Abstract
In recent years, photoluminescent gold nanoclusters have attracted considerable interest in both fundamental biomedical research and practical applications. Due to their ultrasmall size, unique molecule-like optical properties, and facile synthesis gold nanoclusters have been considered very promising photoluminescent agents for biosensing, bioimaging, and targeted therapy. Yet, interaction of such ultra-small nanoclusters with cells and other biological objects remains poorly understood. Therefore, the assessment of the biocompatibility and potential toxicity of gold nanoclusters is of major importance before their clinical application. In this study, the cellular uptake, cytotoxicity, and intracellular generation of reactive oxygen species (ROS) of bovine serum albumin-encapsulated (BSA-Au NCs) and 2-(N-morpholino) ethanesulfonic acid (MES)-capped photoluminescent gold nanoclusters (Au-MES NCs) were investigated. The results showed that BSA-Au NCs accumulate in cells in a similar manner as BSA alone, indicating an endocytotic uptake mechanism while ultrasmall Au-MES NCs were distributed homogeneously throughout the whole cell volume including cell nucleus. The cytotoxicity of BSA-Au NCs was negligible, demonstrating good biocompatibility of such BSA-protected Au NCs. In contrast, possibly due to ultrasmall size and thin coating layer, Au-MES NCs exhibited exposure time-dependent high cytotoxicity and higher reactivity which led to highly increased generation of reactive oxygen species. The results demonstrate the importance of the coating layer to biocompatibility and toxicity of ultrasmall photoluminescent gold nanoclusters.
Highlights
Bioimaging is one of the frontiers in biomedical sciences and has significant impact in clinical and medical research
One example is a new class of photoluminescent gold nanoclusters synthesized within the protein templates, the first synthesis report being on the bovine serum albumin (BSA)-stabilized photoluminescent gold nanoclusters proposed by Xie et al [18]
The cytotoxic effect of Au-MES NCs was more significant on MCF-7 cells than on MDA-MB-231 cells, along with higher intracellular reactive oxygen species (ROS) generation, which is in agreement with the results reported by other authors showing that MDA-MB-231 cells are more resistant to treatment and exhibit properties of cancer stem-like cells [70,71]
Summary
Bioimaging is one of the frontiers in biomedical sciences and has significant impact in clinical and medical research. One example is a new class of photoluminescent gold nanoclusters synthesized within the protein templates, the first synthesis report being on the bovine serum albumin (BSA)-stabilized photoluminescent gold nanoclusters proposed by Xie et al [18]. Other proteins such as insulin [19,20], human transferrin [21], ferritin [22], hemoglobin [23], trypsin [24], and lysozyme [25] have been shown to successfully serve as templates for the formation of photoluminescent Au NCs
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