Carbon-Coated Gold Nanorods: A Facile Route to Biocompatible

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Carbon-Coated Gold Nanorods: A Facile Route to Biocompatible Materials for Photothermal Applications Yusuf Valentino Kaneti, Chuyang Chen, Minsu Liu, Xiaochun Wang, Jia Lin Yang, Robert Allen Taylor, Xuchuan Jiang, and Aibing Yu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b07975 • Publication Date (Web): 04 Nov 2015 Downloaded from http://pubs.acs.org on November 10, 2015

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ACS Applied Materials & Interfaces

Carbon-Coated Gold Nanorods: A Facile Route to Biocompatible Materials for Photothermal Applications Yusuf Valentino Kaneti1, Chuyang Chen1, Minsu Liu2, Xiaochun Wang3, Jia Lin Yang3, Robert Allen Taylor4, 5, Xuchuan Jiang2,∗, Aibing Yu2 1

School of Materials Science and Engineering, The University of New South Wales, Sydney,

NSW 2052, Australia 2

Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia

3

Sarcoma and Nanooncology Group, Adult Cancer Program, prince of Wales Clinical School and

Lowy Cancer Research Centre, Faculty of Medicine, The University of New South Wales, Sydney, NSW, 2052, Australia 4

School of Mechanical and Manufacturing Engineering, The University of New South Wales,

Sydney, NSW, 2052, Australia 5

School of Photovoltaic and Renewable Energy Engineering, The University of New South

Wales, Sydney, NSW 2052, Australia

Abstract Gold nanorods and their core-shell nanocomposites have been widely studied because of their well-defined anisotropy and unique optical properties and applications. This study demonstrates a facile hydrothermal synthesis strategy for generating carbon coating on gold nanorods (AuNRs@C) under mild conditions (99.9%), potassium bromide (KBr, >99%), sodium citrate (NaC6H5O7, 99%), sodium borohydride (NaBH4, 99%), thiol-terminated polyethylene glycol (PEG SH, Mw = 5000) and Dulbecco’s Modified Eagle’s Medium (DMEM) with 1% of penicillin-streptomycin (PS) and 10% of fetal bovine serum (FBS). All glassware was cleaned with fresh aqua regia, rinsed with distilled water, and then dried before use.

2.2 Synthesis of Au seeds The seed solution for AuNRs was prepared based on a previous method with slight modifications.43 In a typical procedure, 5 mL of 0.5 mM HAuCl4 solution was mixed with 5 mL of 0.2 M CTAB solution. Then, 0.6 mL of fresh 0.01 M NaBH4 solution was diluted to 1 mL

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with water and was subsequently added into the Au(III)-CTAB solution under vigorous stirring (1000 rpm). The color of the solution changed from yellow to brownish-yellow, indicating the formation of the gold seeds, while the stirring was stopped after 2 minutes. The seed solution was aged for 30 minutes at room temperature prior to use.

2.3 Synthesis of Au nanorods (AuNRs) The Au seeds were processed further to convert them into AuNRs. In a typical procedure, 1.8 g of CTAB together with 0.7 g of KBr was dissolved in 50 mL of warm distilled water in a 150 mL Erlenmeyer flask. The solution was cooled down to 30 ºC, followed by the addition of 6 mL of 4 mM AgNO3 solution. The mixture was kept undisturbed at 30 ºC for 15 minutes, after which 50 mL of 1 mM HAuCl4 solution and a small amount of HCl (37 wt% in water, 12.1 M) were added. After 15 minutes of slow stirring (400 rpm), 0.9 mL of 0.064 M ascorbic acid was added, and the solution was then vigorously stirred for 2 minutes until it became colorless. The final colorless solution represents the ‘growth solution’, which contained 0.05 M of CTAB and was used straight after preparation. Finally, 0.18 mL of the seed solution was injected into the growth solution. The resultant mixture was stirred for 5 minutes and left undisturbed at 30 ºC for overnight. The products were isolated by centrifugation at 14,000 rpm for 15 minutes, followed by the removal of the supernatant. The precipitates were then re-dispersed in 10 mL of water for further coating experiments. The detailed synthesis conditions of the AuNRs in this study can be found in Table S1 in Supporting Information.

2.4 Synthesis of carbon-coated gold nanorods (AuNRs@C)


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In a typical synthesis procedure, three steps were involved. First, 5 mL of the as-prepared AuNRs solution was added into 10 mL of distilled water with stirring to ensure homogeneous mixing. Second, 5 mL of glucose solution (0.01 M) was dissolved in the above mixture, followed by vigorous stirring for 10 minutes and then sealed in a Teflon-lined stainless-steel autoclave. The autoclave was heated at 180 ºC for 5 h and then cooled to room temperature naturally. The effect of incubation time was explored by interrupting the shell growth at various times: 0, 3, 5, 8 and 24 h, with the other experimental parameters kept constant. Finally, the products were washed thoroughly with water twice, and subsequently stored in water for later use. The steps for the preparation of AuNRs@C are summarized in Figure S2.

2.5 Synthesis of PEG-coated gold nanorods The PEG-coated AuNRs were synthesized by following a previously reported procedure.44 In a typical synthesis, 5 mL of the as-prepared AuNRs solution was added into 10 mL of distilled water under magnetic stirring to ensure homogeneous mixing. Next, 1 mg of PEG-SH (Mw= 5000) was added to the AuNRs solution and stirred for 2 h to covalently modify the surface of the AuNRs with PEG. Finally, the resulting PEG-coated AuNRs were collected by centrifugation at 10,000 rpm for 30 minutes and subsequently washed twice with distilled water. The PEGcoated AuNRs solution was stored at 4 °C to prevent aggregation.

2.6 Characterization The as-prepared AuNRs and AuNRs@C were characterized using various advanced techniques, including: (i) electron microscopy to determine the morphology and size of the nanostructures using a Tecnai G20 transmission electron microscope, with an accelerating voltage of 200 kV


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and a FEI Nova NanoSEM 230 (scanning electron microscopy); (ii) the lattice structure of the AuNRs@C was characterized by HRTEM using a Phillips CM200 field emission gun TEM operated at 200 kV; and (iii) the UV–Vis spectra was obtained using a Cary 5000 UV–Vis NIR spectrophotometer, with a 1 cm quartz cell.

2.7 Photothermal measurements Two methods of temperature measurement were used in the testing of these fluids: thermocouples and an infrared (IR) camera. For the thermocouple measurements (using Delta OHM HD2128.2 T-type), there is one major drawback – the metallic probes of the thermocouples can themselves be heated by the light source (laser power density = 0.17 W/cm2). Thus, the thermocouple probe must be placed outside the incident beam to avoid significant bias error (via direct radiative heating) above the fluid temperature. Since temperatures are needed inside the irradiated spot, the second method (using the infrared camera) was primarily relied upon to give an accurate and reliable temperature measurement. For this method, a Cedip Titanium 560M IR camera was used. This camera produces up to 640 × 512 pixel resolution images at frame rates of up to 100 Hz. The pixels are square with dimension 24 × 24 µm. The CCD chip in the camera is sensitive to wavelengths between 3.6 and 5.1 µm, so only the thermal emission from the fluid is seen in the images as the 0.8 µm laser wavelength is invisible to the camera’s sensor.

