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Synthesis of near infrared-activatable KxWO3 nanorods for photothermal therapy
Accepted Manuscript Synthesis of Near Infrared-Activatable KxWO3 Nanorods for Photothermal therapy Binghui Zheng, Zheng Han, Guang Wu, Yifu Liu, Chuntao Liu, Fangwei Ma PII: DOI: Reference:
S0167-577X(17)31569-0 https://doi.org/10.1016/j.matlet.2017.10.093 MLBLUE 23328
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
9 August 2017 13 October 2017 19 October 2017
Please cite this article as: B. Zheng, Z. Han, G. Wu, Y. Liu, C. Liu, F. Ma, Synthesis of Near Infrared-Activatable KxWO3 Nanorods for Photothermal therapy, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet. 2017.10.093
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis of Near Infrared-Activatable KxWO3 Nanorods for Photothermal therapy Binghui Zheng2, Zheng Han1, Guang Wu1*, Yifu Liu1, Chuntao Liu1, Fangwei Ma1 1 School of Chemistry and Materials Sciences, Heilongjiang University; Harbin 150080, China 2 China Tianchen Engineering Corporation (TCC), Harbin, 150076, China
Corresponding author: Associate professor Guang Wu E-mail: [email protected]
1
Abstract The KxWO3 nanorods with a broad optical absorbance in near infrared (NIR) region have been synthesized by a facile solvothermal reaction in this work. On the merits of this unique photoabsorption, KxWO3 nanorod exhibited an excellent photothermal conversion effect upon NIR 1064 nm laser excitation as evidenced by a rapid, distinct and recyclable photothermal effect both for KxWO3 powder and aqueous dispersion. Further, KxWO3 was finally proved to be an eligible phototherapeutic agent for antitumor treatment and great success has been made in in vitro cancer cell killing and in vivo elimination of solid tumor in living mice, manifesting a potential application prospect of KxWO3 nanorod as photothermal material. Keywords: Tungsten bronze, near-infrared absorption, photothermal therapy. 1. Introduction Developing NIR-harvesting materials is of great significances as it can serve formany related scientific areas such as photocatalytic reactions, solar cells, solar heater, photothermal therapy and so forth. [1-3] However, the NIR-harvesting materials are rare, and even if there are, they generally suffer from their own inevitable shortcomings, including narrowed absorption band, bad physicochemistry stability, lower absorption coefficient and so forth. [4] Fortunately, the emergence of tungsten bronze nanomaterials (MxWO3, where M is alkali metal ions, like Li, Na, K, Rb, Cs) seems like to be able to get out of above scientific predicament considering on their excellent and reliable NIR absorptive properties. Up to now, several kinds of M xWO3 have been applied for the cancer photothermal therapy, in which M xWO3 was employed to induce hyperthermia upon NIR irradiation at the tumor site for irreversible tumor damage. [5-9] However, in this regard, the MxWO3 with bigger alkali metal ions like CsxWO3 and RbxWO3 are not suitable for the photothermal therapy due to the bad biocompatibility of Cs and Rb elements, which may result in an unpredictable systemic toxicity. While for NaxWO3 or LixWO3, the leakage of metal ions would happen because of smaller ionic radius and resultantly weaken the NIR absorption of tungsten bronze. Hence, the ideal candidate is KxWO3 in view of 2
desired biocompatibility, physicochemistry stability and optical properties. However, applying KxWO3 nanomaterials for the photothermal cancer therapy is seldom, which may be due to the great difficulty in low-temperature synthesis and obtaining nanoscale sample directly. In this work, KxWO3 nanorods have been fabricated by a facile method and employed for cancer phototherapy for the first time. 2. Experimental 2.1Synthesis of KxWO3 nanorod Firstly, 0.297 g WCl6 and 0.042 g KOH were dissolved into the 40 ml ethanol to form a homogenous solution. Then, 10 ml acetic acid was introduced and the solution was transferred into 100 ml Teflon-lined autoclave. The solvothermal reaction performed at 200 oC for 24h. After the reaction, the blue powder was collected by centrifugation, washing and drying at 60 oC in vacuum. 