growth rates.36-38 For the third stage (Stage III), the air cylinder breaks into air spheres with a diameter of 2R, forming short AuNRs@PS hybrid nanorods with periodic cavities, the Rayleigh-instability-induced nanostructures. For the fourth stage (Stage IV), two or more adjacent air spheres merge together, forming longer AuNRs@PS hybrid nanorods. Figure 3b-c shows the SEM images of an AuNRs@PS nanotube without cavities (Stage I). When the nanotubes are further annealed, Rayleigh-instability-induced nanostructures of AuNRs@PS can be obtained (Stage III), as shown in Figure 3d, where the periodic cavities (indicated by red arrows) can be seen. At longer thermal annealing times, AuNRs@PS hybrid nanorods can be further fabricated (Stage IV), as shown in Figure 3e. The SEM images of the hybrid nanorods with lower magnifications are also shown in Figure S4a,b, in which the nanorods with a larger scale can be observed. In addition, the TEM image of the hybrid nanorods is displayed in Figure S4c, in which the darker gold nanorods can be identified because of the higher electron densities.

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It should be noted that the undulated structures (Stage II) are difficult to be observed, implying that the undulated structures are relatively unstable compared with the structures in other stages.

Figure 4. (a) SEM images of the [email protected]

k

hybrid nanostructures under different annealing

conditions. (b) Corresponding morphology diagram. From the SEM data of the [email protected]

k

nanostructures (Figure 4a), three distinct

morphologies (hybrid nanotubes, Rayleigh-instability-induced nanostructures, and hybrid nanorods) can be observed. By determining the morphologies of the nanostructures at different annealing temperatures and times, a morphology diagram can be constructed, as plotted in Figure 4b, in which the hybrid nanotubes, Rayleigh-instability-induced nanostructures, and hybrid nanorods are denoted as blue solid diamond, brown solid circle, and green solid triangle, respectively. At higher annealing temperatures and longer times, hybrid nanorods (Stage IV) can be observed. At lower annealing temperatures and shorter times, it is interesting to observe that nanostructures with mixed morphologies, combination of the nanotubes (Stage I) and Rayleigh-instability-induced structures (Stage III) are always present. The results that the unstable undulated structures (Stage II) are not present in the morphology diagrams are similar to those of the previous studies using bare polymers.12-13 The results showing the occurrences of the mixed morphologies, combination of the nanotubes (Stage I) 11



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and Rayleigh-instability-induced structures (Stage III), however, are different from those of the previous studies, in which bare polymers are used.12-13 To explain the differences, the energy diagrams of the different materials under the annealing processes are proposed, as shown in Figure S5. When bare polymers such as PMMA or PS are used, the Rayleigh-instability-induced nanostructures (Stage III) are assumed to be in the metastable state (Figure S5a).12-13 As a result, it is easier to obtain the Rayleighinstability-induced nanostructures (Stage III). When AuNRs@PS hybrid nanostructures are used, in our case here, the Rayleigh-instability-induced nanostructures are supposed to be in the unstable state (Figure S5b). Therefore, mixed morphologies, combination of the nanotubes (Stage I) and Rayleighinstability-induced structures (Stage III), are present. The differences between the energy diagrams are probably caused by the immobile AuNRs cores, which may affect the transformation kinetics of the polymer chains during the annealing processes. It has to be noted that, even though we define the same mixed morphology (combination of nanotubes and the Rayleigh-instability-induced structures) in the morphology diagram of [email protected] k

after the thermal annealing processes at 120 °C and 110 °C for 10 h, higher ratios of the Rayleigh-

instability-induced structures (Stage III) are observed in the [email protected] k hybrid nanostructures for the samples annealed at 120 °C than those annealed at 110 °C. Besides, the morphology transformation rates are observed to be higher at increased annealing temperatures. For instance, under thermal annealing at 130 °C, the [email protected]

k

hybrid nanotubes can convert into nanorods after 1 h; by

comparison, it takes at least 15 h for the nanostructures annealed at 120 °C or 110 °C.