The camera was first calibrated with a calibration file, and the temperature range is set to the narrow range expected for the experiment, namely 0-60 ºC, for a high accuracy. The temperature measured by the IR camera was also verified using a hot plate and a thermocouple (i.e. without


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the laser), which indicated negligible temperature difference measured by the two approaches, suggesting that the calibrated IR camera measurement is reliable and accurate (with an error between 0.1-1 °C). It should be noted, however, that the temperature measured by the IR camera is only of the first 100 µm of the fluid (e.g. the front surface) because the average absorption coefficient for water between 3.6 and 5.1 µm is ~288 cm-1. That is, externally emitted radiation can only arise from the outermost layer since more than 95% of IR emission signal in this spectral range is re-absorbed in a 100 µm thickness of water. For the photothermal measurements, we have selected AuNRs with an aspect ratio of 3.7 as the primary sample.

2.8 Toxicity Evaluation In this study, two types of human soft tissue sarcoma cell lines were used: HT1080 (ATCC® CCL-121™) and GCT (ATCC® TIB-223™). HT1080 is a fibrosarcoma cell line, established from a primary biopsy tissue culture of a primary fibrosarcoma. The sample was taken before any systemic therapies including radio and chemotherapy, to avoid unwanted mutations in the cells. The model cells were plated at cell density 2×103 cells in 100 µL of complete media per well and cultured in 96-well microplates. The complete media included Dulbecco’s Modified Eagle’s Medium (DMEM), 1% of penicillin-streptomycin (PS) and 10% of fetal bovine serum (FBS). Different concentrations of nanoparticles in 2 times of final concentration in 100 µL of the complete media or only control media were added to relevant wells 24 hours after plating. The wells were incubated for the chosen time points (up to 4 days) and then counted or fixed, stained and imaged. All incubations were performed at 37 ºC and 5% CO2. The experiment testing cytotoxic effect of different types of AuNRs against media control was performed triplicately. The procedure to obtain a cell growth curve in this study involved initially adding 2×103, 4×103,


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6×103, and 8×103 of cells with media triplicately into different wells of 96-well flat bottom plates. The cells were cultured at the specific end-point (up to four days) before harvest. The cell number was determined by counting the cells from a small volume of harvested cell culture samples using a hemocytometer every 24 hours under an optical microscope. Each square of the hemocytometer slide grid represents a volume of 10-7/m3, and cells were counted in 10 squares in 1 mL of the cell suspension. Cell suspensions were mixed for uniform distribution and were diluted enough so that the cells did not aggregate. By means of a graphical analysis of the data, the cell growth curve was obtained, in which the stained signals of the valid and cultured cells from the crystal violet colorimetric assay were quantified by a plate reader introduced below.

Cell viability was measured using the crystal violet colorimetric assay for cell counting with following four-day continuous exposure to the nanoparticles. For viability, exponentially growing cells were dispensed into a 96-well flat bottom plate at a concentration of 4×103 cells/well in 200 µl of media, after incubating 24 hours for cell attachment, the nanoparticle solutions (i.e. AuNRs) were diluted appropriately in fresh media and 100 µL of different concentrations of individual NR solutions was added into each well. Triplicate wells per sample were applied. The media was not changed during the incubation. Following four days of incubation at 37 ºC and 5% CO2, each well was washed by Dulbecco’s phosphate buffered saline (DPBS) twice. Next, 0.5% of 100 µL of crystal violet in DPBS solution was added into each well and incubated for 10 minutes at room temperature to fix and stain the cells. Following rinsing with three changes of distilled water, all excess stain was removed and the plate was left upside down for overnight to allow each well to dry completely. After drying, pipette 100 µL of the elution solution (0.1 M Sodium citrate + 100% ethanol) solution into each well and gently


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moved side to side for about 30 minutes at room temperature. Finally, read the absorbance of dye solutions at 540nm on a plate reader (Tecan; Austria) to obtain Optical Density (OD) value. The growth of experimentally treated cells was compared to control cells, by following a previous study.5

3. Results and Discussion 3.1 Synthesis of carbon-coated gold nanorods (AuNRs@C)

Figure 1. TEM images of AuNRs with an average aspect ratio of 5 (a-b); and they can assemble into ordered patterns as a monolayer (a-b) or multilayers (c-d) on substrate(s), through ‘shoulderto-shoulder’ (a-b) or ‘end-to-end’ (c-d) ways.


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To generate the final AuNRs@C, the AuNRs were initially synthesized as described above using a method modified from reported procedures.31, 45 The base AuNRs were then dispersed in an aqueous glucose solution and placed into an autoclave for further coating, following a modified procedure to our recent study on carbon-coated silver nanocables.46 In the present work, glucose was selected as a carbon source because it is already present in the bio-environment and its polymerized structure was observed to be stable (see Figure S1 in the Supporting Information).

Figure 2. TEM images showing the formation process of carbon shell on AuNRs (aspect ratio= 3.7) with increasing time: (a, b) Bare AuNRs at the initial stage; (c, d) 10-nm thick carbon shell after 3-hour reaction; (e, f) 17-nm thick carbon shell after 5-hour reaction; and (g, h) 25-nm thick carbon shell after 8 hours of reaction at 180 °C, respectively.

As indicated in our previous reports,10, 45 the presence of the polymerized glucose layer could be determined through an FT-IR analysis. Glucose is indicated by the presence of C=O vibration peak at around 1612 cm-1 and C=C stretching vibration peak at 1701 cm− 1, along with an O-H


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stretching peak at ~ 3425 cm− 1 and a C-OH stretching vibration at 1015–1374 cm− 1. This implies the existence of a large number of residual hydroxyl groups and intermolecular hydrogen bonds, allowing for a good dispersion in water.

Figure 1 shows the TEM images of the as-prepared AuNRs, with different magnifications. It was found that the surface of AuNRs is smooth, and ≥95% of them is spindle-shaped. By careful measurements of over 200 AuNRs, the average length (L) is ~57 nm and the width (W) of AuNRs is ~12 nm, namely, the aspect ratio (AR=L/W) is ~5. For tunable optical properties, gold nanorods could be fabricated with different aspect ratios (Figure S3) and optical properties (Figure S4). CTAB plays a crucial role in achieving shape and size-controlled gold nanorods. In the synthesis process, CTAB is added during the formation and growth of AuNRs. As such, CTAB forms micelles in the aqueous solution, acting as a “soft template” in the formation of AuNRs. CTAB then acts as a surface stabilizer and controls the direction of growth in the AuNRs. This occurs due to the fact that CTAB interacts specifically with the gold crystalline planes in the order of (100)≈(110)>(111).47 This assists the formation of rod-like or wire-like Au nanoparticles (AuNPs), similar to our previously reported research on silver nanowires.

Figure 2a-b shows the TEM images of the product obtained when the mixture solution with no glucose was reacted under the hydrothermal conditions described in Section 2.4. Clearly, no carbon shell was observed on the surface of the AuNRs. Figure 2c-h shows the TEM images of the AuNRs@C generated at different reaction times. Regardless of the reaction time, from 3-8 h, all of the AuNRs were carbon coated; however, bridges (sintering) existed between the carbon coatings on a small fraction of the AuNRs. Sintering of the carbon shells results from glucose


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which not only polymerized on the surface of AuNRs but also between shells while being heated, consistent with observations made in previous studies of Ag@C,48 Fe@C,49 Ni@C,49 Co@C49, and [email protected] Figure 2c-d shows the TEM images of AuNRs@C obtained after a 3-h hydrothermal reaction, with a centre shell thickness of ~10 nm. After a 5-h reaction, the carbon shell thickness was around 17 nm (Figure 2e-f). After a full 8-h reaction process, the thickness of carbon shell increased to ~25 nm (Figure 2g-h). Clearly, the carbon shell gradually became thicker with increasing time, while the initial shape of the core AuNRs remained unchanged. However, as the reaction time increased, the shape of the carbon shell deviated from a rod-like shape to become more spherical. Such a change allows the particle to reduce the surface energy as the schematic shell growth (Figure S5). A plot of the shell thickness as a function of coating time is given in Figure S6, which shows an almost linear trend, expressed as: y = 3.1471x+ 0.4118 (R2= 0.9963).