2.2Characterization X-ray diffraction analysis (XRD, Shimadzu XD-D1), transmission electron microscope (TEM, ZEISS LEO 922), X-ray photoelectron spectroscopy (XPS, Perkin Elmer PHI 5600), spectrophotometer (JASCO V-670) were employed to investigate the crystal phase, morphology, chemical valence and optical properties of sample, respectively. 2.3 Photothermal therapy HeLa cells and HeLa-cells-bearing female BALB/C nude mice were used for the photothermal therapy investigation. The 1064 nm NIR laser was selected and the powder density was 1.5 W/cm2. The live-dead assay was conducted by Calcein AM and propidium iodide staining. For more details, please see the supporting information. 3. Results and discussion Firstly, we checked the morphological character of as-obtained sample. As shown in Figure 1a, the sample is consisted of many randomly distributed rod-like nanoparticles, and the average diameter of these nanorods is around 20 nm, while the length is up to 100-120 nm. In the XRD pattern of Figure 2b, all the reflective peaks 3
could be definitely indexed to the potassium tungsten bronze (JCPDS No.20-0940). Considering on that KxWO3 is a mixed valence compound, which should be also expressed as KxWx5+W1-x6+O3, we next inspected chemical composition and valence state by XPS analysis. In the full-range XPS survey, (Figure 1c) the binding energies relating to the elements of W, K and O have been found, indicating the successful insertion of K ions into the tungsten oxide lattice and formation of K xWO3 compound. Meanwhile, the atomic ratio of K/W is determined to be 0.31, which is close to the theoretical maximum of 0.33. After the deconvolution, XPS spectra of W 4f core-level could be fitted into two spin-orbit coupling doublets, resulting from two different oxidation states of W5+ and W6+ ions (Figure. 1d). Taken XRD and XPS results together, we firmly proved that the sample obtained in this work was KxWO3 compound with expectant crystal phase and chemical valence state.
Figure.1 (a) TEM image, (b) XRD pattern, (c) Full-range XPS spectra and core-level W4f XPS spectra of KxWO3.
Previously, the tungsten bronze compounds were reported to be excellent NIR absorbent when the particle dimension below certain threshold (usually several hundred nanometers) and the absorption enhanced with smaller size or preferred one-dimensional nanostructure like nanorods or nanofibers. In view of above, an excellent NIR photoabsorption is highly expected for KxWO3 nanorod of this work. 4
Hence, we next studied the photothermal and optical properties K xWO3 nanorod. As shown in the Figure 2a, powder absorbance spectra clearly presented a strong and wide light absorption in the whole range of 200-2500 nm, particularly in the NIR region where it is applicable for the photothermal therapy. The NIR absorption mechanism is thought to be due to localized surface plasma resonance and/or Small polaron absorption. [10-11] To investigate the photothermal conversion effect, we firstly inspected the temperature rise of KxWO3 powder upon 1.5 W/cm2 laser irradiation of 1064 nm. To our surprise, the temperature of irradiated area boosted up to 270 oC from the ambient temperature of 20 oC just after 1 second exposure to NIR laser as record by thermographic image in Figure 2b. Then, the KxWO3 aqueous dispersion of 1 mg/ml was suffered to the same laser irradiation, which also showed an obvious temperature elevation, manifesting the prominent photothemal effect and satisfying the basic requirement for cancer photothermal therapy (Figure 2c). Finally, a good cycling stability has also been found for this material in consideration of negligible change on heating efficiency after 5 cycles (Figure 2d). In this work, the photothermal conversion efficiency (η) of KxWO3 has been calculated to be 25.7 %, (more details in supporting information) which is comparable to other semiconductor nanoparticles, such as Cu2-xSe (22%) and Cu9S5 (25.7%), [8] but it is still lower than noble metal nanoparticles and carbon materials.[12-13]
Figure.2 (a) Powder absorbance spectra of KxWO3 ; (b) thermographicimage of 5
KxWO3powder after NIR 1064 laser irradiation for 1 second; (c) Temperature profile of KxWO3 aqueous dispersion upon laser irradiation (KxWO3:1 mg/ml, laser: 1.5 W/cm2); (d) cycling stability of KxWO3 aqueous dispersion for 5 cycles.
