- Email: [email protected]
Green synthesis of Au–Cu2−xSe heterodimer nanoparticles and their in-vitro cytotoxicity, photothermal assay
Environmental Toxicology and Pharmacology 53 (2017) 29–33
Contents lists available at ScienceDirect
Environmental Toxicology and Pharmacology journal homepage: www.elsevier.com/locate/etap
Green synthesis of Au–Cu2−xSe heterodimer nanoparticles and their in-vitro cytotoxicity, photothermal assay Sireesh Babu Maddinedia,b,
MARK
⁎
a The Key laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, National Engineering Lab for Textile Fiber Materials and Processing Technology (Zhejiang), College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, China b Key Laboratory of Luminescent and Real-Time Analytical Chemistry, Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Ascorbic acid Copper selenium Cytotoxicity Photo thermal therapy
We demonstrate a new route for the synthesis of heterogeneous nanoparticles (NPs) composed of a gold domain (Au) and a heavily doped semiconductor domain (Cu2−xSe) which exhibit a broad localized surface plasmon resonance (LSPR) arising from interactions between two nanocrystal domains. We also demonstrate the in-vitro cytotoxicity and photo thermal efficiency of as prepared Au–Cu2−xSe heterodimer nanoparticles. This work establishes a new way of tuning LSPR by engineering the density of free charge carriers in two interacting domains.
1. 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,b; 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
⁎ Correspondence address: The Key laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, National Engineering Lab for Textile Fiber Materials and Processing Technology (Zhejiang), College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, China. E-mail address: [email protected].
http://dx.doi.org/10.1016/j.etap.2017.05.006 Received 19 January 2017; Received in revised form 1 May 2017; Accepted 5 May 2017 Available online 05 May 2017 1382-6689/ © 2017 Published by Elsevier B.V.
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Fig. 1. Optical absorbance of AuNPs, Cu2-x Se and Au-Cu2-x Se nanocomposite.
tions at 30 °C. After 30 min, the temperature of reaction solution is increased to 45 °C and allowed for stirring for 10 h to obtain a black colored Au-Cu2-xSe colloidal solution. The resulting solution was washed twice with Milli Q water via centrifugation at 10,000 rpm for 10 min, which later was purified via dialysis using a 10 kDa dialysis membrane for about 24 h with Milli Q water.
2.3. In-vitro cytotoxicity assay To investigate the cytotoxicity of the Au-Cu2-xSe NPs, a CKK-8 assay was performed. Hep-2 cells (1 × 105 per mL) in Roswell Park Memorial Institute 1640 medium (RPMI 1640) supplemented with 10% fetal bovine serum (FBS) were added to each well of a 96-well plate (100 μL well−1). Plates were first maintained in an incubator (37 °C, 5% CO2) for 24 h. Then the culture medium was replaced with 2% FBS 1640 medium containing the Au-Cu2-x Se NPs of different concentration (0, 20, 40, 60, 80, 100 μg mL−1) and incubated for another 24 h. Finally, 10 μL of Cell Counting Kit-8 (CCK-8) solution and 90 μL RPMI 1640 were added to each well and left for 30 min. The optical density (OD) of the mixture was measured at 450 nm with a Microplate Reader Model. The cell viability was estimated according to the following equation:
Fig. 2. XRD pattern showed the simultaneous existence of copper selenide and gold crystal phases in Au–Cu2-xSe.
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. 2. Experimental section 2.1. Materials
Cell viability (%) = (ODtrested − ODPBS)/(ODcontrol − ODPBS)
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.
OD control is the optical density of mixture in the absence of nanoparticles, OD PBS is the optical density of PBS in 96 well plate and OD treated is the optical density of mixture in the presence of nanoparticles.
2.2. Synthesis of Au–Cu2-x Se 2.4. Characterization 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 pink colored gold nanocolloid. The obtained nano gold colloid was then washed several times and centrifuged to obtain a pellet which was diluted to 10 mL using Milli Q water. To prepare Au-Cu2-x Se, 0.2 mL of SeO2 (0.25 M) and 0.4 mL of ascorbic acid solution (15 mg/mL) were added to 5 mL of gold colloids and allowed for stirring at room temperature for 10 min. Then, a mixture of Ascorbic acid solution (15 mg/mL) and 0.4 mL CuSO4·5H2O (0.1 M) was added to reaction mixture under vigorous stirring condi-
The UV–vis optical and NIR absorption spectra was recorded using U-3600 spectrophotometer instrument (Hitachi Ltd., Japan). The size and morphology of the Au–Cu2-xSe were analysed by using S-4800 scanning electron microscope (SEM) instrument (Hitachi, Japan). An XD-3 X-ray diffractometer was used for powder X-ray diffraction (XRD) analysis using Cu (36 kV, 20 mA) radiation. A laser with wavelength of 980 nm (1.25 W) with laser spot diameter of 3 mm was used for photo thermal evaluation of Au–Cu2-xSe.
