Er3+@SiO2@Cu2S Hollow

Subscriber access provided by The University of Texas at El Paso (UTEP)

Functional Inorganic Materials and Devices

Up-converting LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S Hollow Nanoplatforms for Self-monitored Photothermal Ablation Hao Suo, Xiaoqi Zhao, Zhang Zhiyu, Yanfang Wu, and Chongfeng Guo ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18184 • Publication Date (Web): 02 Nov 2018 Downloaded from http://pubs.acs.org on November 4, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Up-converting

LuVO4:

Nd3+/Yb3+/Er3+@SiO2@Cu2S

Hollow Nanoplatforms for Self-monitored Photothermal Ablation Hao Suo, Xiaoqi Zhao, Zhiyu Zhang, Yanfang Wu and Chongfeng Guo* National Key Laboratory of Photoelectric Technology and Functional Materials (Culture Base) in Shaanxi Province, National Photoelectric Technology and Functional Materials & Application of Science and Technology International Cooperation Base, Institute of Photonics & PhotonTechnology, Northwest University, Xi’an, 710069, China; --------------------------------------------------------------------------------------------------------------------KEYWORDS: Up-conversion; Luminescent thermometry; Photothermal effects; 808 nm excitation. ABSTRACT: Self-monitored photothermal therapy (PTT) with minimal collateral damages has been emerged as a challenging strategy for antibacterial and cancer treatments, which could be fulfilled via the rational integration of luminescent thermometry and photothermal ablation within a single up-converting (UC) nanoplatform. Herein, 808 nm light-driven dual-functional nanoplatforms LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S were successfully developed using olivelike LuVO4: Nd3+/Yb3+/Er3+ hollow nanoparticles as the thermal-sensing core and ultra-small Cu2S nanoparticles as the photothermal satellite. Irradiated by 808 nm laser, thermal sensing behaviors of samples were evaluated based on the high purity Er3+ green emissions, while the surface-attached Cu2S exhibited superior photothermal effects due to the efficient absorption of incident laser and near-infrared (NIR) emissions from the luminescent core. The feasibility of bi-

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

functional samples acting as self-monitored photothermal agents (PTAs) in sub-tissues and antibacterial agents against drug-resistant bacteria were respectively assessed. Results provide deeper insights into the desirable design of 808 nm-driven multifunctional nanoplatforms with intense UC emission, sensitive thermometry and effective photothermal conversion towards selfmonitored PTT with high therapeutic accuracy. 1. INTRODUCTION Photothermal therapy (PTT) is a minimal-invasive therapeutic strategy for drug-resistant bacteria or cancer using photo-absorbing nanoparticles as microscopic heating sources. Photothermal agents (PTAs) at nanoscale (noble metals, organic compounds, carbon materials, semiconductors, etc.) play the crucial role in the process of PTT via efficiently converting incident energy into heat, which could trigger irreversible damages to cancer or bacteria cells under near-infrared (NIR) laser excitation.1-6 Among those typical PTAs, semiconductor copper chalcogenides (CuxS) with strong NIR absorption provide facile synthesis, low long-term cytotoxicity, high stability and photothermal conversion efficiency, which have been widely explored as prospective candidates for deep-tissue PTT.7-9 However, insufficient heating or undesirable overheating effect would probably occur in the absence of the real-time temperature detection at intracellular level in the process of PTT, leading to ineffective therapy of cancer cells or severe side effects for adjacent normal cells. The integration of fluorescence intensity ratio (FIR) based thermal-sensing function into PTAs is expected to be a promising solution for above technical obstacles by real-time temperature monitoring at subcutaneous levels, which is defined as self-monitored PTT.10-12 As the most promising candidates for real-time PTT thermal-monitors, NIR light-driven up-converting (UC) nanothermometers offer great superiority in biological systems due to their features of minimal


Page 2 of 26

Page 3 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


background auto-fluorescence interference, high penetration depth and spatial resolution.13-16 Especially, Nd3+/Yb3+/Er3+ tri-doped UC thermometers are prospective and superior in biological field using Nd3+ with large absorptive cross section around 808 nm as the sensitizer and Er3+ with appropriate thermally-coupled levels (TCLs) 4S3/2/2H11/2 as activator, where effective Nd3+ → Yb3+ energy transfer process (~ 70%) makes Yb3+ as the intermediate bridge. Compared with widely studied Yb3+-sensitized UC systems, the utilization of 808 nm laser as excitation source in Nd3+-sensitized thermometers would not only minimize the undesired heating effects of normal tissues induced by water molecules, but also increase the penetration depth in biological tissues.17-22 Meanwhile, intense NIR luminescence emitting from Nd3+ and Yb3+ ions under 808 nm irradiation could be further absorbed by NIR-responsive PTAs to improve the photothermal therapeutic effects.3 Therefore, the rational design and construction of multifunctional UC nanoplatforms with intense emission, sensitive thermometry and efficient heat generation under biocompatible 808 nm laser excitation is of great importance and highly demanded in biomedical science towards self-monitored PTT with high therapeutic accuracy and minimal collateral damages.17, 23-25 Lanthanide orthovanadate (LnVO4) with diverse micro/nano-architectures have been demonstrated as ideal single-phased UC hosts with perfect physical, chemical and optical properties, among which hollow nanostructure with large specific area and low density displays vast application prospects in drug delivery and cancer treatment.26-28 Meanwhile, intense green emission with high purity and high thermal sensitivity could be possibly achieved in Er3+ doped LuVO4 owing to its relatively large phonon energy according to our previous investigations.29, 30 Herein, 808 nm light-mediated dual-functional hollow core-shell-satellite nanoplatforms were constructed via electrostatically integrating ultra-small PTAs Cu2S onto the hollow UC



