Haucl4

PEG-GNRs were prepared from cetyltrimethylammonium bromide (CTAB)-stabilized GNRs by exchanging CTAB with mPEG-thiol. The CTAB-stabilized GNRs with an aspect ratio of 4 were synthesized using a seed-mediated growth approach, as previously reported.24 Briefly, 5 mL of 0.5 mM HAuCl₄ (Sigma, St. Louis, USA) and 5 mL of 0.2 M CTAB (Sigma) solutions were prepared and mixed. Then, 600 μL of ice-cold 0.01 M NaBH₄ (Sigma) solution was added to the mixture and sonicated for 4 min at 28 °C, after which the seed solution was allowed to stand at room temperature for 2 h. Growth solution was prepared by sequentially adding 5 mL of 0.001 M HAuCl₄, 250 μL of 0.004 M AgNO₃ (Sigma) and 70 μL of 0.0788 M ascorbic acid (Sigma) to 5 mL of 0.2 M CTAB solution. After gentle mixing, 12 μL of seed solution was mixed with growth solution at room temperature to initiate growth. When the longitudinal absorption peak reached ~800-820 nm, GNRs were centrifuged at 12,000 rpm for 15 min. The supernatant was discarded, and GNRs were re-suspended in distilled water. CTAB was exchanged with mPEG-thiol (2 kDa; Laysan Bio, Arab, USA) by adding 20 mg of mPEG-thiol to 10 mL of 3 optical density (O.D.). 25 (link) GNRs were vortexed vigorously for 1 h, after which unincorporated mPEG-thiol was removed by centrifuging three times at 10,000 rpm for 10 min each.

GNRs were synthesized using the seed-mediated growth approach.25 (link),26 (link) In the first step, a seed solution was prepared to reduce 250 µL of HAuCl₄ (Sigma Chemical Co., St. Louis, Mo, USA) in 9.75 mL of cetyltrimethylammonium bromide 0.1 M (CTAB) and cold-prepared sodium borohydride (600 µL, 0.01 M) (Sigma Chemical Co., St. Louis, Mo, USA). Seeds were kept at 27 °C for two hours before use. Then, 55 µL of ascorbic acid 0.1 M (Sigma Chemical Co., St. Louis, MO, USA) were added to a growth solution containing 75 µL of AgNO₃ 0.01 M (Sigma Chemical Co., St. Louis, MO, USA), 9.5 mL of CTAB 0.1 M, and 500 µL of HAuCl₄ 0.01 M. Next, 250 µL of HCl 0.1 M and finally, 12 µL of the previously prepared seed solution were added. The solution was incubated for 10 minutes at 27 °C before centrifugation at 5900 g for 15 min. The supernatant was then removed, and the pellet was resuspended in Milli-Q water. Vis-NIR absorption spectra were recorded at room temperature using a Perkin Elmer Lambda 25 spectrophotometer. GNRs obtained from synthesis (GNR-CTAB) were observed using a scanning electron microscope with an electronic transmission module (STEM) FEI Inspect F50. The specimens for electron microscopy observation were prepared by dropping GNRs on Formvar carbon-coated copper microgrids (Ted Pella, Inc. Redding, CA, USA), and letting them dry.