DNA-Assisted Exfoliation of Tungsten Dichalcogenides and Their

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DNA-assisted Exfoliation of Tungsten Dichalcogenides and Their Antibacterial Effect Gyeong Sook Bang, Suhyung Cho, Narae Son, Gi Woong Shim, Byung-Kwan Cho, and Sung-Yool Choi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b10136 • Publication Date (Web): 06 Jan 2016 Downloaded from http://pubs.acs.org on January 6, 2016

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ACS Applied Materials & Interfaces

DNA-assisted Exfoliation of Tungsten Dichalcogenides and Their Antibacterial Effect Gyeong Sook Banga#, Suhyung Chob#, Narae Sona, Gi Woong Shima, Byung-Kwan Chob, and Sung-Yool Choia* a

Department of Electrical Engineering and Graphene Research Center, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea. bDepartment of Biological Science and KI for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea,

KEYWORDS. Tungsten dichalcogenides, aqueous exfoliation, two-dimension, nanosheet, DNA, antibacterial effect ABSTRACT

This study reports a method for the facile and high-yield exfoliation of WX2 (X = S, Se) by sonication under aqueous conditions using single-stranded (ss)DNA of high molecular weight. The ssDNA provided a high degree of stabilization and prevented reaggregation, and enhanced the exfoliation efficiency of WX2 nanosheets due to adsorption on the WX2 surface and the electrostatic repulsion of sugars in the ssDNA backbone. The exfoliation yield was higher with

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ssDNA (80%–90%) than without (2%–4%); the yield with ssDNA was also higher than the value previously reported for aqueous exfoliation (~10%). Given that two-dimensional nanomaterials have potential health and environmental applications, we investigated antibacterial activity of exfoliated WX2-ssDNA nanosheets relative to graphene oxide (GO), and found that WSe2ssDNA nanosheets had higher antibacterial activity against Escherichia coli K-12 MG1655 cells than GO. Our method enables large-scale exfoliation in an aqueous environment in a single step with a short reaction time and under ambient conditions, and can be used to produce surfaceactive or catalytic materials that have broad applications in biomedicine and other areas.

INTRODUCTION Two-dimensional (2D) layered nanomaterials have attracted considerable attention owing to their interesting properties. Tungsten dichalcongenides (WX2, where X = S or Se) are a typical layered material with 2D building blocks, with a crystal structure that consists of covalently bonded XW-X single layers that interact via van der Waals forces as graphite. The advantages of WX2 emerge when these materials are down-sized to a single or a few layers. Bulk WX2 is a semiconductor with an indirect band gap of ~1 eV; the band structure undergoes indirect-todirect transition when thinned to a single layer1, which when exfoliated yields 2D nanomaterials with a high surface area that can be useful for producing surface-active and catalytic materials. These transition-metal-dichalcogenide (TMD) materials have a wide range applications in energy storage2-6, the manufacture of electronic7-10 and optoelectronic1, 11, 12 devices, for biomedicine13, 14

, and as biosensors15, 16. WX2 is an insoluble compound, which has hindered the preparation of well-dispersed 2D WX2

nanosheets under aqueous conditions. The poor solubility is a limitation for large-scale production and biological applications of WX2 nanosheets. Various aqueous exfoliation


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approaches have been proposed to generate 2D WX2 nanosheets that have been effective for their mass production.17-19 One of these is Li-intercalation, which is useful but also sensitive to environmental conditions and is associated with changes in the structural and electronic properties of pristine materials. Another method using organic-polymer surfactants in water has very low yield.20, 21 Hence, the aqueous exfoliation of WX2 remains a barrier for obtaining a large quantity of high-quality nanosheets for large-scale use and biological applications. It was recently reported that WS2 nanosheets can adsorb single-stranded (ss)DNA via van der Waals interactions.15, 22-24 In the present study, we report DNA-assisted exfoliation based high-yield preparation of WX2 nanosheets under aqueous conditions. High molecular-weight ssDNA is a flexible, water-soluble biopolymer with polyanions and consists of nucleobases, sugars, and a phosphodiester backbone. The adsorption of ssDNA bases on basal planes of WX2 is favored by high hydrophobicity, while guanine bases of ssDNA can be adsorbed via hydrogen bridges between the primary amines or oxygen of guanine and the chalcogen surface or defective edges of WX2.15,

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The sugar-

phosphate backbone of ssDNA adsorbed on WX2 nanosheets (WX2-ssDNA) can be exposed to deionized (DI) water and stabilized by electrostatic repulsion between WX2-ssDNA nanosheets. Therefore, high molecular-weight ssDNA has great potential as a surfactant for aqueous exfoliation of WX2. Indeed, in the present study it was found to increase the yield of WX2 nanosheets by more than 20-fold (80%–90% with ssDNA vs. 2%–4% without), and WX2ssDNA yield was also higher than the value that was previously obtained by aqueous exfoliation (~10%)20. Exfoliated WX2 nanosheets were characterized by circular dichroism (CD); dynamic light scattering (DLS); transmission electron microscopy (TEM); and Raman, ultraviolet-visible (UV-Vis), and X-ray photoelectron spectroscopy (XPS).


