TiO2 Interfaces for

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Photoelectron Transfer at ZnTPyP Self-assembly/TiO2 Interfaces for Enhanced Two-photon Photodynamic Therapy Yanyan Liu, Xianfu Meng, Han Wang, Zhongmin Tang, Changjing Zuo, Mingyuan He, and Wenbo Bu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b14451 • Publication Date (Web): 22 Dec 2017 Downloaded from http://pubs.acs.org on December 26, 2017

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ACS Applied Materials & Interfaces

Photoelectron

Transfer

at

ZnTPyP

Self-

assembly/TiO2 Interfaces for Enhanced Two-photon Photodynamic Therapy Yanyan Liu, †,* Xianfu Meng,† Han Wang,§ Zhongmin Tang, § Changjing Zuo, ‡ Mingyuan He,† Wenbo Bu†,§* †

Shanghai Key Laboratory of Green Chemistry and Chemical Processes, East China Normal

University, College of Chemistry and Molecular Engineering, 3663 North Zhong-shan Road, Shanghai 200062 (P. R. China) §

State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai

Institute of Ceramics, Chinese Academy of Sciences, 1295 Ding-xi Road, Shanghai 200050 (P. R. China) ‡

Department of Nuclear Medicine, Changhai Hospital of Shanghai, 168 Chang-hai Road,

Shanghai 200433 (P.R. China)

KEYWORDS : ZSN photosemiconductor, amorphous TiO2 , core/shell nanocrystal, two-photon, type-1 PDT

ABSTRACT: Two-photon absorption nanomaterials are highly desirable for deep-tissue clinical diagnostics and orthotopic diseases treatment. Here, a well-designed core/shell nanostructure was

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successfully synthesized with ZnTPyP self-assembly nanocrystal inner core coated by a homogeneous TiO2 layer outside (ZSN-TO). ZSN is a good photosemiconductor, showing both one-photon (OP) and two-photon (TP) absorption properties for red fluorescence emission and electron-hole pairs generation; TiO2 with good biocompatibility plays as the electron acceptor, which can transfer photoelectron from ZSN to TiO2 for highly effective electron-hole separation, favoring the production of long-life superoxide anion (O2·-) by electrons and oxygen, and strong oxidizing hydroxyl radical (·OH) by holes and surrounding H2O. Once pre-treated with ZSN-TO, the simultaneous OP-405 nm or TP-800 nm laser stimulation and flourescent imaging of reactive oxygen species (ROS) showed the dynamical and continuous generation of ROS in HeLa cells, with cytotoxicity significantly increasing via a type-1-like photodynamic therapy (PDT) process. The results demonstrated that the combination of organic ZSN with inorganic TiO2 has great application as excellent photosensitizer for deep tissue fluorescent imaging, and noninvasive disease treatment via two-photon photodynamic therapy (TPDT).

1. INTRODUCTION Porphyrins, a light-harvesting chlorophyll counterpart upon which the formation of planet life depends, are biocompatible and have been extensively studied in diverse areas ranging from biology, physics, and chemistry to molecular devices.1, 2 Meanwhile, as a family of macrocyclic organic molecules, porphyrins can be used as versatile molecular building blocks for controlled fabrication of self-assembled nanomaterials with one or more noncovalent interactions, such as aromatic π-π stacking, hydrogen bonding, van der Waals forces, and axial coordination.3 Synthetic self-assembly from single molecule to nanocrystal can lead to unique structural and optical features for potential application in material science and biological mimicking processes.4 Metalloporphyrin，zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H, 23H-porphine (ZnTPyP) has been


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chosen as an optically active electron donor in the construction of morphology and sizecontrolled nano/microcrystal for photochemical reactions.5,

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As a matter of fact, it is the

