Two-Dimensional Atomically Thin Tin-Based Fluorescent Oxide

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Two-dimensional atomically thin tin based fluorescent oxide synthesized at ambient temperature and its biomedical applications Nallin Sharma, Sunil Pandey, Amit Kumar Sharma, and Hui-Fen Wu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05589 • Publication Date (Web): 22 Feb 2019 Downloaded from http://pubs.acs.org on February 22, 2019

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ACS Sustainable Chemistry & Engineering

Two-dimensional atomically thin tin based fluorescent oxide synthesized at ambient temperature and its biomedical applications Nallin Sharma†1, Sunil Pandey†1, Amit Kumar Sharma†1, Hui-Fen Wu*1, 2, 3, 4 1Department

of Chemistry, National Sun Yat-Sen University, Kaohsiung, 70, Lien-Hai Road, Kaohsiung, 80424, Taiwan 2Doctoral

Degree Program in Marine Biotechnology, National Sun Yat-Sen University, and Academia Sinica, Kaohsiung, 80424, Taiwan 3School

of Pharmacy, Kaohsiung Medical University, Kaohsiung, 807, Taiwan

4Institute

of Medical Science and Technology, National Sun Yat-Sen University, Kaohsiung, 80424, Taiwan *Corresponding author, Phone: +886-7-5252000-3955; Fax: +886-7-5253909 Email: [email protected] † Authors have equal contribution

Abstract Synthesis of atomically thin tin oxide nanosheets using non-hydrolytic sol-gel method at ambient temperature is reported in the present work. After 10 minutes of probe sonication and 7 days of incubation at ambient temperature, ultra-thin tin oxide nanosheets (SnONS) of 2nm to 5µm were formed due to interaction between tin chloride and acetone. The most up surging property of SnONS was inherent yellow fluorescence (λex= 420 and λem= 540nm), phenomenon rarely reported with respect to tin based nanosheets. The relative quantum yield of SnONS was ~16%. The origin of fluorescence in SnONS is speculated to originate from multiple transition in oxygen states of Sn, as confirmed by X-ray photoelectron spectroscopy. For biological applications SnONS were phase transferred from acetone to water without compromising the fluorescent properties of SnONS. Image cytometry (Nucleo-Counter® NC-3000™) and laser confocal microscopy were used for comprehending the cellular biocompatibility and internalization of nanoparticles inside the cells (biological imaging). With respect to control (100%) viability and vitality of the cancer cells were found to be 60.4 and 64% respectively after 12 hours of interaction with SnONS.

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Key Words: Atomically thin Tin oxide nanosheets, Non-hydrolytic sol-gel, yellow fluorescence, oxygen vacancies, Biological Imaging, Introduction In the pursuit of deciphering the intrinsic properties of materials in various dimensions, there are massive efforts to alter the properties of novel nanomaterials over last few decades 1–5. By carving the size and shape of the nanomaterials, their unique optical and physical properties can be conveniently unmasked

6

and explored for battery of biological applications. Recently, lower

dimensional materials have gained tremendous fame for applications in electronics and medicine 7.

These nanomaterials typically range from two dimensional (2D) to quasi-1D nanotubes and

wires and finally to zero-dimensional (0D) quantum dots 8. After the exemplary success in the discovery of 2D graphene, there is a flood of numerous 2D materials called nano-flakes or nanosheets, recognized by their typical molecular thickness 9. Two-dimensional materials belonging to group IV elements exhibit interesting optical properties owing to their delocalized electron networks

10.

Nano-sheets or nano-flakes exhibit very high surface area and unique optical

properties generated due to unidirectional quantum confinement 11. Among metallic nano-sheets, transition metal dichalcogenides (TMDs) and transition metal oxide (TMOs) are widely explored nano-sheets. MoS2, WS2, etc. and MoO3 and oxygen deficient MoO3-x nano-sheets are some typical examples that are investigated recently for chemical and biological applications

12–18.

Another

important category of metallic nanomaterials is semiconductor metal oxides such as TiO2, BiWO6 and ZnO

19–22.

Tin or Sn occupy a special place among elements of group IV due to spin-orbit

coupling, an ideal property for many electronic applications such as topological insulators 10. Due to its unique properties, tin oxide nanostructures have been fabricated in 2D and 0D recently. 0D tin oxide quantum dots have been used intensively for solar cell

23,24,

transparent conducting

electrodes 25, and sensors for detecting gases 26. Despite several attempts, fabrication of atomically thin oxide remains an exasperating task, particularly in liquid-based exfoliation system. Highly sophisticated tools have been exploited for synthesis of ultra-thin tin based 2D structures

27–30,

which demands a more facile approach for

synthesis of ultrathin tin oxide nanosheets. Non-hydrolytic sol-gel method is extremely trusted for synthesis of metal oxide nanoparticles over past few years31–34. In the present work, non-hydrolytic 2|Page ACS Paragon Plus Environment

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sol-gel method is exploited for the synthesis of atomically thin SnONS in acetone at ambient temperature. The entire process of SnONS was achieved in 7 days at ambient temperature. The most striking property of the SnONS was inherent yellow fluorescence after 7 days of incubation, a unique trait, which unlocks plethora of biomedical applications. Non-hydrolytic sol-gel, unlike other water-based sol-gel methods, is ideal for chiseling the size of materials to nanoscale as well as obtaining high stability of the nano-materials and purity at ambient temperature35. Moreover, water-based sol-gel methods are highly complicated due to the multiple roles of water as ligand and solvent in controlling the significant steps in sol-gel synthesis such as condensation and aggregation 36. For biomedical applications like bio-imaging and bio-sensors, the solubility as well as optical properties of the SnONS becomes quintessential aspect. The aqueous solubility of fluorescent SnONS was achieved simple method involving rotary evaporation at 70°C, without compromising the inherent fluorescence of SnONS. Due to high aqueous stability, achieved after the simple processing, SnONS were used for biological imaging of A549 cells. Also, the biocompatibility of SnONS was studied using NucleoCounter® NC-3000™. The overall results were highly promising, thus proving the significance of proposed material for biomedical applications. Materials and Methods Materials Tin Chloride (SnCl2) was purchased from Alfa aeser, USA. Acetone used in the experiment was HPLC grade, purchased from J.T. Baker, USA. Blood used for biocompatibility assays were donated voluntarily by lab members. A549 cells were procured from the Bioresource Collection and Research Center (BCRC), Taiwan. Culture medium F12K medium was procured from Sigma, UK. Fetal bovine serum (FBS) was procured from HyClone Culture Media (GE Healthcare, USA) and Pen-Strep from Sigma, UK. Phosphate buffered saline (PBS) was used at pH 7.4 and DI water was used throughout the experiment as aqueous diluent wherever necessary. Non-hydrolytic sol-gel method for synthesis of SnONS The entire synthesis of SnONS was done as follows: 100 mg of anhydrous tin chloride (SnCl2) was dissolved in 10 ml of analytical grade acetone and probe sonicated for 20 minutes (20W, 10 sec. ON and 2 sec. OFF cycle). The resulting solution was incubated at ambient temperature for 7 days 3|Page ACS Paragon Plus Environment


