Supporting Information

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1 Supporting Information Highly Concentrated Seed-Mediated Synthesis of Monodispersed Gold Nanorods Kyoungweon Park, 1,2 Ming-siao Hsiao, 1,2 Yoon-Jae Yi, 1,2 Sarah Izor, 1,2 Hilmar Koerner, 1 Ali Jawaid, 1,2 and Richard A. Vaia 1, * 1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio , United States 2 UES,Inc Dayton Ohio 45432, United States richard.vaia@us.af.mil Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-1

2 Table of Contents Methods... S4 Table S.1. The protocol for conventional scale-up reaction (ms/ng, where m is the scale-up factor for seed concentration and n is the scale-up factor for reactant concentration)... S6 Table S.2. The characteristics of the Au NR products synthesized with different seed and reactant concentration.... S6 Table S.3. The protocol for deterministic scale-up reaction (ms/1g+ng growth)... S7 The effect of CTAB concentration on the growth of Au NRs... S8 Figure S.1. The effect of CTAB concentration on the formation of Au NRs. a) UV-vis extinction spectra as a function of [CTAB] from 0.01 M to 0.3 M. b) L-LSPR, O.D. at L-LSPR and O.D. at 400 nm were monitored to estimate the quality of the Au NRs synthesized from different CTAB concentration.... S9 Evaluation of the quality of Au NRs.... S10 Table S.4. The correlation of the ratio between the intensity of transverse peak to that of longitudinal peak measured by spectral analysis and the fraction of byproduct measured by TEM analysis.... S11 Figure S.2. The estimation of product impurity by the correlation of the fraction of byproduct measured by spectral analysis and TEM analysis.... S11 Table S.5. The correlation of fwhm measured by spectral analysis and polydispersity of aspect ratio measured by TEM analysis.... S12 Figure S.3. The estimation of product quality( polydispersity) based on the correlation of fwhm measured by spectral analysis and polydispersity measured by TEM analysis.... S12 Evaluation of characteristics of Au NRs resulting from increasing seed concentration or increasing reactant concentration... S13 Figure S.4. Evaluation of characteristics of Au NRs resulting from increasing seed concentration. The change of a) volume and particle concentration b) aspect ratio c) polydispersity and, d) product purity of Au NRs as a function of seed concentration... S14 Figure S.5. Evaluation of characteristics of Au NRs resulting from increasing reactant concentration. The change of a) volume b) aspect ratio c) polydispersity and, d) product purity of Au NRs as a function of seed concentration... S15 The growth of Au NRs in 1S/1G and 10S/10G growth solution... S16 Figure S.6. The effect of simultaneous increasing seed and reactant concentration on the growth mechanism and morphology of Au NRs. a) The changes in L-LSPR during the growth in 1S/1G and 10S/10G reaction UV-vis spectra (upper) b) the change in optical extinction at 390nm c) Mean Au NR radius as function of time for 1S/1G and 10S/10G reaction obtained by fitting scattering data from growing nanorod solutions. d) Raw scattering data taken from 1S/1G growth. e) TEM images of Au Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-2

3 NRs synthesized from 1S/1G and 10S/10G. The scale bar is 100 nm. f) The distribution of aspect ratio of Au NRs grown from 1S/1G and 10S/10G.... S18 The effect of scale-up seed and reactant concentration on the Au NR growth in solution containing BDAC... S19 Figure S.7. UV-vis spectra of Au NR solution obtained from the growth solution containing CTAB(0.1 M) and BDAC(0.125 M) with either higher seed concentration (100S/1G) or higher Au precursor concentration(1s/4g) were compared with that of 1S/1G growth.... S20 Synthesis of Au NRs in 20S/1G+20G reaction condition... S21 Figure S.8. UV-vis-NIR spectra of Au NRs grown from 20S/1G+20G condition. Here, aliquots from the initial 20S/1G seed-rod solution were removed at different points (t 1 = min) and the same volume of 2nd growth solution (20G) was supplied (20S/1G+20G).... S21 References... S22 Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-3