photogenerated electron-hole pairs that enables the formation of reactive oxygen species (ROS), which is important in catalysis as well as in PDT. Nevertheless, few reports have focused on the efficient electron generation and utilization, and the abundant properties of ZnTPyP selfassembled nanocrystal in electronics and optics have not been taken full advantage of. A multi-photon process occurs when more than one photon is simultaneously absorbed within a luminary for electron activation through virtual states. In contrast with the traditional onephoton technique, multi-photon transition, through the nonlinear optical process, can provide a high spatial resolution for deep-tissue clinical diagnostics with little damage to samples, and an extended phototherapy window (i.e., 700-1000 nm) for orthotopic tumor treatment with good space-selectivity.7, 8 In the past decades, a series of multi-photon absorbing organic dyes, such as FITC, DAPI, and Rose Bengal, 9 and a number of inorganic nanoparticles, such as gold nanorods, graphene quantum dots and ZnS nanocrystals,10-13 have been exploited as multi-photon agents. Usually, the rich chemical structures of organic dyes endow them with sufficient multi-photon absorption cross-section for high fluorescence quantum yields. However, the hydrophobicity, general cellular toxicity, and incidental fluorescence-quenching restrict their applications in biology. Inorganic nanomaterials with stable chemical structures and easily modified surfaces are suitable for studies in the life sciences, but the unfortunate side effects such as the inflexible optics, difficult biodegradation and potential high toxicity have greatly hindered their developments in the clinic.14,

15

ZSN is composed of porphyrins, retaining the original

characteristics of the building molecules, while generating some new chemical and physical properties that are significantly different from monomeric ZnTPyP.16,

17

To the best of our


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knowledge, there have been no efforts focusing on the multi-photon properties of ZSN or its application as multi-photon excited agents for disease diagnosis and therapy. Here, we report for the first time the synthesis of ZSN@TiO2 (ZSN-TO) with hexagonal ZSN nanocrystal coated by an amorphous TiO2 layer outside. ZSN playing as the good photosemiconductor shows both one-photon (OP, visble light) and two-photon (TP, near infrared light) absorption properties for red fluorescence emission and photoelectron-hole pairs generation. TiO2, with excellent biocompatibility, serves as an electron acceptor inducing photoelectron transfer from ZSN to the conduction band (CB) of TiO2 for highly effective electron-hole separation, favoring the reaction between electrons and oxygen for O2·generation, and the holes with water molecules for strong oxidizing hydroxyl radical (·OH).18-21 The simultaneous OP-405 nm or TP-800 nm laser stimulation and ROS flourescence imaging experiments show the dynamical and continuous generation of ROS in ZSN-TO-PLL pre-treated HeLa cells, with the cytotoxicity increasing significantly via the type-1-like PDT effect due to photoelectric synergistic of ZSN and TiO2. This core/shell ZSN-TO nanocrystal has great potential for OP/TP-excited fluorescent imagings and noninvasive diseases treatment through the PDT and TPDT process in both skin layer and deep tissues. 2. EXPERIMENTAL SECTION 2.1. Materials and Reagents. Cetyltrimethyl ammonium bromide (CTAB), sodium hydroxide (NaOH), hydrochloric acid (HCl, 36%~38%), methanol, dimethyl sulfoxide (DMSO), acetonitrile and ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). Titanium diisopropoxidebis (acetylacetonate) (TDAA), 1, 3-diphenylisobenzofuran (DPBF), and poly-l-lysine (PLL) were obtained from sigma-aldrich. The Zinc 5, 10, 15,20-


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tetra(4-pyridyl)-21H, 23H-porphine (ZnTPyP), and P-benzoquinone were purchased from J&K Scientific LTD. All reagents were of analytical grade and were used without further purification. 2.2. Self-assembly synthesis of ZSN nanocrystal. Hydrophobic ZnTPyP exposed to an acidic aqueous solution was protonated to hydrophilic ZnTPyP-H44+. Cetyltrimethyl ammonium bromide (CTAB) surfactant solutions were prepared in basic condition with the concentration greater than the corresponding critical micelle concentration to ensure the formation of surfactant micelles. During the synthetic process, the encapsulation and self-assembly of ZnTPyP was initiated by the adding of the acidic ZnTPyP-H44+ stock solution into the basic surfactants solution. The morphologies of final products can be adjusted by surfactant concentrations and pH. Briefly, CTAB was dissolved in NaOH solution ([CTAB] 2 mM, [NaOH] 10 mM]. 0.5 mL of ZnTPyP solution [0.01 M ZnTPyP dissolved in 0.2 M HCl] was quickly injected into 9.5 mL the above solution with mild stirring for 5 min. Then the mixture was subsequently centrifuged at 15000 rpm and washed with ethanol for three times to remove surfactant, and the hexagonal nanodisks were acquired. 2.3. Synthesis of ZSN-TO. To coat TiO2 on ZSN, TDAA methanol solution (VTDAA : VMeOH = 1:50) was cautiously added (every 30 min, 25 µL at a time, two times) into 8 ml ZSN dissolved in CTAB solution ([CTAB] 0.2mM, pH = 11.0 adjusted by NaOH). After the introduction of the titanium source, the reaction was continued for another two hours, and the final uniform forming of core-shell ZSN-TO was collected by centrifugation. It was noting that the surfactants concentration of the ZnTPyP-MOF reaction solution was finely controlled at around 0.1 mM, with the pH tuned to around 11.0. 2.4. The decoration of poly-l-lysine (PLL) on nanocrystals. The specific process was as follows: 200 µl ZSN or ZSN-TO was added into the PLL solution (1 mL, 1 mg/mL, pH 7.4 PBS