30
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Fig. 3. SEM images (A,B,C) and EDS spectrum (D) of Au-Cu2-x Se nanocomposite.
formation of Au–Cu2-xSe NPs. On the other hand, the spectra of Cu2-xSe NPs showed the NIR absorbance peak centred at 1086 nm (Wolf et al., 2015). In addition, the optical absorbance spectrum is extremely flatter in the NIR region from 850 nm to 1400 nm. The Cu2-xSe NCs synthesized in this work have high cation vacancies and hence behave as a heavily doped p-type semiconductor. The LSPR absorbance in Cu2-xSe is due to the high concentration of free holes. The phenomenon of shifting of LSPR absorbance can be explained as follows. It can be expected that the holes from the Cu2-xSe could diffuse into Au domain which leads to the decreased electron density on the Au domain. This results in the decreased absorbance leading to the redshift in the LSPR band. In contrast, the NIR LSPR characteristic to the Cu2-xSe domain was simultaneously broadened and depressed. This phenomenon of broadened NIR-LSPR is due to the reduced hole concentration in the Cu2-xSe domain. On the other hand, the LSPR wavelength for both the materials depends on the refractive index of the surrounding medium. The relatively low refractive index of the Au will lead to the blue-shift in the LSPR of the Cu2-xSe domain, while the high refractive index of Cu2-xSe will serve to red-shift in the LSPR of the Au domain. This difference in the refractive indices and charge redistribution made the Au–Cu2-xSe to obtain a new optical absorption spectrum through tailoring charge density in the NP domains. However, the coupling effect of plasmonic components of other materials such as gold and Cu9S5 is already reported (Ding et al., 2014) Fig. 2, shows the XRD pattern of synthesized Au–Cu2-xSe. The XRD pattern of Au–Cu2-xSe represented the presence of diffraction peaks corresponding to both Au and berzelianite Cu2-x Se with characteristic planes of (111), (200) and (220) corresponding to gold. Additionally, the presence of planes at (111), (311) corresponding to Cu2-x Se signifying the formation of Au–Cu2-xSe.
Fig. 4. Cell viability of Hep-2 cells induced by Au-Cu2-x Se nanocomposite (P < 0.05).
3. 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 found that the shift in the SPR band of Au NPs from 520 nm to 550 nm is observed after the
31
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Fig. 5. (A) Temperature elevation of Au-Cu2-xSe aqueous solutions at different concentrations under laser irradiation (B) Temperature elevation profiles of 50 ppm Au-Cu2-xSe NPs aqueous solution under different laser power densities.
4. Conclusions
SEM images showed the decoration of small AuNPs onto the surface of Cu2-x Se (Fig. 3A–C). From Fig. 3C, it is clear that gold nanoparticles are adsorbed in the centre of the Cu2-x Se particles surface. On the other hand, EDS spectrum also confirmed the formation of Au-Cu2-x Se with presence of Au, Cu and Se elements in the spectrum (Fig. 3C,D).
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-xSe towards Hep-2 cells. Also, the synthesized material is shown to exhibit as good photothermal agent.
3.1. In-vitro cytotoxicity assay A CCK-8 assay is performed to know the potential of synthesized Au–Cu2-xSe for biomedical applications. It is well reported that the semiconductor chalcogenides are found to exhibit potential biomedical applications and hence it is necessary to develop a method for the fabrication of less toxic nanoparticles. For example, aqueous dispersible platelet-like Cu9S5 chalcogenides were used as photothermal agents to kill cancer cells in vivo because of their high heat conversion efficiency of about 25.7% (Tian et al., 2011). The relative cell viability of Hep-2 cells treated with Au–Cu2-xSe nanocomposite of various concentrations for about 24 h is known by CCK-8 assay. It is found that the Au–Cu2-xSe nanocomposite showed no significant cytotoxicity against Hep-2 cells, even at a higher concentration of 80 μg/mL for 24 h (Fig. 4). Hence, the synthesized Au–Cu2-xSe nanocomposite is less toxic enough that can be used in biomedical applications. From these studies, it is concluded that the amount of Au–Cu2-xSe nanocomposite that can be used for biomedical applications for in-vivo cell studies is below 80 μg/mL. These results are supported by bimolecular capped plasmonic gold and silver nanoparticles that are reported to exhibit their biocompatible nature (Sireesh Babu et al., 2015, 2017)
Acknowledgements Mr. SBM greatly acknowledges the help of South west University, Chongqing, China for giving platform and funding to do this research. References Balitskii, O.A., Sytnyk, M., Stangl, J., Primetzhofer, D., Groiss, H., Heiss, W., 2014. Tuning the localized surface plasmon resonance in Cu 2-x Se nanocrystals by postsynthetic ligand exchange. ACS Appl. Mater. Interfaces 6, 2–7. http://dx.doi.org/10.1021/ am504296y. Barbosa, S., Agrawal, A., Rodríguez-Lorenzo, L., Pastoriza-Santos, I., Alvarez-Puebla, R.A., Kornowski, A., Weller, H., Liz-Marzán, L.M., 2010. Tuning size and sensing properties in colloidal gold nanostars. Langmuir 26, 14943–14950. http://dx.doi. org/10.1021/la102559e. Bastús, N., Merkoçi, F., Piella, J., Puntes, V., 2014. Synthesis of highly monodisperse citrate-stabilized silver nanoparticles of up to 200 nm: kinetic control and catalytic properties. Chem. Mater. 