4 Methods Materials: Hexadecyltrimethylammonium bromide (CTAB) was purchased from GFS chemicals. Benzyldimethylhexadecylammonium chloride (BDAC) was purchased from TCI America. HAuCl 4, AgNO 3, sodium borohydride and L-ascorbic acid were purchased from Aldrich. Synthesis of Au seeds: The Au seeds were prepared according to the typical synthetic route. 1, g of CTAB was added to 10 ml of 0.25 mm HAuCl 4. The solution was briefly sonicated (30 sec) and kept in warm water bath (40 C) for 5 min to completely dissolve CTAB and kept at 25 C for 10 min (solution A). A 0.01 M NaBH 4 solution was prepared and kept in the refrigerator (3 C) for 10 min. A 0.6 ml of 0.01M NaBH 4 solution was quickly added dropwise to solution A while it was stirring at 800 rpm. The color of the solution instantly became light brown. Stirring was continued for 1 minute. Seeds aged for 5 min were used for all experiments. Synthesis of Gold Nanorods (Au NRs): The Au NRs were prepared according to the typical seed-growth method 1,2. The concentration of seeds and reactants were varied according to the scale-up factor. For the 1S/1G reaction, the growth solution was prepared by mixing HAuCl 4 (50 µl, 0.1 M), AgNO 3 (8 µl, 0.1 M), CTAB (0.364 g), and Milli-Q water (9515 µl) at room temperature. Next, ascorbic acid (53 µl, 0.1M) was added to the growth solution as a mild reducing agent. Finally, 10 µl of the seed solution was added into the growth solution. For the simple scale-up of seed concentration or reactant concentration, either volume of the seed solution or the concentration of the reactants were increased accordingly (Table S.1). The characteristics of the resulting products are summarized in Table S.2. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-4

5 For the deterministic scale-up (Schematic in paper), seed-rods were synthesized in the ms/1g reaction, and the 2nd growth solution that contained higher concentration of reactants was prepared separately and added at the end of growth stage II of the seed-rods. Either the volume of the seed solution or the concentration of the reactants was increased according to the scale-up factor (Table S.3). To maintain a constant total reaction solution volume, the reactant solution was prepared at higher concentration if needed (for example, 1 M HAuCl 4 solution was prepared for 200G solution). Characterization: UV-vis-NIR spectra were acquired with a Cary 5000 UV-vis-NIR spectrophotometer. Morphology and mean size of nanoparticles were determined by TEM (Philips CM200 LaB6 at 200 kv) and STEM (FEI Talos at 200 kv). For each sample, more than 1000 particles were measured to obtain the average size and the size distribution. In general, spectroscopic measurements validated by TEM were preferred to TEM alone since the former ensure a more uniform sampling of the ensemble by avoiding bias due to shape segregation and subjective sampling inherent in TEM sample preparation of polydisperse rod and rod-sphere mixtures. 3 Synchrotron experiments were carried out at the SAXS/WAXS beamline of the Advanced Light Source at Lawrence Berkeley National Laboratory at 10 kev (1.24 Å) from a bend magnet and focused via a Mo/B4C double multilayer monochromator. SAXS on the seed solutions was carried out using a high speed Dectris Pilatus 1M detector. 2D images were reduced using Nika macros 4 for Igor Pro. Images were corrected for transmission and background. The reduced data was fit using Irena macros 5 for Igor Pro. The scattering intensity is plotted and fit with a combination of sphere form factor, scatterer size distribution and a Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-5