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buffer that contained 0.5 M NaCl) and then gently stirred for 20 min. Finally, the PLL-modified nanoparticles were washed three time and resuspended in phosphate buffer saline (PBS). 2.5. ROS detection in vitro. The generation of reactive oxygen species in live cells was firstly examined by 2',7'-dichlorofluorescin diacetate (DCFH-DA). DCFH-DA diffusing into cells, can be deacetylated by cellular esterases to a non-fluorescent compound, which is further oxidized by ROS into 2',7'-dichlorofluorescein (DCF) characteristic of excitation and emission maxima of 488 and 525 nm. The simultaneous one/multi-photon laser stimulation and visible laser imaging experiments were carried out to demonstrate the dynamically continuous generation of ROS in different ROIs in HeLa cells subjected to the combined treatment of ZSN-TO-PLL and one/multi-photon laser illumination. HeLa cells (3 × 104 cells/well in plates) were incubated for 12 h, and then 1 mL DMEM solutions of ZSN-TO-PLL ([Zn] 12.85 ppm) were added into the culture dish. After co-incubation for 8 h, the cells were then washed with serum-free culture medium and resuspended in Dulbecco’s Modified Eagle’s Medium (DMEM) containing DCFHDA (Beyotime Institute of Biotechnology) (1:1000) to measure ROS. After 20-min incubation in the dark, cells were twice washed sequentially with DMEM followed by PBS. The synchronous multi-photon laser stimulation at 800 nm and visible laser imaging at 488 nm for 19 s led to the significantly enhanced DCF fluorescence intensity, which can be visualized on the dynamic imaging by Nikon A1R MP microscopy. 3. RESULTS AND DISCUSSION 3.1. Characterizations of ZSN-TO. ZSN nanocrystals were fabricated by a typical bottomup self-assembly method. Due to the acid-base neutralization reaction, the acidified ZnTPyPH44+ was deprotonated in an alkaline condition, and then the insoluble ZnTPyP was assembled into the hydrophobic micellar interiors for the highly ordered three-dimensional ZSN formation,


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Figure 1. SEM, TEM and XPS characteristics of (a-d) ZSN and (e-h) ZSN-TO. with the scanning electron microscope (SEM) and transmission electron microscope (TEM) showed in Figure 1 a-c. To direct the coating of TiO2 on ZSN, a CTAB-assisted approach was employed.22 As shown in Figure 1 e-g, the uniform core-shell composite architecture was prepared with the [Zn] : [Ti] in ZSN-TO approximately 1.028, which was determined through the inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of trace chemical elements. X-ray photoelectron spectroscopy (XPS) was carried out to investigate the chemical and bonding environment of the nanocrystals (Figure 1 d and Figure 1 h). In contrast with ZSN, two new peaks occurred at 464.8 eV and 458.9 eV in ZSN-TO, which corresponded to Ti 2p1/2 and Ti 2p3/2 binding energies respectively (Figure S1, Supporting Information),23 further indicating the successful surface coating of TiO2 on ZSN. For the high biocompatibility and dispersibility of nanocrystals in water, the products were decorated with poly-l-lysine (PLL) through electrostatic attraction.24 The dynamic light scattering (DLS) measurement shows that the conjugation of PLL makes the as-prepared nanoparticles monodisperse in water with a much narrower bandwidth than before (Figure S2, Supporting Information).