and opto-morphological changes in the structure was recorded periodically. The reaction is completed after 7 days till the color of the solution turns dark red when observed under ambient light. The green fluorescence was observed after 3 days and becomes yellow under UV lamp (λem=365nm). The dark red solution was collected carefully and subjected to rotary evaporation till dark red viscous slurry was observed. To this solution, appropriate amount of water is added (fluorescence of SnONS was highly sensitive to ratio of slurry and water) and stored for further use. Cell culture and in vitro biocompatibility A549 lung cancer cell lines were cultured using F12K media supplemented with 10% FBS and Pen-Strep. The cells were passaged till they obtained stable 80% confluency in T-25 flasks (obtained after passage #3). The cells were used for further experiments after they attained a cell density of 2 x 106 cells/ml. 0.35mg/ml of SnONS were mixed with ~106 and allowed to interact for 12 hours at 37°C. 19 µl of above solution was mixed with 1 µl of reaction solution 13 provided by the company. Samples were loaded on specialized A8 and studied for viability. For cell vitality, the samples were mixed with solution 5 and above procedure was performed. The results were compared with relevant controls. Optical stability of SnONS was assessed in different pH, serum, salt and various metals commonly encountered in biological system. Biological Imaging and Hemocompatibility To facilitate the entry of nanosheets inside the biological cells, the bigger particles were separated by centrifugation of aqueous SnONS solution at 6000 rpm for 5 minutes. The supernatant was collected and mixed with ~104 cells/ml. After a short incubation of 3 hours, the cells were observed using live 3D imaging system. Hemolysis studies were performed as per earlier method37. 100% hemolysis (+ve) was induced by treating red blood cells using Triton X 100 and PBS was used as negative control (-ve, 1.4 ml PBS was added in 600µl of red blood cells). Various volumes of SnONS (50, 40, 30, 20, 10µl) was added in 600µl of blood cells and further diluted using 14 ml PBS (pH 7). After incubation for 5 minutes the absorbance at 540 nm was recorded and results were interpreted based on positive control. Characterization of Fluorescent SnONS Optical characterization such as UV-Vis absorption spectroscopy was conducted using Evolution™ 201 (Thermo Fisher, USA) and fluorescence spectroscopic readings were recorded 4|Page ACS Paragon Plus Environment

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using Hitachi Fluorescence Spectrophotometer F-2700 (Hitachi, Japan). Time-resolved Photoluminescence (TRPL) for fluorescence lifetime and decay was studied on Edinburgh Instruments OB920 Time-Resolved and SteadyState Fluorescence Spectrometer (Edinburgh Instruments, UK). Transmission Electron Microscopy (TEM) and High-Resolution TEM (HOURSTEM) for analyzing the morphology of nanosheets was done using Philips CM200 (Philips, Netherlands) and JEOL 3010 AEM (JEOL, Japan) respectively. Samples were prepared using dilute concentrations of SnONs was drop cast on copper grids and dried in an oven at 60℃ overnight. CrysTBox (Czechia) crystallography tools software was used to analyze the SAED patterns for developing representative cartoons for SnONs nanosheets. Atomic Force Microscopy (AFM) was done using Digital Instruments Nanoscope III SPM Scanning Probe AFM. μRaman spectroscopy was carried out by HORIBA HOURS800 using 633nm laser at 16mW power with 1800 grating; the sample was used as the prepared for AFM study. Electrochemical analysis of nanomaterials was conducted on CHI Instruments D800 (CH Instruments, USA) with Pt, Ag/AgCl & Glassy carbon electrode as a counter, reference & working electrodes respectively. Cellular imaging fo A549 cells were carried out on Olympus FV 1000 Confocal Laser scanning microscope at excitation 405nm and emission at 515nm. Cellular viability and vitality assays 100 were done on NucleoCounter® NC-3000™ (Chemometec, Denmark).

Results and Discussions Non-hydrolytic sol-gel method for synthesis of SnONS Atomically thin fluorescent tin oxide nanosheets were synthesized in three cardinal steps as depicted in the scheme1. Primarily, solution of SnCl2 and acetone was sonicated (20W, 2 Sec ON and 5 sec OFF cycle) for 10 minutes to initiate the formation of 2D nanosheets (Step1). Promptly after the sonication, clear mixture of acetone and SnCl2 was kept undisturbed for 7 days at ambient temperature (Step 2). This step is called “non-hydrolytic sol-gel method”, most commonly used for synthesis of metal oxide nanoparticles35,36,38. The time dependent changes in color of the solution was key indicator of completion of the reaction. The color of the solution was transformed to clear yellow after 3 days (Fig. 1A, Bright light). The solution turns blood red after 7 days of incubation, thus indicating the completion of formation of fluorescent SnONS (Fig. 1A, Bright light). A significant observation was formation of white precipitate after completion of the reaction 5|Page ACS Paragon Plus Environment


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(day 7), an important feature of non-hydrolytic sol-gel method. This step is called aggregation which initiates the formation of nanoparticles at the liquid solid interface35,39. The photograph represented in Fig. 1c (bright light) are supernatant collected periodically. The wide spread hydrolytic or aqueous sol-gel method suffer from certain fundamental problems rending it suitable for metal oxide nanoparticles synthesis36. High reactivity of metal oxide and dual role of water as ligand and solvent makes significant chemical reaction like condensation and aggregation on a daunting task to control. Due to these complexities, it becomes rather challenging task to control the morphology of nanoparticles, also, the nanoparticles are amorphous. Other hand nonhydrolytic/ sol-gel method discourage the involvement of water; which exclude some fundamental thermodynamic barriers posed by water

36.