6 structure factor of unity (no agglomeration). A lognormal size distribution was assumed based on TEM and prior data. 6 The intensity distribution exhibited two Guinier knees that were fit with two lognormal distributions of spherical scatterers (flat normalized residuals close to 0). Table S.1. The protocol for conventional scale-up reaction (ms/ng, where m is the scale-up factor for seed concentration and n is the scale-up factor for reactant concentration) Volume of seed solution (ml) [HAuCl 4 ] (mm) [AgNO 3 ] (mm) [ascorbic acid] (mm) [CTAB] (mm) 1S/1G ms/ng m 0.01 n 0.25 n 0.08 n Total reaction solution (ml) Table S.2. The characteristics of the Au NR products synthesized with different seed and reactant concentrations. 1S aspect ratio product purity polydispersity 200S aspect ratio product purity polydispersity 1G % 14.87% % 25.00% 2G % 14.86% % 24.00% 3G % 16.25% % 22.00% 4G % 17.40% % 22.00% 5G % 16.64% % 18.00% 10S 1G % 23.00% % 26.00% 2G % 18.00% % 25.00% 3G % 14.00% % 24.00% 4G % 16.00% % 23.00% 5G % 12.00% % 18.00% 50S 1G % 23.00% % 15.63% 2G % 22.00% % 16.90% 3G % 23.00% % 17.61% 4G % 22.00% % 18.13% 5G % 19.00% % 18.25% 100S 1G % 25.00% % 15.74% 300S 400S 500S Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-6

7 2G % 24.00% % 17.22% 3G % 22.00% % 18.00% 4G % 22.00% % 18.19% 5G % 18.00% % 19.71% Table S.3. The protocol for the deterministic scale-up reaction (ms/1g+ng growth) 1 st growth (seed-rods) ms/1g 2 nd growth ng Volume of seed (ml) [HAuCl 4 ] (mm) [AgNO 3 ] (mm) [ascorbic acid] (mm) [CTAB] (mm) m n 0.25 n 0.08 n Total reaction solution (ml) Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-7

8 The effect of CTAB concentration on the growth of Au NRs The concentration of CTAB is the dominant factor to induce the anisotropic shape of NRs. The range of concentration of CTAB used to prepare NRs is from just above the critical micelle concentration (CMC, ~0.9 mm to 0.1 M in the literature). However, the effect of the concentration of CTAB on the formation of Au NRs was not studied. We found that as the concentration of CTAB increased up to 0.1 M, the yield of the NRs as well as the aspect ratio increased, which could be seen from the decreasing transverse surface plasmon intensity/increasing longitudinal surface plasmon (L-LSPR) intensity and the red shift of the L- LSPR (Figure S.1). This result can be rationalized by the enhanced CTAB adsorption on the surface of the growing particle. The adsorption of surfactant onto an interface involves the straightforward processes of diffusion of surfactant molecule (monomer) from the bulk to the surface. The adsorption of monomer onto the surface disturbs the monomer/micelle equilibrium, and micelles can kinetically break up, releasing monomer, which can then diffuse and kinetically adsorb onto the surface. Also, micelles can directly adsorb onto the surface. Therefore, by increasing the CTAB concentration, the preferential adsorption on the growing gold particles can be promoted to produce more NRs than spherical particles. A similar quality of NRs was obtained from CTAB concentrations varied between 0.1 M to 0.2 M. However, further increasing the CTAB concentration above 0.2 M impeded the growth of good quality of NRs due to the increase in viscosity, which disrupts the diffusion of reactants. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-8

9 O.D. at 400nm O.D. O.D.at L-LSPR L-LSPR a b M 0.2M 0.18M 0.16M 0.14M 0.12M 0.1M 0.08M 0.06M 0.04M 0.02M 0.01M Wavelength(nm) [CTAB] (M) Figure S.1. The effect of CTAB concentration on the formation of Au NRs. a) UV-vis extinction spectra as a function of [CTAB] from 0.01M to 0.3M. b) L-LSPR, O.D. at L-LSPR and O.D. at 400 nm were monitored to estimate the quality of the Au NRs synthesized from different CTAB concentration. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-9