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Figure 2. (a) UV/Vis absorption spectra of monomer ZnTPyP, self-assembled ZSN, and core/shell ZSN-TO. (b) Photoluminescence spectra of ZnTPyP and ZSN excited by 405 nm, 500 nm, and 800 nm respectively. (c) Electron paramagnetic resonance for ROS detection before (c1: TEMP-1O2) and after (c2: TEMP-1O2, c3: DMPO-O2·-, c4: DMPO-·OH) visible light irradiation for 60 s. Comparison of ROS production between Control, TiO2, ZSN and ZSN-TO following light irradiation: (d) The photocatalytic degradation of RhB by visible light treatment, and the decay in DPBF fluorescence by (e) 500 nm monochromatic light and (f) 800 nm light irradiation. 5 min light irradiation alternates with 5 min dark treatment. 3.2. ZSN-TO for ROS production and photocatalystic degradation of RhB. Typical UV/Vis spectra for monomer molecular ZnTPyP and self-assembled ZSN are shown in Figure 2 a. Compared with the Soret band of monomeric ZnTPyP at 415 nm, ZSN displayed three split Soret bands at 415, 455 and 485 nm with an obvious bathochromic shift, which was the characteristic of three-dimensional porphyrin J-aggregates, and could favor electron transfer through the tightly π-conjugated electrons of the closely packed porphyrins for enhanced photocatalytic activity.25 Photoluminescence (PL) spectra showed that ZnTPyP can only be excited at a wavelength of approximate 405 nm for strong red fluorescence spanning 600 nm to 700 nm; by contrast, the excitation spectra of ZSN was significantly broadened, with obivious red fluorescence at 500 nm light irradiation; however, OP-800 nm gave no luminescence for both ZnTPyP and ZSN (Figure


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2 b), due to the low absorption around 800 nm. Electron spin resonance (ESR) was performed to confirm the specific types of produced reactive oxygen species with TEMP or DMPO as spin trap agents.26 As shown in Figure 2 c, for monomeric ZnTPyP under visible light irradiation, only a 1:1:1 triplet signal of TEMP-1O2 was detected, meaning that the photo-induced product of ZnTPyP was just singlet oxygen. For ZSN, visible light irradiation gave not only the 1O2 but also the dramatic rise of O2·- and ·OH, demonstrated by the emerging characteristic peaks of DMPOO2·- in ethonal and DMPO-·OH in water (Figure 2 c). As shown in Figure 2 d, visible light irradiation brought the fastest decolorization of RhB in ZSN-TO group, signaling the favorable synergistic effect within ZSN and TO for enhanced photocatalysis (Figure S3 and S4). The amperometric i-t curves (Figure S5) showed switchable photocurrent of the ZSN-TO responding to the cyclic on/off light irradiation, with the intensity of photocurrent being significantly higher when compared with pure ZSN or TiO2, further demonstrating the out-layer TiO2 that contributed to the increase of photocurrent intensity by transferring the photoinduced electrons in ZSN to TiO2. DPBF, whose fluorescence is irreversibly quenched by 1O2, O2·- and ·OH, has long been used for reactive species detection. As shown in Figure 2 e, the on/off states of selected 500 nm light determine the formation/pausing of ROS. It is noteworthy that after three-fractional irradiation, the absorption peak of DPBF in the ZSN-TO group completely disappeared, while for ZSN and TiO2, the absorption peak intensity all kept above 70%, signaling that ROS production rate in ZSN-TO solution was much higher than that obtained in ZSN or TiO2 alone. It should be noted that OP-800 nm cannot activate ZSN for ROS generation (Figure 2 f). 3.3. One-photodynamic activity of ZSN-TO. Before the practical application in vitro, MTT assay was first performed to evaluate the effects of ZSN-PLL and ZSN-TO-PLL on cells. The


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Figure 3. (a) Photoluminescence images of ZSN-PLL in HeLa cells. 405 nm and 488 nm laser gave the same luminescence with the maxima emission around 650 nm (the red and green fluorescence just mean the position of ZSN-PLL in cells, but not the actual fluorescent color). (b)The simultaneous OP-405 nm laser stimulation and ROS fluorescence imaging at various time points in ZSN-TO-PLL pre-treated HeLa cells, and the ratio of the ROS fluorescence mean intensity at specific time/the mean intensity of DCF at the initial time in 1# ROI with 405 nm stimulation area, 2# ROI without light irradiation, and the 3# ROI background area. (c) Actin morphology of HeLa cells incubated with ZSN-TO-PLL before and after 405 nm laser irradiation. DAPI (a nuclear staining dye, blue) and Actin-Tracker Green (an actin filament staining dye, green). (d) The cell viability of HeLa pre-treated with PBS, TiO2, ZSN-PLL, or ZSN-TO-PLL, without (black line) or with (red line) visible light irradiation for 1 min. Scale bars = 50 µm. ACS Paragon Plus Environment