26, 2836–2846. http://dx.doi.org/10.1021/cm500316k. Blanch, A.J., Döblinger, M., Rodríguez-Fernández, J., 2015. Simple and rapid high-yield synthesis and size sorting of multibranched hollow gold nanoparticles with highly tunable NIR plasmon resonances. Small 11, 4550–4559. http://dx.doi.org/10.1002/ smll.201500095. Comin, A., Manna, L., 2014. New materials for tunable plasmonic colloidal nanocrystals. Chem. Soc. Rev. 43, 3957–3975. http://dx.doi.org/10.1039/c3cs60265f. Ding, X., Liow, C.H., Zhang, M., Huang, R., Li, C., Shen, H., Liu, M., Zou, Y., Gao, N., Zhang, Z., Li, Y., Wang, Q., Li, S., Jiang, J., 2014. Surface plasmon resonance enhanced light absorption and photothermal therapy in the second near-infrared window. J. Am. Chem. Soc. 136, 15684–15693. http://dx.doi.org/10.1021/ ja508641z. Dondapati, S.K., Sau, T.K., Hrelescu, C., Klar, T.A., Stefani, F.D., Feldmann, J., 2010. Label-free biosensing based on single gold nanostars as plasmonic transducers. ACS Nano 4, 6318–6322. http://dx.doi.org/10.1021/nn100760f. Dorfs, D., Härtling, T., Miszta, K., Bigall, N.C., Kim, M.R., Genovese, A., Falqui, A., Povia, M., Manna, L., 2011. Reversible tunability of the near-infrared valence band plasmon resonance in Cu2- xSe nanocrystals. J. Am. Chem. Soc. 133, 11175–11180. http://dx. doi.org/10.1021/ja2016284. Dreaden, E.C., Alkilany, A.M., Huang, X., Murphy, C.J., El-Sayed, M a., 2012. The golden age: gold nanoparticles for biomedicine. Chem. Soc. Rev. 41, 2740. http://dx.doi. org/10.1039/c1cs15237h. El-Sayed, I.H., Huang, X., El-Sayed, M.A., 2005. Surface plasmon resonance scattering and absorption of anti-EGFR antibody conjugated gold nanoparticles in cancer
3.2. In-vitro photothermal assay The photo thermal effect of Au-Cu2-xSe nanocomposite was first studied by monitoring the temperature change of 0.2 mL of Au-Cu2-x Se NPs solution under the irradiation of a 980 nm cw laser. At laser power density of 0.85 W/cm2, with the NP concentration varied from 6.25 to 50 ppm, the solution temperature elevation increased from 9.5 to 14.1 °C after 10 min laser irradiation (Shown in Fig. 5A). Similarly, when NPs concentration was fixed at 50 ppm, an obvious power density dependent temperature rise was also observed (Shown in Fig. 5B). On the other hand, the presence of gold nanoparticles on Cu2-x Se enhances the Cu2-x Se absorption in Au-Cu2-xSe hybrids, resulting in the increase of molar extinction coefficient of Au-Cu2-xSe in the NIR region, rendering them as more efficient nanoheaters (Ding et al., 2014). 32
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Luther, J.M., Jain, P.K., Ewers, T., Alivisatos, a.P., 2011. Localized surface plasmon resonances arising from free carriers in doped quantum dots. Nat. Mater. 10, 361–366. http://dx.doi.org/10.1038/nmat3004. Manthiram, K., Alivisatos, A.P., 2012. Tunable localized surface plasmon resonances in tungsten oxide nanocrystals. J. Am. Chem. Soc. 134, 3995–3998. http://dx.doi.org/ 10.1021/ja211363w. Mattox, T.M., Bergerud, A., Agrawal, A., Milliron, D.J., 2014. Influence of shape on the surface plasmon resonance of tungsten bronze nanocrystals. Chem. Mater. 26, 1779–1784. http://dx.doi.org/10.1021/cm4030638. Neyshtadt, S., Kriegel, I., Rodríguez-Fernández, J., Hug, S., Lotsch, B., Da Como, E., 2015. Electronically coupled hybrid structures by graphene oxide directed self-assembly of Cu\n 2-x\n S nanocrystals. Nanoscale 7, 6675–6682. http://dx.doi.org/10.1039/ C5NR00656B. Oh, E., Susumu, K., Goswami, R., Mattoussi, H., 2010. One-phase synthesis of watersoluble gold nanoparticles with control over size and surface functionalities. Langmuir 26, 7604–7613. http://dx.doi.org/10.1021/la904438s. Pissuwan, D., Niidome, T., Cortie, M.B., 2011. The forthcoming applications of gold nanoparticles in drug and gene delivery systems. J. Control. Release 149, 65–71. http://dx.doi.org/10.1016/j.jconrel.2009.12.006. Saha, K., Agasti, S., Kim, C., Li, X., Rotello, V., 2012. Gold nanoparticles in chemical and biological sensing. Chem. Rev. 112, 2739–2779. http://dx.doi.org/10.1021/ cr2001178. Sireesh Babu, M., Badal Kumar, M., Shivendu, R., Nandita, D., 2015. Diastase assisted green synthesis of sizecontrollable gold nanoparticles. RSC Adv. 5, 26727–26733. http://dx.doi.org/10.1039/c5ra03117f. Sireesh Babu, M., Badal Kumar, M., Kiran Kumar, A., 2017. Environment friendly approach for size controllable synthesis ofbiocompatible Silver nanoparticles using diastase. Environ. Toxicol. Pharmacol. 49, 131–136. http://dx.doi.org/10.1016/j. etap.2016.11.019. Stratakis, M., Garcia, H., 2012. Catalysis by supported gold nanoparticles: beyond aerobic oxidative processes. Chem. Rev. 112, 4469–4506. http://dx.doi.org/10.1021/ cr3000785. Tian, Q., Jiang, F., Zou, R., Liu, Q., Chen, Z., Zhu, M., Yang, S., Wang, J., Wang, J., Hu, J., 2011. Hydrophilic Cu 9S 5 nanocrystals: a photothermal agent with a 25.7% heat conversion efficiency for photothermal ablation of cancer cells in vivo. ACS Nano 5, 9761–9771. http://dx.doi.org/10.1021/nn203293t. Wolf, A., Kodanek, T., Dorfs, D., 2015. Tuning the LSPR in copper chalcogenide nanoparticles by cation intercalation, cation exchange and metal growth. Nanoscale 7, 19519–19527. http://dx.doi.org/10.1039/c5nr05425g. Ye, X., Zheng, C., Chen, J., Gao, Y., Murray, C.B., 2013. Using binary surfactant mixtures to simultaneously improve the dimensional tunability and monodispersity in the seeded growth of gold nanorods. Nano Lett. 13, 765–771. http://dx.doi.org/10. 1021/nl304478h. Zhao, Y., Pan, H., Lou, Y., Qiu, X., Zhu, J., Burda, C., 2009. Plasmonic Cu 2-xS nanocrystals: optical and structural properties of copper-deficient copper(I) sulfides. J. Am. Chem. Soc. 131, 4253–4261. http://dx.doi.org/10.1021/ja805655b.