nanothermometers LuVO4: Nd3+/Yb3+/Er3+, while the thin silica layer was further coated to improve their biocompatibility and the absorption of Cu2S.31 Irradiated by 808 nm laser, highly sensitive thermometry based on the spectrally pure green emissions and efficient light-to-heat conversions were simultaneously realized in the Cu2S coated hollow nanoplatforms. Finally, the feasibility of samples acting as self-monitored PTAs in sub-tissues and antibacterial agents against drug-resistant bacteria were elaborately explored, respectively. 2. EXPERIMENTAL SECTION Materials and reagents. High purity (99.99%) rare earth oxides (Lu2O3, Nd2O3, Yb2O3 and Er2O3), analytical grade reagents (A. R.) ammonium vanadate (NH4VO3), nitric acid, urea, tetraethyl orthosilicate (TEOS), ammonium hydroxide (NH4OH, 25 wt%), sodium citrate (Na3C6H5O7·2H2O), sodium sulfide (Na2S·9H2O), copper chloride dehydrate (CuCl2·2H2O) and aminopropyltrimethoxysilane (APTMS) were directly used as starting materials without further purification. Additionally, agar medium, nutrient broth, phosphate buffered saline (PBS), Escherchia coli (E. coli, ATCC25922) and Staphylococcus aureus (S. aureus, ATCC6538) were also used in present experiments. Synthesis of olive-like LuVO4 hollow nanoparticles. Blank and 1.5%Nd3+/10%Yb3+/1.5%Er3+ tridoped LuVO4 nanoparticles were prepared via the first step co-precipitation and subsequent hydrothermal reaction. In the typical procedure, diluted HNO3 solution was first used to dissolve 1 mmol of Ln2O3 (Ln = Lu, Nd, Yb and Er) with heating and continuous agitating, and then 100 mL of de-ionized (DI) water and 9 g of urea were introduced (pH = 4). After heating for 2 h at 85 oC

in water bath, the resulting precipitate was separated by centrifuge and then washed with

ethanol and DI water in turn to get the spherical precursors. Subsequently, the precursors were ultrasonically re-dispersed in a mixing solution including 20 mL of DI water and 0.5 mmol of


Page 4 of 26

Page 5 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


NH4VO3, in which the pH value was set as 6 using HNO3 with continuously stirring for 15 min. Then, the resulting solutions were transferred into 50 mL Teflon-lined autoclaves and heated at 190 °C for 10 h. Finally, the faint-yellow precipitates were collected by centrifuge and then washed by ethanol and DI water for three times, and the olive-like hollow nanoparticles were obtained after drying in air at 70 oC for 12 h. Synthesis of LuVO4@SiO2 nanoparticles. The obtained nanoparticles was further coated with the smooth layer of SiO2 via a modified Stӧber process, and the samples were firstly redispersed in the 75 mL of DI water and ethanol (1:4) by ultrasonication. Subsequently, 0.6 mL of NH4OH and 0.15 mL of TEOS were added dropwise with moderately agitation for 6 h. As washing with DI water and ethanol, resulting suspension was centrifugally separated and dried at 70 oC for 12 h to get the LuVO4@SiO2 samples, and then further heated at 600 oC for 2 h (1 oC/min)

to enhance the UC emissions.

Synthesis of LuVO4@SiO2@Cu2S nanoplatforms. Ultra-small Cu2S nanoparticles with negative charge were synthesized as follows. First, 2 mL of Na2S·9H2O (0.04 M) were introduced into 100 mL of aqueous solutions containing 0.02 g of Na3Cit and 0.014 g of CuCl2·2H2O under stirring for 5 min. After heating in water at 90 oC for 15 min, the resulting dark-green solution of Cu2S nanoparticles was transferred to ice-cold water at 4 oC for further use. To functionalize samples with positive-charged amino group (-NH2), 0.1 g of LuVO4@SiO2 nanoparticles were ultrasonically dispersed in 50 mL ethanol, followed by adding dropwise 0.15 mL of APTMS with stirring for 12 h. After that, 40 mL of Cu2S solution was fully mixed with amino group modified sample with stirring for 2 h, which was collected by centrifuge and then washed by ethanol and DI water for three times. Finally, olive-like LuVO4@SiO2@Cu2S hollow nanoparticles were formed after drying at 70 oC for 12 h.



Self-monitored photothermal process of LuVO4@SiO2@Cu2S nanoparticles in sub-tissues. In the typical ex vivo experiments, we firstly injected 200 μL of PBS solutions containing LuVO4@SiO2@Cu2S nanoparticles (1 mg/mL) in a fresh chicken breast at depth of about 2 mm. Through adjusting the 808 nm laser density, the temperature change induced by photothermal effects of samples was monitored through the FIR technique based on UC signals in sub-tissues and infrared thermal camera. Antibacterial activity of LuVO4@SiO2@Cu2S nanoparticles in vitro. All materials and glassware used in this test were sterilized by autoclaving at 120 °C for 20 min. E. coli and S. aureus were transferred to sterile nutrient broth and diluted by the sterile water, and then 100 μL of PBS solutions containing LuVO4@SiO2@Cu2S nanoparticles (1 mg/mL) or blank PBS buffer were fully mixed with diluted bacterial solutions. 808 nm light was tightly focused on above two solutions for 15 min (denoted as +UCNPs+NIR group and +NIR), whereas the same two groups without 808 nm laser exposure were named as +UCNPs and control group. It is noteworthy that the power density was set as 1.2 W/cm2 in present experiments in view of the biological safety and photothermal effects. Finally, 20 μL of bacterial solutions were fully dispersed in the agar slant culture mediums and maintained at 37 oC for 24 h in air, and then the bacteria colony numbers of each group were calculated. It is noteworthy that this experiment was repeated for three times to ensure the reliability of results. Characterization. Powder X-ray diffractometer (Rigaku-Dmax) was employed to measure the X-ray diffraction (XRD) pattern, and Bruker EQUINOX55 spectrometer is utilized to record the Fourier transform infrared (FT-IR) spectrum. X-ray photoelectron spectrum (XPS) was measured by the Kratos X-ray photoelectron spectrometer (Britain) with Al-Kα excitation. The morphologies of all samples were measured using a Hitachi SU-8010 field emission scanning