Figure 3. UV-Visible spectra of AuNRs@C with different shell thicknesses. The surface plasmon resonances are centered at ~800 nm (bare AuNRs with aspect ratio of 3.7), 820 nm (10nm shell), 830 nm (17-nm shell) and 850 nm (25-nm shell), respectively.


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The UV-Vis absorption properties of the AuNRs@C were measured. Figure 3 shows UV-Vis absorption spectra of AuNRs@C with different carbon shell thicknesses. For non-coated AuNRs, two characteristic plasmon bands were observed: one strong longitudinal band is centered at ~800 nm, which was caused by electron oscillation along the long axis; while another weak plasmon resonance centered at ~520 nm could be attributed to the transverse resonance mode. This surface plasmon resonance is similar to that of Au nanospheres with diameter of ~15 nm. As the thickness of the carbon shell increased from 10, 17, to 25 nm, the strong longitudinal absorption peaks were observed to shift to a longer wavelength of ~820, ~830 and ~850 nm, respectively. The shift was probably caused by the changes in scattering and absorption due to the change in effective refractive index of polymerized glucose relative to water.51

As carbon possesses a higher refractive index (ncarbon =1.6–2.0) than water (nwater = 1.33), the carbon coating is likely to induce an increase in the effective dielectric constant.20, 51 This is further supported by previous studies on the optical properties of other amorphous carbon-coated near infrared (NIR) light absorbing metal nanostructures such as Cu@C50 and Co@C,52 where the red-shift in the optical properties of carbon-coated metal nanoparticles were also attributed to the increase of the effective dielectric constant of the surrounding medium (water) due to the higher refractive index of carbon shell relative to water. Moreover, the absorption intensity of the AuNRs@C gradually decreased with increasing shell thickness (with the total solid mass (carbon + gold) normalized). This may be caused by the polymerized glucose that can weaken the gold surface electron oscillation, and subsequently affect the intensity of surface plasmon resonance.21-22 Specifically, the exact position of the plasmon band is very sensitive both to


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particle size and shape and to the optical and electronic properties of the medium surrounding the particle.53

The above TEM and UV results clearly indicate that the proposed hydrothermal strategy could be used for the synthesis of AuNRs@C with tunable aspect ratios and optical properties. By this newly developed synthesis method, there were no individual carbon particles formed in the final product, suggesting that self-nucleation of carbonized glucose have been significantly suppressed in this reaction system, due to the existence of the AuNRs that can act as the nucleation centers for glucose polymerization.45 Interestingly, although not the focus of this study, this newly developed synthesis strategy can be just as easily applied to other gold nanoparticles (e.g. spheres, cubes or triangles), as shown in Figure S7 (Supporting Information).

The effect of reaction time on the formation of carbon shell on the AuNPs was also studied. As shown in Figure S7a-b, no carbon coating was observed around the AuNPs, suggesting that in the current system, a reaction time of 1.5-3 hours was not sufficient for the nucleation of carbon nanoparticles. However, as the reaction time was increased to 4.5 hours, a large clump of carbon was observed outside the AuNPs, indicating the nucleation and initial formation of carbon nanoparticles as a result of the carbonization of glucose (Figure S7c). As the reaction time was prolonged to 8 hours, a complete formation of the carbon shell from the carbon nanoparticles was obtained (Figure S7d). A further increase in reaction time to 24 hours yielded a thicker carbon shell of ~50 nm around the AuNPs, suggesting the growth of the carbon shell continues with increasing reaction time (Figure S7e).


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3.2 Structural features of AuNRs@C

Figure 4. TEM and HRTEM images showing the AuNRs (a-b) and the AuNRs@C (c-d), with characteristic crystalline lattices of Au{200}, Au{220} and Au{111}, while the carbonaceous shell is amorphous (d).


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To inspect the crystal structure of the AuNRs before and after carbon coating, high-resolution TEM (HRTEM) was employed. Figure 4 shows the morphology and crystal structures of both pure AuNRs (Figure 4a-b) and AuNRs@C (Figure 4c-d). A careful inspection of a single AuNR circled in Figure 4a shows that the obtained AuNR was well crystallized with clear lattice fringes (Figure 4b), in which the Au{111} planes were predominant, with a lattice spacing of ~0.238 nm. Further analysis shows that Au{200} and Au{220} crystallographic planes were also identified, with d-spacing of ~0.204 nm and 0.145 nm, respectively.54 The angles between Au{111} and Au{200} or {220} were separately measured to be 54.5º and 35.3º in the selected Au nanorod. These results are in good agreement with previous reports.30-31

For comparison, the lattice structures of the AuNRs@C were also inspected by HRTEM, as shown in Figure 4c. Figure 4d shows the HRTEM image of a single AuNR@C from the circled section in Figure 4c, indicating that the well-crystallized structure of the AuNRs was not affected by the carbon surface coating under hydrothermal conditions. It was found that the Au core is dominated by {200} crystallographic planes with a growth direction of . The carbon shell of the AuNRs@C was amorphous (as marked by the dotted line in Figure 4d). Graphitic carbon shells were not present as they can only be obtained by heat treatments at temperatures of 6001000 °C.55-56

The generated AuNRs@C core-shell composites exhibit few unique structural features. The first feature is their stability at temperatures of < 200°C. The formation and growth of the carbon shell was conducted under mild hydrothermal conditions (160-180 °C), which suggests that such a polymerized glucose shell is stable at the temperature of ≤180 °C. This is consistent with our


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recent report on carbon-coated silver nanocables.3 Secondly, the carbon shell is rich of OH and C=O groups, as the shell is composed of polymerized glucose. This allows for easy dispersion of core-shell AuNRs@C in water and further linkage of biomolecules to the surface of the AuNRs@C composites in future application.57

3.3 Photothermal properties of AuNRs@C Because of their anisotropic shapes, AuNRs exhibit two distinct SPR bands, a weak transverse resonance mode at ~520 nm and an intense longitudinal resonance mode in the red/near infrared range (650-900 nm). The longitudinal mode can be adjusted from visible to near infrared regions by increasing the AuNRs aspect ratio.58 This enables their in-vivo biomedical applications, as NIR light has minimal absorption by skin and tissue, leading to minimal heating of healthy tissue and deeper tissue penetration (up to 10 cm).59-60 Furthermore, AuNRs have emerged as highly tunable plasmonic nanostructures that may be synthesized in bulk with narrow size distributions and optical absorption coefficients 104 to 106-fold higher than that of the conventional organic fluorochromes. On a per gram basis, the absorption coefficients of AuNRs well-exceed those of gold nanospheres and nanoshells.26, 58 These properties allow for many exciting possibilities for applications of AuNRs for NIR-resonant biomedical imaging modalities such as OCT, PAT, TPL and X-ray computed tomography (X-ray CT) and for hyperthermia therapy and gene/drug delivery. AuNRs have also previously been shown to be more efficient than Au nanoshells for photothermal therapy as they required lower laser intensity and they were more easily removed from the body than Au nanoshells.61 In comparison, other potential materials for photothermal treatments such as CuS nanoparticles often suffer from low photothermal conversion efficiency. With an 808 nm laser intensity setting, the laser power intensity required to cause sufficient cell


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death in the in vitro monolayer setting with Cu2S NPs was approximately 48-72 times higher than the conservative limit of ∼ 0.33 W/cm2 for human skin exposure (without nanoparticles).62

Figure 5. Photothermal tests of AuNRs@C (aspect ratio of ~3.7 and shell thickness of 17 nm). (a) Digital thermal images of the solutions as recorded by the IR camera (as depicted in Figure S5) show that higher the particle concentration results in a higher rise in temperature; and (b) temperature changes as a function of irradiation time and particle concentration (20, 50, and 200 µM) under 0.17 W/cm2 light irradiation.