diagnostics: applications in oral cancer. Nano Lett. 5, 829–834. http://dx.doi.org/10. 1021/nl050074e. Eustis, S., el-Sayed, M.a., 2006. Why gold nanoparticles are more precious than pretty gold: noble metal surface plasmon resonance and its enhancement of the radiative and nonradiative properties of nanocrystals of different shapes. Chem. Soc. Rev. 35, 209–217. http://dx.doi.org/10.1039/b514191e. Hessel, C.M., Pattani, V.P., Rasch, M., Panthani, M.G., Koo, B., Tunnell, J.W., Korgel, B.A., 2011. Copper selenide nanocrystals for photothermal therapy. Nano Lett. 11, 2560–2566. http://dx.doi.org/10.1021/nl201400z. Hsu, S., On, K., Tao, A., 2011. Localized surface plasmon resonances of anisotropic semiconductor nanocrystals. J. Am. Chem. Soc. 133, 19072–19075. http://dx.doi. org/10.1021/ja2089876. Jain, P.K., Manthiram, K., Engel, J.H., White, S.L., Faucheaux, J.A., Alivisatos, A.P., 2013. Doped nanocrystals as plasmonic probes of redox chemistry. Angew. Chem. Int. Ed. 52, 13671–13675. http://dx.doi.org/10.1002/anie.201303707. Jans, H., Huo, Q., 2012. Gold nanoparticle-enabled biological and chemical detection and analysis. Chem. Soc. Rev. 41, 2849. http://dx.doi.org/10.1039/c1cs15280g. Kriegel, I., Jiang, C., Rodríguez-Fernández, J., Schaller, R.D., Talapin, D.V., Da Como, E., Feldmann, J., 2012. Tuning the excitonic and plasmonic properties of copper chalcogenide nanocrystals. J. Am. Chem. Soc. 134, 1583–1590. http://dx.doi.org/10. 1021/ja207798q. Kriegel, I., Rodríguez-Fernández, J., Wisnet, A., Zhang, H., Waurisch, C., Eychmüller, A., Dubavik, A., Govorov, A.O., Feldmann, J., 2013. Shedding light on vacancy-doped copper chalcogenides: shape-controlled synthesis, optical properties, and modeling of copper telluride nanocrystals with near-infrared plasmon resonances. ACS Nano 7, 4367–4377. http://dx.doi.org/10.1021/nn400894d. Ku, G., Zhou, M., Song, S., Huang, Q., Hazle, J., Li, C., 2012. Copper sulfide nanoparticles as a new class of photoacoustic contrast agent for deep tissue imaging at 1064 nm. ACS Nano 6, 7489–7496. http://dx.doi.org/10.1021/nn302782y. Li, W., Zamani, R., Gil, P.R., Pelaz, B., Ibáñez, M., Cadavid, D., Shavel, A., Alvarez-puebla, R.A., Parak, W.J., Arbiol, J., Cabot, A., 2013. CuTe Nanocrystals: shape and size control, plasmonic properties, and use as SERS probes and photothermal agents. J. Am. Chem. Soc. 135, 7098–7101. http://dx.doi.org/10.1021/ja401428e. Liu, X., Swihart, M.T., 2014. Heavily-doped colloidal semiconductor and metal oxide nanocrystals: an emerging new class of plasmonic nanomaterials. Chem. Soc. Rev. 43, 3908–3920. http://dx.doi.org/10.1039/c3cs60417a. Liu, X., Law, W.C., Jeon, M., Wang, X., Liu, M., Kim, C., Prasad, P.N., Swihart, M.T., 2013. Cu2-xSe nanocrystals with localized surface plasmon resonance as sensitive contrast agents for In vivo photoacoustic imaging: demonstration of sentinel lymph node mapping. Adv. Healthcare Mater. 2, 952–957. http://dx.doi.org/10.1002/adhm. 201200388. Lounis, S.D., Runnerstrom, E.L., Bergerud, A., Nordlund, D., Milliron, D.J., 2014a. Influence of dopant distribution on the plasmonic properties of indium tin oxide nanocrystals. J. Am. Chem. Soc. 136, 7110–7116. Lounis, S.D., Runnerstrom, E.L., Llordés, A., Milliron, D.J., 2014b. Defect chemistry and Plasmon physics of colloidal metal oxide Nanocrystals. J. Phys. Chem Lett. 5, 1564–1574. http://dx.doi.org/10.1021/jz500440e.