12


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Figure 5. (a) SEM images of the AuNRs@PS53

k

hybrid nanostructures under different annealing

conditions. (b) Corresponding morphology diagram. Similar results are observed for AuNRs tethered with PS ligands of higher molecular weights. Figure 5a,b shows the morphology diagrams of AuNRs@PS53

k

using different thermal annealing

temperatures and times. The morphology transformation rates are also observed to be higher at increased annealing temperatures. For instance, under thermal annealing at 120 °C, the [email protected] k hybrid nanotubes can convert into nanorods after 3 h; by comparison, it takes at least 24 h for the nanostructures annealed at 110 °C. When higher molecular weights of PS are used, we expect that the transformation rates will be lower, as demonstrated in the previous study.13 On the contrary to what we have expected, AuNRs@PS with higher molecular weights of PS have higher transformation rates in the Rayleigh instability transformation. The unexpected outcomes may result from the presence of the gold nanorods in the hybrid materials; for instance, the graft densities and the packing behaviors of polystyrene tethered on the gold nanorods may influence the transformation kinetics of the nanostructures from nanotubes to nanorods.

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After the formation of the AuNRs@PS hybrid nanorods, we also study the transformation processes of the hybrid nanorods without the confinement of the nanopores. The AuNRs@PS hybrid nanorods are annealed in ethylene glycol, which was preheated to 120 °C. The morphologies of the AuNRs@PS nanostructures with different molecular weights of PS (5.8 and 53 kg/mol) are observed to transform from nanorods to nanoclusters, as shown in Figure S6. The diameters of the [email protected] k and AuNRs@PS53 k nanoclusters are ~337 and 346 nm, respectively.

Conclusion In conclusion, we investigate the morphology transformation processes of the hybrid nanotubes restricted in the nanochannels of AAO membranes annealed at various temperatures and times. The AuNRs@PS nanotubes are first fabricated in the nanopores by the solution wetting method. During the thermal annealing processes, the Rayleigh-instability-driven transformations of the nanostructures are triggered by the reduction of the interfacial energies between the nanotubes and the inner air cylinders. Morphologies at four different stages (Stages I-IV) are identified, which are nanotubes (I), undulated structures (II), Rayleigh-instability-induced structures (III), and nanorods (IV). The morphology diagrams of the AuNRs@PS nanostructures demonstrate that the morphology transformation rates are higher at increased annealing temperatures. In the future, we will further prepare AuNRs with different aspect ratios to study the effect of aspect ratios on the morphology transformation processes, such as gold nanoparticles (AuNPs) tethered with polymer ligands.

ASSOCIATED CONTENT Supporting Information available 14


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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsanm.XXXXXXX. Experimental section; SEM images of AAO templates and polycarbonate filters; DSC curves of polymers; SEM and TEM images of the hybrid nanorods and nanoclusters.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected]. ORCID Jiun-Tai Chen: 0000-0002-0662-782X Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the ﬁnal version of the manuscript. Funding This work was financially supported by the Center for Emergent Functional Matter Science of National Chiao Tung University from The Featured Areas Research Center Pro-gram within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan. This work was also supported by the Ministry of Science and Technology of the Republic of China (MOST-107-2628-E009-004-MY3).