Inspired by above result, we then conducted the cancer photothermal therapy with KxWO3 nanorod. A power density of 2 W/cm2, which is a reasonable value and has been used in many works, was employed for NIR-mediated group. (Supporting information part.3) Firstly, we checked the biocompatibility of KxWO3 nanorod by a MTT method to determine the HeLa cell viability after incubation with K xWO3 for 24 h at different concentrations. It revealed a very limited cytotoxicity because of high cell viability, and the cells metabolic activity was higher than 85 % even under a concentration of 1 mg/ml (Figure 3a). Then, we carried out the in vitro photothermal treatment using Calcein AM and propidium iodide staining to visualize living (green fluorescence) and dead cells (red fluorescence), respectively. As can be seen in Figure 3b-e, untreated cells, cells treated with KxWO3 and cells treated with NIR irradiation showed a bright green color only, thus illustrating no detectable cell deaths. In contrast, striking red fluorescence is discernable for the NIR-mediated and KxWO3-enriched cells, indicating a marked phototherapy effect. We next investigated the in vivo photothermal treatment effect on HeLa tumor-bearing nude mice. The antitumor effect is evaluated by the relative tumor size. Similar to the in vitro results, the tumor suppression did not happen for the mice received K xWO3 treatment or NIR irradiation group as the tumor kept growing all the time, which suggesting that KxWO3 itself or NIR alone made no therapeutic outcome. While for mice received KxWO3 injection plus 1064 nm irradiation, the tumor size decreased remarkably and eventually vanished at 5th day post treatment. Hence, KxWO3-mediated photothermal treatment may provide novel option and contribute to the advance of NIR mediated photothermal therapy for cancer management.
6
Figure.3 (a) Cell viability after incubation with KxWO3at different concentrations; (b)-(e) Fluorescence images of HeLa cells after different treatment; (c) Tumor volume of mice after different treatment (five mice in each group); (d) Representative photographs of mice at 14th after different treatment.
4. Conclusions In this work, a facile method has been made for fabricating K xWO3 nanorod, which possessed excellent NIR-harvesting ability, phothermal conversion effect and biocompatibility. On the basis of above, successful antitumor outcome was realized in cell assay and animal experiment. Acknowledgements This work was financially supported by Postdoctoral Fund of Heilongjiang province of China (No. LBH-Z14208) and open foundation of Key Laboratory of Functional Inorganic Material Chemistry (Heilongjiang University), Ministry of Education, China. References [1]. G. Li, C. Guo, M. Yan, S. Liu, CsxWO3 nanorods: Realization of full-spectrum-responsivephotocatalyticactivities from UV, visible to near-infrared region, Appl. Catal. B 183 (2016) 142-148. [2] J.H. Seo, D. Kim, S. Kwon, M. Song, M. Choi, S.Y. Ryu, H.W. Lee, Y. C. Park, J. D. Kwon, K. Nam, Y. Jeong, J. Kang, C.S. Kim, High efficiency inorganic/organic hybrid tandem solar cells, Adv. Mater. 24 (2012) 4523-4527. 7
[3] M. M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, H.J. Snaith, Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites, Science 2 (2012) 643-647. [4] C. Guo, S. Yin, P. Zhang, M. Yan, K. Adachi, T. Chonan, T. Sato, Novel synthesis of homogenous CsxWO3 nanorods with excellent NIR shielding properties by a water controlled-release solvothermal process, J. Mater. Chem. 20 (2010) 8227-8229. [5] W. Guo, C. Guo, N. Zheng, T. Sun, S. Liu, Cs xWO3 Nanorods coated with polyelectrolyte multilayersas a multifunctional nanomaterial for bimodal imaging-guided photothermal/photodynamic cancer treatment, Adv. Mater. 