Moreover, in the present case, acetone provides

oxygen35 and control significant parameters such as shape, size and crystallinity of the nanomaterials. The C=O bond associated with acetone has slow reaction rate, leading to synthesis of crystalline structure along C the stability of nanomaterials in the solution

39.

Due to such

fundamental properties metal oxide, especially tin-based oxides were used for detection of acetone for a long time 40–43. In step III, the transformation of SnONS from acetone to water is explained for biological applications like Bio-imaging, sensors, etc. it is mandatory to make the nanoparticles stable in aqueous Solution. The red solution (fig.1A, upper panel) final (day 7); was concentrated/ precipitated by rotary evaporation to obtain red slurry. Relevant amount of water was added (1:5 slurry to water) and solution was stirred for 10 minutes. This aqueous solution of SnONS was used for further experimental considerations. To explore the possibility of other solvents, we carried out the similar reaction with ethanol, toluene, n-hexane, and pyridine. As shown in Fig. S1 (A-D), none of the solvents produced any fluorescence even after 20 days of incubation thus proving the usefulness of acetone in the present synthesis strategy. Optical properties of SnONS UV-visible analysis (Figure 1B) shows time dependent changes in the optical spectra. Immediately after sonication, a decay curve can be seen with no obvious peak. The emergence of the peak at ~330nm along with a hump at ~490nm can be observed at day 2. The peaks become more interesting at day 3 when hint of green fluorescence appears as displayed in figure 1A (UV light). There was a decrease in the intensity of the peak at 330nm and enhancement at 430nm. After 6|Page ACS Paragon Plus Environment

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completion of the reaction at day 7 (final), there was a significant enhancement in both the peaks. As discussed earlier the solution turns bright red (indicator of completion, fig. 1A, Bright light) and yellow fluorescence can be observed after completion of the reaction (fig. 1A, UV light, Day 7). The stability of the SnONS solution was scrutinized for 30 days. After incubation of solution for 30 days, month, fluorescence as well as peaks at 490 and 430 nm disappear and the peak at 330 nm remains same. These finding helps us to speculate the cardinal role of peaks beyond 400 nm at the instigation of fluorescence. The lateral dimension and thickness of the nanosheets can bring these spectral changes. A prominent peak at ~430 nm is quite unusual for tin oxide nanomaterials by the earlier findings10,44. This peaks might be associated with the fluorescence of nano-sheets and a subject of further investigation with respect to concrete mechanism of inception of fluorescence in SnONS. Figure S2 shows absorption of SnCl2 in various other solvents such as ethanol, toluene, n-hexane and pyridine (fig. S2 A-D). As evident from the data, no signature peaks of fluorescent SnONS can be observed. Most of the peaks were in the range of 200-300 nm with slight change in pyridine (~320 nm, fig. S2D). As mentioned earlier, these peaks are not associated with fluorescent SnONS synthesized in acetone.



Scheme 1: Schematic representation of key steps involved in the synthesis of yellow fluorescent Tin Oxide nanosheets and aqueous transformation of the same. The entire process takes place in multiple steps of sonication and non-hydrolytic sol gel synthesis at ambient temperature. 8|Page ACS Paragon Plus Environment

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Fig. 1: (A) Time-dependent absorption spectrometry of formation of fluorescent SnONS. (B) Fluorescence spectroscopy of SnONS at day 5, days 6 and day 7 and the highest of Day Final (max intensity) of incubation. The Red sift in emission can be seen with the increase in the time of interaction between acetone and tin chloride. (C) Image representing bright light (upper panel) and under UV lamp exposure (lower panel) of fluorescent SnONS.



Figure 1C shows the fluorescence spectra of SnONS collected after 3-7 days of incubation. As evident from fig. 1A (UV light), the inception of fluorescence take place at day 3 and the corresponding emission at ~500 nm (fig. 1C, Day 4) can be observed. For day 5 and 6, the fluorescence becomes brighter (fig. 1A, Bright light, Day 5-6), there was enhancement in the intensity of peak at 520 nm. However, after the completion of the reaction (Day 7), a red shifted peak at 542 nm was observed (fig. 1C, Day 7) along with yellow fluorescence (UV light, Day 7). The red shift of ~22 nm could be due to transition in the oxidation states from SnO to SnO1.65 as supported by XPS (fig. 3). Inception of fluorescence can be attributed to electron hopping among multiple oxidations of Sn which is discussed in fig. 3 and S3. The quantum yield of SnONS (𝝋𝑺) was calculated using quinine sulfate (0.125 mM prepared in H2SO4) as standard solution (quantum yield 𝝋𝑺𝒕𝒅 = 54.9%) based on the following equation: 𝑭(𝑨𝑼𝑪)𝑺𝒕𝒅 𝑨𝒃𝒔𝑺 𝜼𝑺𝒕𝒅

𝝋𝒔 = 𝝋𝑺𝒕𝒅 𝑭(𝑨𝑼𝑪)𝒔 𝑨𝒃𝒔𝑺𝒕𝒅 𝜼𝒔 ………….… (1) where 𝐹(𝐴𝑈𝐶)𝑆𝑡𝑑 and 𝐹(𝐴𝑈𝐶)𝑆 represent the area under curve of the fluorescence curve from standard and the sample solution; 𝐴𝑏𝑠𝑆𝑡𝑑 and 𝐴𝑏𝑠𝑆 represent maximum absorbance of standard and sample solution; 𝜂𝑆𝑡𝑑 and 𝜂𝑆 represent refractive index of standard and sample solution respectively. The quantum yield was calculated to be 15.88% with reference to quinine sulfate. To venture more into the fluorescent properties of SnONs nano-sheets, time-resolved photoluminescence spectra was performed (fig. 2A). Exciton at 420nm is having a maximum intensity of 3 x 102 counts; shows a short lifespan photo decay of τ2 of 2.27 nm and τ one 9.84nm. Short-lived, ~80ns photoluminescence suggests higher recombination rate for SnONS nanosheet. The trap states introduced by different ratios of O2- ions lead to trapping of the electron from the conduction band; whereas the deep trap states are responsible for trapping of the holes from the valence band. Eventually, the trapped electrons and holes eject fast form trap states via tunneling and recombine radiatively; this is in whole the photoemission thorough shallow and deep trap states. 3.5eV broad bandgap with high recombination rate arises two possibilities, the trapping of electrons in the shallow traps followed by their radiative recombination after escaping from these

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trap states or radiative recombination of photo-injected electron-hole pairs when the holes recombine with electrons after de-trapping from the deep trap levels through tunneling effect.

