Manipulating the Anisotropic Structure of Gold Nanostars using Good s Buffers

Transcription

1 SUPPLEMENTAL INFORMATION Manipulating the Anisotropic Structure of Gold Nanostars using Good s Buffers Kavita Chandra, Kayla S.B. Culver, Stephanie E. Werner, Raymond C. Lee, and Teri W. Odom,,* Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, 60208, United States Department of Chemistry, Northwestern University, Evanston, Illinois, 60208, United States *Correspondence to: todom@northwestern.edu Figure S1. Percent of AuNS particles in solution increases with stirring speed... S2 Figure S2. Increase in stirring time causes a red shift in the peak wavelength of AuNS... S3 Figure S3. MES buffer unable to produce AuNS at any ph or concentration... S4 Table S1. Particle size of AuNS at their highest R buffer ratio... S5 Figure S4. TEM images of AuNS after a month... S6 Figure S5. Stability of the LSP peak of HEPES AuNS in different storage conditions... S7 Figure S6. Reaction rate spectra of AuNS... S8 Figure S7. Spectra of AuNS synthesized at varying ph... S9 Figure S8. Photographs of the solutions at varying buffer concentrations... S10 Figure S9. DLS of AuNS synthesized at varying concentrations... S11 Figure S10. Low magnification images of HEPES, EPPS, and MOPS AuNS... S12 Figure S11. HR-TEM images of HEPES AuNS synthesized at 700 R HEPES... S13 Figure S12. HR-TEM images of EPPS AuNS synthesized at 2500 R EPPS... S14 Figure S13. HR-TEM images of MOPS AuNS synthesized at 1100 R MOPS... S15 S1

2 Figure S1: Percent of AuNS particles in solution increases with stirring speed. Growth solutions were stirred for 30 min at the designated RPM and then left in the dark overnight TEM grids were made and analysis of particles was conducted through ImageJ. For each stirring time point, particles were measured. For all three buffers, there was an overall increase in the percentage of AuNS. MOPS had the greatest heterogeneity only reaching ~65% S2

3 Figure S2: Increase in stirring time causes a red shift in the peak wavelength of AuNS. The final primary peak wavelength of (a) HEPES, (b) EPPS, and (c) MOPS AuNS after being stirred for varying lengths of time at rotations per minute (RPM). The growth solutions were stirred for varying times and then left over night to allow for the reaction to be completed. The spectra were taken 24 h after stirring. With an increase in stirring time, there was a red shift in the peak wavelength for all three types of buffers. For HEPES and EPPS AuNS, a plateau in the LSP resonance occurred around 6 min of stirring. There was no clear effect of the different stirring speeds on the peak wavelength. S3

4 Figure S3: MES buffer did not produce AuNS at any ph or concentration. MES absorption spectra (a, b) and corresponding particle size (c, d) for 100 to 2500 R MES were collected at two phs: 6.7 and MES was tested through the entire buffering range from These are two representative samples to show spectra above and below the pk a of MES. At a high ph, the solutions were unable to form particles in solution except at the lowest concentration of 20 mm. At ph < pk a, MES was able to form spherical particles in solution. S4

5 Table S1: AuNS particle size at the highest R buffer ratio. The overall particle size through DLS and branch length were measured by analyzing TEM pictures through ImageJ. Approximately branches were measured manually to obtain the average branch length. Representative images were taken across the entire TEM grid. Buffer Type R buffer Hydrodynamic diameter (nm) Average branch length (nm) HEPES nm ± 6 nm 21 ± 2 nm EPPS nm ± 10 nm 43 ± 2 nm MOPS nm ± 8 nm 36 ± 4 nm S5

6 Figure S4: TEM images of AuNS from different buffers after a month. TEM images of HEPES, EPPS, and MOPS particles one day and 30 days after synthesis. HEPES and EPPS particles maintained the morphology over time; however, the MOPS particles mostly turned into spheres. S6

