Cross relaxation induced pure red upconversion in activatorand sensitizer- rich lanthanide nanoparticles

Transcription

1 Cross relaxation induced pure red upconversion in activatorand sensitizer- rich lanthanide nanoparticles Wei Wei, Yan Zhang, Rui Chen, Julian Goggi, 丄丄 Na Ren, Ling Huang, Kishore K. Bhakoo, Handong Sun,, Timothy Thatt Yang Tan *, School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore , Singapore Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore , Singapore Centre for Disruptive Photonic Technologies (CDPT), Nanyang Technological University, Singapore , Singapore Singapore Bioimaging Consortium (A*STAR), Helios, 07-10, 11 Biopolis Way, Singapore , Singapore 丄 Institute of Advanced Materials, Nanjing Tech University, Nanjing , China 1

2 EXPERIMENTAL SECTION Materials. YbCl 3 6H 2 O (99.99%), YCl 3 6H 2 O (99.99%), GdCl 3 6H 2 O (99.9%), LuCl 3 6H 2 O (99.99%), TmCl 3 6H 2 O (99.9%), ErCl 3 6H 2 O (99.9%), HoCl 3 6H 2 O (99.9%), NaOH (98%), NH 4 F (98%), 1-octadecene (90%), oleic acid (90%), citric acid (99.5%) were purchased from Sigma-Aldrich. The solvents, such as hexane, ethanol and methanol were provided by Aik Moh, Singapore. Iohexol was manufactured by GE healthcare (Shanghai) Co. Ltd. All the chemicals were used without further purification. Synthesis of oleic acid (OA) capped NaYbF 4 :Tm, NaYbF 4 :Er and NaYbF 4 :Ho, NaYF 4 :Yb/Tm (20%/1%), NaYF 4 :Yb/Tm (20%/10%), NaYF 4 :Yb/Er (20%/1%) and NaYF 4 :Yb/Er (20%/50%) UCNPs. A total amount of 0.4 mmol RECl 3 6H 2 O (RE = Yb, Y, Tm, Er, Ho) were added into a three-necked flask containing the mixture of 1-octadecene (7 ml) and oleic acid (3 ml) under vigorous stirring at room temperature (the ratio of RE varied according to the experiment requirements). The resulting mixture was then heated to 150 C for 0.5 h, and then cooled down to room temperature. After that a methanol solution (5 ml) of NH 4 F (1.6 mmol) and NaOH (1 mmol) was added into the flask. The temperature was then increased to 160 C in order to remove the methanol from the mixture. Once the methanol was evaporated completely, the above mixture was heated to 310 C for 1 h under an argon environment. Then the reaction mixture was cooled down to room temperature. The as-prepared nanoparticles were collected and precipitated by the addition of ethanol, followed by centrifugation, then washed with water and ethanol for several times, and finally dispersed in hexane. Solvothermal synthesis of OA capped NaREF 4 :Yb 20%/Tm (1%, 10%), NaREF 4 :Yb 20%/Er (1%, 25%, 10%), NaR- EF 4 :Yb 20%/Ho (1%, 50%) microrods. Typically, 1.5 ml aqueous solution containing 0.3 g NaOH was mixed with 5 ml of ethanol and 5 ml of OA under stirring. Subsequently, 2 ml of RECl 3 (0.2 mol/l, RE= Yb, Y, Gd, Lu, Tm, Er and Ho) and 1 ml of NH 4 F (2 mol/l). Then the solution was transferred into a 20 ml of Teflon-lined autoclave and heated at 200 C for 7 h. The obtained microrods were collected by centrifugation, washed with water and ethanol several times, and finally dispersed in hexane. Synthesis of water-soluble NaYbF 4 :Tm (10%) UCNPs modified by citric acid. The water-soluble NaYbF 4 :Tm (10%) UCNPs were prepared through a ligand exchange route. 10 mg OA capped NaYbF 4 :Tm (10%) UCNPs were mixed with the aqueous solution of citric acid (30 mg/ml), whose ph value was adjusted to 4. Under vigorous stirring for 10 h, the citric acid functionalized NaYbF 4 :Tm (10%) UCNPs were obtained. The as-prepared products were washed with water three times. Characterization. Transmission Electron Microscopy (TEM) images were obtained by using a JEOL-1400 microscope operating at 100 kv. High-resolution Transmission Electron Microscopy (HRTEM) measurements were carried out on a JEOL-2010 at 300 kv. X-ray diffraction (XRD) analysis was conducted on a D8 Advance Bruker powder X-ray diffractometer with Cu Kα radiation (λ = Å) from 10 to 70 at a step of 0.02 /s. To acquire the UC emission spectra, the nanoparticles were dispersed in hexane in a standard quartz cuvette at room temperature, and then were recorded by a Fluoromax-4, Horiba Jobin Yvon Spectrofluorometer. The 980 nm excitation light source was a diode laser coupled to a 100 µm (core) optical fiber. For the UC fluorescence lifetime measurements, the chopper wheel was replaced by a homemade one and the repetition rate of the mechanical chopper was maintained at 500 Hz to generate pulses with pulse width of 0.15 ms. The detector output was stored on a digital phosphor oscilloscope (Tektronix DPO 7254) and averaged over 500 periods to improve the signal-to-noise ratio. The fluorescence lifetime curves conform to an exponential fit with reconvolution: ( )= ( ) ( )/ (1) Where A is the amplitude of the component at time zero, τ is the corresponding lifetime, and IRF is the instrument response function. CT phantom images were collected from an Inveon CT system (Siemens Inc., Washington DC) using following parameters: pixel resolution µm; 80 KVp, 60 µa; field of view mm x mm; rotation steps 220, binning 4, exposure time 470 ms/rotation. 2