Notes The authors declare no competing ﬁnancial interest

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References 1. Huang, X.; El-Sayed, I. H.; Qian, W.; El-Sayed, M. A., Cancer Cell Imaging and Photothermal Therapy in the near-Infrared Region by Using Gold Nanorods. J. Am. Chem. Soc. 2006, 128, 2115-2120. 2. von Maltzahn, G.; Centrone, A.; Park, J. H.; Ramanathan, R.; Sailor, M. J.; Hatton, T. A.; Bhatia, S. N., Sers‐Coded Gold Nanorods as a Multifunctional Platform for Densely Multiplexed near‐Infrared Imaging and Photothermal Heating. Adv. Mater. 2009, 21, 3175-3180. 3. Wei, Q.; Ji, J.; Shen, J., Synthesis of near‐Infrared Responsive Gold Nanorod/Pnipaam Core/Shell Nanohybrids Via Surface Initiated Atrp for Smart Drug Delivery. Macromol. Rapid Commun. 2008, 29, 645-650. 4. Takahashi, H.; Niidome, T.; Nariai, A.; Niidome, Y.; Yamada, S., Photothermal Reshaping of Gold Nanorods Prevents Further Cell Death. Nanotechnology 2006, 17, 4431. 5. Niidome, T.; Akiyama, Y.; Shimoda, K.; Kawano, T.; Mori, T.; Katayama, Y.; Niidome, Y., In Vivo Monitoring of Intravenously Injected Gold Nanorods Using near‐Infrared Light. Small 2008, 4, 1001-1007. 6. Jayabal, S.; Pandikumar, A.; Lim, H. N.; Ramaraj, R.; Sun, T.; Huang, N. M., A Gold NanorodBased Localized Surface Plasmon Resonance Platform for the Detection of Environmentally Toxic Metal Ions. Analyst 2015, 140, 2540-2555. 7. Pastoriza-Santos, I.; Pérez-Juste, J.; Liz-Marzán, L. M., Silica-Coating and Hydrophobation of Ctab-Stabilized Gold Nanorods. Chem. Mater. 2006, 18, 2465-2467. 8. Xie, Y.; Guo, S.; Ji, Y.; Guo, C.; Liu, X.; Chen, Z.; Wu, X.; Liu, Q., Self-Assembly of Gold Nanorods into Symmetric Superlattices Directed by Oh-Terminated Hexa (Ethylene Glycol) Alkanethiol. Langmuir 2011, 27, 11394-11400. 9. Liu, K.; Zheng, Y.; Lu, X.; Thai, T.; Lee, N. A.; Bach, U.; Gooding, J. J., Biocompatible Gold Nanorods: One-Step Surface Functionalization, Highly Colloidal Stability, and Low Cytotoxicity. Langmuir 2015, 31, 4973-4980. 10. Nie, Z.; Fava, D.; Rubinstein, M.; Kumacheva, E., “Supramolecular” Assembly of Gold Nanorods End-Terminated with Polymer “Pom-Poms”: Effect of Pom-Pom Structure on the Association Modes. J. Am. Chem. Soc. 2008, 130, 3683-3689. 11. Wang, K.; Jin, S.-M.; Xu, J.; Liang, R.; Shezad, K.; Xue, Z.; Xie, X.; Lee, E.; Zhu, J., ElectricField-Assisted Assembly of Polymer-Tethered Gold Nanorods in Cylindrical Nanopores. ACS nano 2016, 10, 4954-4960. 12. Chen, J.-T.; Zhang, M.; Russell, T. P., Instabilities in Nanoporous Media. Nano Lett. 2007, 7, 183-187. 16


Page 17 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


13. Tsai, C.-C.; Chen, J.-T., Rayleigh Instability in Polymer Thin Films Coated in the Nanopores of Anodic Aluminum Oxide Templates. Langmuir 2013, 30, 387-393. 14. Tsai, C.-C.; Chen, J.-T., Effect of the Polymer Concentration on the Rayleigh-Instability-Type Transformation in Polymer Thin Films Coated in the Nanopores of Anodic Aluminum Oxide Templates. Langmuir 2015, 31, 2569-2575. 15.

Weissleder, R., A Clearer Vision for in Vivo Imaging. Nature Biotechnology 2001, 19, 316-317.

16. Jain, P. K.; Huang, X.; El-Sayed, I. H.; El-Sayed, M. A., Noble Metals on the Nanoscale: Optical and Photothermal Properties and Some Applications in Imaging, Sensing, Biology, and Medicine. Accounts of chemical research 2008, 41, 1578-1586. 17. Vigderman, L.; Zubarev, E. R., High-Yield Synthesis of Gold Nanorods with Longitudinal Spr Peak Greater Than 1200 Nm Using Hydroquinone as a Reducing Agent. Chem. Mater. 2013, 25, 14501457. 18. Nikoobakht, B.; El-Sayed, M. A., Preparation and Growth Mechanism of Gold Nanorods (Nrs) Using Seed-Mediated Growth Method. Chem. Mater. 2003, 15, 1957-1962. 19. Masuda, H.; Fukuda, K., Ordered Metal Nanohole Arrays Made by a Two-Step Replication of Honeycomb Structures of Anodic Alumina. Science 1995, 268, 1466-1468. 20. Hulteen, J. C.; Martin, C. R., A General Template-Based Method for the Preparation of Nanomaterials. Journal of Materials Chemistry 1997, 7, 1075-1087. 21. Li, A.; Müller, F.; Birner, A.; Nielsch, K.; Gösele, U., Hexagonal Pore Arrays with a 50–420 Nm Interpore Distance Formed by Self-Organization in Anodic Alumina. J. Appl. Phys. 1998, 84, 60236026. 22. Martin, C. R., Template Synthesis of Electronically Conductive Polymer Nanostructures. Accounts of chemical research 1995, 28, 61-68. 23. Steinhart, M.; Wendorff, J.; Greiner, A.; Wehrspohn, R.; Nielsch, K.; Schilling, J.; Choi, J.; Gösele, U., Polymer Nanotubes by Wetting of Ordered Porous Templates. Science 2002, 296, 19971997. 24. Cepak, V. M.; Martin, C. R., Preparation of Polymeric Micro-and Nanostructures Using a Template-Based Deposition Method. Chem. Mater. 1999, 11, 1363-1367. 25. Mei, S.; Feng, X.; Jin, Z., Polymer Nanofibers by Controllable Infiltration of Vapour Swollen Polymers into Cylindrical Nanopores. Soft matter 2013, 9, 945-951. 26. Chen, J. T.; Lee, C. W.; Chi, M. H.; Yao, I. C., Solvent‐Annealing‐Induced Nanowetting in Templates: Towards Tailored Polymer Nanostructures. Macromol. Rapid Commun. 2013, 34, 348-354. 17