Page 6 of 26

Page 7 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electron microscope (FE-TEM) and a FEI TF-20 transmission electron microscope (TEM) with the energy dispersive X-ray spectrometer, and carbon-coated nickel grids were used for TEM observation of samples dispersed in ethanol. A Cary 5000 UV-Vis-NIR spectrophotometer was used to measure the absorption spectrum, and UC emission spectra were investigated at different temperature on a FLS920 fluorescence spectrophotometer equipped with a semiconductor 808 nm laser and an Oxford OptistatDN2 nitrogen cryogenics temperature controlling system. The settling time of each temperature point was set as 20 min in the measurement of temperaturedependent UC spectra. The digital photos were taken under 808 nm excitation (P = 0.1 W/cm2) at room temperature by dispersing 0.1 mg of samples in 2 mL of ethanol after ultrasound for 0.5 h. The laser-induced temperature evolutions of samples and surface of chicken breast were realtime monitored by infrared thermal camera (InfReC R500). 3. RESULTS AND DISCUSSION 3.1.

Structure

and

morphology.

The

synthetic

procedures

of

the

olive-like

LuVO4@SiO2@Cu2S nanoparticles with hollow structure could be summarized as the follows: the co-precipitated synthesis of spherical precursor, hydrothermal preparation of hollow olivary LuVO4 nanoparticles, coating silica layers on LuVO4 particles and the electrostatic conjunction of ultra-small Cu2S nanoparticles on the surface of amino group-modified LuVO4@SiO2, as shown in Figure 1a. XRD patterns of as-prepared Nd3+/Yb3+/Er3+ tri-doped samples at each stage together with the standard card of LuVO4 (JCPDS No. 72-0270) were measured in Figure 1b to identify their crystal structures and phase purities. No obvious peaks were observed in the precursor except for two broad diffraction bands, which may be identified as amorphous Lu(OH)CO3.32 Tetragonal-phased LuVO4 crystal was formed with high crystallinity under the hydrothermal treatment, while no other diffraction peaks from SiO2 and Cu2S were detected after



the subsequent coating processes due to the thin silica layers and small amount of Cu2S. FT-IR spectroscopy was measured to further verify the compositions of prodcuts at each stage (Figure S1), in which the absorptions peaked at 3432 and 1630 cm-1 were assigned to the O-H stretching and bending vibrations from water. The characteristic adsorption peaks of O-C-O (1531 and 1398 cm-1) and CO32- (843, 758 and 692 cm-2) in the precursor further comfirmed its component of carbonate hydroxide salt.17 After the hydrothermal reaction and modification, strong absorptions from V-O (829 cm-1), Lu-O (459 cm-1) and Si-O-Si (1093 cm-1) vibrations emerged with the vanished carbonate group, sugggesting the successful formation of LuVO4 crystals and SiO2 layers. Moreover, the existence of copper chalcogenides and valence state of Cu atom were confirmed using XPS survey spectra, from which the bonding energy informations of Yb, Lu, V, Si, O and C elements were detcted in the full spectrum of LuVO4: Nd3+/Yb3+/Er3+@SiO2 (Figure 1c). After coating with copper chalcogenides, two characteristic peaks from Cu 2p3/2 and 2p1/2 appeared at 932.7 and 952.5 eV without any satellite peaks (Figure 1d), indicating the monovalent feature of Cu atom. The characteristic feature (L3VV at 917.5 eV) detected in Auger Cu LMM spectrum further confirmed the univalence of Cu atom (Figure 1e).33


Page 8 of 26

Page 9 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) The synthetic routes of olive-like LuVO4@SiO2@Cu2S hollow nanoparticles and (b) XRD patterns of Nd3+/Yb3+/Er3+ tri-doped samples at each stage; (c) typical XPS survey spectra of LuVO4@SiO2 and LuVO4@SiO2@Cu2S; (d) Cu 2p XPS spectrum and (e) Auger Cu LMM spectrum of Cu2S-coated nanoparticles. To explore the microstructures of products at every step, SEM and TEM images of Nd3+/Yb3+/Er3+ tri-doped samples were respectively displayed in Figure 2 with different magnification. The precursor particles presented monodispersed spherical nanostructure with homogeneous size of about 170 nm (Figure S2), which were acted as templates for the following reactions. After the hydrothermal process, the spherical precursor transferred to highly uniform and dispersed olive-like LuVO4 nanoparticle with an obvious hole on the surface (Figure 2a). The TEM image of a single nanoparticle evidently revealed its hollow structure with the average particle size of about 200 and 350 nm in width and length, which was constructed by numerous ultra-small ellipsoids (Figure 2d). Above evolution process from spherical templates to olive-like nanoparticles with hollow features could be elucidated based on the Kirkendall effects.26 Under weak acidic conditions, free Lu3+ ions on the surfaces of slowly-dissolved Lu(OH)CO3 nanospheres firstly reacts with VO43- to form LuVO4 shells, which prevents the direct chemical reaction between VO43- and internal Lu3+. With the proceeding of hydrothermal reaction, core Lu3+ ions diffuse to outside through the LuVO4 shells with a faster diffusion rate than that of VO43- ions, resulting in the disappearance of carbonate hydroxide core and the formation of interior holes.27 Through a Stöber procedure and subsequently heating process at 600 oC for 2 h, a smooth silica layer was coated on the surface of LuVO4 nanoparticles with the average thickness of about 5 nm, while the high dispersibility of original products were well maintained (Figure 2b and 2e). Finally, numbers of ultra-small Cu2S nanoparticles with the mean size of