3 Cytotoxicity assessment of citric acid modified NaYbF 4 :Tm (10%) UCNPs. SiHa cells were maintained in Dulbecco s modified Eagle s medium (DMEM) supplemented with 10% fetal bovine serum (FBS), penicillin (100 unit/ml), and streptomycin (100 mg/ml). Cells were cultured at 37 C with 5% CO 2 and saturated humidity. Cytotoxicity was assessed using PrestoBlue (Life Technologies, Singapore) assays. Briefly, cells were plated in 96-well plates with a cell density of 10 4 cells per well and allowed to grow into full confluence. And then the medium was replaced with serum-free medium containing UCNPs of different concentrations and the cells were incubated for 8 h, 16 h or 24 h, separately. At each time point, the culture medium was replaced with 0.1 ml of the PrestoBlue solution (10% diluted with a culture medium without FBS). After 30 min incubation, fluorescence analysis was carried out with a SpectraMax M2 microplate reader (Molecular Devices, USA), using an excitation wavelength of 560 nm and an emission wavelength of 595 nm. Cell numbers were calculated using a standard curve correlating known cell numbers with fluorescent values. The cytotoxicity was expressed as the percentage of cell viability compared to that of untreated control cells. In vitro confocal UC fluorescence imaging. 10 µg/ml citric acid modified NaYbF 4 :Tm (10%) UCNPs were incubated with SiHa cells (10 6 /well) for 20 h at 37 C under 5% CO 2. After washed with phosphate buffered saline (PBS) for three times, the UC fluorescence imaging was performed on a modified Nikon A1R-si scanning unit equipped with an external 980 nm laser. The UC fluorescence signals were detected in the nm channel. 3

4 Figure S1. TEM images and the size distribution of β-naybf 4 :Tm (10%) UCNPs. Figure S2. UC emission spectra of 1, 25 and 50 mol% Ho 3+ ions doped NaYbF 4 UCNPs. Inset shows the corresponding fluorescence photographs of NaYbF 4 :Ho UCNPs with the concentration of Ho 3+ varying from low to high. Note CR effect induced pure red UC does not exist at high Ho 3+ doping level as indicated in the schematic illustration. 4

5 Table S1. TEM images, XRD and UC emission spectra of NaYF 4 :20%Yb/Ln (Ln=Tm, Er, Ho) at varying activator (Ln=Tm, Er, Ho) concentration. NaYF 4 :Yb/Ln(20%/X) TEM XRD UC emission X=25% X=50% Ln=Tm Ln=Tm X=10% Ln=Ho Ln=Ho X=50% 5

6 Table S2. TEM images, XRD and UC emission spectra of NaGdF 4 :20%Yb/Ln (Ln=Tm, Er, Ho) at varying activator (Ln=Tm, Er, Ho) concentration. NaGdF 4 :Yb/Ln(20%/X) TEM XRD UC emission X=25% X=50% Ln=Tm Ln=Tm X=10% Ln=Ho Ln=Ho X=50% 6