To explore the AuNRs@C produced here as an alternative material for photothermal hyperthermia treatments, aqueous suspensions of AuNRs@C with different shell thicknesses were evaluated by measuring their temperature rise under laser irradiation, with a fixed low laser power intensity of 0.17 W/cm2, which is below the acceptable limit of 808 nm laser intensity


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setting for human skin exposure (0.33 W/cm2). This experiment represents an important in vitro performance test which determines the relative performance and tunability of these materials as effective photothermal absorbers. The set up for this test is shown in Figure S8 (Supporting Information). To match the central wavelength (λ= 800 nm) of the applied diode laser, we chose AuNRs with AR=3.7 and the longitudinal plasmonic absorption band centered at ~800 nm (Figure 2). This falls within the ‘near infrared therapeutic window’ (650-800 nm), usually used in biomedical applications.11 It should be noted that the nanorod’s longitudinal mode of plasmon resonance is utilized here, so having a thicker carbon layer at the rod’s ends is expected to diminish absorption efficiency. Thus, it is critical to conduct the macro-scale photothermal tests of this study to ensure the performance is acceptable.

Figure 5 shows the temperature change (∆T) of the suspension containing AuNRs@C particles with an aspect ratio of 3.7 and a shell thickness of 17 nm. Different colors from blue, green to red (Figure 5a) indicate the temperature rise with the concentration increase of AuNRs@C, from ∆T= 7.8, 9.3 to 10.8 ºC, corresponding to the particle concentrations of 20, 50 to 200 µM (Figure 6b), respectively. As expected, higher concentrations of AuNRs@C absorb more light in a shorter path length (e.g., volume) and, thus create a correspondingly larger temperature rise in the interrogation window. Additionally, while pure water absorbs some light under the same irradiation conditions (∆T= ~4.6 ºC), all of the nanoparticle samples achieve considerably higher temperatures. In addition, the rapid increase in temperature occurs within the initial 200 seconds and then begins to asymptotically approach a steady state temperature at long irradiation times, regardless of the particle concentrations (Figure 5b).


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The effect of the thickness of the carbon shell on the photothermal properties of AuNRs was also examined. Figure 6 shows the photothermal properties of AuNRs@C with different shell thicknesses, measured using the set-up shown in Figure S8. The color changes from blue (cold) to red (hot) indicate the temperature rise within the AuNRs@C suspension. The detailed temperature changes were recorded and shown in Figure 6b. Within the first 600 seconds of irradiation, the temperature rise is rapid for all three AuNRs@C and non-coated AuNRs. The temperature asymptotically approaches a steady state after 1200 seconds of irradiation. Due to the reduced light absorption of the functional coating, the three AuNRs@C exhibit lower temperature changes of 10.5 to 9.5 and 8.4 ºC corresponding to 10, 17 to 25 nm shell, respectively, than that of pure AuNRs (∆T= ~11 ºC) under similar conditions.

A similar trend was observed for Au@SiO2, in which a thicker SiO2 shell led to a decrease in the resulting temperature rise, e.g., a 5-nm thick SiO2 shell resulted in a loss of 5 °C in temperature rise as compared to bare AuNRs.53 The above results indicate that there is a reduction in the absorption with thicker carbon shell due to the change in the effective complex refractive index of the particle. However, considering the low laser power of our instrument (0.17 W/cm2), a temperature rise of 11 °C after 600 s irradiation is respectable. In previous studies, a laser power ranging from 3-22.3 W/cm2 was used to generate a temperature rise of 10-50 °C.24-25, 53, 63 This indicates that heating and the extent of surface modification are competing parameters which should be optimized for the particular application. In general, the carbon shell should be properly adjusted so as not to make it too thick to avoid significant reductions of the photothermal absorption of the core AuNRs. Additionally, it is important that the shell is not too thin to avoid exposure of any cytotoxic residual CTAB on the surface of the AuNRs. Fortunately, the


22

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flexibility of our coating method allows for adjustment of the shell thickness by simply modifying the reaction time.

Based on the above analysis, both pure AuNRs and AuNRs@C can lead to significant temperature increases by laser irradiation, which indicates their potential in photothermal therapy or through combining with targeted drug molecules. Depending on the treatment method, temperature rises of only 8-10 oC might be sufficient, however a higher temperature rise is highly possible with increased irradiation intensity and/or higher particle concentration. This is further supported by a number of previous studies.27, 63 For example, Hu et al.63 observed a significant rise in the ∆T of [email protected] aqueous solution from 10 to 22 °C, after 10 minutes of irradiation, with an increase in laser power from 10.8 to 22.3 W/cm2. Similarly in the report by Bian et al.27, increasing the laser power from 1 to 4 W/cm2 caused a significant increase in ∆T of their graphene-isolated Au nanocrystal solution from 6 to 50 °C after 6 minutes of laser irradiation. Furthermore, they also noted an increase in ∆T of graphene-isolated Au nanocrystal solution from 27 to 47 °C by increasing the particle concentration from 0.05 to 0.6 mg/mL, at a fixed laser power of 3 W/cm2. This is consistent with our finding in which an increase in AuNRs@C particle concentration from 20 to 200 µM, resulted in a change in ∆T from 7 to 11 °C, at a comparatively lower laser power of 0.17 W/cm2.


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Page 24 of 50

Figure 6. Photothermal tests of AuNRs@C (aspect ratio of ~3.7 and different shell thicknesses). (a) IR images of aqueous suspensions of AuNRs@C with a shell thickness of 17 nm at different laser irradiating times: 30, 60, 90, 180, 360 and 840 seconds, with a power of 0.17 W/cm2; and (b) temperature changes as a function of irradiation time and shell thicknesses from 0 nm (bare AuNRs), 10 nm, 17 nm, to 25 nm, respectively. The concentration of each suspension was adjusted to give an extinction intensity of 1.0 at 800 nm.

A comparison showing the heating efficiency of the prepared AuNRs@C composites against other widely used nanoparticles is shown in Table 1. As seen from Table 1, the AuNRs@C coreshell composites of this work can generate almost similar heating efficiency as [email protected],63 AuNRs@Pt,23 and graphene/AuNPs27 at a significantly lower input light intensity and particle concentration. Furthermore, the AuNRs@C can generate roughly half of the temperature


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increase achieved by AuNRs@mSiO2,24 AuNRs/PPy,25 and hollow Au nanoflowers64 at a much lower concentration/laser power as can be seen in the table. These results indicate good photothermal properties of the prepared AuNRs@C core-shell composites.

Table 1 A comparison of the heating efficiency of the prepared AuNRs@C composites against previously reported nanoparticles. Materials

Size

Power

Conc.

