Abstract
Gold nanoparticles (Au NPs) have been thoroughly investigated for anti-cancer therapy. However, their undesired high gold content remains a problem when injected into the body for drug delivery applications. In this report, we made an effort to conjugate the curcumin molecules on the surface of gold quantum clusters (Au QCs) by a novel in situ synthesis method which provides an alternative route to not only reduce the metallic content but also increase the water solubility of curcumin and the loading efficiency. Here, curcumin itself acts as a reducing and capping agent for the synthesis of Au QCs. The UV–vis absorption, fluorescence, transmission electron microscopy, and electrospray ionization mass spectrometry results confirmed the synthesis of fluorescent Au QCs. Curcumin-conjugated Au NPs (C-Au NPs) and glutathione (GSH)-conjugated Au QCs (GSH-Au QCs) were also synthesized to visualize the effect of particle size and the capping agent, respectively, on the cytotoxicity to normal and cancer cells. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that the curcumin-conjugated Au QCs (C-Au QCs) were less cytotoxic to normal cells while almost the same cytotoxic to cancer cells in comparison to curcumin itself, which indicates that curcumin preserves its anticancer property even after binding to the Au QCs. However, C-Au NPs and GSH-Au QCs did not show any cytotoxicity against the normal and cancer cells at the concentration used. The western blot assay indicated that C-Au QCs promote apoptosis in cancer cells. Further, the in vivo study on severe combined immunodeficiency mice showed that C-Au QCs also inhibited the tumor growth efficiently without showing significant toxicity to internal organs.
Highlights
Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is a polyphenol and the main functional component of turmeric derived from the rhizome of a medicinal plant “Curcuma longa”.1 Curcumin has been used as the main ingredient of Indian spices and traditional ayurvedic medicines since ancient times in the Asian countries.[2]
The synthesis of Au QCs using curcumin as both a reducing and capping agent is very crucial regarding the solubility of curcumin
The UV−vis spectroscopic study of curcumin in dimethyl sulfoxide (DMSO) and the alkaline medium shows two distinct absorption bands at ∼262 and ∼425 nm, which are related to the n−π* and π−π* transitions, respectively (Figure 1a).[1,27]
Summary
Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is a polyphenol and the main functional component of turmeric derived from the rhizome of a medicinal plant “Curcuma longa”.1 Curcumin has been used as the main ingredient of Indian spices and traditional ayurvedic medicines since ancient times in the Asian countries.[2]. X-ray photoelectron spectroscopy (XPS) study was performed to analyze the functional groups of curcumin involved in binding with C-Au QCs (Figure 4).
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