Page 10 of 26

about 8 nm were detected and well-absorbed on the surface of -NH2 group modified LuVO4@SiO2

products

through

electrostatic

interaction,

resulting

in

a

typical

core@shell@satellites configuration (Figure 2c and 2f). Well-resolved lattice fringes with interplanar spacing of 3.53 and 2.02 Å in the inner core and the surface-attached satellites were clearly observed in the high-resolution TEM (HR-TEM) image (Figure 2g), corresponding to (200) and (110) crystal plane of tetragonal LuVO4 (JCPDS No. 72-0270) and hexagonal Cu2S (JCPDS No.26-1116). Figure 2h displayed the high-angle annular dark-field scanning TEM (HAADF-STEM) image of a single nanoparticle, in which the clear bright-dark contrasts between the margin and internal void further demonstrated the hollow structure of LuVO4 nanoparticles. The elemental mapping images were employed to disclose the elemental composition and distributions of samples, in which Lu, Yb, Nd, Er, V, O, Si, Cu, S were all detected and uniformly distributed in a single olive-like nanoparticle, further suggesting the successful construction of Nd3+/Yb3+/Er3+ tri-doped LuVO4@SiO2@Cu2S hollow nanoplatform.


Page 11 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. SEM and TEM images of Nd3+/Yb3+/Er3+ tri-doped (a, d) LuVO4, (b, e) annealed LuVO4@SiO2 and (c, f) LuVO4@SiO2@Cu2S; (g) HR-TEM and (h) HADDF-STEM image along with the element mapping profiles of LuVO4@SiO2@Cu2S nanoparticles. 3.2. UC emission and photothermal effects. In order to figure out the effects of coated SiO2 layers and Cu2S nanoparticles on the fluorescent properties, the emission spectra in visible and NIR region of Nd3+/Yb3+/Er3+ tri-doped LuVO4, LuVO4@SiO2 and LuVO4@SiO2@Cu2S nanoparticles were measured and displayed in Figure 3a under 808 nm excitation (P = 0.1 W/cm2) using a comparable method, respectively. Pure green emission bands peaked at 524 and 553 nm from 2H11/2/4S3/2 → 4I15/2 transitions of Er3+ were detected in the UC spectra of three samples, while the NIR area ranging from 850 to 1150 nm was composed of three emissions at 878, 1063 and 982 nm originated from the 4F3/2 → 4I9/2, 4I11/2 (Nd3+) and 2F5/2 → 2F7/2 transitions (Yb3+). After coating a thin layer of SiO2, it is found that the emission intensity in both visible and NIR region were partly weakened due to the light-scattering effects of both incident and emission lights and surface quenching groups on the silica layer. With further conjugating Cu2S ultra-small nanoparticles on the LuVO4@SiO2, the emission intensity of samples continuously declined, especially in NIR region (Figure S3), owing to the high absorbency of dark-green Cu2S.34 To better confirm the exact absorption range of Cu2S nanoparticles, the absorption spectra of PBS solution containing Cu2S, tri-doped LuVO4@SiO2 and LuVO4@SiO2@Cu2S were performed in Figure 3b, and blank PBS buffer without distinct absorption was set as control. Compared with tri-doped LuVO4@SiO2, the absorption within the biological window area was greatly increased in Cu2S-modified samples due to the broad absorption band of Cu2S nanoparticles ranging from 600 to 1200 nm, which overlapped well with the NIR emissions from tri-doped LuVO4 samples under 808 nm excitation. Therefore, efficient absorption of Cu2S at



Page 12 of 26

808 nm laser and NIR emissions emitted from the UC nanoparticles are responsible for the quenched luminescence in tri-doped LuVO4@SiO2@Cu2S hollow nanoplatforms. Even so, ultrabright green emissions with high purity were still clearly observed in LuVO4@SiO2@Cu2S dispersed in ethanol solution under 808 nm excitation (P = 0.1 W/cm2) for naked eyes, as visualized in the set of Figure 3a. To explore the potentiality of the present nanoplatforms as NIR-responsive PTAs, the photothermal

effects

of

Nd3+/Yb3+/Er3+

tri-doped

LuVO4,

LuVO4@SiO2

and

LuVO4@SiO2@Cu2S along with blank LuVO4@SiO2@Cu2S powder samples were real-time evaluated by the infrared thermal camera in Figure 3c under 808 nm excitation (P = 1 W/cm2). As the exposure time proceeded to 195 s, the temperature rapidly increased from initial temperature and then reached the maximum points for Cu2S-modified samples, whereas the temperature increments (∆T) were nearly negligible about 4.6 and 6.8 K for Nd3+/Yb3+/Er3+ tridoped LuVO4 and LuVO4@SiO2 samples. The increased non-radiative (NR) rates induced by much quenching groups on hydrophilic SiO2 layers may be responsible for the small improvement of ∆T after coating a thin silica layer on tri-doped LuVO4. The modification of Cu2S ultra-small nanoparticles on the surface of tri-doped LuVO4@SiO2 triggered remarkable enhancements of ∆T (~ 36.4 K), resulting from the high absorbency and photothermal efficiency of the attached Cu2S with the excitation of 808 nm laser. Notably, the introduction of dopant ions into LuVO4@SiO2@Cu2S nanoparticles generated more heat than that of undoped sample (~ 27.2 K), further confirming the reabsorption process of Cu2S at NIR emissions arising from the core LuVO4: Nd3+/Yb3+/Er3+.3 As schematically proposed in Figure 3d, the surface-attached Cu2S nanoparticles could efficiently produce massive heat via two absorption pathways, namely the incident 808 nm light and intense NIR luminescence emitted from the UC nanoparticles, which


Page 13 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


endows olive-like LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S hollow nanoplatforms with tremendous prospects as NIR-driven PTAs.