29 (2017) 1604157. [6] G. Tian, X. Zhang, X. Zheng, W. Yin, L. Ruan, X. Liu,L. Zhou, L. Yan, S. Li, Z. Gu,Y. Zhao, Multifunctional RbxWO3 nanorods for simultaneous combined chemo-photothermal therapy and photoacoustic/CT imaging, Small 10 (2014), 4160-4170. [7] D. Ni, J. Zhang, J. Wang, P. Hu, Y. Jin, Z. Tang, Z. Yao, W. Bu, J. Shi, Oxygen vacancy enables markedly enhanced magnetic resonance imaging-guided photothermal therapy of a Gd3+-doped contrast agent, ACS Nano 11 (2017), 4256-4264. [8] C. Guo, H. Yu, B. Feng, W. Gao, M. Yan,Z. Zhang, Y. Li, S. Liu, Highly efficient ablation of metastatic breast cancer using ammonium-tungsten-bronze nanocube as a novel 1064 nm laser-driven photothermal agent, Biomaterials 52 (2015) 407-416. [9] C. Guo, S. Yin, H. Yu, S. Liu, Q. Dong, T. Goto, Z. Zhang, Y. Li, T. Sato, Photothermal ablation cancer therapy using homogeneous Cs xWO3 nanorods with broad near infrared absorption, Nanoscale 5 (2013) 6469-6478. [10] K. Manthiram, A. P. Alivisatos, Tunable Localized Surface Plasmon Resonances in Tungsten Oxide Nanocrystals, J. Am. Chem. Soc. 134 (2012) 3995-3998. [11] O. F. Schirmer, V. Wittwer, G. Baur, G. Brandt, Dependence of WO3 electrochromic absorption on crystallinity, J. Electrochem. Soc. 124 (1977) 749-753. [12] L. M. Maestro, P. Haro-González, B. Rosal, J. Ramiro, A. J. Caamaňo, E. Carrasco, A. Juarranz, F. SanzRodrĺguez, J. G. Solé, D. Jaque, Heating efficiency of multi-walled carbon nanotubes in the first and second biological windows, Nanoscale 5 (2013) 7882-7889. [13] D. Jaque, L. M. Maestro, B. Rosal, P. Haro-Gonzalez, A. Benayas, J. L. Plaza, E. M. Rodrĺgueza, J. G. Solé, Nanoparticles for photothermal therapies, Nanoscale 6 (2014) 9494-9530.
8
Highlights：
KxWO3 nanorods have been synthesized by a low-temperature solvothermal process.
KxWO3 nanorods exhibited excellent near infrared absorption and photothermal performance;
KxWO3 nanorods as phototherapeutic agent could eliminate the solid tumor from the mice.
9
Graphical abstract
10
S0167-577X(17)31569-0 https://doi.org/10.1016/j.matlet.2017.10.093 MLBLUE 23328
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
9 August 2017 13 October 2017 19 October 2017
Please cite this article as: B. Zheng, Z. Han, G. Wu, Y. Liu, C. Liu, F. Ma, Synthesis of Near Infrared-Activatable KxWO3 Nanorods for Photothermal therapy, Materials Letters (2017), doi: https://doi.org/10.1016/j.matlet. 2017.10.093
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis of Near Infrared-Activatable KxWO3 Nanorods for Photothermal therapy Binghui Zheng2, Zheng Han1, Guang Wu1*, Yifu Liu1, Chuntao Liu1, Fangwei Ma1 1 School of Chemistry and Materials Sciences, Heilongjiang University; Harbin 150080, China 2 China Tianchen Engineering Corporation (TCC), Harbin, 150076, China
Corresponding author: Associate professor Guang Wu E-mail: [email protected]
1
Abstract The KxWO3 nanorods with a broad optical absorbance in near infrared (NIR) region have been synthesized by a facile solvothermal reaction in this work. On the merits of this unique photoabsorption, KxWO3 nanorod exhibited an excellent photothermal conversion effect upon NIR 1064 nm laser excitation as evidenced by a rapid, distinct and recyclable photothermal effect both for KxWO3 powder and aqueous dispersion. Further, KxWO3 was finally proved to be an eligible phototherapeutic agent for antitumor treatment and great success has been made in in vitro cancer cell killing and in vivo elimination of solid tumor in living mice, manifesting a potential application prospect of KxWO3 nanorod as photothermal material. Keywords: Tungsten bronze, near-infrared absorption, photothermal therapy. 