∆T

Time

(nm)

(W/cm2)

(µg/mL)

(°C)

(s)

Au@C NRs (10-nm shell)*

50

0.17

10.4

11

600

Au@C NRs (17-nm shell)*

50

0.17

10.4

9.5

600

[email protected]

50-60

10.8

20

10

600

AuNRs@mSiO224

50

3

20

22

180

AuNRs/PPy25

50

3

23.2

25

400

AuNRs@Pt23

60

10

100

15

400

Graphene/AuNPs27

65

1

300

7

360

Hollow Au nanoflowers64

115

9

400

21

600

Cu2S plates62

500-600

0.51#

250

17.3

300

* = This work, # used 980 nm laser; others used 808 nm laser

In general, the absorption of light would be at a maximum on the surface of the AuNRs (inside the shell). However, these experiments were conducted at steady state and the Biot number for such nanoparticles (including the shell in the characteristic length) can be calculated to be 0.05) and they are in the similar variation range as other study.67

Further analysis of Figure 7 showed that there was a noticeable increase in the cytotoxicity of CTAB-capped AuNRs with increasing concentration and this increase in toxicity could be attributed to free/unbound CTAB molecules which could originate from inadequate purification or desorption of CTAB from the surface of the AuNRs.32, 40 To confirm this theory, the CTABcapped AuNRs were centrifuged and excessively washed for 5 times with distilled water prior to incubation with the cells to remove unbound CTAB molecules (e.g. the samples labeled as "washed CTAB-capped AuNRs" in Figure S11). The cytotoxicity test results show that the


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Page 30 of 50

excessively washed CTAB-capped AuNRs were found to be significantly less cytotoxic than the as-prepared CTAB-capped AuNRs in both the HT1080 and the GCT cell lines, particularly at a concentration of >0.01 mg/mL. The drawback is that the excessive washing caused severe aggregation of the AuNRs (Figure S11a) compared to the as-prepared CTAB-capped AuNRs (Figure S11b) and this may limit the efficiency of the AuNRs to enter into cells. Aggregation occurs because CTAB plays a crucial role in directing the nanorod growth in one direction and preventing aggregation of the AuNRs by forming a bilayer on the surface of the nanorods.32 Other evidence that indirectly supports the toxicity of CTAB is the negligible toxicity of PEGcoated AuNRs compared to CTAB-capped AuNRs (Figure 7). As CTAB is toxic to living cells, a shell material which can minimize the toxicity associated with CTAB is necessary. In this study, we have successfully demonstrated the application of carbon coating to reduce the cytotoxicity caused by CTAB.

Overall, this study demonstrates the use a hydrothermal coating of biocompatible sugar (glucose) molecules on the surface of AuNRs for bio-applications. Furthermore, it also provides new insights into the heat generation capabilities and dose-dependent toxicity of AuNRs@C particles. Furthermore, the study also highlights the exemplary photothermal potential of the AuNRs@C with a low-power light source and their excellent biocompatibility in the concentration range of 0.005-0.05 mg/mL. The carbonaceous shell produced in this work is a soft, amorphous coating generated under hydrothermal conditions, largely different from the crystalline graphene layer generated by chemical deposition (CVD) method, as reported by Bian et al.

27

Moreover, the

produced carbon shell is chemically adsorbed to the surface of the AuNRs and its thickness can be easily controlled by simply adjusting the hydrothermal reaction time, as shown by the TEM


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images in Figure 2. This provides advantages over PEG molecules which are often only weakly adsorbed on the surface of AuNRs and are hard to control in terms of thickness. Hence, our AuNRs@C composites exhibit unique structural features and properties which are different from PEG- and graphene-coated Au nanoparticles for potential bio-applications. Furthermore, aside from being biocompatible, these thin amorphous carbon shells help to maintain the strong plasmonic absorption of the underlying AuNRs. Nonetheless, these AuNRs/C composites will be further modified in our future work with other biocompatible polymers to maximize their photothermal and cytotoxicity properties so that these particles can be applied for the photothermal destruction of sarcoma cancer cells, and for more detailed experiments such as cellular uptake and intracellular distribution.

4. Conclusions This study has demonstrated a simple hydrothermal synthesis method for the preparation of novel carbon coated gold nanorods (AuNRs@C) core-shell nanostructures with unique structural features and exemplary functional properties, as highlighted below: •

A facile and widely applicable coating strategy. This study has demonstrated a facile, yet highly controllable, hydrothermal strategy for the synthesis of carbon-coated gold nanorods (AuNRs@C) with good homogeneity and scalability, under moderate reaction conditions ( 500°C). Using this method, the thickness of the carbon shell can be easily adjusted from a few to tens nanometers, depending on the requirements. Furthermore, the proposed method was also found to be applicable to other Au nanoparticles (cubes, spheres) for achieving carbon-coated Au


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Page 32 of 50

nanostructures. This synthesis strategy may be extended to other materials such as metal oxides for a wide range of applications. •

Modifiable carbon structures. The carbon shells reported in this work have some unique structural features: (1) amorphous but stable at low temperatures of 90% cell viability, in the concentration range of 0.005-0.05 mg/mL, toward two soft tissue sarcoma cell lines (HT1080, ATCC® CCL-121™; and GCT, ATCC® TIB-223™).

Ultimately, these findings enable specifically tailored carbon-metal or metal oxide nanostructures which are ideally suited to tomorrow’s biomedical applications.


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Supporting Information. Synthesis conditions, optical properties and TEM of gold nanorods with different aspect ratios and their corresponding optical properties, the plot showing the variation in the thickness of the carbon shell with increasing reaction time and the applicability of the proposed carbon coating method to other Au nanostructures. The Supporting Information is available free of charge on the ACS Publications website.

Acknowledgments. We gratefully acknowledge the financial support of the Australian Research Council (ARC DP1096185, FT0990942) for this work. The authors also acknowledge access to the UNSW node of the Australian Microscopy and Microanalysis Research Facilities (AMMRF) and the facilities at Monash University.

References 1.

Dreaden, E. C.; Alkilany, A. M.; Huang, X.; Murphy, C. J.; El-Sayed, M. A., The Golden

Age: Gold Nanoparticles for Biomedicine. Chem. Soc. Rev. 2012, 41, 2740-2779. 2.

Sapsford, K. E.; Algar, W. R.; Berti, L.; Gemmill, K. B.; Casey, B. J.; Oh, E.; Stewart,

M. H.; Medintz, I. L., Functionalizing Nanoparticles with Biological Molecules: Developing Chemistries that Facilitate Nanotechnology. Chem. Rev. 2013, 113, 1904-2074. 3.

Dreaden, E. C.; Mackey, M. A.; Huang, X.; Kang, B.; EI-Sayed, M. A., Beating Cancer

in Multiple Ways Using Nanogold. Chem. Soc. Rev. 2011, 40, 3391-3404. 4.

Taylor, R.; Coulombe, S.; Otanicar, T.; Phelan, P.; Gunawan, A.; Lv, W.; Rosengarten,

G.; Prasher, R.; Tyagi, H., Small Particles, Big Impacts: A Review of the Diverse Applications of Nanofluids. J. Appl. Phys. 2013, 113, 011301.


33


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

5.

Page 34 of 50

Yang, J. L.; Qu, X. J.; Russell, P. J.; Goldstein, D., Regulation of Epidermal Growth

Factor Receptor in Human Colon Cancer Cell Lines by Interferon α. Gut 2004, 53, 123-129. 6.

Jin, S.; Ma, X.; Ma, H.; Zheng, K.; Liu, J.; Hou, S.; Meng, J.; Wang, P. C.; Wu, X.;

Liang, X.-J., Surface Chemistry-Mediated Penetration and Gold Nanorod Thermotherapy in Multicellular Tumor Spheroids. Nanoscale 2013, 5, 143-146. 7.

Chen, R.; Zheng, X.; Qian, H.; Wang, X.; Wang, J.; Jiang, X., Combined Near-IR

Photothermal Therapy and Chemotherapy Using Gold-Nanorod/Chitosan Hybrid Nanospheres to Enhance the Antitumor Effect. Biomater. Sci. 2013, 1, 285-293. 8.