Figure 3. (a) 808 nm excited emission spectra in visible and NIR regions of Nd3+/Yb3+/Er3+ tridoped (1) LuVO4, (2) LuVO4@SiO2 and (3) LuVO4@SiO2@Cu2S nanoparticles along with the luminescent image of Cu2S-modified sample; (b) Vis-NIR absorption spectra of Cu2S, tri-doped LuVO4@SiO2 and LuVO4@SiO2@Cu2S dispersed in PBS solutions along with blank PBS solution; (c) photothermal effects of powder samples versus excitation time; (d) schematic illustration of two absorption pathways of Cu2S-modified samples for photothermal conversions. 3.3. Optical thermal-sensing behaviors. The effects of silica layers and cuprous sulfides on thermal sensitivity were validated by the temperature-dependent UC spectra within green region in Nd3+/Yb3+/Er3+ tri-doped LuVO4, LuVO4@SiO2 and LuVO4@SiO2@Cu2S under the excitation of 808 nm light, as presented in Figure 4a and S4 (normalized at 524 nm). It is noteworthy that the power density was set as 0.1 W/cm2 to avoid the photothermal effects of sample. The enhancement of temperature from 280 to 490 K triggered the monotonous decline of



4S

3/2

Page 14 of 26

→ 4I15/2 transition in three products, and the value of intensity ratio of quasi-thermal

balanced TCLs 2H11/2 and 4S3/2 can be mathematically written as:14

FIR 

I 524 nm h2 A2 N 2 2 A2 g 2 E E exp( )  B exp( )   I 553nm h1 A1 N1 1 A1 g1 KT KT (1)

where I, ħ, N, ω, A and g are the integrated intensity, Planck’s constant, electron occupation number, angular frequency, spontaneous emission rate and degeneracy, respectively. The Boltzmann’s constant and energy gap between TCLs are denoted by K and ∆E, and ω2A2g2 /ω1A1g1 defines the coefficient B. Mono-logarithm of FIR value was dynamically plotted as a function of inverse temperature in Figure S5, and the energy separation ∆E was computed from the optimal fitting straight line to be 749.46 ± 7.68, 720.86 ± 7.21 and 750.26 ± 4.56 cm-1 for tridoped LuVO4, LuVO4@SiO2 and LuVO4@SiO2@Cu2S nanoparticles, respectively. The calculated B values and regression parameters of the fitting curves were obtained to be about 22.62 ± 0.58 (R12 = 0.999), 23.72 ± 0.34 (R22 = 0.999) and 24.77 ± 0.38 (R32 = 0.999) from the fitting exponential curves of FIR values versus temperature. As a vital parameter for practical applications, thermal sensitivity quantitatively evaluates the thermal-sensing performances of optical sensors, namely absolute and relative sensitivity (Sa and Sr). The change and relative changing rate of FIR value along with temperature are respectively defined as Sa and Sr using the following expressions:17 Sa 

dFIR E =FIR dT KT 2

(2)

Sr 

dFIR E = FIR  dT KT 2

(3)


Page 15 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


As plotted in Figure 4b, Sr values of three samples achieved the maximum around 1.4% K-1 at 280 K owing to their close energy separation between TCLs, while the optimal values of Sa were slightly improved from 0.0111 to 0.0122 K-1 after coating SiO2 layer and Cu2S nanoparticles on the original tri-doped LuVO4. Since Cu2S nanoparticles were conjugated on the surface of UC samples by electrostatic absorption, the difference of Cu2S absorption at two green emissions may directly influence the FIR value and thermal sensitivity, in which the contents of Cu2S plays a crucial role. However, ultra-small Cu2S nanoparticles showed minimal absorptions in range of 500-600 nm (Figure 3b), while the band positions are too close between two emissions at 524 and 553 nm. Thus, thermal sensitivity could hardly be affected when the content of attached Cu2S is small or moderate, which is accordance with our present results. When the UC nanoparticle is modified with high concentration of Cu2S, the FIR value would greatly increased at room temperature even under low excitation density due to serious laser-induced heating effects of Cu2S, where the thermal calibration curve and sensitivity could not be accurately measured.35 And the little influence of SiO2 layer on the thermal sensitivity may be attributed to the extremely thin thickness of SiO2 layer (~ 5 nm). The obtained values of thermal sensitivity are superior and comparable with the reported sensitivity values of other Er3+-based optical thermometers,14, 36 which provided great possibility of accurate thermometry with high signal-tonoise ratio using LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S hollow nanoplatforms as 808 nm-driven optical thermometers. 3.4. Self-monitored PTT in sub-tissues. Real-time thermal reading at sub-tissue levels is urgently required for PTT of cancer cells located in deep-tissues to minimally damage the adjacent normal cells.11 Therefore, the feasibility and applicability of olive-like LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S hollow nanoparticles acting as self-monitored photothermal agents



in sub-tissues were further assessed by ex vivo experiment. As shown in Figure 4c, a chicken tissue was subcutaneously injected with 200 μL of PBS solutions containing as-prepared samples (1 mg/mL) at around 2 mm, and the 808 nm laser beam irradiation with different power density at the injected position for 5 min. After that, the thermal evolutions were simultaneously realtime monitored via two approaches, namely the FIR technique and infrared thermometry. In our design, as-prepared nanoplatforms play two roles under 808 nm excitation during this process: one is producing massive heats used for PTT by efficient photothermal conversions of Cu2S, another is real-time monitoring the sub-tissue temperatures in the injected positions by LuVO4: Nd3+/Yb3+/Er3+@SiO2. Meanwhile, the conventional infrared thermometer was also employed as a contrast to record the surface temperature. As plotted in Figure 4d, the steady-state temperatures on the surface and injected point of chicken tissues linearly increased from 294 to 308 K and from 295 to 338 K as adjusting the excitation density from 0.18 to 1.25 W/cm2, respectively. Meanwhile, 808 nm laser irradiation hardly induced heating effects in the chicken tissues without any injections (control group) within the present experimental range. Effective heat diffusion through intra-tissue and tissue-air triggered such a remarkable difference of temperature between sub-tissue and surface, suggesting that collateral damages of adjacent normal tissues could easily occur when monitoring the surface temperature instead of sub-tissue temperature in the process of PTT.23 Thus, the integration of FIR thermal monitor into photothermal agents could realize fast-response and accurate self-temperature determination in subcutaneous tissues under 808 nm excitation, which open a feasible strategy for real-time controlled PTT using LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S hollow nanoplatforms as selfmonitored PTAs.