1. Introduction Developing NIR-harvesting materials is of great significances as it can serve formany related scientific areas such as photocatalytic reactions, solar cells, solar heater, photothermal therapy and so forth. [1-3] However, the NIR-harvesting materials are rare, and even if there are, they generally suffer from their own inevitable shortcomings, including narrowed absorption band, bad physicochemistry stability, lower absorption coefficient and so forth. [4] Fortunately, the emergence of tungsten bronze nanomaterials (MxWO3, where M is alkali metal ions, like Li, Na, K, Rb, Cs) seems like to be able to get out of above scientific predicament considering on their excellent and reliable NIR absorptive properties. Up to now, several kinds of M xWO3 have been applied for the cancer photothermal therapy, in which M xWO3 was employed to induce hyperthermia upon NIR irradiation at the tumor site for irreversible tumor damage. [5-9] However, in this regard, the MxWO3 with bigger alkali metal ions like CsxWO3 and RbxWO3 are not suitable for the photothermal therapy due to the bad biocompatibility of Cs and Rb elements, which may result in an unpredictable systemic toxicity. While for NaxWO3 or LixWO3, the leakage of metal ions would happen because of smaller ionic radius and resultantly weaken the NIR absorption of tungsten bronze. Hence, the ideal candidate is KxWO3 in view of 2
desired biocompatibility, physicochemistry stability and optical properties. However, applying KxWO3 nanomaterials for the photothermal cancer therapy is seldom, which may be due to the great difficulty in low-temperature synthesis and obtaining nanoscale sample directly. In this work, KxWO3 nanorods have been fabricated by a facile method and employed for cancer phototherapy for the first time. 2. Experimental 2.1Synthesis of KxWO3 nanorod Firstly, 0.297 g WCl6 and 0.042 g KOH were dissolved into the 40 ml ethanol to form a homogenous solution. Then, 10 ml acetic acid was introduced and the solution was transferred into 100 ml Teflon-lined autoclave. The solvothermal reaction performed at 200 oC for 24h. After the reaction, the blue powder was collected by centrifugation, washing and drying at 60 oC in vacuum. 2.2Characterization X-ray diffraction analysis (XRD, Shimadzu XD-D1), transmission electron microscope (TEM, ZEISS LEO 922), X-ray photoelectron spectroscopy (XPS, Perkin Elmer PHI 5600), spectrophotometer (JASCO V-670) were employed to investigate the crystal phase, morphology, chemical valence and optical properties of sample, respectively. 2.3 Photothermal therapy HeLa cells and HeLa-cells-bearing female BALB/C nude mice were used for the photothermal therapy investigation. The 1064 nm NIR laser was selected and the powder density was 1.5 W/cm2. The live-dead assay was conducted by Calcein AM and propidium iodide staining. For more details, please see the supporting information. 3. Results and discussion Firstly, we checked the morphological character of as-obtained sample. As shown in Figure 1a, the sample is consisted of many randomly distributed rod-like nanoparticles, and the average diameter of these nanorods is around 20 nm, while the length is up to 100-120 nm. In the XRD pattern of Figure 2b, all the reflective peaks 3
could be definitely indexed to the potassium tungsten bronze (JCPDS No.20-0940). Considering on that KxWO3 is a mixed valence compound, which should be also expressed as KxWx5+W1-x6+O3, we next inspected chemical composition and valence state by XPS analysis. In the full-range XPS survey, (Figure 1c) the binding energies relating to the elements of W, K and O have been found, indicating the successful insertion of K ions into the tungsten oxide lattice and formation of K xWO3 compound. Meanwhile, the atomic ratio of K/W is determined to be 0.31, which is close to the theoretical maximum of 0.33. After the deconvolution, XPS spectra of W 4f core-level could be fitted into two spin-orbit coupling doublets, resulting from two different oxidation states of W5+ and W6+ ions (Figure. 1d). Taken XRD and XPS results together, we firmly proved that the sample obtained in this work was KxWO3 compound with expectant crystal phase and chemical valence state.
Figure.1 (a) TEM image, (b) XRD pattern, (c) Full-range XPS spectra and core-level W4f XPS spectra of KxWO3.