33
Contents lists available at ScienceDirect
Environmental Toxicology and Pharmacology journal homepage: www.elsevier.com/locate/etap
Green synthesis of Au–Cu2−xSe heterodimer nanoparticles and their in-vitro cytotoxicity, photothermal assay Sireesh Babu Maddinedia,b,
MARK
⁎
a The Key laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, National Engineering Lab for Textile Fiber Materials and Processing Technology (Zhejiang), College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, China b Key Laboratory of Luminescent and Real-Time Analytical Chemistry, Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing 400715, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Ascorbic acid Copper selenium Cytotoxicity Photo thermal therapy
We demonstrate a new route for the synthesis of heterogeneous nanoparticles (NPs) composed of a gold domain (Au) and a heavily doped semiconductor domain (Cu2−xSe) which exhibit a broad localized surface plasmon resonance (LSPR) arising from interactions between two nanocrystal domains. We also demonstrate the in-vitro cytotoxicity and photo thermal efficiency of as prepared Au–Cu2−xSe heterodimer nanoparticles. This work establishes a new way of tuning LSPR by engineering the density of free charge carriers in two interacting domains.
1. 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,b; 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
⁎ Correspondence address: The Key laboratory of Advanced Textile Materials and Manufacturing Technology of Ministry of Education, National Engineering Lab for Textile Fiber Materials and Processing Technology (Zhejiang), College of Materials and Textiles, Zhejiang Sci-Tech University, Hangzhou 310018, China. E-mail address: [email protected].
http://dx.doi.org/10.1016/j.etap.2017.05.006 Received 19 January 2017; Received in revised form 1 May 2017; Accepted 5 May 2017 Available online 05 May 2017 1382-6689/ © 2017 Published by Elsevier B.V.
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Fig. 1. Optical absorbance of AuNPs, Cu2-x Se and Au-Cu2-x Se nanocomposite.
tions at 30 °C. After 30 min, the temperature of reaction solution is increased to 45 °C and allowed for stirring for 10 h to obtain a black colored Au-Cu2-xSe colloidal solution. The resulting solution was washed twice with Milli Q water via centrifugation at 10,000 rpm for 10 min, which later was purified via dialysis using a 10 kDa dialysis membrane for about 24 h with Milli Q water.
2.3. In-vitro cytotoxicity assay To investigate the cytotoxicity of the Au-Cu2-xSe NPs, a CKK-8 assay was performed. Hep-2 cells (1 × 105 per mL) in Roswell Park Memorial Institute 1640 medium (RPMI 1640) supplemented with 10% fetal bovine serum (FBS) were added to each well of a 96-well plate (100 μL well−1). Plates were first maintained in an incubator (37 °C, 5% CO2) for 24 h. Then the culture medium was replaced with 2% FBS 1640 medium containing the Au-Cu2-x Se NPs of different concentration (0, 20, 40, 60, 80, 100 μg mL−1) and incubated for another 24 h. Finally, 10 μL of Cell Counting Kit-8 (CCK-8) solution and 90 μL RPMI 1640 were added to each well and left for 30 min. The optical density (OD) of the mixture was measured at 450 nm with a Microplate Reader Model. The cell viability was estimated according to the following equation:
Fig. 2. XRD pattern showed the simultaneous existence of copper selenide and gold crystal phases in Au–Cu2-xSe.
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. 2. Experimental section 2.1. Materials
Cell viability (%) = (ODtrested − ODPBS)/(ODcontrol − ODPBS)
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.
OD control is the optical density of mixture in the absence of nanoparticles, OD PBS is the optical density of PBS in 96 well plate and OD treated is the optical density of mixture in the presence of nanoparticles.
2.2. Synthesis of Au–Cu2-x Se 2.4. Characterization 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 pink colored gold nanocolloid. The obtained nano gold colloid was then washed several times and centrifuged to obtain a pellet which was diluted to 10 mL using Milli Q water. To prepare Au-Cu2-x Se, 0.2 mL of SeO2 (0.25 M) and 0.4 mL of ascorbic acid solution (15 mg/mL) were added to 5 mL of gold colloids and allowed for stirring at room temperature for 10 min. Then, a mixture of Ascorbic acid solution (15 mg/mL) and 0.4 mL CuSO4·5H2O (0.1 M) was added to reaction mixture under vigorous stirring condi-
The UV–vis optical and NIR absorption spectra was recorded using U-3600 spectrophotometer instrument (Hitachi Ltd., Japan). The size and morphology of the Au–Cu2-xSe were analysed by using S-4800 scanning electron microscope (SEM) instrument (Hitachi, Japan). An XD-3 X-ray diffractometer was used for powder X-ray diffraction (XRD) analysis using Cu (36 kV, 20 mA) radiation. A laser with wavelength of 980 nm (1.25 W) with laser spot diameter of 3 mm was used for photo thermal evaluation of Au–Cu2-xSe.