10 Evaluation of the quality of Au NRs The characterization of Au NRs has been mostly conducted via analysis of UV vis NIR spectroscopy and TEM. Spectroscopic measurements provide a better relative representation of quality due to a more uniform sampling of the ensemble, since they avoid bias due to shape segregation and subjective sampling inherent in TEM sample preparation of polydisperse rod and rod-sphere mixtures. 3 All spectra were plotted using OriginPro 9.1. and analyzed via peak analyzer to obtain peak position, intensity, full width half maximum, and the ratio between T- LSPR to L-LSPR. The product purity is defined by the overall ratio of AuNR product to other undesired, nanoparticle impurities, which can be approximately estimated by the ratio between the intensity of transverse peak to that of longitudinal peak. To quantify the product purity, this ratio (R) was taken from extinction spectra and normalized by longitudinal surface plasmon peak (ev). The resulting quantity shows linear relationship with the fraction of impurity measured with TEM analysis (Figure S.2). The empirical equation was established based on this relationship. Product purity = 1 the fraction of impurity R The fraction of impurity = [1.04 ( L LSPR ( ev ) 0.01 ] ) The full width half maximum (fwhm) of the solution L-LSPR has been used as an indicator to approximate polydispersity of aspect ratio since the L-LSPR of the ensemble is the superposition of the inherent L-LSPR from each AuNR in solution. The linear relationship was found between fwhm weighted by L-LSPR in ev and the polydispersity measured by TEM analysis (Figure. S.3). The empirical equation was established based on this relationship. Polydispersity = 0.28 (fwhm) (L LSPR ) Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-10

11 TEM analysis Table S.4. The correlation of the ratio between the intensity of transverse peak to that of longitudinal peak measured by spectral analysis and the fraction of byproduct measured by TEM analysis. Fraction of byproduct O.D.at T LSPR R = O.D.at L LSPR L-LSPR(nm) L-LSPR(eV) R/L-LSPR TEM analysis (O.D. at T-LSPR /O.D. at L-LSPR ) L-LSPR(eV) Equation y = a + b*x Weight No Weighting Residual Sum of Squares Pearson's r Adj. R-Square Value Standard Error TEM analysis Intercept TEM analysis Slope Figure S.2. The estimation of product impurity by the correlation of the fraction of byproduct measured by spectral analysis and TEM analysis. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-11

12 Polydispersity Table S.5. The correlation of fwhm measured by spectral analysis and polydispersity of aspect ratio measured by TEM analysis. L-LSPR(nm) L-LSPR(eV) fwhm(ev) fwhm*l-lspr Stdev (L/d) (FWHM)x(L-LSPR) Equation y = a + b*x Weight No Weighting Residual Sum of Squares 8.15E-04 Pearson's r Adj. R-Square Value Standard Error Stdev (L/d) Intercept Stdev (L/d) Slope Figure S.3. The estimation of product quality( polydispersity) based on the correlation of fwhm measured by spectral analysis and polydispersity measured by TEM analysis. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-12

13 Evaluation of characteristics of Au NRs resulting from increasing seed concentration or increasing reactant concentration Figure S.4. shows characteristics of Au NRs resulting from increasing seed concentration. The seed concentration was increases from 1S to 500S at 1G ([HAuCl4]= M) condition. These characteristics are summarized in Figure 1 and discussed in detail in the manuscript. Note that either the linear relationship between the scale-up factor and the particle concentration and the hyperbolic relationship between the scaleup factor and the volume of the rods strongly holds up to the factor of ~60 as shown in Figure S.4a. Figure S.5. shows characteristics of Au NR resulting from increasing reactant concentration. the impact of increasing reactant concentration was investigated from 1G to 10G for a conventional seed addition (1S). These characteristics are summarized in Figure 1 and discussed in detail in the manuscript. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-13

14 polydispersity product purity volume(nm 3 ) particle conc (nm) Aspect ratio a 3.5x10 4 b 5 3.0x x x x x x10 3 c Scale up factor [seed] d Scale up factor [seed] Scale up factor [seed] Scale up factor [seed] Figure S.4. Evaluation of characteristics of Au NRs resulting from increasing seed concentration. The change of a) volume and particle concentration b) aspect ratio c) polydispersity and, d) product purity of Au NRs as a function of seed concentration Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-14