Previously, the tungsten bronze compounds were reported to be excellent NIR absorbent when the particle dimension below certain threshold (usually several hundred nanometers) and the absorption enhanced with smaller size or preferred one-dimensional nanostructure like nanorods or nanofibers. In view of above, an excellent NIR photoabsorption is highly expected for KxWO3 nanorod of this work. 4
Hence, we next studied the photothermal and optical properties K xWO3 nanorod. As shown in the Figure 2a, powder absorbance spectra clearly presented a strong and wide light absorption in the whole range of 200-2500 nm, particularly in the NIR region where it is applicable for the photothermal therapy. The NIR absorption mechanism is thought to be due to localized surface plasma resonance and/or Small polaron absorption. [10-11] To investigate the photothermal conversion effect, we firstly inspected the temperature rise of KxWO3 powder upon 1.5 W/cm2 laser irradiation of 1064 nm. To our surprise, the temperature of irradiated area boosted up to 270 oC from the ambient temperature of 20 oC just after 1 second exposure to NIR laser as record by thermographic image in Figure 2b. Then, the KxWO3 aqueous dispersion of 1 mg/ml was suffered to the same laser irradiation, which also showed an obvious temperature elevation, manifesting the prominent photothemal effect and satisfying the basic requirement for cancer photothermal therapy (Figure 2c). Finally, a good cycling stability has also been found for this material in consideration of negligible change on heating efficiency after 5 cycles (Figure 2d). In this work, the photothermal conversion efficiency (η) of KxWO3 has been calculated to be 25.7 %, (more details in supporting information) which is comparable to other semiconductor nanoparticles, such as Cu2-xSe (22%) and Cu9S5 (25.7%), [8] but it is still lower than noble metal nanoparticles and carbon materials.[12-13]
Figure.2 (a) Powder absorbance spectra of KxWO3 ; (b) thermographicimage of 5
KxWO3powder after NIR 1064 laser irradiation for 1 second; (c) Temperature profile of KxWO3 aqueous dispersion upon laser irradiation (KxWO3:1 mg/ml, laser: 1.5 W/cm2); (d) cycling stability of KxWO3 aqueous dispersion for 5 cycles.
Inspired by above result, we then conducted the cancer photothermal therapy with KxWO3 nanorod. A power density of 2 W/cm2, which is a reasonable value and has been used in many works, was employed for NIR-mediated group. (Supporting information part.3) Firstly, we checked the biocompatibility of KxWO3 nanorod by a MTT method to determine the HeLa cell viability after incubation with K xWO3 for 24 h at different concentrations. It revealed a very limited cytotoxicity because of high cell viability, and the cells metabolic activity was higher than 85 % even under a concentration of 1 mg/ml (Figure 3a). Then, we carried out the in vitro photothermal treatment using Calcein AM and propidium iodide staining to visualize living (green fluorescence) and dead cells (red fluorescence), respectively. As can be seen in Figure 3b-e, untreated cells, cells treated with KxWO3 and cells treated with NIR irradiation showed a bright green color only, thus illustrating no detectable cell deaths. In contrast, striking red fluorescence is discernable for the NIR-mediated and KxWO3-enriched cells, indicating a marked phototherapy effect. We next investigated the in vivo photothermal treatment effect on HeLa tumor-bearing nude mice. The antitumor effect is evaluated by the relative tumor size. Similar to the in vitro results, the tumor suppression did not happen for the mice received K xWO3 treatment or NIR irradiation group as the tumor kept growing all the time, which suggesting that KxWO3 itself or NIR alone made no therapeutic outcome. While for mice received KxWO3 injection plus 1064 nm irradiation, the tumor size decreased remarkably and eventually vanished at 5th day post treatment. Hence, KxWO3-mediated photothermal treatment may provide novel option and contribute to the advance of NIR mediated photothermal therapy for cancer management.
6
Figure.3 (a) Cell viability after incubation with KxWO3at different concentrations; (b)-(e) Fluorescence images of HeLa cells after different treatment; (c) Tumor volume of mice after different treatment (five mice in each group); (d) Representative photographs of mice at 14th after different treatment.