Fig. 2: (A) Time-resolved photoluminescence study of day final SnONs; (B) Band gap analysis for the time-dependent day representing synthesis of SnONs. The optical Band gap of the tin oxide nano-sheets in (fig 2B) was calculated using Tauc’s plot45. The optical band gap of the nano-sheets was dependent on the time of interaction between the precursor and acetone at ambient temperature. The average band gap of the nanosheets was ~3.65 eV, which signifies the formation of SnONS nanostructures46 and quantum confined twodimensional nanosheets in our case. The optical band gap decreases from ~3.65 eV to 3.5eV concerning time as seen in the fig. 2B. This slight alteration in the band gap could be due to the number of layers associated with tin oxide nano-sheets. In fig. 3, the peaks indicated by Xray photelectron spectroscopy details vaious Sn sates namely as Sn(0) metal, SnO, SnO2, SnO1.65. All the peaks are assigned as per the standard data provided by NIST47. As shown in figure 3(A) the final day elemental scan of Sn shows Sn3d5/2 and Sn3d3/2 having various deconvoluted states Sn 3d5/2 peak namely SnO(485.6), Sn(0) metal(486.4), SnO1.65(486.8); Sn 3d3/2 shows peaks at SnO(494.5) and SnO1.65(495.25). Oxygen 1s in fig 3(B) shows increase in SnO(530.2) and SnO1.65(530.6) where as contrasting decrease in SnO2(531.7) confirminutesg the changes in the oxidation states in SnONS supporting the emergence of fluoroscene due to varying oxidation to the Surface of SnONS.



Fig. 3(A) Elemental scan of 3d5/2 and 3d3/2 states of Sn showing peaks for SnO, Sn metal SnO1.65 and SnO2 at 485.6, 486.4, 486.8 and 495.2 eV respectively in final (day 7) SnONS. (B) Showing various Oxygen bonding with Sn as SnO, SnO1.65, and SnO2 at 530.2, 530.6 and 531.7 eV respectively.

On comparing the Xray photoelectron spectroscopy peaks of final day from the initail and transient days in fig S3 graph showing (i) and (ii) for initial(day 1) and transient(day 3) day respectively, changes can be seen in the Sn 3d5/2 and 3d3/2 states such as prominutesent increase in SnO and SnO1.65 oxidative Sn states over Sn(0) metal and SnO2 in Oxygen 1s states from SnO2(495.3) to SnO1.65(495.25) which is further noted in day final states. with the incubation days are also supported by the optical bandgap calculation and tauc’s plot above in fig. 2B. Morphological studies of tin oxide nanosheets SnONs After sonication of SnCl2 and acetone solution for 10 minutes, 2D nanosheets of 2nm-5µm can be seen in fig. S4A and B. This justifies the role sonication in 2D transformation of the nanosheet. HrTEM image (Fig. 4B) show distinct stacking behavior of few atomic Sn sheets with the lattice fringes width of 0.43±0.04 nm. The moiré pattern can be observed in the higher stacked sheets in (Fig.4B) with the overlapped lattice fringes. SAED show hexagonal arrangement with bright diffracted spots corresponding to (011) and (110) plane orientation of tin oxide nanosheets similar to as earlier reported h-BN 48 and MoS2 49.


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Fig. 4: (A) TEM representative of SnONS sheets; (B) HrTEM representative of selected area in TEM image showing lattice fringe width of 0.429nm (inset); (C) Cartoon representation of oxygen deficiency in SnONS sheets (blue: Sn; red: O); (D) & (E) SAED representative of SnONs; (F) Cartoon representing hexagonal symmetry of SnONS

AFM (Fig. 5A, 4D) show the sheet of tin oxide having size and thickness height profiling data show ~1.3nm and ~1.7nm (Fig 5B, 5D). To show the multiple stacking as shows in HrTEM image (Fig. 4B). Obtained AFM data and images are in good coordination to some earlier findings 27,50. The various thickness could be attributed to the presence of unstable oxidation of tin oxide.



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Fig. 5: (A) AFM analysis highlighting the particular area of the sheet; (B) Height profile of marked area relatable to 1.3nm from the sheet in A; (C) AFM image of another area in the sheet; (D) Height profile analysis of marked area in C; Structural analysis using Raman Spectroscopy and Electrochemical studies To elucidate the formation of SnONS, the spectroscopic analysis from Raman is strongly dependent upon the local bonding sites as well as to its corresponding global band structure. We performed Micro Raman of samples at different time intervals (Fig. 6A). As displayed immediately after the sonication of tin chloride and acetone (marked initial), the presence of elemental tin 113 cm-1 can be clearly witnessed yet there is a shift in our observation as a contrast to previous finding

10.

However, there was a significant change in the Raman spectra with the time of incubation. After 3 days (transient) showing Eg and A1g peaks positioned at 113 and 211cm-1. At this stage, the instigation of fluorescence occurs (Fig. 1A) probably due to the presence of mixed oxidation states of tin oxides as several small vibrations are observed in the range of 400-700 cm-1. The presence of mixed oxidation states leads to electron transfer between the two oxidation states as supported by XPS. Finally, after 7 days of the interaction between acetone and tin chloride, the presence (marked final) of SnO having Eg and A1g prominent at peak positioned 117 and wide stretched 211 cm-1 well known from literature 51,52. and SnO2 having modes A1g, A2u and B2g modes at 604, LO mode vibration positioned at 698 and 853cm-1 respectively are in well agreement to the literature 14 | P a g e ACS Paragon Plus Environment

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53,54 can be observed based on the Raman spectra the peaks associated with SnO and SnO

2 becomes

more prominent (Fig. 6A). CHI D800 was used for cyclic voltammetry studies taking Ag/AgCl as reference and Pt as the counter electrode. Before analysis, Ar gas was purged into the test cell to eliminate any possibility of free radical. Later to avoid atmospheric oxygen diffusion continuous optimized Ar flow was maintained. In the figure, comparative analysis for as-synthesized Tin sheets. The occurrence of the anodic peak at the potential of 0.3V indicating strong potential for StONs2 in inset whereas in comparison to the one in acetone shows no such wave at this potential yet emergence of small Sn potential at -0.17V for which no other state is prominent in the CV curve. These results prominutesent the mixed association of SnONS oxidative states of tin oxide.

