Supporting information for JACS A Two-Dimensional Biodegradable Niobium Carbide (MXene) for Photothermal Tumor Eradication in NIR-I and NIR-II Biowindows Han Lin, 1,2 Shanshan Gao, 1,2 Chen Dai, 1 Yu Chen, 1 * and Jianlin Shi 1 * 1 State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, P. R. China. E-mail: chenyu@mail.sic.ac.cn; jlshi@mail.sic.ac.cn 2 University of Chinese Academy of Sciences, Beijing, 100049, P.R. China. S1
Table of Contents Part A. Supplementary figures Part B. Supplementary tables Part C. Supplementary discussions Part D. References S2
Part A. Supplementary figures Figure S1. (a) Elemental mapping for original Nb 2 AlC crystallites. (b) Elemental mapping for HF-etched Nb 2 AlC (multilayer Nb 2 C). (b) Elemental mapping of HF-etched Nb 2 AlC (multilayer Nb 2 C NSs). (c) Elemental mapping and corresponding element-linear scanning of TPAOH-intercalated Nb 2 C NSs (single-layer Nb 2 C). S3
Figure S2. Electron energy loss spectra (EELS) of Nb 2 C NSs. Figure S3. Atomic displacements of the corresponding Raman-active modes of Nb 2 AlC. S4
Figure S4. EDS profile confirms the presence of Nb, C, and finite O elements S5
Figure S5. (a) XPS spectra of Nb 2 AlC and Nb 2 C NSs in the region containing all possible elements. (b) XPS spectra of Nb 2 AlC and Nb 2 C NSs in the region of Al element. (c) XPS spectra of Nb 2 C NSs in C 1s region. (d) XPS spectra of Nb 2 C NSs in O 1s region. S6
Figure S6. TEM images of Nb 2 C NSs (a) before and (d) after obvious surface oxidation. Insets are corresponding HRTEM images. XPS spectra of Nb 2 C NSs in Nb 3d region (b) before and (e) after obvious surface oxidation. Content distributions of surface oxidation species (NbO x ) of Nb 2 C NSs (c) before and (f) after obvious surface oxidation. S7
Figure S7. (a) XRD pattern and (b) EDS profile of Nb 2 C-PVP treated with H 2 O 2 in PBS. S8
Figure S8. (a) Schematics of surface modification of Nb 2 C nanosheets using PVP (Nb 2 C-PVP). (b) FTIR spectra of PVP, Nb 2 C NSs and Nb 2 C-PVP, indicating the successful surface modification of Nb 2 C with PVP. (c) Zeta potential profile of Nb 2 C NSs and Nb 2 C-PVP NSs dispersed in water. (d) UV-vis-NIR spectra of Nb 2 C NSs and Nb 2 C-PVP NSs dispersed in water show almost no decline for optical absorption after the PVP surface modification, indicating the well-maintained photothermal performance of Nb 2 C-PVP. S9
Figure S9. (a) Thermogravimetric analysis (TGA) and (b) normalized weight loss distribution diagram of Nb 2 C NSs and Nb 2 C-PVP NSs (Ramping rate: 5 o C per min, protective gas: Ar). The loss-on-ignition (LOI) of Nb 2 C NSs and Nb 2 C-PVP NSs were 1.04 % and 21.4 % within the selected temperature interval from 30 o C to 500 o C. The LOI of Nb 2 C NSs originated from the ignition of bound water on the surface of Nb 2 C NSs. Compared to the LOI of Nb 2 C-PVP NSs, additional PVP were burnt out. Hence the loading amount of PVP could be calculated by the discrepancy of normalized LOIs between Nb 2 C-PVP NSs and Nb 2 C NSs. The result turned out that the loading amount of PVP in Nb 2 C-PVP NSs was 20.36 %. S10
Figure S10. (a) Nb 2 C NSs of varied concentrations (80, 40, 20, 10, and pure water) were exposed to an 808 nm laser at power density of 1.0 W cm -2. (b) Nb 2 C NSs of varied concentrations (80, 40, 20, 10, and pure water) were exposed to a 1064 nm laser at power density of 1.0 W cm -2. S11
Figure S11. Photothermal heating curve of water solutions containing 80 μg ml -1 of Nb 2 C NSs, 100 μg ml -1 of Au NRs, 100 μg ml -1 of ICG and 80 μg ml -1 of Ti 3 C 2 NSs. S12