Chen, P.-J.; Hu, S.-H.; Fan, C.-T.; Li, M.-L.; Chen, Y.-Y.; Chen, S.-Y.; Liu, D.-M., A

Novel Multifunctional Nano-Platform with Enhanced Anti-Cancer and Photoacoustic Imaging Modalities Using Gold-Nanorod-Filled Silica Nanobeads. Chem. Commun. 2013, 49, 892-894. 9.

Ren, F.; Bhana, S.; Norman, D. D.; Johnson, J.; Xu, L.; Baker, D. L.; Parrill, A. L.;

Huang, X., Gold Nanorods Carrying Paclitaxel for Photothermal-Chemotherapy of Cancer. Bioconjugate Chem. 2013, 24, 376-386. 10.

Chen, C.; Jiang, X.; Kaneti, Y. V.; Yu, A., Design and Construction of Polymerized-

Glucose Coated Fe3O4 Magnetic Nanoparticles for Delivery of Aspirin. Powder Tech. 2013, 236, 157-163. 11.

Hewakuruppu, Y. L.; Dombrovsky, L. A.; Chen, C.; Timchenko, V.; Jiang, X.; Baek, S.;

Taylor, R. A., Plasmonic "Pump-Probe" Method to Study Semi-Transparent Nanofluids. Appl. Opt. 2013, 52, 6041-6050. 12.

Zhu, C.; Peng, H.-C.; Zeng, J.; Liu, J.; Gu, Z.; Xia, Y., Facile Synthesis of Gold Wavy

Nanowires and Investigation of Their Growth Mechanism. J. Am. Chem. Soc. 2012, 134, 2023420237.


34

Page 35 of 50

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.

Langille, M. R.; Personick, M. L.; Zhang, J.; Mirkin, C. A., Defining Rules for the Shape

Evolution of Gold Nanoparticles. J. Am. Chem. Soc. 2012, 134, 14542-14554. 14.

Zhang, J.; Langille, M. R.; Personick, M. L.; Zhang, K.; Li, S.; Mirkin, C. A., Concave

Cubic Gold Nanocrystals with High-Index Facets. J. Am. Chem. Soc. 2010, 132, 14012-14014. 15.

Ming, T.; Feng, W.; Tang, Q.; Wang, F.; Sun, L.; Wang, J.; Yan, C., Growth of

Tetrahexahedral Gold Nanocrystals with High-Index Facets. J. Am. Chem. Soc. 2009, 131, 16350-16351. 16.

Wang, Y.; Black, K. C. L.; Luehmann, H.; Li, W.; Zhang, Y.; Cai, X.; Wan, D.; Liu, S.-

Y.; Li, M.; Kim, P.; Li, Z.-Y.; Wang, L. V.; Liu, Y.; Xia, Y., Comparison Study of Gold Nanohexapods, Nanorods, and Nanocages for Photothermal Cancer Treatment. ACS Nano 2013, 7, 2068-2077. 17.

Soni, S.; Tyagi, H.; Taylor, R. A.; Kumar, A., Role of Optical Coefficients and Healthy

Tissue-Sparing Characteristics in Gold Nanorod-Assisted Thermal Therapy. Int. J. Hyperthermia 2013, 29, 87-97. 18.

Taylor, R. A.; Kai Wong, J.; Baek, S.; Hewakuruppu, Y.; Jiang, X.; Chen, C.; Gunawan,

A., Nanoparticle-Assisted Heating Utilizing a Low-Cost White Light Source. J. Nanotechnol. Eng. Med. 2014, 4, 040903-040903. 19.

Kennedy, L. C.; Bickford, L. R.; Lewinski, N. A.; Coughlin, A. J.; Hu, Y.; Day, E. S.;

West, J. L.; Drezek, R. A., A New Era for Cancer Treatment: Gold-Nanoparticle-Mediated Thermal Therapies. Small 2011, 7, 169-183. 20.

Zhang, Z.; Wang, J.; Chen, C., Gold Nanorods Based Platforms for Light-Mediated

Theranostics. Theranostics 2013, 3, 223-238.


35


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

21.

Page 36 of 50

Chen, H.; Shao, L.; Li, Q.; Wang, J., Gold Nanorods and Their Plasmonic Properties.

Chem. Soc. Rev. 2012, 42, 2679-2724. 22.

Alkilany, A. M.; Thompson, L. B.; Boulos, S. P.; Sisco, P. N.; Murphy, C. J., Gold

Nanorods: Their Potential for Photothermal Therapeutics and Drug Delivery Tempered by the Complexity of Their Biological Interactions. Adv. Drug Deliv. Rev. 2012, 64, 190-199. 23.

Tang, J.; Jiang, X.; Wang, L.; Zhang, H.; Hu, Z.; Liu, Y.; Wu, X.; Chen, C., Au@Pt

Nanostructures: A Novel Photothermal Conversion Agent For Cancer Therapy. Nanoscale 2014, 6, 3670-3678. 24.

Tang, H.; Shen, S.; Guo, J.; Chang, B.; Jiang, X.; Yang, W., Gold Nanorods@mSiO2

with A Smart Polymer Shell Responsive to Heat/Near-Infrared Light for Chemo-Photothermal Therapy. J. Mater. Chem. 2012, 22, 16095-16103. 25.

Du, C.; Wang, A.; Fei, J.; Zhao, J.; Li, J., Polypyrrole-Stabilized Gold Nanorods with

Enhanced Photothermal Effect Towards Two-Photon Photothermal Therapy. J. Mater. Chem. B. 2015, 3, 4539-4545. 26.

Maltzahn, G. v.; Park, J.-H.; Agrawal, A.; Bandaru, N. K.; Das, S. K.; Sailor, M. J.;

Bhatia, S. N., Computationally Guided Photothermal Tumor Therapy Using Long-Circulating Gold Nanorod Antennas. Cancer Res. 2009, 69, 3892-3900. 27.

Bian, X.; Song, Z.-L.; Qian, Y.; Gao, W.; Cheng, Z.-Q.; Chen, L.; Liang, H.; Ding, D.;

Nie, X.-K.; Chen, Z.; Tan, W., Fabrication of Graphene-Isolated-Au-Nanocrystal Nanostructures for Multimodal Cell Imaging and Photothermal-Enhanced Chemotherapy. Sci. Rep. 2014, 4, 1-9. 28.

Zhang, Z.; Wang, L.; Wang, J.; Jiang, X.; Li, X.; Hu, Z.; Ji, Y.; Wu, X.; Chen, C.,

Mesoporous Silica-Coated Gold Nanorods as a Light-Mediated Multifunctional Theranostic Platform for Cancer Treatment. Adv. Mater. 2012, 24, 1418-1423.


36

Page 37 of 50

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


29.

Zhang, Y.; Qian, J.; Wang, D.; Wang, Y.; He, S., Multifunctional Gold Nanorods with

Ultrahigh Stability and Tunability for In Vivo Fluorescence Imaging, SERS Detection, and Photodynamic Therapy. Angew. Chem. Int. Ed. 2013, 52, 1148-1151. 30.

Jana, N. R.; Gearheart, L.; Murphy, C. J., Seed-Mediated Growth Approach for Shape-

Controlled Synthesis of Spheroidal and Rod-Like Gold Nanoparticles Using a Surfactant Template. Adv. Mater. 2001, 13, 1389-1393. 31.

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. 32.

