In this paper, we report a benzothiazole-functionalized cyanine fluorescence probe and demonstrate that it is selectively reactive to bisulfite, an intermediate indicator for oxidative stress. The selective reaction can be monitored by distinct ratiometric fluorescence variation favorable for cell imaging and visualization. The original probe can be regenerated in high yield through the elimination of bisulfite from the product by peroxides such as hydrogen peroxide, accompanied by fluorescence turning on at 590 nm, showing a potential application for the detection of peroxides. We successfully applied this probe for fluorescence imaging of bisulfite in cancer cells (MCF-7) treated with bisulfite and hydrogen peroxide as well as a selective detection limit of 0.34 μM bisulfite in aqueous solution.

Because of their biocompatibility and biosafety, pegylated Au NPs (Au@PEG), as a nanodrug-carrier, have been widely applied in different biomedical applications, including imaging and drug delivery systems. Under such conditions, the biosafety of Au@PEG has attracted tremendous attention. However, only a small number of studies focused on the neurotoxicity of Au@PEG used as drug delivery carriers not to mention reducing the neurotoxicity of Au@PEG. To address this issue, the adverse effects of Au@PEG on human neuroblastoma SHSY5Y cells were first investigated. The results showed that 4.5 nm Au@PEG significantly induced cell apoptosis through upregulating reactive oxygen species (ROS) production and disordering the mitochondrial membrane potential. To further evaluate whether the neurotoxicity of Au@PEG could be improved through conjugating antioxidants on the surface of Au@PEG, Trolox (a vitamin E analogue)-functionalized Au@PEG (Au@Trolox) was synthesized. The results showed that the neurotoxicity of Au@PEG on SHSY5Y cells could be significantly improved by Au@Trolox. Next, mice were subjected to administration of 4.5 nm Au@PEG and Au@Trolox for 3 months. An increase of oxidative stress and a decrease in the activity of key antioxidant enzymes including glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and catalase (CAT) were observed after long-term injection of Au@PEG. More importantly, both the apoptosis of neurons and the activation of astrocytes were observed in the hippocampus of mice injected with Au@PEG. In contrast, the adverse effects of Au@PEG could be improved when injected with Au@Trolox. In short, the present study provided new insights into the toxicity evaluation of nanoparticles and would help to better understand and prevent the neurotoxicity of nanomaterials used in pharmaceutics.

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