30
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Fig. 3. SEM images (A,B,C) and EDS spectrum (D) of Au-Cu2-x Se nanocomposite.
formation of Au–Cu2-xSe NPs. On the other hand, the spectra of Cu2-xSe NPs showed the NIR absorbance peak centred at 1086 nm (Wolf et al., 2015). In addition, the optical absorbance spectrum is extremely flatter in the NIR region from 850 nm to 1400 nm. The Cu2-xSe NCs synthesized in this work have high cation vacancies and hence behave as a heavily doped p-type semiconductor. The LSPR absorbance in Cu2-xSe is due to the high concentration of free holes. The phenomenon of shifting of LSPR absorbance can be explained as follows. It can be expected that the holes from the Cu2-xSe could diffuse into Au domain which leads to the decreased electron density on the Au domain. This results in the decreased absorbance leading to the redshift in the LSPR band. In contrast, the NIR LSPR characteristic to the Cu2-xSe domain was simultaneously broadened and depressed. This phenomenon of broadened NIR-LSPR is due to the reduced hole concentration in the Cu2-xSe domain. On the other hand, the LSPR wavelength for both the materials depends on the refractive index of the surrounding medium. The relatively low refractive index of the Au will lead to the blue-shift in the LSPR of the Cu2-xSe domain, while the high refractive index of Cu2-xSe will serve to red-shift in the LSPR of the Au domain. This difference in the refractive indices and charge redistribution made the Au–Cu2-xSe to obtain a new optical absorption spectrum through tailoring charge density in the NP domains. However, the coupling effect of plasmonic components of other materials such as gold and Cu9S5 is already reported (Ding et al., 2014) Fig. 2, shows the XRD pattern of synthesized Au–Cu2-xSe. The XRD pattern of Au–Cu2-xSe represented the presence of diffraction peaks corresponding to both Au and berzelianite Cu2-x Se with characteristic planes of (111), (200) and (220) corresponding to gold. Additionally, the presence of planes at (111), (311) corresponding to Cu2-x Se signifying the formation of Au–Cu2-xSe.
Fig. 4. Cell viability of Hep-2 cells induced by Au-Cu2-x Se nanocomposite (P < 0.05).
3. 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 found that the shift in the SPR band of Au NPs from 520 nm to 550 nm is observed after the
31
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Fig. 5. (A) Temperature elevation of Au-Cu2-xSe aqueous solutions at different concentrations under laser irradiation (B) Temperature elevation profiles of 50 ppm Au-Cu2-xSe NPs aqueous solution under different laser power densities.
4. Conclusions
SEM images showed the decoration of small AuNPs onto the surface of Cu2-x Se (Fig. 3A–C). From Fig. 3C, it is clear that gold nanoparticles are adsorbed in the centre of the Cu2-x Se particles surface. On the other hand, EDS spectrum also confirmed the formation of Au-Cu2-x Se with presence of Au, Cu and Se elements in the spectrum (Fig. 3C,D).
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-xSe towards Hep-2 cells. Also, the synthesized material is shown to exhibit as good photothermal agent.
3.1. In-vitro cytotoxicity assay A CCK-8 assay is performed to know the potential of synthesized Au–Cu2-xSe for biomedical applications. It is well reported that the semiconductor chalcogenides are found to exhibit potential biomedical applications and hence it is necessary to develop a method for the fabrication of less toxic nanoparticles. For example, aqueous dispersible platelet-like Cu9S5 chalcogenides were used as photothermal agents to kill cancer cells in vivo because of their high heat conversion efficiency of about 25.7% (Tian et al., 2011). The relative cell viability of Hep-2 cells treated with Au–Cu2-xSe nanocomposite of various concentrations for about 24 h is known by CCK-8 assay. It is found that the Au–Cu2-xSe nanocomposite showed no significant cytotoxicity against Hep-2 cells, even at a higher concentration of 80 μg/mL for 24 h (Fig. 4). Hence, the synthesized Au–Cu2-xSe nanocomposite is less toxic enough that can be used in biomedical applications. From these studies, it is concluded that the amount of Au–Cu2-xSe nanocomposite that can be used for biomedical applications for in-vivo cell studies is below 80 μg/mL. These results are supported by bimolecular capped plasmonic gold and silver nanoparticles that are reported to exhibit their biocompatible nature (Sireesh Babu et al., 2015, 2017)
Acknowledgements Mr. SBM greatly acknowledges the help of South west University, Chongqing, China for giving platform and funding to do this research. References Balitskii, O.A., Sytnyk, M., Stangl, J., Primetzhofer, D., Groiss, H., Heiss, W., 2014. Tuning the localized surface plasmon resonance in Cu 2-x Se nanocrystals by postsynthetic ligand exchange. ACS Appl. Mater. Interfaces 6, 2–7. http://dx.doi.org/10.1021/ am504296y. Barbosa, S., Agrawal, A., Rodríguez-Lorenzo, L., Pastoriza-Santos, I., Alvarez-Puebla, R.A., Kornowski, A., Weller, H., Liz-Marzán, L.M., 2010. Tuning size and sensing properties in colloidal gold nanostars. Langmuir 26, 14943–14950. http://dx.doi. org/10.1021/la102559e. Bastús, N., Merkoçi, F., Piella, J., Puntes, V., 2014. Synthesis of highly monodisperse citrate-stabilized silver nanoparticles of up to 200 nm: kinetic control and catalytic properties. Chem. Mater. 