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data indicated that both ZSN-PLL and ZSN-TO-PLL in the dark had no significant cytotoxicity even at a high concentration of nanocrystals ([Zn]: 51.4 ppm) (Figure S6). One direct piece of evidence for PDT assessment is the immediate generation and fluorescence imaging of ROS by confocal laser scanning microscopy (CLSM). Figure 3 a showed that ZSN-TO-PLL in cells can be excited by both 405 nm and 488 nm, with the same emission maxima around 650 nm. 2',7'dichlorofluorescin diacetate (DCFH-DA) in cells can be deacetylated by cellular esterases to a non-fluorescent compound 2',7'-dichlorofluorescin (DCHF) that is oxidized by ROS into 2',7'dichlorofluorescein (DCF), characteristic of excitation and emission maxima of 488 and 525 nm. Here 405 nm laser was set as the stimulation source with relatively high power, and meanwhile, the intensity of 488 nm imaging laser was purposely weakened to inhibit the imaging laserinduced cells response. Time-serial stimulation and imaging experiments showed that 405 nm light alone or combined with TiO2 could not lead to the production of additional ROS. For ZSNPLL, the intensity of ROS fluorescence had visible changes in the region of interest (ROI) after being stimulated by a continuous-wave laser at 405 nm for 30 s, and for cells pre-cultured with ZSN-TO-PLL, intracellular ROS fluorescence intensity showed the greatest increase with the same treatment, signaling an effective OP-induced output of ROS by ZSN-TO, which was in agreement with previous studies on ROS in solution (Figure S7). To capture the dynamic formation of ROS at simultaneous 405 nm laser stimulation, CLSM equipped with a high-speed resonant scanner was used. As shown in Figure 3 b, 405 nm laser irradiation can start the ROS generation in 1# ROI immediately, with the intracellular fluorescence intensity of DCF markedly increasing by 224.5% within 80 s; by contrast, the amount of ROS has little change in 2# ROI without 405 nm laser stimulation, indicating the high performed PDT of ZSN-TO. The cytotoxicity was further evaluated through morphological changes of the actin filaments. As


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shown in Figure 3 c, the actin was well-organized and spread around the nucleus in ZSN-TOPLL co-cultured HeLa cells. Upon irradiation with 405 nm for 60 s, the actin retracted and condensed into the nucleus, indicating significant damage to the cytoskeleton of the cells.27 Compared with other groups, remarkably decreased the cells’ survival rate was observed in cells treated with both ZSN-TO-PLL and visible light irradiation, signaling an effective PDT by ZSNTO (Figure 3d). 3.4. Two-photon fluorescence of ZSN-TO. To study two-photon flourescence property of ZSN, a mode-locked femtosecond Ti : Sapphire NIR pulsed-laser (MaiTai, Deepsee 80 MHz) was applied. As shown in Figure 4a, ZSN deposited on the glass slice can be excited by 800 nm NIR femtosecond pulsed-laser, with the PL spectra mostly consistent with that induced by OP-405 nm laser, indicating ZSN two-photon absorption and fluorescence characteristics. It should be noted

Figure 4. (a) The two-photon fluorescence signals and the corresponding emission spectra received at varied wavelength areas of the dried ZSN on a glass substrate with femtosecond pulsed laser excitation at 800 nm. (b) Photoluminescence images of ZSN-PLL in HeLa cells. OP-405 nm and TP-800 nm laser gave the same luminescence with the maxima emission around 650 nm (the red and green fluorescence just mean the position of ZSN-PLL in cells, but not the actual fluorescent color). Scale bars = 50 µm.


