Green synthesis of Au–Cu2−xSe heterodimer nanoparticles and their in-vitro cytotoxicity, photothermal assay
Graphical abstract
Introduction
Recently, noble metal nanoparticles have gained scientific interest due to their exceptional property of localized surface plasmon resonance (LSPR) in the near-infrared (NIR) or visible region. This property of LSPR is mainly depending on shape, size and composition of nanoparticles (Eustis and el-Sayed, 2006, Barbosa et al., 2010, Oh et al., 2010, Ye et al., 2013, Bastús et al., 2014, Blanch et al., 2015). These plasmonic modes are mainly obtained due to the collective oscillation of negatively charged free carriers (electrons). Plasmonic nanomaterials are reported to have a multitude of applications in various fields of science and technology such as catalysis (Stratakis and Garcia 2012), medicine (El-Sayed et al., 2005, Pissuwan et al., 2011, Dreaden et al., 2012) and sensors (Dondapati et al., 2010, Jans and Huo, 2012, Saha et al., 2012). In recent years, doped semiconductors nanoparticles have developed as new plasmonic materials of researcher’s interest. For instance, vacancy-doped copper chalcogenides (Cu2−x Y, x> 0, Y = Te, S, Se) are growing as the starting point for the fast developing field of semiconductor plasmonics (Zhao et al., 2009, Hsu et al., 2011, Luther et al., 2011, Kriegel et al., 2012, Manthiram and Alivisatos, 2012, Kriegel et al., 2013, Comin and Manna, 2014, Liu and Swihart, 2014, Lounis et al., 2014a, Lounis et al., 2014b, Mattox et al., 2014, Neyshtadt et al., 2015).
Copper chalcogenide materials exhibit LSPRs in the NIR spectral region because of the presence of charge carriers. The plasmonic modes of semiconductor chalcogenides are due to the collective oscillation of holes, which are positively charged charge carriers. It is known that the plasmonic modes of metallic nanoparticles are principally “locked” after their preparation. On the other hand, the LSPR of vacancy-doped Cu2-x Y nanoparticles can be tuned by adjusting levels of vacancy doping. The vacancy levels can be created by different methods such as ligand exchange (Balitskii et al., 2014), addition of an external oxidizing agent (Dorfs et al., 2011), postsynthetic thermal treatment (Hsu et al., 2011), simple exposure to atmospheric oxygen (Dorfs et al., 2011, Kriegel et al., 2012).
Semiconductor copper chalcogenides find various applications in different fields such as bioimaging (Ku et al., 2012, Liu et al., 2013), photothermal therapy (Hessel et al., 2011, Tian et al., 2011), Surface enhanced raman spectroscopy (SERS) (Li et al., 2013) and as plasmonic probes (Jain et al., 2013). These chalcogenide materials with doping are being used now days to tune the NIR LSPR as new photo thermal agents. The combination of plasmonic modes of two different materials (vacancy-doped semiconductors and metals) is of increasing demand due to unexplored phenomena obtained from the interaction of two intrinsically dissimilar plasmonic modes of materials. For example, Ding et al. reported that Au–Cu9S5 composite exhibited the coupling effect of plasmonic components of both gold and Cu9S5 (Ding et al., 2014). In addition, their biocompatibility and high photothermal transduction efficiency made these composite materials as excellent applicants for phototherapy and bioimaging. Hence, there is an increasing demand for development of new hybrid materials that involve the coupling effect of plasmonic components of metal and semiconductor chalcogenides. The present work reported the development of Au-Cu2-xSe as new photo thermal agents that exhibit broad range of NIR absorption. We have also studied their in-vitro cytotoxicity against Hep-2 cell.
Section snippets
Materials
All reagents were purchased from sigma aldrich suppliers and used without purification. Ascorbic acid, Hydrogen tetrachloroaurate trihydrate (HAuCl4·3H2O), Selenium dioxide (SeO2), Copper sulphate hexa hydrate (CuSO4·5H2O), Sodium citrate. Milli Q water was used for all the experiments.
Synthesis of Au–Cu2-x Se
Initially, gold nanoparticles (AuNPs) were prepared by using a standard reducing agent, sodium citrate. In brief, 2 mL of 1% sodium citrate was added 0.689 mL of HAuCl4 (1 M) and allowed for stirring to obtain a
Results and discussion
The formation of Au–Cu2-xSe is known by the color change of solution from ruby red (mixture of gold nanoparticles and copper, selenium precursors) to black. A comparitive optical absorbance of Au–Cu2-xSe NPs with that of original Au NPs and Cu2-xSe is shown in Fig. 1. A LSPR peak at 520 nm was found for the pure Au NPs synthesized by using sodium citrate. On the other hand, the LSPR absorbance peak for Au–Cu2-xSe NPs is found to be broader and flatter when compared to original Au NPs. It is also
Conclusions
In this work, we have prepared Au–Cu2-xSe nanocomposite and established its utility as in-vitro photothermal agent. The UV–vis spectrum confirmed the presence of a plasmonic peak in the visible region and a flat absorption band in NIR region. The plasmonic interactions of gold and Cu2-xSe domains demonstrated a novel method for tuning plasmon resonance absorption spectra across a broad range of wavelength. Further the cytotoxicity studies revealed the lower cytotoxicity of synthesized Au–Cu2-x
Acknowledgements
Mr. SBM greatly acknowledges the help of South west University, Chongqing, China for giving platform and funding to do this research.
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