Alkilany, A. M.; Nagaria, P. K.; Wyatt, M. D.; Murphy, C. J., Cation Exchange on the

Surface of Gold Nanorods with a Polymerizable Surfactant: Polymerization, Stability, and Toxicity Evaluation. Langmuir 2010, 26, 9328-9333. 33.

Connor, E. E.; Mwamuka, J.; Gole, A.; Murphy, C. J.; Wyatt, M. D., Gold Nanoparticles

Are Taken Up by Human Cells but Do Not Cause Acute Cytotoxicity. Small 2005, 1, 325-327. 34.

Zeng, Q.; Zhang, Y.; Ji, W.; Ye, W.; Jiang, Y.; Song, J., Inhibitation of Cellular Toxicity

of Gold Nanoparticles by Surface Encapsulation of Silica Shell for Hepatocarcinoma Cell Application. ACS Appl. Mater. Interfaces 2014, 6, 19327-19335. 35.

Tebbe, M.; Kuttner, C.; Männel, M.; Fery, A.; Chanana, M., Colloidally Stable and

Surfactant-Free Protein-Coated Gold Nanorods in Biological Media. ACS Appl. Mater. Interfaces 2015, 7, 5984-5991. 36.

Choi, R.; Yang, J.; Choi, J.; Lim, E.-K.; Kim, E.; Suh, J.-S.; Huh, Y.-M.; Haam, S.,

Thiolated Dextran-Coated Gold Nanorods for Photothermal Ablation of Inflammatory Macrophages. Langmuir 2010, 26, 17520-17527.


37


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

37.

Page 38 of 50

Park, J.-H.; von Maltzahn, G.; Xu, M. J.; Fogal, V.; Kotamraju, V. R.; Ruoslahti, E.;

Bhatia, S. N.; Sailor, M. J., Cooperative Nanomaterial System to Sensitize, Target, and Treat Tumors. Proc. Natl. Acad. Sci. 2010, 107, 981-986. 38.

Takahashi, H.; Niidome, Y.; Niidome, T.; Kaneko, K.; Kawasaki, H.; Yamada, S.,

Modification of Gold Nanorods Using Phosphatidylcholine to Reduce Cytotoxicity. Langmuir 2006, 22, 2-5. 39.

Hsiao, C.-W.; Chen, H.-L.; Liao, Z.-X.; Sureshbabu, R.; Hsiao, H.-C.; Lin, S.-J.; Chang,

Y.; Sung, H.-W., Effective Photothermal Killing of Pathogenic Bacteria by Using Spatially Tunable Colloidal Gels with Nano-Localized Heating Sources. Adv. Funct. Mater. 2015, 25, 721-728. 40.

Alkilany, A. M.; Nagaria, P. K.; Hexel, C. R.; Shaw, T. J.; Murphy, C. J.; Wyatt, M. D.,

Cellular Uptake and Cytotoxicity of Gold Nanorods: Molecular Origin of Cytotoxicity and Surface Effects. Small 2009, 5, 701-708. 41.

Zhang, Y.; Xu, D.; Li, W.; Yu, J.; Chen, Y., Effect of Size, Shape, and Surface

Modification on Cytotoxicity of Gold Nanoparticles to Human HEp-2 and Canine MDCK Cells. J. Nanomater. 2012, 2012, 7. 42.

Raja, G. R.; Wilma, P.; Liesbeth, H.; Patrick, C.; Hans, J.; Fijs, W. B. v. L.; Cees, O.;

Srirang, M.; Ton, G. v. L., In Vitro Toxicity Studies of Polymer-Coated Gold Nanorods. Nanotechnology 2010, 21, 145101. 43.

Ye, X.; Jin, L.; Caglayan, H.; Chen, J.; Xing, G.; Zheng, C.; Doan-Nguyen, V.; Kang, Y.;

Engheta, N.; Kagan, C. R.; Murray, C. B., Improved Size-Tunable Synthesis of Monodisperse Gold Nanorods Through the Use of Aromatic Additives. ACS Nano 2012, 6, 2804-2817.


38

Page 39 of 50

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


44.

Zhang, X.-D.; Wu, D.; Shen, X.; Chen, J.; Sun, Y.-M.; Liu, P.-X.; Liang, X.-J., Size-

Dependent Radiosensitization of PEG-Coated Gold Nanoparticles for Cancer Radiation Therapy. Biomater. 2012, 33, 6408-6419. 45.

Chen, C.; Sun, X.; Jiang, X.; Niu, D.; Yu, A.; Liu, Z.; Li, J., A Two-Step Hydrothermal

Synthesis Approach to Monodispersed Colloidal Carbon Spheres. Nanoscale Res. Lett. 2009, 4, 971-976. 46.

Chen, C.; Suryanto, B. H. R.; Zhao, C.; Jiang, X.; Yu, A., Direct Hydrothermal Synthesis

of Carbonaceous Silver Nanocables for Electrocatalytic Applications. Small 2015, 11, 35563556. 47.

Johnson, C. J.; Dujardin, E.; Davis, S. A.; Murphy, C. J.; Mann, S., Growth and Form of

Gold Nanorods Prepared by Seed-Mediated, Surfactant-Directed Synthesis. J. Mater. Chem. 2002, 12, 1765-1770. 48.

Asoro, M. A.; Kovar, D.; Ferreira, P. J., Effect of Surface Carbon Coating on Sintering of

Silver Nanoparticles: In Situ TEM Observations. Chem. Comm. 2014, 50, 4835-4838. 49.

Jiao, J.; Seraphin, S.; Wang, X.; Withers, J. C., Preparation and Properties of

Ferromagnetic Carbon Coated Fe, Co, and Ni Nanoparticles. J. Appl. Phys. 1996, 80, 103-108. 50.

Li, J.; Liu, C.-Y., Carbon-Coated Copper Nanoparticles: Synthesis, Characterization and

Optical Properties. New. J. Chem. 2009, 33, 1474-1477. 51.

Kabyemela, B. M.; Adschiri, T.; Malaluan, R. M.; Arai, K., Glucose and Fructose

Decomposition in Subcritical and Supercritical Water: Detailed Reaction Pathway, Mechanisms, and Kinetics. Ind. Eng. Chem. Res. 1999, 38, 2888-2895. 52.

Li, J.; Liu, C.-Y.; Xie, Z., Synthesis and Surface Plasmon Resonance Properties of

Carbon-Coated Cu and Co Nanoparticles. Mater. Res. Bull. 2011, 46, 743-747.


39


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

53.

Page 40 of 50

Mallick, S.; Sun, I.-C.; Kim, K.; Yi, D. K., Silica Coated Gold Nanorods for Imaging and

Photo-Thermal Therapy of Cancer Cells. J. Nanosci. Nanotech. 2013, 13, 3223-3229. 54.

Yang, X.; Salles, V.; Kaneti, Y. V.; Liu, M.; Maillard, M.; Journet, C.; Jiang, X.;

Brioude, A., Fabrication of Highly Sensitive Gas Sensor Based on Au Functionalized WO3 Composite Nanofibers by Electrospinning. Sens. Actuators B 2015, 220, 1112-1119. 55.

Qiang, R.; Du, Y.; Zhao, H.; Wang, Y.; Tian, C.; Li, Z.; Han, X.; Xu, P., Metal Organic

Framework-derived Fe/C Nanocubes toward Efficient Microwave Absorption. J. Mater. Chem. A 2015, 3, 13426-13434. 56.

Li, Y.; Zhou, C.; Xie, X.; Shi, G.; Qu, L., Spontaneous, Catalyst-Free Formation of

Nitrogen-Doped Graphitic Carbon Nanocages. Carbon 2010, 48, 4190-4196. 57.