Fig. 6: (A) Raman analysis highlighting signature peaks atomically thin tin oxide nanosheets SnONs (B) Cyclic voltammograms of SnONS nanosheets showing typical redox properties with Initial and Final (inset) states. 3D cell Imaging, Cell vitality, and Biocompatibility studies Fig. 7A shows 3D laser confocal microscopy images of A549 cancer cell treated with fluorescent SnONs. The image contains smaller SnONS within the bulk of cells and more concentrated towards the periphery. The larger lateral size of SnONS (as shown in TEM analysis) is incompetent to enter the cell thorough endocytosis. The microenvironment of cancer cell allows particles of no more than 40nm to enter the cells for efficient bioimaging applications of the nanomaterial. To circumvent this issue, an appropriate amount of SnONS was centrifuged to remove the larger



particles. The supernatant was supposed to contain smaller fine sheets of SnONS and hence used as labeling agent.

The cells were incubated with 300µl of SnONS for 12 h. Figure 7A and 7B represent the bright field and fluorescent images of A549 cells treated with SnONS after its internalization in the cell. It was found that at even at such low concentration and in cellular microenvironment, the nanomaterial was stable enough to exhibit strong fluorescent signals. The merged image of both bright field and dark field is shown in Fig. 7C. Fig. 7D shows the hemocompatibility assessment of SnONS. The red blood cells were incubated with different volumes (10-50µ) SnONS. It was found that the nanomaterial had negligible inimical effect on hemolysis of blood cells at 30µl (~5%) solution when compared with +ve (100% hemolysis induced by 10 mM Triton X100) and -ve control (induced by adding DI water). The cellular viability analysis is based on the number of live and dead cells while cellular vitality is the assessment of healthy cells in a total population of living cells in the sample. In comparison to the viable cells in the control sample (Fig. S6), cells treated with SnONS exhibit more than 60% viability at a density of 2x106 cells/ml. The vitality index represents more than 65% healthy cells in the live cell population (Fig. S7). The results suggest that fluorescent SnONS is highly biocompatible with least damage to cellular physiology.


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Fig. 7: (A) Bright field image of A549 cancer cell using Laser confocal microscopy; (B) Fluorescence image of cancer cells incubated with SnONS; (C) Merged image of bright and fluorescence image (D) Concentration-dependent hemolysis activity of SnONS incubated with blood samples at 37℃ for 30 minutes and absorbance recorded at 540 nm. The comprehensive response of SnONS in vitro with cancer cells and human blood was taken a step forward to analyze the change in its characteristic properties under influence of serum components such as common metal salts and varying pH ranges. The metal concentrations usually found in serum such as Cu (2.83-5.5 µM/L), Zn (0.66-1.0 µg/ml), Fe (55-160 µg/dL), Cr (1.3-2.2 µg/ml in blood), Co (0.9-3.4 µg/ml) were used to analyze the change in the optical properties of SnONs. The signature absorbance of SnONS @ 243 nm was found to be stable in all the salt concentrations (Fig. S6) when compared with controls. There was a minutesor change in the intensity at 243 nm (characteristic peak of SnONS) arising due to dilution or probably surface interaction with the metals. However, largely this change does not signify substantial modification in the morphology of SnONS and thus suggesting its stability at such metal concentrations. The fluorescence response of the SnONS was found to be more robust where there was no significant 17 | P a g e ACS Paragon Plus Environment


change in the intensities at 520 nm following excitation at 420 nm wavelength. This is also indicative of the stable fluorescence of the metal oxide. The enhancement of fluorescence in presence of Cr and other metal is due to profoundly known phenomenon called metal enhanced fluorescence, commonly observed in various earlier work55–57 At different pH levels, from pH 5 to 9, we found that absorption intensity at 243 nm was significantly high at pH 9 while least at pH 7 (Fig. S5). Such a drastic change in absorption intensity indicate the formation of larger particles of SnONS at alkaline conditions which may attribute to the breakdown of surface defects due to oxygen and stabilization by hydroxyl radicals. At pH 7, the change in absorption intensity at 243 nm indicate the morphological stability of SnONS. This also complies with its stable response in vitro conditions. The fluorescence signals remained nearly less deviating with relatively highest at pH 6 and 7. Conclusion Non-hydrolytic or non-aqueous sol-gel method is an exceptionally significant way for synthesis of fluorescent atomically thin SnONS using acetone as stabilizer as well as oxygen donor. The entire reaction was carried out at ambient temperature, thus making the proposed method highly economical and eco-friendly. After ~7 days of incubation, ultrathin nano-sheets of 2nm to 5µm was observed along with yellow fluorescence (Quantum yield ~16%) under UV light. Fluorescent SnONS exhibited high optical-stability and bio-compatibility after phase transfer from acetone to water. Owing to fluorescence in water, SnONS was successfully used for biologically imaging using laser confocal microscopy. Overall, fluoresce in 2D nano-sheets like tin oxides can unlock many crucial applications like drug delivery, bio-sensors and biological imaging. Acknowledgment We thank the Ministry of Science and Technology (MOST), Taiwan for supporting this work with the grant number of MOST 107-2113-M-110-011-MY3.