4. Conclusions In this work, a facile method has been made for fabricating K xWO3 nanorod, which possessed excellent NIR-harvesting ability, phothermal conversion effect and biocompatibility. On the basis of above, successful antitumor outcome was realized in cell assay and animal experiment. Acknowledgements This work was financially supported by Postdoctoral Fund of Heilongjiang province of China (No. LBH-Z14208) and open foundation of Key Laboratory of Functional Inorganic Material Chemistry (Heilongjiang University), Ministry of Education, China. References [1]. G. Li, C. Guo, M. Yan, S. Liu, CsxWO3 nanorods: Realization of full-spectrum-responsivephotocatalyticactivities from UV, visible to near-infrared region, Appl. Catal. B 183 (2016) 142-148. [2] J.H. Seo, D. Kim, S. Kwon, M. Song, M. Choi, S.Y. Ryu, H.W. Lee, Y. C. Park, J. D. Kwon, K. Nam, Y. Jeong, J. Kang, C.S. Kim, High efficiency inorganic/organic hybrid tandem solar cells, Adv. Mater. 24 (2012) 4523-4527. 7
[3] M. M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, H.J. Snaith, Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites, Science 2 (2012) 643-647. [4] C. Guo, S. Yin, P. Zhang, M. Yan, K. Adachi, T. Chonan, T. Sato, Novel synthesis of homogenous CsxWO3 nanorods with excellent NIR shielding properties by a water controlled-release solvothermal process, J. Mater. Chem. 20 (2010) 8227-8229. [5] W. Guo, C. Guo, N. Zheng, T. Sun, S. Liu, Cs xWO3 Nanorods coated with polyelectrolyte multilayersas a multifunctional nanomaterial for bimodal imaging-guided photothermal/photodynamic cancer treatment, Adv. Mater. 29 (2017) 1604157. [6] G. Tian, X. Zhang, X. Zheng, W. Yin, L. Ruan, X. Liu,L. Zhou, L. Yan, S. Li, Z. Gu,Y. Zhao, Multifunctional RbxWO3 nanorods for simultaneous combined chemo-photothermal therapy and photoacoustic/CT imaging, Small 10 (2014), 4160-4170. [7] D. Ni, J. Zhang, J. Wang, P. Hu, Y. Jin, Z. Tang, Z. Yao, W. Bu, J. Shi, Oxygen vacancy enables markedly enhanced magnetic resonance imaging-guided photothermal therapy of a Gd3+-doped contrast agent, ACS Nano 11 (2017), 4256-4264. [8] C. Guo, H. Yu, B. Feng, W. Gao, M. Yan,Z. Zhang, Y. Li, S. Liu, Highly efficient ablation of metastatic breast cancer using ammonium-tungsten-bronze nanocube as a novel 1064 nm laser-driven photothermal agent, Biomaterials 52 (2015) 407-416. [9] C. Guo, S. Yin, H. Yu, S. Liu, Q. Dong, T. Goto, Z. Zhang, Y. Li, T. Sato, Photothermal ablation cancer therapy using homogeneous Cs xWO3 nanorods with broad near infrared absorption, Nanoscale 5 (2013) 6469-6478. [10] K. Manthiram, A. P. Alivisatos, Tunable Localized Surface Plasmon Resonances in Tungsten Oxide Nanocrystals, J. Am. Chem. Soc. 134 (2012) 3995-3998. [11] O. F. Schirmer, V. Wittwer, G. Baur, G. Brandt, Dependence of WO3 electrochromic absorption on crystallinity, J. Electrochem. Soc. 124 (1977) 749-753. [12] L. M. Maestro, P. Haro-González, B. Rosal, J. Ramiro, A. J. Caamaňo, E. Carrasco, A. Juarranz, F. SanzRodrĺguez, J. G. Solé, D. Jaque, Heating efficiency of multi-walled carbon nanotubes in the first and second biological windows, Nanoscale 5 (2013) 7882-7889. [13] D. Jaque, L. M. Maestro, B. Rosal, P. Haro-Gonzalez, A. Benayas, J. L. Plaza, E. M. Rodrĺgueza, J. G. Solé, Nanoparticles for photothermal therapies, Nanoscale 6 (2014) 9494-9530.
8
Highlights：
KxWO3 nanorods have been synthesized by a low-temperature solvothermal process.
KxWO3 nanorods exhibited excellent near infrared absorption and photothermal performance;
KxWO3 nanorods as phototherapeutic agent could eliminate the solid tumor from the mice.
9
Graphical abstract
10