Shouhu, X.; Lingyun, H.; Wanquan, J.; Xinglong, G.; Yuan, H.; Zuyao, C., A Facile

Method to Fabricate Carbon-Encapsulated Fe3O4 Core/Shell Composites. Nanotechnology 2007, 18, 035602-035608. 58.

Alkilany, A. M.; Thompson, L. B.; Boulos, S. P.; Sisco, P. N.; Murphy, C. J., Gold

Nanorods: Their Potential for Photothermal Therapeutics and Drug Delivery, Tempered by the Complexity of Their Biological Interactions. Adv. Drug. Deliv. Rev. 2012, 64, 190-199. 59.

Zhang, Z.; Wang, J.; Chen, C., Gold Nanorods Based Platforms for Light-Mediated

Theranostics. Theranostics 2013, 3, 223-238. 60.

Jokerst, J. V.; Thangaraj, M.; Kempen, P. J.; Sinclair, R.; Gambhir, S. S., Photoacoustic

Imaging of Mesenchymal Stem Cells in Living Mice via Silica-Coated Gold Nanorods. ACS Nano 2012, 6, 5920-5930.


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Page 41 of 50

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


61.

Kessentini, S.; Barchiesi, D., Quantitative Comparison of Optimized Nanorods,

Nanoshells and Hollow Nanospheres for Photothermal Therapy. Biomed. Opt. Exp. 2012, 3, 590604. 62.

Tian, Q.; Tang, M.; Sun, Y.; Zou, R.; Chen, Z.; Zhu, M.; Yang, S.; Wang, J.; Wang, J.;

Hu, J., Hydrophilic Flower-Like CuS Superstructures as An Efficient 980 nm Laser-Driven Photothermal Agent for Ablation of Cancer Cells. Adv. Mater. 2011, 23, 3542-3547. 63.

Hu, X.; Zhao, Y.; Hu, Z.; Saran, A.; Hou, S.; Wen, T.; Liu, W.; Ji, Y.; Jiang, X.; Wu, X.,

Gold Nanorods Core/AgPt Alloy Nanodots Shell: A Novel Potent Antibacterial Nanostructure. Nano Res. 2013, 6, 822-835. 64.

Han, J.; Li, J.; Jia, W.; Yao, L.; Li, X.; Jiang, L.; Tian, Y., Photothermal Therapy of

Cancer Cells using Novel Hollow Gold Nanoflowers. Int. J. Nanomed. 2014, 9, 517-526. 65.

Owens, R. B.; Smith, H. S.; Nelson-Rees, W. A.; Springer, E. L., Epithelial Cell Cultures

From Normal and Cancerous Human Tissues. J. Natl. Cancer Inst. 1976, 56, 843-849. 66.

Kroll, A.; Pillukat, M.; Hahn, D.; Schnekenburger, J., Interference of Engineered

Nanoparticles with In Vitro Toxicity Assays. Arch. Toxicol. 2012, 86, 1123-1136. 67.

Uboldi, C.; Bonacchi, D.; Lorenzi, G.; Hermann, M. I.; Pohl, C.; Baldi, G.; Unger, R. E.;

Kirkpatrick, C. J., Gold Nanoparticles Induce Cytotoxicity in the Alveolar Type-II Cell Lines A549 and NCIH441. Part. Fibre Toxicol. 2009, 6, 18. 68.

Qiu, Y.; Liu, Y.; Wang, L.; Xu, L.; Bai, R.; Ji, Y.; Wu, X.; Zhao, Y.; Li, Y.; Chen, C.,

Surface Chemistry and Aspect Ratio Mediated Cellular Uptake of Au Nanorods. Biomater. 2010, 31, 7606-7619.


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GRAPHICAL ABSTRACT DESCRIPTION Carbon-coated gold nanorods (AuNRs@C) have been successfully synthesized through a facile hydrothermal carbonization of glucose under mild reaction conditions, which can be applied to other forms of gold nanostructures. The resulting, well-controlled AuNRs@C has unique structural properties (amorphous shell with hydrophilic OH groups on surface). This leads to exemplary photothermal and biocompatible properties – a highly attractive material for tomorrow’s biomedical applications.


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Figure 1 TEM images of AuNRs with an average aspect ratio of 5 (a-b); and they can assemble into ordered patterns as a monolayer (a-b) or multilayers (c-d) on substrate(s), through ‘shoulder-to-shoulder’ (a-b) or ‘end-to-end’ (c-d) ways. 82x96mm (300 x 300 DPI)



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Figure 2 TEM images showing the formation process of carbon shell on AuNRs (aspect ratio= 3.7) with increasing time: (a, b) Bare AuNRs at the initial stage; (c, d) 10-nm thick carbon shell after 3-hour reaction; (e, f) 17-nm thick carbon shell after 5-hour reaction; and (g, h) 25-nm thick carbon shell after 8 hours of reaction at 180 °C, respectively. 104x64mm (300 x 300 DPI)


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Figure 3 UV-Visible spectra of AuNRs@C with different shell thicknesses. The surface plasmon resonances are centered at ~800 nm (bare AuNRs with aspect ratio of 3.7), 820 nm (10-nm shell), 830 nm (17-nm shell) and 850 nm (25-nm shell), respectively. 82x72mm (300 x 300 DPI)



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Figure 4 TEM and HRTEM images showing the AuNRs (a-b) and the AuNRs@C (c-d), with characteristic crystalline lattices of Au{200}, Au{220} and Au{111}, while the carbonaceous shell is amorphous (d). 191x221mm (300 x 300 DPI)


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Figure 5 Photothermal tests of AuNRs@C (aspect ratio of ~3.7 and shell thickness of 17 nm). (a) Digital thermal images of the solutions as recorded by the IR camera (as depicted in Figure S5) show that higher the particle concentration results in a higher rise in temperature; and (b) temperature changes as a function of irradiation time and particle concentration (20, 50, and 200 µM) under 0.17 W/cm2 light irradiation. 82x129mm (300 x 300 DPI)



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Figure 6 Photothermal tests of AuNRs@C (aspect ratio of ~3.7 and different shell thicknesses). (a) IR images of aqueous suspensions of AuNRs@C with a shell thickness of 17 nm at different laser irradiating times: 30, 60, 90, 180, 360 and 840 seconds, with a power of 0.17 W/cm2; and (b) temperature changes as a function of irradiation time and shell thicknesses from 0 nm (bare Au NRs), 10 nm, 17 nm, to 25 nm, respectively. The concentration of each suspension was adjusted to give an extinction intensity of 1.0 at 800 nm. 82x122mm (300 x 300 DPI)


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Figure 7 Column-graph showing the concentration-dependent cytotoxicity of AuNRs@C (aspect ratio ~ 3.7 and shell thickness = 17 nm) toward two kinds of cell lines: (a) HT1080 (a fibrosarcoma); and (b) GCT cells (a fibrous histiocytoma), verified bycell viability which was determined by comparing the percentage of viable cells to untreated control, using the crystal violet colorimetric assay method. All the measurements were conducted triplicately. 82x135mm (300 x 300 DPI)



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Carbon-coated gold nanorods (AuNRs@C) have been successfully synthesized through a facile hydrothermal carbonization of glucose under mild reaction conditions, which can be applied to other forms of gold nanostructures. The resulting, well-controlled AuNRs@C has unique structural properties (amorphous shell with hydrophilic OH groups on surface). This leads to exemplary photothermal and biocompatible properties – a highly attractive material for tomorrow’s biomedical applications. 35x13mm (300 x 300 DPI)


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Carbon-Coated Gold Nanorods: A Facile Route to Biocompatible

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