In vitro study of enhanced photodynamic cancer cell killing effect by nanometer-thick gold nanosheets
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rtment of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA 3 University of Wisconsin Carbone Cancer Center, Madison, Wisconsin 53705, USA § Ziyi Zhang and Dalong Ni contributed equally to this work. 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 8 October 2019 / Revised: 11 July 2020 / Accepted: 18 July 2020
ABSTRACT Photodynamic therapy (PDT) by near-infrared (NIR) irradiation is a promising technique for treating various cancers. Here, we reported the development of free-standing wafer-scale Au nanosheets (NSs) that exhibited an impressive PDT effect. The Au NSs were synthesized by ionic layer epitaxy at the air-water interface with a uniform thickness in the range from 2 to 8.5 nm. These Au NSs were found very effective in generating singlet oxygen under NIR irradiation. In vitro cellular study showed that the Au NSs had very low cytotoxicity and high PDT efficiency due to their uniform 2D morphology. Au NSs could kill cancer cells after 5 min NIR irradiation with little heat generation. This performance is comparable to using 10 times mass loading of Au nanoparticles (NPs). This work suggests that two-dimensional (2D) Au NSs could be a new type of biocompatible nanomaterial for PDT of cancer with an extraordinary photon conversion and cancer cell killing efficiency.
KEYWORDS gold nanosheet, ionic layer epitaxy, surface plasmon, photodynamic effect, cancer therapy
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Introduction
Cancer is one of the deadliest diseases for human beings. Numerous research efforts have been implemented for cancer cell killing. Among all currently available treatments, photodynamic therapy (PDT) is an attractive technique for killing various cancer cells [1, 2]. It is a noninvasive procedure that involves light, photosensitizers and tissue oxygen, and causes minimal damage to surrounding tissues. It, therefore, induces minimal damage to human bodies and has fewer side effects comparing to surgery, chemotherapy and radiation therapy [3–5]. Near infrared (NIR) light is usually employed for PDT treatment because it has deep tissue penetration [6]. Nanomaterials that absorb NIR light and generate reactive oxygen species (ROS) are usually used as photosensitizers for PDT to kill cancer cells. Au nanoparticles (NPs) are well known for their chemical inertness and low cytotoxicity [7], and has been considered as a good candidate for PDT in cancer treatment [8, 9]. It has been reported that the morphologies of metal nanomaterials have a very strong influence on their optical properties and surface reactivity [10–14]. It was found that singlet oxygen (one of the ROS) can be generated by photoirradiation at the longitudinal bands, but not at the transverse band of Au nanorods [15]. Large surface area with large dimensions would enhance the surface plasmon resonance in longer wavelength range and promotes singlet oxygen generation. Therefore, an ultr
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