26, 2836–2846. http://dx.doi.org/10.1021/cm500316k. Blanch, A.J., Döblinger, M., Rodríguez-Fernández, J., 2015. Simple and rapid high-yield synthesis and size sorting of multibranched hollow gold nanoparticles with highly tunable NIR plasmon resonances. Small 11, 4550–4559. http://dx.doi.org/10.1002/ smll.201500095. Comin, A., Manna, L., 2014. New materials for tunable plasmonic colloidal nanocrystals. Chem. Soc. Rev. 43, 3957–3975. http://dx.doi.org/10.1039/c3cs60265f. Ding, X., Liow, C.H., Zhang, M., Huang, R., Li, C., Shen, H., Liu, M., Zou, Y., Gao, N., Zhang, Z., Li, Y., Wang, Q., Li, S., Jiang, J., 2014. Surface plasmon resonance enhanced light absorption and photothermal therapy in the second near-infrared window. J. Am. Chem. Soc. 136, 15684–15693. http://dx.doi.org/10.1021/ ja508641z. Dondapati, S.K., Sau, T.K., Hrelescu, C., Klar, T.A., Stefani, F.D., Feldmann, J., 2010. Label-free biosensing based on single gold nanostars as plasmonic transducers. ACS Nano 4, 6318–6322. http://dx.doi.org/10.1021/nn100760f. Dorfs, D., Härtling, T., Miszta, K., Bigall, N.C., Kim, M.R., Genovese, A., Falqui, A., Povia, M., Manna, L., 2011. Reversible tunability of the near-infrared valence band plasmon resonance in Cu2- xSe nanocrystals. J. Am. Chem. Soc. 133, 11175–11180. http://dx. doi.org/10.1021/ja2016284. Dreaden, E.C., Alkilany, A.M., Huang, X., Murphy, C.J., El-Sayed, M a., 2012. The golden age: gold nanoparticles for biomedicine. Chem. Soc. Rev. 41, 2740. http://dx.doi. org/10.1039/c1cs15237h. El-Sayed, I.H., Huang, X., El-Sayed, M.A., 2005. Surface plasmon resonance scattering and absorption of anti-EGFR antibody conjugated gold nanoparticles in cancer
3.2. In-vitro photothermal assay The photo thermal effect of Au-Cu2-xSe nanocomposite was first studied by monitoring the temperature change of 0.2 mL of Au-Cu2-x Se NPs solution under the irradiation of a 980 nm cw laser. At laser power density of 0.85 W/cm2, with the NP concentration varied from 6.25 to 50 ppm, the solution temperature elevation increased from 9.5 to 14.1 °C after 10 min laser irradiation (Shown in Fig. 5A). Similarly, when NPs concentration was fixed at 50 ppm, an obvious power density dependent temperature rise was also observed (Shown in Fig. 5B). On the other hand, the presence of gold nanoparticles on Cu2-x Se enhances the Cu2-x Se absorption in Au-Cu2-xSe hybrids, resulting in the increase of molar extinction coefficient of Au-Cu2-xSe in the NIR region, rendering them as more efficient nanoheaters (Ding et al., 2014). 32
Environmental Toxicology and Pharmacology 53 (2017) 29–33
S.B. Maddinedi
Luther, J.M., Jain, P.K., Ewers, T., Alivisatos, a.P., 2011. Localized surface plasmon resonances arising from free carriers in doped quantum dots. Nat. Mater. 10, 361–366. http://dx.doi.org/10.1038/nmat3004. Manthiram, K., Alivisatos, A.P., 2012. Tunable localized surface plasmon resonances in tungsten oxide nanocrystals. J. Am. Chem. Soc. 134, 3995–3998. http://dx.doi.org/ 10.1021/ja211363w. Mattox, T.M., Bergerud, A., Agrawal, A., Milliron, D.J., 2014. Influence of shape on the surface plasmon resonance of tungsten bronze nanocrystals. Chem. Mater. 26, 1779–1784. http://dx.doi.org/10.1021/cm4030638. Neyshtadt, S., Kriegel, I., Rodríguez-Fernández, J., Hug, S., Lotsch, B., Da Como, E., 2015. Electronically coupled hybrid structures by graphene oxide directed self-assembly of Cu\n 2-x\n S nanocrystals. Nanoscale 7, 6675–6682. http://dx.doi.org/10.1039/ C5NR00656B. Oh, E., Susumu, K., Goswami, R., Mattoussi, H., 2010. One-phase synthesis of watersoluble gold nanoparticles with control over size and surface functionalities. Langmuir 26, 7604–7613. http://dx.doi.org/10.1021/la904438s. Pissuwan, D., Niidome, T., Cortie, M.B., 2011. The forthcoming applications of gold nanoparticles in drug and gene delivery systems. J. Control. Release 149, 65–71. http://dx.doi.org/10.1016/j.jconrel.2009.12.006. Saha, K., Agasti, S., Kim, C., Li, X., Rotello, V., 2012. Gold nanoparticles in chemical and biological sensing. Chem. Rev. 112, 2739–2779. http://dx.doi.org/10.1021/ cr2001178. Sireesh Babu, M., Badal Kumar, M., Shivendu, R., Nandita, D., 2015. Diastase assisted green synthesis of sizecontrollable gold nanoparticles. RSC Adv. 5, 26727–26733. http://dx.doi.org/10.1039/c5ra03117f. Sireesh Babu, M., Badal Kumar, M., Kiran Kumar, A., 2017. Environment friendly approach for size controllable synthesis ofbiocompatible Silver nanoparticles using diastase. Environ. Toxicol. Pharmacol. 49, 131–136. http://dx.doi.org/10.1016/j. etap.2016.11.019. Stratakis, M., Garcia, H., 2012. Catalysis by supported gold nanoparticles: beyond aerobic oxidative processes. Chem. Rev. 112, 4469–4506. http://dx.doi.org/10.1021/ cr3000785. Tian, Q., Jiang, F., Zou, R., Liu, Q., Chen, Z., Zhu, M., Yang, S., Wang, J., Wang, J., Hu, J., 2011. Hydrophilic Cu 9S 5 nanocrystals: a photothermal agent with a 25.7% heat conversion efficiency for photothermal ablation of cancer cells in vivo. ACS Nano 5, 9761–9771. http://dx.doi.org/10.1021/nn203293t. Wolf, A., Kodanek, T., Dorfs, D., 2015. Tuning the LSPR in copper chalcogenide nanoparticles by cation intercalation, cation exchange and metal growth. Nanoscale 7, 19519–19527. http://dx.doi.org/10.1039/c5nr05425g. Ye, X., Zheng, C., Chen, J., Gao, Y., Murray, C.B., 2013. Using binary surfactant mixtures to simultaneously improve the dimensional tunability and monodispersity in the seeded growth of gold nanorods. Nano Lett. 13, 765–771. http://dx.doi.org/10. 1021/nl304478h. Zhao, Y., Pan, H., Lou, Y., Qiu, X., Zhu, J., Burda, C., 2009. Plasmonic Cu 2-xS nanocrystals: optical and structural properties of copper-deficient copper(I) sulfides. J. Am. Chem. Soc. 131, 4253–4261. http://dx.doi.org/10.1021/ja805655b.