Page 18 of 19

27. Chang, C.-W.; Chi, M.-H.; Chu, C.-W.; Ko, H.-W.; Tu, Y.-H.; Tsai, C.-C.; Chen, J.-T., Microwave-Annealing-Induced Nanowetting: A Rapid and Facile Method for Fabrication of OneDimensional Polymer Nanomaterials. RSC Adv. 2015, 5, 27443-27448. 28. Ko, H.-W.; Chang, C.-W.; Chi, M.-H.; Chu, C.-W.; Cheng, M.-H.; Fang, Z.-X.; Luo, K.-H.; Chen, J.-T., Hierarchical Hybrid Nanostructures: Controlled Assembly of Polymer-Encapsulated Gold Nanoparticles Via a Rayleigh-Instability-Driven Transformation under Cylindrical Confinement. RSC Adv. 2016, 6, 54539-54543. 29.

Gans, R. v., über Die Form Ultramikroskopischer Goldteilchen. Ann. Phys. 1912, 342, 881-900.

30. Huang, X.; Neretina, S.; El‐Sayed, M. A., Gold Nanorods: From Synthesis and Properties to Biological and Biomedical Applications. Adv. Mater. 2009, 21, 4880-4910. 31. Kekicheff, P.; Spalla, O., Refractive Index of Thin Aqueous Films Confined between Two Hydrophobic Surfaces. Langmuir 1994, 10, 1584-1591. 32. Yu, C.; Irudayaraj, J., Quantitative Evaluation of Sensitivity and Selectivity of Multiplex Nanospr Biosensor Assays. Biophysical journal 2007, 93, 3684-3692. 33. Sultanova, N.; Kasarova, S.; Nikolov, I., Characterization of Optical Properties of Optical Polymers. Optical and Quantum Electronics 2013, 45, 221-232. 34. Chen, H.; Kou, X.; Yang, Z.; Ni, W.; Wang, J., Shape-and Size-Dependent Refractive Index Sensitivity of Gold Nanoparticles. Langmuir 2008, 24, 5233-5237. 35. Wasserman, S. R.; Biebuyck, H.; Whitesides, G. M., Monolayers of 11-Trichlorosilylundecyl Thioacetate: A System That Promotes Adhesion between Silicon Dioxide and Evaporated Gold. Journal of Materials Research 1989, 4, 886-892. 36. Rayleigh, L., On the Instability of Jets. Proceedings of the London mathematical society 1878, 1, 4-13. 37. Plateau, J., Experimental and Theoretical Statics of Liquids Subject to Molecular Forces Only. Transl. Annu. Rep. Simthsonian Inst. 1873, 1863− 1866. 38. Nichols, F., Surface-(Interface-) and Volume-Diffusion Contributions to Morphological Changes Driven by Capillarity. Trans. Aime 1965, 233, 1840-1848.

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Controlled Assembly of Polymer-Tethered Gold Nanorods via a Rayleigh-Instability-Driven Transformation: Implications for Biomedical Applications Tang-Yao Chiu, Ming-Hsiang Cheng, Chun-Wei Chang, Hao-Wen Ko, and Jiun-Tai Chen*

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Controlled Assembly of Polymer-Tethered Gold Nanorods via a

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