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.
Highlights
To date, metal nanostructures have attracted a great deal of attention because of their intriguing electronic, optical, and catalytic properties [1–7]
The Au nanostructures were readily synthesized by reacting HAuCl4 and ethylenediaminetetraacetic acid (EDTA) tetrasodium salt in an aqueous solution at room temperature
The formation of the Au nanostructures is summarized in Scheme 1, illustrating that the morphology of the Au nanostructures is controlled by adjusting the EDTA tetrasodium salt concentration
Summary
Metal nanostructures have attracted a great deal of attention because of their intriguing electronic, optical, and catalytic properties [1–7]. In the past few decades, Au nanostructures of various shapes, including nanospheres [8–10], nanorods [11–19], nanowires [20–26], polyhedrons [27–32], nanoplates [33–35], nanoshells [36–38], and branched forms [39–49], have been extensively explored because of their shape-dependent surface plasmon resonance properties [50–53]. The fascinating surface plasmon resonance properties of Au nanostructures enable their effective implementation in a wide variety of biomedical applications, such as cancer therapy, bio-imaging, biological sensing, and diagnostics [54–58]. To obtain Au nanostructures exhibiting optical properties active in the NIR region, intricate methods including multiple steps, many reagents, or long reaction times have been applied. A method using two (or more) appropriate capping reagents with different binding affinities has been developed to obtain kinetic control of the growth rates on various crystal planes, resulting in the formation of non-spherical Au nanostructures. The development of Au nanostructure preparation that yields NIR absorption is of prime importance for the successful extension to practical applications
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