References (1)

Xing, Z.; Tian, J.; Asiri, A. M.; Qusti, A. H.; Al-Youbi, A. O.; Sun, X. Two-Dimensional Hybrid Mesoporous Fe2O3–graphene Nanostructures: A Highly Active and Reusable


Page 18 of 26

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


Peroxidase Mimetic toward Rapid, Highly Sensitive Optical Detection of Glucose. Biosens. Bioelectron. 2014, 52, 452–457. DOI: 10.1016/j.bios.2013.09.029. (2)

Kalantar-zadeh, K.; Ou, J. Z.; Daeneke, T.; Mitchell, A.; Sasaki, T.; Fuhrer, M. S. Two Dimensional and Layered Transition Metal Oxides. Applied Materials Today. 2016, pp 73–89. DOI: 10.1016/j.apmt.2016.09.012.

(3)

Chen, Y.; Wang, L.; Shi, J. Two-Dimensional Non-Carbonaceous Materials-Enabled Efficient Photothermal Cancer Therapy. Nano Today. 2016, pp 292–308. DOI: 10.1016/j.nantod.2016.05.009.

(4)

Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5 (4), 263–275. DOI: 10.1038/nchem.1589.

(5)

Sharker, S. M.; Kim, S. M.; Lee, J. E.; Choi, K. H.; Shin, G.; Lee, S.; Lee, K. D.; Jeong, J. H.; Lee, H.; Park, S. Y. Functionalized Biocompatible WO3 Nanoparticles for Triggered and Targeted in Vitro and in Vivo Photothermal Therapy. J. Control. Release 2015, 217, 211–220. DOI: 10.1016/j.jconrel.2015.09.010.

(6)

Bhimanapati, G. R.; Lin, Z.; Meunier, V.; Jung, Y.; Cha, J.; Das, S.; Xiao, D.; Son, Y.; Strano, M. S.; Cooper, V. R.; et al. Recent Advances in Two-Dimensional Materials beyond Graphene. ACS Nano. 2015, pp 11509–11539. DOI: 10.1021/acsnano.5b05556.

(7)

Wilcoxon, J. P.; Abrams, B. L. Synthesis, Structure and Properties of Metal Nanoclusters. Chem. Soc. Rev. 2006, 35 (11), 1162–1194. DOI: 10.1039/b517312b.

(8)

Tiwari, J. N.; Tiwari, R. N.; Kim, K. S. Zero-Dimensional, One-Dimensional, TwoDimensional and Three-Dimensional Nanostructured Materials for Advanced Electrochemical Energy Devices. Progress in Materials Science. 2012, pp 724–803. DOI: 10.1016/j.pmatsci.2011.08.003.

(9)

Xie, J. Le; Guo, C. X.; Li, C. M. Construction of One-Dimensional Nanostructures on Graphene for Efficient Energy Conversion and Storage. Energy Environ. Sci. 2014, 7 (8), 2559. DOI: 10.1039/C4EE00531G.

(10)

Chaudhary, R. P.; Saxena, S.; Shukla, S. Optical Properties of Stanene. Nanotechnology



2016, 27 (49). DOI: 10.1088/0957-4484/27/49/495701. (11)

Bouet, C.; Tessier, M. D.; Ithurria, S.; Mahler, B.; Nadal, B.; Dubertret, B. Flat Colloidal Semiconductor Nanoplatelets. Chemistry of Materials. 2013, pp 1262–1271. DOI: 10.1021/cm303786a.

(12)

Pastrana, Y. A.; Torres, J.; López-Carreño, L. D.; Martínez, H. M. The Influence of Oxygen on the Structural and Optical Properties of MoO3 Thin Films Prepared Using the Laser-Assisted Evaporation Technique. J. Supercond. Nov. Magn. 2013, 26 (7), 2475– 2478. DOI: 10.1007/s10948-012-1721-z.

(13)

Alsaif, M. M. Y. A.; Latham, K.; Field, M. R.; Yao, D. D.; Medhekar, N. V.; Beane, G. A.; Kaner, R. B.; Russo, S. P.; Ou, J. Z.; Kalantar-Zadeh, K. Tunable Plasmon Resonances in Two-Dimensional Molybdenum Oxide Nanoflakes. Adv. Mater. 2014, 26 (23), 3931– 3937. DOI: 10.1002/adma.201306097.

(14)

Balendhran, S.; Walia, S.; Nili, H.; Ou, J. Z.; Zhuiykov, S.; Kaner, R. B.; Sriram, S.; Bhaskaran, M.; Kalantar-Zadeh, K. Two-Dimensional Molybdenum Trioxide and Dichalcogenides. Adv. Funct. Mater. 2013, 23 (32), 3952–3970. DOI: 10.1002/adfm.201300125.

(15)

Liu, T.; Wang, C.; Gu, X.; Gong, H.; Cheng, L.; Shi, X.; Feng, L.; Sun, B.; Liu, Z. Drug Delivery with PEGylated MoS2 Nano-Sheets for Combined Photothermal and Chemotherapy of Cancer. Adv. Mater. 2014, 26 (21), 3433–3440. DOI: 10.1002/adma.201305256.

(16)

Cheng, L.; Liu, J.; Gu, X.; Gong, H.; Shi, X.; Liu, T.; Wang, C.; Wang, X.; Liu, G.; Xing, H.; et al. PEGylated WS2 Nanosheets as a Multifunctional Theranostic Agent for in Vivo Dual-Modal CT/Photoacoustic Imaging Guided Photothermal Therapy. Adv. Mater. 2014, 26 (12), 1886–1893. DOI: 10.1002/adma.201304497.

(17)

Pandey, S.; Sharma, A. K.; Sharma, K. H.; Nerthigan, Y.; Khan, M. S.; Hang, D.-R.; Wu, H.-F. Rapid Naked Eye Detection of Alkaline Phosphatase Using α-MoO3-x Nano-Flakes. Sensors Actuators B Chem. 2018, 254, 514–518. DOI: 10.1016/j.snb.2017.06.123.

(18)

Hang, D.-R.; Sharma, K. H.; Chen, C.-H.; Islam, S. E. Enhanced Photocatalytic


Page 20 of 26

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


Performance of ZnO Nanorods Coupled by Two-Dimensional α-MoO3 Nanoflakes under UV and Visible Light Irradiation. Chem. – A Eur. J. 2016, 22 (36), 12777–12784. DOI: 10.1002/chem.201602141. (19)

Vinodgopal, K.; Bedja, I.; Kamat, P. V. Nanostructured Semiconductor Films for Photocatalysis . Photoelectrochemical Behavior of SnO2/TiO2 Composite Systems and Its Role in Photocatalytic Degradation of a Textile Azo Dye. Analyzer 1996, 4756 (33), 2180–2187. DOI: 10.1021/cm950425y.