Page 16 of 26

Page 17 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure

4.

Temperature-dependent

(a)

UC

spectral

mapping

for

LuVO4:

Nd3+/Yb3+/Er3+@SiO2@Cu2S and (b) absolute/relative sensitivity of tri-doped LuVO4, LuVO4@SiO2 and LuVO4@SiO2@Cu2S under the excitation of 808 nm laser; (c) Scheme of experimental setups and (d) the plot of sub-tissue and surface temperature in chicken breast injected with Cu2S-modified samples versus power density of 808 nm laser, and chicken breast without any injection was set as a control. 3.5. Photothermal ablation efficiency against bacteria. The versatility and applicability of olive-like LuVO4: Nd3+/Yb3+/Er3+@SiO2@Cu2S hollow nanoplatforms acting as NIR-driven antibacterial agents was further assessed based on surface plating method using Gram-negative E. coli and Gram-positive S. aureus as bacterium models.37 As visually represented in Figure 5a, bacteria were incubated with PBS buffer or samples dispersed in PBS solution, while another two groups under the same incubation were further irradiated with focused 808 nm light for 15



Page 18 of 26

min. Figure 5b plotted the calculated survival rates of E. coli and S. aureus under abovementioned incubated conditions, in which no significant differences in numbers of bacterial strains were observed between control and +NIR or +UCNPs groups. Such high bacterial viabilities over 90% (p-value > 0.05) suggested that single NIR laser excitation or as-obtained nanoparticles were almost harmless to bacterial growth of E. coli and S. aureus in our experiments. In sharp contrasts, the survival rates of bacterial colonies in +UCNPs+NIR group were rapidly declined to 3.4% and 3.8% (p-value < 0.001) for E. coli and S. aureus after 808 nm laser irradiation. As displayed in Figure S6, the cell membranes of E. coli and S. aureus were severely distorted and disrupted by the photothermal effects of olive-like hollow nanoparticles upon exposure to 808 nm irradiation, leading to the outflow of intracellular low-molecular-mass species and the final death of bacteria.38 Consequently, the obtained superior antibacterial activity

against

drug-resistant

bacteria

endows

NIR-responsive

LuVO4:

Nd3+/Yb3+/Er3+@SiO2@Cu2S hollow nanoplatforms with vast application prospects in combating bacterial infections.


Page 19 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) Digital photographs and (b) bacterial viability of E. coli and S. aureus colonies under different incubated conditions. 4. CONCLUSIONS In summary, dual-functional up-converting nanoplatforms have been constructed via electrostatically conjugating photothermal nanoagents Cu2S on the surface of olive-like hollow nanothermometers LuVO4: Nd3+/Yb3+/Er3+@SiO2. The Cu2S-modified samples not only greatly exhibited excellent photothermal effects via simultaneously absorbing the incident light and intense NIR emissions from luminescent cores, but also provided high thermal sensitivity (Sa ~ 0.0122 K-1, Sr ~ 1.4% K-1) based on intense green UC emissions with high purity under 808 nm excitation. Subcutaneous temperature increment from 295 to 338 K, resulting from the photothermal conversion of samples injected in sub-tissues, was real-time detected via FIR technique as adjusting excitation density from 0.18 to 1.25 W/cm2. In vitro antibacterial experiments demonstrated the remarkable photothermal ablation efficiency of samples against bacteria E. coli and S. aureus (~ 95%). Above results open an effective avenue towards minimally invasive PTT with intracellular temperature feedback via designing NIR-driven multifunctional up-converting nanoplatforms. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org.



Page 20 of 26

FT-IR spectra of samples; SEM of precursors; integrated visible and NIR emission intensity of samples; Temperature-dependent UC spectra and FIR of samples; SEM of bacteria incubated with different conditions. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ACKNOWLEDGMENTS This work was supported by National Natural Science Foundation of China (No. 51672215, 11274251), Research Fund for the Doctoral Program of Higher Education of China (RFDP) (No.20136101110017), Foundation of Shaanxi Province Educational Department (15JS101), and Northwest University Doctorate Dissertation of Excellence Funds (YYB17004). REFERENCES

(1) Chen, G. Y.; Qiu, H. L.; Prasad, P. N.; Chen, X. Y. Upconversion Nanoparticles: Design, Nanochemistry, and Applications in Theranostics. Chem. Rev. 2014, 114, 5161-5214. (2) Shanmugam, V.; Selvakumar, S.; Yeh, C. S. Near-infrared Light-responsive Nanomaterials in Cancer Therapeutics. Chem. Soc. Rev. 2014, 43, 6254-6287. (3) Zhang, Z. Y.; Suo, H.; Zhao, X. Q.; Sun, D.; Fan, L.; Guo, C. F. NIR-to-NIR Deep Penetrating

Nanoplatforms

Y2O3:

Nd3+/Yb3+@SiO2@Cu2S

towards

Photothermal Ablation. ACS Appl. Mater. Interfaces 2018, 10, 14570-144576.