15 polydispersity product purity volume(nm 3 ) Aspect ratio a b 8x x10 4 6x x x10 4 3x x10 4 c 1x Scale up factor [reatant] 0.25 d Scale up factor [reactant] Scale up factor [reactant] Scale up factor [reactant] Figure S.5. Evaluation of characteristics of Au NRs resulting from increasing reactant concentration. The change of a) volume b) aspect ratio c) polydispersity and, d) product purity of Au NRs as a function of seed concentration Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-15

16 The growth of Au NRs in 1S/1G and 10S/10G growth solution The growth of Au NRs in 1S/1G and 10S/10G was compared. Synthetic condition was shown in Table S.1. The Au NR growth from both solutions was monitored in-situ by UV-vis spectroscopy and small angle X-ray scattering (SAXS) using a customized set-up (a detailed description can be found in the Methods section). Figure. S.6a shows changes of localized surface plasmon resonance (LSPR) peak of the longitudinal peak position as a function of time. In 1S/1G growth solution, distinct L-LSPR peak was detected in 5 min around 700 nm, which kept shifting to 850 nm for the next 15 min indicating fast growth in the longitudinal direction. The L-LSPR peak started to show gradual blue shifts, which means that the transversal growth takes over the longitudinal growth. These spectral shifts are the signature of typical CTABbased Au NR growth. A similar trend was observed in the 10S/10G reaction at a faster time frame. Distinct peak was detected earlier in 3 min and rapidly reached the maximum around 820 nm, which was followed by a fast blue shift. Figure S.6b shows the optical extinction at 390 nm as a function of time. 7 The optical extinction at 390 nm is caused by interband transitions from Au, which are independent of particle shape. Increasing absorption at 390 nm reflects an increase of the total volume of particles since there is no additional nucleation in the seedmediated growth reaction. In the case of the 1S/1G reaction, the intensity became constant around 66 min, while in the 10S/10G reaction, the maximum intensity was reached in 20 min confirming the higher reactant concentration accelerated the growth of rods. Figure S.6c shows the mean radius of Au nanorods estimated from SAXS analysis as function of time during the reaction. The radius was extracted from I(q) by fitting the scattering curves to a rod form factor. The change in radius can readily be seen in the raw scattering data (Figure S.6d) in the shift of the minima in Bessel oscillation at higher q values toward lower q as expected. The radius of the Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-16

17 rods from 10x reaction reaches equilibrium much faster (500 s) at a smaller a final radius of 8 nm, compared to the 1x reaction (1500 s, 11 nm), in agreement with TEM of the final products and aspect ratio from UV-vis. Figure S.6f shows the distribution of aspect ratio measured from the TEM images taken from NRs grown from 1S/1G and 10S/10G reaction. It is noticeable that the particles from the 10x reaction contain a significant fraction of spherical particles (L/d~1). This is due to the higher reaction rate. Anisotropic growth begins after seeds grow to a certain size to accommodate micellar adsorption. In 10S/10G reaction, the growth of seeds becomes faster, but preferential surfactant adsorption does not accompany the particle growth resulting in more spherical particles. The average aspect ratio is 1.7, which is smaller compared to that from the 1S/1G reaction, which is 2.1. Decreasing aspect ratio in 10S/10G reaction is also due to the accelerated reaction rate. The reduction rate becomes much faster than the adsorption rate of the micelle to form a secure bilayer, transversal growth from adatom addition starts earlier, which results in decreasing length and increasing diameter. Therefore, two major drawbacks of Au NR growth in higher reactant concentration is increasing the fraction of byproducts (spherical particles) and decreasing aspect ratio, which are closely related to the increasing reduction rate in stage I and II; reduction rate surpasses the micellar adsorption rate. It is not practicable to increase surfactant concentration to speed up the micellar adsorption rate since the surfactant solution becomes too viscous, which hinders the overall diffusion. 8 Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-17