(20)

Zhou, Y.; Zhang, Q.; Lin, Y. H.; Antonova, E.; Bensch, W.; Patzke, G. R. One-Step Hydrothermal Synthesis of Hierarchical Ag/Bi2WO6 Composites: In Situ Growth Monitoring and Photocatalytic Activity Studies. Sci. China-Chemistry 2013, 56 (4), 435– 442. DOI: 10.1007/S11426-013-4846-4.

(21)

Chakrabarti, S.; Dutta, B. K. Photocatalytic Degradation of Model Textile Dyes in Wastewater Using ZnO as Semiconductor Catalyst. J. Hazard. Mater. 2004, 112 (3), 269– 278. DOI: 10.1016/j.jhazmat.2004.05.013.

(22)

Wang, Y.; Wang, X.; Antonietti, M. Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: From Photochemistry to Multipurpose Catalysis to Sustainable Chemistry. Angewandte Chemie - International Edition. 2012, pp 68–89. DOI: 10.1002/anie.201101182.

(23)

Emin, S.; Singh, S. P.; Han, L.; Satoh, N.; Islam, A. Colloidal Quantum Dot Solar Cells. Sol. Energy 2011, 85 (6), 1264–1282. DOI: 10.1016/j.solener.2011.02.005.

(24)

Jun, H. K.; Careem, M. A.; Arof, A. K. Quantum Dot-Sensitized Solar Cells-Perspective and Recent Developments: A Review of Cd Chalcogenide Quantum Dots as Sensitizers. Renewable and Sustainable Energy Reviews. 2013, pp 148–167. DOI: 10.1016/j.rser.2013.01.030.

(25)

Minami, T. Transparent Conducting Oxide Semiconductors for Transparent Electrodes. Semicond. Sci. Technol. 2005, 20 (4), S35–S44. DOI: 10.1088/0268-1242/20/4/004.

(26)

Mosadegh Sedghi, S.; Mortazavi, Y.; Khodadadi, A. Low Temperature CO and CH4 Dual Selective Gas Sensor Using SnO2 Quantum Dots Prepared by Sonochemical Method.



Sensors Actuators, B Chem. 2010, 145 (1), 7–12. DOI: 10.1016/j.snb.2009.11.002. (27)

Zhu, F.; Chen, W.; Xu, Y.; Gao, C.; Guan, D.; Liu, C.; Qian, D.; Zhang, S.-C.; Jia, J. Epitaxial Growth of Two-Dimensional Stanene. Nat. Mater. 2015, 14 (10), 1020–1025. DOI: 10.1038/nmat4384.

(28)

Saxena, S.; Chaudhary, R. P.; Shukla, S. Stanene: Atomically Thick Free-Standing Layer of 2D Hexagonal Tin. Sci. Rep. 2016. DOI: DOI:10.1038/srep31073.

(29)

Xu, C. Z.; Chan, Y. H.; Chen, P.; Wang, X.; Flötotto, D.; Hlevyack, J. A.; Bian, G.; Mo, S. K.; Chou, M. Y.; Chiang, T. C. Gapped Electronic Structure of Epitaxial Stanene on InSb(111). Phys. Rev. B 2018. DOI: 10.1103/PhysRevB.97.035122.

(30)

Ezawa, M. Monolayer Topological Insulators: Silicene, Germanene, and Stanene. J. Phys. Soc. Japan 2015, 84 (12). DOI: 10.7566/JPSJ.84.121003.

(31)

Styskalik, A.; Skoda, D.; Barnes, C.; Pinkas, J. The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review. Catalysts 2017. DOI: 10.3390/catal7060168.

(32)

Debecker, D. P.; Hulea, V.; Mutin, P. H. Mesoporous Mixed Oxide Catalysts via NonHydrolytic Sol-Gel: A Review. Applied Catalysis A: General. 2013. DOI: 10.1016/j.apcata.2012.11.002.

(33)

Joo, J.; Kwon, S. G.; Yu, J. H.; Hyeon, T. Synthesis of ZnO Nanocrystals with Cone, Hexagonal Cone, and Rod Shapes via Non-Hydrolytic Ester Elimination Sol-Gel Reactions. Adv. Mater. 2005. DOI: 10.1002/adma.200402109.

(34)

Koo, B.; Park, J.; Kim, Y.; Choi, S. H.; Sung, Y. E.; Hyeon, T. Simultaneous Phase- and Size-Controlled Synthesis of TiO2nanorods via Non-Hydrolytic Sol-Gel Reaction of Syringe Pump Delivered Precursors. J. Phys. Chem. B 2006. DOI: 10.1021/jp065372u.

(35)

Niederberger, M. Nonaqueous Sol–Gel Routes to Metal Oxide Nanoparticles. Acc. Chem. Res. 2007, 40 (9), 793–800. DOI: 10.1021/ar600035e.

(36)

Corriu, R. J. P.; Leclercq, D. Recent Developments of Molecular Chemistry for Sol–Gel Processes. Angew. Chemie Int. Ed. English 1996. DOI: 10.1002/anie.199614201.

(37)

Pandey, S.; Sharma, K. H.; Sharma, A. K.; Nerthigan, Y.; Hang, D.-R.; Wu, H.-F.


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


Comparative Photothermal Performance among Various Sub-Stoichiometric 2D OxygenDeficient Molybdenum Oxide Nanoflakes and In Vivo Toxicity. Chem. - A Eur. J. 2018, 24 (29), 7417–7427. DOI: 10.1002/chem.201705734. (38)

Cozzoli, P. D.; Curri, M. L.; Agostiano, A.; Chimica, D.; Bari, U.; Orabona, V.; Chimico, P.; Ipcf, F. ZnO Nanocrystals by a Non-Hydrolytic Route : Synthesis and Characterization. Growth (Lakeland) 2003, 4756–4762. DOI: 10.1021/jp027533

(39)

Niederberger, M.; Garnweitner, G. Organic Reaction Pathways in the Nonaqueous Synthesis of Metal Oxide Nanoparticles. Chem. - A Eur. J. 2006. DOI: 10.1002/chem.200600313.