diagnostics: applications in oral cancer. Nano Lett. 5, 829–834. http://dx.doi.org/10. 1021/nl050074e. Eustis, S., el-Sayed, M.a., 2006. Why gold nanoparticles are more precious than pretty gold: noble metal surface plasmon resonance and its enhancement of the radiative and nonradiative properties of nanocrystals of different shapes. Chem. Soc. Rev. 35, 209–217. http://dx.doi.org/10.1039/b514191e. Hessel, C.M., Pattani, V.P., Rasch, M., Panthani, M.G., Koo, B., Tunnell, J.W., Korgel, B.A., 2011. Copper selenide nanocrystals for photothermal therapy. Nano Lett. 11, 2560–2566. http://dx.doi.org/10.1021/nl201400z. Hsu, S., On, K., Tao, A., 2011. Localized surface plasmon resonances of anisotropic semiconductor nanocrystals. J. Am. Chem. Soc. 133, 19072–19075. http://dx.doi. org/10.1021/ja2089876. Jain, P.K., Manthiram, K., Engel, J.H., White, S.L., Faucheaux, J.A., Alivisatos, A.P., 2013. Doped nanocrystals as plasmonic probes of redox chemistry. Angew. Chem. Int. Ed. 52, 13671–13675. http://dx.doi.org/10.1002/anie.201303707. Jans, H., Huo, Q., 2012. Gold nanoparticle-enabled biological and chemical detection and analysis. Chem. Soc. Rev. 41, 2849. http://dx.doi.org/10.1039/c1cs15280g. Kriegel, I., Jiang, C., Rodríguez-Fernández, J., Schaller, R.D., Talapin, D.V., Da Como, E., Feldmann, J., 2012. Tuning the excitonic and plasmonic properties of copper chalcogenide nanocrystals. J. Am. Chem. Soc. 134, 1583–1590. http://dx.doi.org/10. 1021/ja207798q. Kriegel, I., Rodríguez-Fernández, J., Wisnet, A., Zhang, H., Waurisch, C., Eychmüller, A., Dubavik, A., Govorov, A.O., Feldmann, J., 2013. Shedding light on vacancy-doped copper chalcogenides: shape-controlled synthesis, optical properties, and modeling of copper telluride nanocrystals with near-infrared plasmon resonances. ACS Nano 7, 4367–4377. http://dx.doi.org/10.1021/nn400894d. Ku, G., Zhou, M., Song, S., Huang, Q., Hazle, J., Li, C., 2012. Copper sulfide nanoparticles as a new class of photoacoustic contrast agent for deep tissue imaging at 1064 nm. ACS Nano 6, 7489–7496. http://dx.doi.org/10.1021/nn302782y. Li, W., Zamani, R., Gil, P.R., Pelaz, B., Ibáñez, M., Cadavid, D., Shavel, A., Alvarez-puebla, R.A., Parak, W.J., Arbiol, J., Cabot, A., 2013. CuTe Nanocrystals: shape and size control, plasmonic properties, and use as SERS probes and photothermal agents. J. Am. Chem. Soc. 135, 7098–7101. http://dx.doi.org/10.1021/ja401428e. Liu, X., Swihart, M.T., 2014. Heavily-doped colloidal semiconductor and metal oxide nanocrystals: an emerging new class of plasmonic nanomaterials. Chem. Soc. Rev. 43, 3908–3920. http://dx.doi.org/10.1039/c3cs60417a. Liu, X., Law, W.C., Jeon, M., Wang, X., Liu, M., Kim, C., Prasad, P.N., Swihart, M.T., 2013. Cu2-xSe nanocrystals with localized surface plasmon resonance as sensitive contrast agents for In vivo photoacoustic imaging: demonstration of sentinel lymph node mapping. Adv. Healthcare Mater. 2, 952–957. http://dx.doi.org/10.1002/adhm. 201200388. Lounis, S.D., Runnerstrom, E.L., Bergerud, A., Nordlund, D., Milliron, D.J., 2014a. Influence of dopant distribution on the plasmonic properties of indium tin oxide nanocrystals. J. Am. Chem. Soc. 136, 7110–7116. Lounis, S.D., Runnerstrom, E.L., Llordés, A., Milliron, D.J., 2014b. Defect chemistry and Plasmon physics of colloidal metal oxide Nanocrystals. J. Phys. Chem Lett. 5, 1564–1574. http://dx.doi.org/10.1021/jz500440e.
33