Shape-Controlled Synthesis of Au Nanostructures Using EDTA Tetrasodium Salt and Their Photothermal Therapy Applications

Abstract

Tuning the optical properties of Au nanostructures is of paramount importance for scientific interest and has a wide variety of applications. Since the surface plasmon resonance properties of Au nanostructures can be readily adjusted by changing their shape, many approaches for preparing Au nanostructures with various shapes have been reported to date. However, complicated steps or the addition of several reagents would be required to achieve shape control of Au nanostructures. The present work describes a facile and effective shape-controlled synthesis of Au nanostructures and their photothermal therapy applications. The preparation procedure involved the reaction of HAuCl₄ and ethylenediaminetetraacetic acid (EDTA) tetrasodium salt, which acted as a reducing agent and ligand, at room temperature without the need for any toxic reagent or additives. The morphology control from spheres to branched forms and nanowire networks was easily achieved by varying the EDTA concentration. Detailed investigations revealed that the four carboxylic groups of the EDTA tetrasodium salt are essential for effective growth and stabilization. The produced Au nanowire networks exhibited a broad absorption band in the near-infrared (NIR) region, thereby showing efficient cancer therapeutic performance by inducing the selective photothermal destruction of cancerous glioblastoma cells (U87MG) under NIR irradiation.

Keywords: EDTA tetrasodium salt; gold; nanostructure; photothermal therapy.

Figure 1

Transmission electron microscopy (TEM) images of Au nanostructures prepared using different molar ratios of HAuCl₄ to ethylenediaminetetraacetic acid (EDTA) tetrasodium salt: (a) 1:8, the inset is the high-resolution TEM (HR-TEM) image of panel (a); (b) 1:6; (c) 1:4; (d) Absorption spectra of Au nanostructures in panels (a–c).

Scheme 1

Schematic illustration of morphology control by adjusting the molar ratio of HAuCl₄ to EDTA tetrasodium salt.

Figure 2

Characteristics of Au nanowire networks: (a,b) TEM images with different magnifications, the inset is the fast Fourier transform (FFT) image obtained from the panel (b); (c) HR-TEM images; (d) X-ray diffraction (XRD) pattern, red vertical lines indicate peak positions and relative intensities of bulk Au.

Figure 3

TEM images of the samples at different stages of the reaction: (a) 2 min; (b) 5 min; (c) 10 min; (d) 15 min; (e) 20 min; (f) 25 min; (g) 45 min; (h) 60 min.

Figure 4

Optical microscope images of cancerous glioblastoma cells (U87MG) cells incubated (a) without; (b) with the Au nanowire networks, after irradiation for 10 min with a 980-nm near-infrared (NIR) CW diode laser and subsequent staining with 0.4% trypan blue.