Highly

Efficient

Page 21 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4) Wang, D. M.; Liu, B.; Quan, Z. W.; Li, C. X.; Hou, Z. Y.; Xing, B. G.; Lin, J. New Advances on the Marrying of UCNPs and Photothermal Agents for Imaging-Guided Diagnosis and the Therapy of Tumors. J. Mater. Chem. B 2017, 5, 2209-2230. (5) Chen, G. Y.; Roy, I.; Yang, C. H.; Prasad, P. N. Nanochemistry and Nanomedicine for Nanoparticle-based Diagnostics and Therapy. Chem. Rev. 2016, 116, 2826-2885. (6) Jaque, D.; Martínez Maestro, L.; del Rosal, B.; Haro-Gonzalez, P.; Benayas, A.; Plaza, J. L.; Rodríguez, M. E.; García-Solé, J. Nanoparticles or Photothermal Therapies. Nanoscale 2014, 6, 9494-9530. (7) Tian, Q. W.; Hu, J. Q.; Zhu, Y. H.; Zou, R. J.; Chen, Z. G.; Yang, S. P.; Li, R. W.; Su, Q. Q.; Han, Y.; Liu, X. G. Sub-10 nm Fe3O4@Cu2-xS Core-Shell Nanoparticles for Dual-Modal Imaging and Photothermal Therapy. J. Am. Chem. Soc. 2013, 135, 8571-8577. (8) Deng, X. R.; Li, K.; Cai, X. C.; Liu, B.; Wei, Y.; Deng, K. R.; Xie, Z. X.; Wu, Z. J.; Ma, P. M.; Hou, Z. Y.; Cheng, Z. Y.; Lin, J. A Hollow-Structured CuS@Cu2S@Au Nanohybrid: Synergistically Enhanced Photothermal Efficiency and Photoswitchable Targeting Effect for Cancer Theranostics. Adv. Mater. 2017, 29, 1701266. (9) Lv, R. C.; Yang, P. P.; Hu, B.; Xu, J. T.; Shang, W. T.; Tian, J. In Situ Growth Strategy to Integrate Up-Conversion Nanoparticles with Ultrasmall CuS for Photothermal Theranostics. ACS Nano 2017, 11, 1064-1072. (10) Xu, X.; Wang, Z.; Lei, P. P.; Yu, Y. N.; Yao, S.; Song, S. Y.; Liu, X. L.; Su, Y.; Dong, L. L.; Feng, J.; Zhang, H. J. -NaYb(Mn)F4:Er3+/Tm3+@NaYF4 UCNPs as “Band-Shape” Luminescent Nanothermometers over a Wide Temperature Range. ACS Appl. Mater. Interfaces 2015, 7, 20813-20819.



(11) Zhu, X. J.; Feng, W.; Chang, J.; Tan, Y. W.; Li, J. C.; Chen, M.; Sun, Y.; Li, F. Y. Temperature-feedback Upconversion Nanocomposite for Accurate Photothermal Therapy at Facile Temperature. Nat. commun. 2016, 7, 10437-10446. (12) Ximendes, E. C.; Santos, W. Q.; Rocha, U.; Kagola, U. K.; Sanz-Rodríguez, F.; Fernández, N.; Gouveia-Neto, A. S.; Bravo, D.; Domingo, A. M.; Rosal, B.; Brites, C. D. S.; Carlos, L. D.; Jaque, D.; Jacinto, C. Unveiling in Vivo Subcutaneous Thermal Dynamics by Infrared Luminescent Nanothermometers. Nano lett. 2016, 16, 1695-1703. (13) Rosal, B.; Ximendes, E.; Rocha, U.; Jaque, D. In Vivo Luminescence Nanothermometry: From Materials to Applications. Adv. Opt. Mater. 2017, 5, 1600508. (14) Brites, C. D. S.; Lima, P. P.; Silva, N. J. O.; Millán, A.; Amaral, V. S.; Palacio, F.; Carlos, L. D. Thermometry at the Nanoscale. Nanoscale 2012, 4, 4799-4829. (15) Rodríguez-Sevilla, P.; Zhang, Y. H.; Haro-González, P.; Sanz-Rodríguez, F.; Jaque, F.; Solé, J. G.; Liu, X. G.; Jaque, D. Thermal Scanning at the Cellular Level by an Optically Trapped Upconverting Fluorescent Particle. Adv. Mater. 2016, 28, 2421-2426. (16) Quintanilla, M.; Liz-Marzán, L. M. Guiding Rules for Selecting a Nanothermometer. Nano toady 2018, 19, 126-145. (17) Suo, H.; Zhao, X. Q.; Zhang, Z. Y.; Guo, C. F. 808 nm Light-triggered Thermometer-Heater Up-converting Platform Based on Nd3+-sensitized Yolk-shell GdOF@SiO2. ACS Appl. Mater. Interfaces 2017, 9, 43438-43448. (18) Wang, Z.; Zhang, P.; Yuan, Q. H.; Xu, X.; Lei, P. P.; Liu, X. L.; Su, Y.; Dong, L. L.; Feng, J.; Zhang, H. J. Nd3+-sensitized NaLuF4 Luminescent Nanoparticles for Multimodal Imaging and Temperature Sensing Under 808 nm Excitation. Nanoscale 2015, 7, 17861-17870.


Page 22 of 26

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19) Liu, B.; Li, C. X.; Yang, P. P.; Hou, Z. Y.; Lin, J. 808-nm-light-excited Lanthanide-doped Nanoparticles: Rational Design, Luminescence Control and Theranostic Applications. Adv. Mater. 2017, 29, 1605434-1605458. (20)

Huang,

X.

Y.