Figure S12. (a) Absorbance spectra of Au nanorods (Au NRs) dispersed in water at varied concentrations (100, 50, 25, and 12.5 μg ml -1 ). Inset: The extinction coefficient of Au NRs could be calculated by normalized absorbance intensity at λ = 808 nm divided by the characteristic length of the cell (A/L) at varied concentrations. The result turned out to be 9.02 Lg -1 cm -1, which is similar to the previous literature. 1 (b) Photothermal heating curve of Au NRs with varied concentrations (100, 50, 25, and 12.5 μg ml -1 ) exposed to an 808 nm laser at power density of 1.0 W cm -2. S13
Figure S13. The photothermal performance parameters, including mass extinction coefficient (ε) and photothermal conversion efficiency (η), of various materials in the literatures. Each symbol indicates a set of material category and the corresponding detailed description of each data point is presented in table S2. S14
Figure S14. Relative viabilities of 4T1 and U87 cells after being incubated with varied concentrations (0, 12, 25, 50, 100, and 200 μg ml -1 ) of Nb 2 C-PVP nanosheets. S15
Figure S15. Digital photographs of (a) mouse serum only, the corresponding photothermal heating curve under radiation of 808 nm laser, and photothermal heating curve under radiation of 1064 nm laser. Digital photographs of Nb 2 C-PVP NSs (50 μg ml -1 ) incubated with the fresh mouse serum, the corresponding photothermal heating curve under radiation of 808 nm laser, and photothermal heating curve under radiation of 1064 nm laser for different durations including (b) 0 h, (c) 2 h, (d) 6 h, (e) 12 h, and (f) 24 h, respectively. The power density of 808 and 1064 nm NIR laser are 1.25 W cm -2. S16
Figure S16. Confocal laser scanning microscopic (CLSM) images of 4T1 cells incubated with Nb 2 C-PVP at the concentration of 100 μg ml -1 for 0, 1, 2, 4, and 8 h. For each panel, the images from top to bottom show 2D mappings of DAPI fluorescence intensity of selected regions, 2D mappings of FITC fluorescence intensity of selected regions, 2D mappings of overlays of the former two fluorescence intensities, and three-dimensional (3D) confocal fluorescence reconstructions of Nb 2 C-PVP endocytosed 4T1 cells. S17
Figure S17. In vitro and in vivo PA imaging. (a) Schematics of PA imaging. PA imaging is a newly emerged biomedical imaging modality based on the photo-acoustic signal conversion effect of light-absorbers and offers notably enhanced imaging depth and spatial resolution compared to traditional in vivo optical imaging. (b) In vitro PA values and (d) PA images of Nb 2 C-PVP nanosheet solutions as a function of concentration (0.031, 0.062, 0.125, 0.25, 0.5, 1.0, and 2.0 mg ml -1 with respect to Nb). (c) In vivo PA value temporal evolution and (e) PA images of the tumor site at different time intervals (0, 0.5, 1, 2, 4, 8, 12, 24, and 48 h) post injection. S18
Figure S18. (a) Intracellular biodegradation behavior and structural evolution of Nb 2 C-PVP NSs in 4T1 cells by bio-tem observation after different incubation durations (1, 2, 3, and 7 d). Scale bars: 500 nm of 1 day, 200 nm of 2 and 3 day, and 100 nm of 5 day. (b) Intracellular Nb content in 4T1 cells after the co-incubation of Nb 2 C-PVP NSs with 4T1 cells for different incubation durations (1, 2, 3, and 5 d). S19
Figure S19. (a) Long-term Nb biodistribution after the intravenous administration of Nb 2 C-PVP into 4T1 tumor-bearing mice for 7 th day. (b) Accumulated Nb (in faeces and urine) excretion out of the mice body after the administration of Nb 2 C-PVP for different durations (2 h, 6 h, 12 h, 24 h, 36 h and 48 h). S20
Figure S20. Photographs of 4T1 tumor-bearing mice after the control and different treatments in 16 days period. S21
Part B. Supplementary tables Table S1. Raman active phonon modes of Nb 2 AlC from theoretical calculations and experiments (in cm -1 ). S22