18 Frequency(%) intensity, a.u. d q, A -1 e f x reaction Average L/d =1.7 1x reaction Average L/d= Aspect ratio Figure S.6. The effect of simultaneous increasing see and reactant concentration on the growth mechanism and morphology of Au NRs. a) The changes in L-LSPR during the growth in 1S/1G and 10S/10G reaction UV-vis spectra (upper) b) the change in optical extinction at 390 nm c) Mean Au nanorod radius as function of time for 1S/1G and 10S/10G reaction obtained by fitting scattering data from growing nanorod solutions. d) Raw scattering data taken from 1S/1G growth. e) TEM images of Au NRs synthesized from 1S/1G and 10S/10G. The scale bar is 100nm. f) The distribution of aspect ratio of Au NRs grown from 1S/1G and 10S/10G. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-18

19 The effect of scale-up seed and reactant concentration on the Au NR growth in solution containing BDAC The impact of both increasing seed concentration and Au precursor concentration on impairing quality of NRs is amplified when the additives are involved to tune the aspect ratio. BDAC is added to produce longer aspect ratio of nanorods up to L/d=6 in typical seed mediated route. 2 UV-vis spectra of Au NR production obtained from the growth solution containing CTAB and BDAC with either higher seed concentration (100S/1G) or higher Au precursor concentration (1S/4G) were compared with that of 1S/1G growth. Higher seed concentration severely deteriorates the quality of Au NRs resulting dramatic increase in byproduct fraction and no effect on promoting the growth of longer nanorods. With higher Au precursor concentration, the aspect ratio of nanorods is much lower than 1G growth. Stronger micelle adsorption of CTAB/BDAC mixed surfactants disrupts the symmetry breaking of Au seeds at stage I resulting nanocubes along with nanorods. The higher Au precursor concentration accelerates the reduction rate which becomes much faster than the adsorption rate of the micelle to form a secure bilayer, transversal growth from adatom addition starts earlier, which results in decreasing length and increasing diameter. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-19

20 O.D S 1G S 4G S 1G Wavelength(nm) Figure S.7. UV-vis spectra of Au NR solution obtained from the growth solution containing CTAB(0.1M) and BDAC(0.125M) with either higher seed concentration (100S/1G) or higher Au precursor concentration(1s/4g) were compared with that of 1S/1G growth. Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-20

21 O.D. Synthesis of Au NRs in 20S/1G+20G reaction condition Figure 2 in the manuscript summarizes AuNR synthesis where 20S seeds were grown in 1G growth solution, followed by the addition of the same volume of 20G growth solution (referred as "20S/1G+20G" hereinafter, see Schematic in paper) to obtain 10 times higher concentration of Au NRs with the same volume of rods as in 1S/1G condition (final scale-up factor of 10). Figure S.8 shows the UV-vis spectra of the Au NR solutions, which were taken 24hr after seed-rod addition and analyzed to estimate the characteristics of Au NRs shown in Figure min 60min 20min 15min 10min 5min 1min Wavelength(nm) Figure S.8. UV-vis-NIR spectra of Au NRs grown from 20S/1G+20G condition. Here, aliquots from the initial 20S/1G seed-rod solution were removed at different points (t 1 = min) and the same volume of 2nd growth solution (20G) was supplied (20S/1G+20G). Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-21

22 References 1. K. Park, L. F. Drummy, R. C. Wadams, H. Koerner, D. Nepal, L. Fabris and R. A. Vaia, Chemistry of Materials, 2013, 25, B. Nikoobakht and M. A. El-Sayed, Chemistry of Materials, 2003, 15, L. K. Wolf, Journal, 2012, 90, J. Ilavsky, Journal of Applied Crystallography, 2012, 45, J. Ilavsky and P. R. Jemian, J. Appl. Cryst., 2009, 42, H. Koerner, R. I. MacCuspie, K. Park and R. A. Vaia, Chem. Mater., 2012, 24, J. A. Edgar, A. M. McDonagh and M. B. Cortie, ACS Nano, 2012, 6, V. Sharma, K. Park and M. Srinivasarao, Materials Science and Engineering: R: Reports, 2009, 65, Park et al. Conc Seed-Mediated Synth AuNRs, ACS AMI 2017 S-22