7 Figure S5: Stability of the LSP resonance peak of HEPES AuNS under different storage conditions. The HEPES AuNS particles were stored either in the growth solution or centrifuged and resuspended in water. These solutions were either then stored at 4 Cor at room temperature. The storage conditions that caused the smallest shift in LSP peak was in the original growth solution at 4 C, where only a 9-nm LSP shift occurred after 20 days and 15-nm over 40 days, indicating excellent structural and colloidal stability. Blue-shifts in the LSP under other storage conditions are due to AuNS re-shaping, similarly seen with MOPS AuNS solutions blue-shift over a month corresponding to particle shape changing (Fig. S4). Particle aggregation was not affected by storage conditions. S7

8 Figure S6: Reaction rate spectra of AuNS. Absorbance spectra of (a) HEPES, (b) EPPS, and (c) MOPS AuNS during the course of the synthesis at R buffer = 700. Spectra were taken every 2 min until the reaction was completed. EPPS and MOPS AuNS solutions had two LSP peaks, and HEPES AuNS solutions had one peak. The reaction time for MOPS was longer than that of HEPES and EPPS. S8

9 Figure S7: Spectra of AuNS synthesized at varying ph. Absorbance spectra of (a) HEPES, (b) EPPS, and (c) MOPS AuNS synthesized at varying ph within the buffering range of each buffer. HEPES AuNS were formed throughout the buffering range but with decreased absorbance with increased ph. EPPS AuNS formed below and slightly above the pk a of the buffer. When the ph was much greater than the pk a of the buffer, EPPS AuNS were unable to form. MOPS solutions showed the lowest tolerance to changes in ph and were unable to form AuNS above the pk a of the buffer. S9

10 Figure S8: Photographs of AuNS solutions at varying buffer concentrations. AuNS solutions synthesized with (a) HEPES, (b) EPPS, and (c) MOPS at varying concentrations ranges. MOPS could produce AuNS in the smallest concentration range compare with EPPS and HEPES. EPPS was able to produce AuNS in the largest concentration range from R EPPS = 400 to S10

11 Figure S9: DLS of AuNS synthesized at varying concentrations. The AuNS solutions were synthesized from 100 to 2500 R buffer. With an increase in R EPPS, EPPS AuNS particle size increased whereas HEPES and MOPS AuNS particle size plateaued or solutions aggregated. These measurements were taking through DLS, which determines the size distribution of particles (typically spheres) in solution. Since our particles are anisotropic, the hydrodynamic diameter measurements serve only as an estimate of their overall size. S11

12 Figure S10: Low magnification images of MOPS AuNS. Zoomed-out TEM images of (a) HEPES, (b) EPPS, and (c) MOPS AuNS. All scale bars are 100 nm. For HEPES and EPPS AuNS, there are fewer spheres in solution. These images demonstrate show the large distribution of particle shapes for MOPS AuNS solutions. Based on analysis of 300+ particles, we found that 53% of the MOPS solutions contained spherical byproducts. S12

13 Figure S11: HR-TEM images of HEPES AuNS synthesized at 700 R HEPES. (a) HEPES AuNS branches grew in the [111] direction. The dotted white boxes indicate the area analyzed by FFT (below). AuNS particles were on an amorphous carbon mesh grid that produced the ring-like structure in the FFT. The presence of the ring depended on the sample thickness (i.e. AuNS branch thickness) and the intensity of the electron beam. S13

14 Figure S12: HR-TEM images of EPPS AuNS synthesized at 2500 R EPPS. EPPS AuNS grew in the [110] direction. The dotted white boxes indicate the area analyzed by FFT (below). AuNS particles were on an amorphous carbon mesh grid that produced the ring-like structure in the FFT. The presence of the ring depended on the sample thickness (i.e. AuNS branch thickness) and the intensity of the electron beam. S14

15 Figure S13: HR-TEM images of MOPS AuNS synthesized at 1100 R MOPS. MOPS AuNS grew in the [110] direction. The dotted white boxes indicate the area analyzed by FFT (below). AuNS particles were on an amorphous carbon mesh grid that produced the ring-like structure in the FFT. The presence of the ring depended on the sample thickness (i.e. AuNS branch thickness) and the intensity of the electron beam. S15