7 Table S3. TEM images, XRD and UC emission spectra of NaLuF 4 :20%Yb/Ln (Ln=Tm, Er, Ho) at varying activator (Ln=Tm, Er, Ho) concentration. NaLuF 4 :Yb/Ln(20%/X) TEM XRD UC emission X=25% X=50% Ln=Tm Ln=Tm X=10% Ln=Ho Ln=Ho X=50% 7

8 Figure S3. Power dependence characteristics of (a) NaYbF 4 :Tm (1%) and (b) NaYbF 4 :Tm (10%) UCNPs. Figure S4. Power dependence characteristics of (a) NaYbF 4 :Er (1%) and (b) NaYbF 4 :Er (50%) UCNPs. 8

9 Figure S5. Fluorescence lifetime curves and the corresponding fitted lines of the different excited state transitions in NaYbF 4 :Tm UCNPs with different Tm 3+ concentrations: (a) 1 D 2 3 F 4 (λ em =450 nm), (b) 1 G 4 3 H 6 (λ em =475 nm), (c) 3 F 3 3 H 6 (λ em =696 nm). The solid line represents the theoretical fitted line. The black dotted line represents the instrument response function. Table S4. Fluorescence decay time of the different excited state transitions in NaYbF 4 :Tm UCNPs with different Tm 3+ concentrations. Tm 3+ concentration (mol%) Transition τ decay ( µs ) 1 D 2 3 F 4 (λ em =450 nm) N.A. N.A. N.A. 1 G 4 3 H 6 (λ em =475 nm) N.A. N.A. N.A. 3 F 3 3 H 6 (λ em =696 nm)

10 Figure S6. Fluorescence lifetime curves and the corresponding fitted lines of the different excited state transitions in NaYbF 4 :Er UCNPs with different Er 3+ concentrations: (a) 4 S 3/2 4 I 15/2 (λ em =540 nm) and (b) 4 F 9/2 4 I 15/2 (λ em =660 nm). The solid line represents the theoretical fitted line. The black dotted line represents the instrument response function. Table S5. Fluorescence decay time of the different excited state transitions in NaYbF 4 :Er UCNPs with different Er 3+ concentrations. Er 3+ concentration (mol%) Transition τ decay ( µs ) 4 S 3/2 4 I 15/2 (λ em =540 nm) F 9/2 4 I 15/2 (λ em =660 nm) N.A. 10

11 Figure S7. Proposed UC mechanism of Ho 3+ ions doped UCNPs at both low and high concentration doping level. Table S6. Calculated energy value of simplified energy levels to the ground level for Tm 3+ and Er 3+ ions, and the energy gap of selected transitions in Tm 3+ and Er 3+. Activator Energy level Energy (cm -1 ) Transition E (cm -1 ) 1 D D 2 3 H G Tm 3+ Er 3+ 3 F H 6 3 F F H G 4 3 H H F F 4 3 F H F 7/ H 11/ S 3/ F 9/ I 9/ I 11/ I 13/ I 15/2 0 4 F 7/2 4 F 9/ I 13/2 4 F 7/

12 Figure S8. In vitro cell viabilities of SiHa cells incubated with different concentrations of the citric acid modified NaYbF 4 :Tm (10%) UCNPs at 37 C for 8, 16 and 24 h, respectively. Figure S9. Confocal fluorescence images of SiHa cells incubated with citric acid modified NaYbF 4 :Tm (10%) UCNPs at 10 µg/ml for 20 h. (a) UC fluorescence image (the channel used for image collection was from 430 nm to 780 nm) (b) Bright field image; (c) Fluorescence image of nuclei stained with DAPI (d) Merged confocal images of (a) and (c). 12

13 Figure S10. (a) CT images and (b) the measured CT values (Hounsfild units, HU) of the citric acid modified NaYbF 4 :Tm (10%), Iohexol and NaYF 4 :Yb/Tm (20%/1%) with different concentrations in water. Figure S11. UC emission spectra of 1, 5, 10, 15 and 20 mol% Tm 3+ ions doped NaYbF 4 :Tm UCNPs with wavelength range varying from 300 to 900 nm, covering UV and NIR region. 13