(40)

Kolmakov, A.; Zhang, Y.; Cheng, G.; Moskovits, M. Detection of CO and O2 Using Tin Oxide Nanowire Sensors. Adv. Mater. 2003, 15 (12), 997–1000. DOI: 10.1002/adma.200304889.

(41)

Mubeen, S.; Lai, M.; Zhang, T.; Lim, J. H.; Mulchandani, A.; Deshusses, M. A.; Myung, N. V. Hybrid Tin Oxide-SWNT Nanostructures Based Gas Sensor. Electrochim. Acta 2013, 92, 484–490. DOI: 10.1016/j.electacta.2013.01.029.

(42)

Mwakikunga, B. W.; Ray, S. S.; Mokwena, M.; Dewar, J.; Geibelhaus, I.; Singh, T.; Fischer, T.; Mathur, S. Tin Dioxide Nano-Wire Device for Sensing Kinetics of Acetone and Ethanol towards Diabetes Monitoring. In Proceedings of IEEE Sensors; 2013. DOI: 10.1109/ICSENS.2013.6688338.

(43)

Jiang, H.; Chu, G.; Gong, H.; Qiao, Q. Tin Chloride Catalysed Oxidation of Acetone with Hydrogen Peroxide to Tetrameric Acetone Peroxide. J. Chem. Res. 1999, 288–289. DOI: 10.1039/a809955c.

(44)

Tammina, S. K.; Mandal, B. K.; Ranjan, S.; Dasgupta, N. Cytotoxicity Study of Piper Nigrum Seed Mediated Synthesized SnO2 Nanoparticles towards Colorectal (HCT116) and Lung Cancer (A549) Cell Lines. J. Photochem. Photobiol. B Biol. 2017, 166, 158– 168. DOI: 10.1016/j.jphotobiol.2016.11.017.

(45)

Tauc, J.; Grigorovici, R.; Vancu, A. Optical Properties and Electronic Structure of Amorphous Germanium. Phys. status solidi 1966, 15 (2), 627–637. DOI:



10.1002/pssb.19660150224. (46)

Sun, G.; Qi, F.; Li, Y.; Wu, N.; Cao, J.; Zhang, S.; Wang, X.; Yi, G.; Bala, H.; Zhang, Z. Solvothermal Synthesis and Characterization of Ultrathin SnO Nanosheets. Mater. Lett. 2014, 118, 69–71. DOI: 10.1016/j.matlet.2013.12.048.

(47)

Alexander V. Naumkin, Anna Kraut-Vass, Stephen W. Gaarenstroom, and C. J. P. NIST X-ray Photoelectron Spectroscopy Database 20. DOI: 10.18434/T4T88K.

(48)

Song, L.; Ci, L.; Lu, H.; Sorokin, P. B.; Jin, C.; Ni, J.; Kvashnin, A. G.; Kvashnin, D. G.; Lou, J.; Yakobson, B. I.; et al. Large Scale Growth and Characterization of Atomic Hexagonal Boron Nitride Layers. Nano Lett. 2010, 10 (8), 3209–3215. DOI: 10.1021/nl1022139.

(49)

Zhan, Y.; Liu, Z.; Najmaei, S.; Ajayan, P. M.; Lou, J. Large-Area Vapor-Phase Growth and Characterization of MoS 2 Atomic Layers on a SiO 2 Substrate. Small 2012, 8 (7), 966–971. DOI:10.1002/smll.201102654.

(50)

Atkin, P.; Orrell-Trigg, R.; Zavabeti, A.; Mahmood, N.; Field, M. R.; Daeneke, T.; Cole, I. S.; Kalantar-zadeh, K. Evolution of 2D Tin Oxides on the Surface of Molten Tin. Chem. Commun. 2018, 54 (17), 2102–2105. DOI:10.1039/C7CC09040D.

(51)

Eifert, B.; Becker, M.; Reindl, C. T.; Giar, M.; Zheng, L.; Polity, A.; He, Y.; Heiliger, C.; Klar, P. J. Raman Studies of the Intermediate Tin-Oxide Phase. Phys. Rev. Mater. 2017, 1 (1), 014602. DOI:10.1103/PhysRevMaterials.1.014602.

(52)

Wang, X.; Zhang, F. X.; Loa, I.; Syassen, K.; Hanfland, M.; Mathis, Y.-L. Structural Properties, Infrared Reflectivity, and Raman Modes of SnO at High Pressure. Phys. status solidi 2004, 241 (14), 3168–3178. DOI:10.1002/pssb.200405231.

(53)

Wu, Q.-H.; Song, J.; Li, J. High Oxygen Vacancy Tin Oxide Synthesized by Combustion Chemical Vapor Deposition (CCVD). Surf. Interface Anal. 2008, 40 (11), 1488–1492. DOI:10.1002/sia.2944.

(54)

Gao, T.; Wang, T. Vapor Phase Growth and Optical Properties of Single-Crystalline SnO2 Nanobelts. Mater. Res. Bull. 2008, 43 (4), 836–842. DOI:10.1016/j.materresbull.2007.05.004.


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


(55)

Aslan, K.; Lakowicz, Æ. J. R.; Geddes, Æ. C. D. Metal-Enhanced Fluorescence Using Anisotropic Silver Nanostructures : Critical Progress to Date. Anal. Bioanal. Chem. 2005, 926–933. DOI:10.1007/s00216-005-3195-3.

(56)

Geddes, C. D.; Lakowicz, J. R. Metal-Enhanced Fluorescence. In Journal of Fluorescence; 2002. DOI:10.1023/A:1016875709579.

(57)

Pribik, R.; Aslan, K.; Zhang, Y.; Geddes, C. D. Metal-Enhanced Fluorescence from Chromium Nanodeposits. J. Phys. Chem. C 2008. DOI:10.1021/jp8071124.



An Ecofriendly non-hydrolytic sol-gel method for synthesis of atomically thin yellow fluorescent SnONS is reported at room temperature. Due to stable fluorescence in water, SnONS were used for biological Imaging. 276x129mm (150 x 150 DPI)

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Two-Dimensional Atomically Thin Tin-Based Fluorescent Oxide

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