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that OP-800 nm irradiation gave no luminescence emission. In Figure 4 b, after co-culturing with HeLa cells for 8 h, ZSN-PLL was smoothly swallowed into the cytoplasm of HeLa cells, with the same emission fluorescence, when excited by OP-405 nm and TP-800 nm respectively. To further confirm the location of ZSN-PLL in cells, three-dimensional section images were performed. As the z-axis moves from top (0 µm) to bottom (10 µm, ∆z = 0.3 µm), we clearly observed the fluorescence signals at all levels of the cells, which truly reflected the location of the nanocrystals in the cytoplasm rather than on the surface of HeLa cells (Figure S8). 3.5. Two-photon PDT activity of ZSN-TO. Based on the above exploration into PDT ability and TP absorption of ZSN, the TPDT was further studied at the cellular level. Studies have shown that OP-800 nm cannot activate the luminescence and PDT effect of ZSN. However, with the 800-nm femtosecond laser local-stimulation (the red squares in Figure S9), the intracellular ROS fluorescence signals increased markedly by 61.4% for ZSN-PLL and by 245.2% for ZSNTO-PLL within 20 s. These results powerfully demonstrate ZSN-TO-PLL’s TPDT capability and the effective ROS generation due to the synergistic effect of the inner ZSN and outer TiO2. The simultaneous TP laser stimulation and visible laser imaging experiments in Figure 5 a-b show the dynamically continuous generation of ROS in ZSN-TO-PLL pre-treated HeLa cells, as demonstrated by the rapidly growing ROS fluorescence intensity in TP-800 nm femtosecond laser stimulating position (red box, as 1# ROI). By contrast, the signals are almost unchanged in 2# ROI without TP-800-nm light treatment, and the background consistently maintains a low signal for 3# ROI. To investigate the cytotoxicity caused by the laser radiation itself or the TPinduced PDT, cultured cells were scanned with the 800 nm femtosecond pulsed laser, and cell viability was evaluated by MTT (Figure 5 c). In the absence of the nanocrystals, there were no signs of cytotoxicity caused by the NIR femtosecond pulsed laser, thereby demonstrating the low


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Figure 5. The simultaneous TP-800 nm laser stimulation and ROS fluorescence imaging at various time points in ZSN-TO-PLL pre-treated HeLa cells (a), and the ratio of the ROS fluorescence mean intensity at specific time/the mean intensity of DCF at the initial time in 1# ROI with 405 nm stimulation area, 2# ROI without light irradiation, and the 3# ROI background area (b). (c) Cell viability of HeLa pre-treated with PBS, TiO2, ZSN-PLL, or ZSN-TO-PLL, and then scanned at 800 nm NIR pulse laser. Scale bars = 50 µm. cytotoxicity from NIR radiation. Meanwhile, ZSN and ZSN-TO nanocrystals can release toxic ROS after absorbing TP energy, as indicated by the decreased viability rates of cells. In fact, it is ZSN that plays the key role in TPDT, and TiO2 contributes efficiently to capturing the photogenerated electrons for ROS continuous generation.28, 29


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4. CONCLUSIONS A composite architecture with hexagonal nanocrystal ZSN coated with amorphous TiO2 was successfully synthesized. ZSN exhibited excellent OP/TP absorption and fluorescent property with little toxicity to living cells. Once coated with TiO2, the photoexcited electrons in ZSN were mostly injected into the CB of TiO2, which could increase the electron activity to interact with surrounding O2 for long-life O2·- generation, and the residual holes with H2O for the production of strong oxidizing ·OH. Due to photoelectric synergistic of ZSN and TiO2, the cell death rate increased significantly via the type-1-like PDT effect. The combination of such newly proposed OP/TP excitation ZSN with biocompatible TiO2 has potential applications in NIR fluorescent imaging to monitor the biological changes in deep tissues and noninvasive disease treatment through the TPDT process. ASSOCIATED CONTENT Supporting Information. Detailed experiments for DLS studies, XPS analysis, ESR studies for ROS detection in solution, photocatalystic degradation of RhB, photocurrent measure, MTT studies for cells viability, and the OP and TP stimulation for the studies of ROS in cells (PDF). AUTHOR INFORMATION Corresponding Author *E-mail address: [email protected] *E-mail address: [email protected]; [email protected]

ACKNOWLEDGMENT


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This work has been financially supported by National Science Foundation for the Young Scientists of China (Grant No. 51702211), National Funds for Distinguished Young Scientists of China (Grant No. 51725202), National Natural Science Foundation of China (Grant No. 51372260, 81471714),

and Shanghai Excellent Academic Leaders Program (Grant

No.16XD1404000). ABBREVIATIONS ZSN, ZnTPyP self-assembly nanocrystal; TO, TiO2; PLL, poly-l-lysine; OP, one-photon; TP, two-photon; ROS, reactive oxygen species; CB, conduction band; PDT, photodynamic therapy; ROI, region of interest; PL, photoluminescence; SEM, scanning electron microscope; TEM, transmission electron microscope; ICP-OES, inductively coupled plasma optical emission spectrometry; XPS, X-ray photoelectron spectroscopy; DLS, dynamic light scattering.

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NaYF4:Yb/Tm-TiO2

inorganic

photosensitizers

for

NIR-triggered


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TOC 150x140mm (300 x 300 DPI)


TiO2 Interfaces for

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