Table S2. The photothermal performance parameters (mass extinction coefficient and photothermal conversion efficiency) of various nanoagents in the literatures. Category Materials Mass Extinction Coefficient (ε, Lg -1 cm -1 ) Photothermal Conversion Efficiency (η, %) Wavelength (λ, nm) NRs Au nanorods 1 13.9 Lg -1 cm -1 21 % 808 nm 2D Nano-GO 2 3.6 Lg -1 cm -1 808 nm 2D Nano-rGO 3 24.6 Lg -1 cm -1 808 nm 2D MoS 2 4, 5 29.2 or 28.4 24.37% 808 nm Lg -1 cm -1 2D WS 6 2 23.8 Lg -1 cm -1 44.3 % 808 nm 2D TiS 7 2 26.8 Lg -1 cm -1 808 nm 2D SnS nanosheets 8 16.2 Lg -1 cm -1 24 % 808 nm Bulk SnS bulk 8 8.2 Lg -1 cm -1 36.1 % 808 nm 2D Ti 3 C 2 9, 10 25.2 or 29.1 30.6 % 808 nm Lg -1 cm -1 2D Nb 2 C 37.6 or 35.4 36.5 or 46.65 % 808 or 1064 nm Lg -1 cm -1 2D Ta 2 NiS 11 5 25.6 Lg -1 cm -1 35 % 808 nm 2D Ti x Ta 1-x S y O 12 z 38.1 Lg -1 cm -1 39.2 % 808 nm QDs BP QDs 13 14.8 Lg -1 cm -1 28.4 % 808 nm NDs MoSe 2 nanodots 14 17.4 Lg -1 cm -1 46.5 % 785 nm NPs BP NPs 15 2.1 Lg -1 cm -1 36.8 % 808 nm Atom Per carbon atom 16 0.35 Lg -1 cm -1 1064 nm S23
Part C. Supplementary discussions Discussion S1. Raman spectrum analysis. First principles phonon calculations demonstrate that four Raman-active optical modes (A 1g + E 1g + 2E 2g ) are present in Nb 2 AlC phases (Figure S4 and Table S1). The A 1g symmetry out-of-plane vibrations of Nb and C atoms consist of ω 4 mode. Therefore, if the Al interlayer is removed, the peaks of these vibrations are expected to red-shift and change their shape, analogous to Ti 4 AlN 3 phase versus that of Ti 4 N 3 MXenes. The E 1g symmetry (irreducible representation) vibration, ω 2, contain in-plane (shear) mode of Nb and C atoms. These peaks remain in the Nb 2 C spectrum after etching away Al from Nb 2 AlC, but their intensity will decline presumably due to the increased interlayer spacing of the MXene structure. The E 2g modes including ω 1 and ω 3 modes are in-plane oscillations of Nb and C atoms, coupled to the minor oscillations of Al atoms (Figure 1g). After etching, the Al atoms are exchanged out by lighter atoms (such as H, F, and O). Therefore, the intensities of such coupled oscillations are suppressed more than those of the E 1g oscillations mentioned above. This feature presented in the Nb 2 C spectrum indicates the removal of the Al layer. The in-plane E 2g symmetry ω 3 mode consists of small oscillations of Nb and C atoms coupled to high-amplitude oscillations of Al. Elimination of Al would have the most impact on this peak. Indeed, diminishing of this peak confirms the successful removal of Al layer (Figure 2b). S24
Discussion S2. In vitro and in vivo PA imaging. Owing to the strong NIR-absorbance and photothermal conversion efficiency of Nb 2 C-PVP in the NIR region, PA imaging was further carried out by using the Nb 2 C-PVP as contrast agents (CAs) (Figure 11a). The PA images of a series solutions of Nb 2 C-PVP at different concentrations clearly show their contrast-enhancement performances (Figure 11b,d). Based on these results, 4T1 tumor-bearing mice were intravenously administrated with Nb 2 C-PVP (20 mg kg -1 ), and PA images were acquired at varied time points of post-injection (Figure 11c,e). Compared to the pre-contrast image, it is clear that the intensity of PA signal increases from 0.37 a.u. to 0.85 a.u., and the tumor site is gradually enlightened, showing a maximum signal in around 24 h post-injection, largely due to the accumulation of nanosheets through the EPR effect. Thereafter, the signal of the tumor site starts to decrease, suggesting that the nanosheets captured by tumor tissue are being gradually excreted out. S25
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