Giant

Enhancement

of

Upconversion

Emission

in

(NaYF4:Nd3+/Yb3+/Ho3+)/(NaYF4:Nd3+/Yb3+) Core/shell Nanoparticles Excited at 808 nm. Opt. Lett. 2015, 40, 3599-3602. (21) Wang, Y. F.; Liu, G. Y.; Sun, L. D.; Xiao, J. W.; Zhou, J. C.; Yan, C. H. Nd3+-Sensitized Upconversion Nanophosphors: Efficient In Vivo Bioimaging Probes with Minimized Heating Effect. ACS Nano 2013, 7, 7200-7206. (22) Zhou, B.; Shi, B. Y.; Jin, D. Y.; Liu, X. G. Controlling Upconversion Nanocrystals for Emerging Applications. Nat. Nanotechnol. 2015, 10, 924-936. (23) Carrasco, E.; Rosal, B.; Sanz-Rodríguez, F.; Fuente, Á. J.; Gonzalez, P. H.; Rocha, U.; Kumar, K. U.; Jacinto, C.; Solé, J. G.; Jaque, D. Intratumoral Thermal Reading During PhotoThermal Therapy by Multifunctional Fluorescent Nanoparticles. Adv. Funct. Mater. 2015, 25, 615-626. (24) Chen, G. Y.; Ågren, H.; Ohulchanskyy, T. Y.; Prasad, P. N. Light Upconverting Core-shell Nanostructures: Nanophotonic Control for Emerging Applications. Chem. Soc. Rev. 2015, 44, 1680-1713. (25) Marciniak, L.; Pilch, A.; Arabasz, S.; Jin, D. Y.; Bednarkiewicz, A. Heterogeneously Nd3+ Doped Single Nanoparticles for NIR-induced Heat Conversion, Luminescence, and Thermometry. Nanoscale 2017, 9, 8288-8297.



(26) Yang, X. Y.; Xu, L.; Zhai, Z.; Cheng, F. F.; Yan, Z. Z.; Feng, X. M.; Zhu, J. J.; Hou, W. H. Submicrometer-sized Hierarchical Hollow Spheres of Heavy Lanthanide Orthovanadates: Sacrificial Template Synthesis, Formation Mechanism, and Luminescent Properties. Langmuir 2013, 29, 15992-16001. (27) Kang, X. J.; Yang, D. M.; Dai, Y. L.; Shang, M. M.; Cheng, Z. Y.; Zhang, X.; Lian, H. Z.; Ma, P. A.; Lin, J. Poly(acrylic acid) Modified Lanthanide-doped GdVO4 Hollow Spheres for Upconversion Cell Imaging, MRI and PH-dependent Drug Release. Nanoscale 2013, 5, 253-261. (28) Zhang, J.; Wang, Y. H.; Xu, Z. G.; Zhang, H. X.; Dong, P. Y.; Guo, L. N.; Li, F. H.; Xin, S. Y.; Zeng, W. Preparation and Drug-delivery Properties of Hollow YVO4: Ln3+ and Mesoporous YVO4:Ln3+@nSiO2@mSiO2 (Ln = Eu, Yb, Er, and Ho). J. Mater. Chem. B 2013, 1, 330-338. (29) Suo, H.; Guo, C. F.; Zheng, J. M.; Zhou, B.; Ma, C. G.; Zhao, X. Q.; Li, T.; Guo, P.; Goldys, E. M. Sensitivity Modulation of Up-converting Thermometry Through Engineering Phonon-energy of Matrix. ACS Appl. Mater. Interfaces 2016, 8, 30312-30319. (30) Wu, Y. F.; Suo, H.; He, D.; Guo, C. F. Highly Sensitive Up-conversion Optical Thermometry Based on Yb3+-Er3+ Codoped NaLa(MoO4)2 Green Phosphors. Mater. Res. Bull. 2018, 106, 14-18. (31) Yang, P. P.; Gai, S. L.; Lin. J. Functionalized Mesoporous Silica Materials for Controlled Drug Delivery. Chem. Soc. Rev. 2012, 41, 3679-3698. (32) Suo, H.; Zhao, X. Q.; Zhang, Z. Y.; Shi, R.; Wu, Y. F.; Xiang, J. M.; Guo, C. F. Local Symmetric Distortion Boosted Photon Up-conversion and Thermometric Sensitivity in Lanthanum Oxide Nanospheres. Nanoscale 2018, 10, 9245-9251.


Page 24 of 26

Page 25 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Zhang, J.; Yu, J. G.; Zhang, Y. M.; Li, Q.; Gong, J. R. Visible Light Photocatalytic H2Production Activity of CuS/ZnS Porous Nanosheets Based on Photoinduced Interfacial Charge Transfer. Nano Lett. 2011, 11, 4774-4779. (34) Wang, Y.; Yang, G. X.; Wang, Y. L.; Zhao, Y. P.; Jiang, H. Z.; Han, Y. Y.; Yang, P. P. Multiple Imaging and Excellent Anticancer Efficiency of An Upconverting Nanocarrier Mediated by Single Near Infrared Light. Nanoscale 2017, 9, 4759-4769. (35) Marciniak, L.; Waszniewska, K.; Bednarkiewicz, A.; Hreniak, D.; Strek, W. Sensitivity of A Nanocrystalline Luminescent Thermometer in High and Low Excitation Density Regimes. J. Phys. Chem. C 2016, 120, 8877-8882. (36) Wang, X. F.; Liu, Q.; Bu, Y. Y.; Liu, C. S.; Liu, T.; Yan, X. H. Optical Temperature Sensing of Rare-Earth Ion Doped Phosphors. RSC Adv. 2015, 5, 86219-86236. (37) Yin, W. Y.; Yu, J.; Lv, F. T.; Yan, L.; Zheng, L. R.; Gu, Z. J.; Zhao, Y. L. Functionalized Nano-MoS2 with Peroxidase Catalytic and Near-Infrared Photothermal Activities for Safe and Synergetic Wound Antibacterial Applications. ACS Nano 2016, 10, 11000-11011. (38) Jia, X. H.; Ahmad, I.; Yang, R.; Wang, C. Versatile Graphene-based Photothermal Nanocomposites for Effectively Capturing and Killing Bacteria, and for Destroying Bacterial Biofilms. J. Mater. Chem. B 2017, 5, 2459-2467.



TABLE OF CONTENTS


Page 26 of 26

Er3+@SiO2@Cu2S Hollow

Recommend Documents