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Various nanomaterials have been shown to exhibit antimicrobial activity.27, 28 WX2 nanosheets showed antibacterial activity in phosphate-buffered saline (PBS) against Escherichia coli and in an in vitro oxidation test. Our exfoliation method using ssDNA is facile and potentially scalable, and can be applied to the exfoliation of various layered materials, large-scale production of 2D nanosheets, antibacterial coating, and generation of multifunctional composites.

RESULTS AND DISCUSSION To produce high WX2-nanosheet yields, we directly sonicated bulk WX2 powder using high molecular-weight ssDNA in DI water. First, DNA was heated at 95oC for 2 h to obtain ssDNA; WX2 bulk powders were added to the ssDNA solution, which was followed by sonication for 3 h with a tip sonicator. The dispersion of the mixture was verified by the naked eye. The solution was centrifuged at 2000 rpm for 20 min and the sediment was discarded to remove unexfoliated WX2 flakes. A control sample without ssDNA was prepared by the same protocol. The exfoliated yield was estimated from the volume of the sediment, which was greater in the absence than in the presence of ssDNA (Supporting Information, Figure S1a and S1b). The yield was 80%–90% with and 2%–4% without ssDNA, indicating that the addition of high molecular-weight ssDNA is highly effective for WX2 exfoliation in DI water. CD spectra were obtained in order to access the conformation of heat denatured DNA (Supporting Information, Figure S2). A positive peak at around 276 nm and a negative peak at 249 nm with approximately the same intensity and cross point at 262 nm were observed, which is consistent with data reported for ssDNA molecules.29,

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Upon addition of WX2, the CD

spectrum of WX2-ssDNA showed no changes in the positions of positive and negative peaks; however, a decrease in amplitude was observed, which may be explained by reduced helicity of


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the DNA.30 These results suggest that the ssDNA structure was retained in WX2-ssDNA but that helicity was decreased by adsorption of ssDNA onto WX2 nanosheets. The supernatant with free ssDNA was centrifuged at 9000 rpm for 30 min; the supernatant was replaced with fresh DI water, and the solution was sonicated for 3 min followed by centrifugation at 9000 rpm for 30 min to remove free ssDNA. This washing process was repeated several times and the removal of ssDNA was estimated from a DNA peak observed in the supernatant by UV-Vis spectroscopy after each centrifugation. After washing, WX2-ssDNA was prepared by re-dispersing the final sediment by sonication for 30 min. The exfoliation process is illustrated in Figure 1D. The resulting dispersion had a dark green color for WS2-ssDNA with a mass concentration of 0.87 mg/ml and a dark Indian-pink color for WSe2-ssDNA with a concentration of 0.81 mg/ml, and was stable over a few days with no aggregation (Figure S1c). The aqueous stability of WX2ssDNA was determined by measuring zeta potential, which was −37.3 mV for WS2-ssDNA and −36.1 mV for WSe2-ssDNA. WX2-ssDNA nanosheets are negatively charged owing to the phosphate backbone of ssDNA, which stabilized the sheets through electrostatic repulsion. The thickness of WS2-ssDNA nanosheets by atomic force microscopy (AFM) measurement was 1.4– 2.6 nm, suggesting its single-layer structure (Figure 1C). The light spot on the WS2 layer indicates the adsorbed DNA fragment. The size of WX2-ssDNA nanosheets was determined based on hydrodynamic size distributions by DLS and AFM distribution statistics, and was found to be in the range of 65–650 nm for WS2-ssDNA and 64–550 nm for WSe2-ssDNA (Figure 1B and Figure S3 of Supporting Information). An AFM analysis with cross-sectional line profiles showed that the thickness of most of the WX2-ssDNA nanosheets was < 10 nm (Supporting Information, Figure S3), which encompasses ssDNA fragments adsorbed on WX2 nanosheets.


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Figure 1. (A, B) UV-Vis spectrum (A) and hydrodynamic size distribution (B) of WX2-ssDNA dispersion. (C) AFM image and corresponding line scan for WS2-ssDNA nanosheets on a SiO2/Si substrate. (D) Schematic illustration of the exfoliation of WX2 bulk powder in the presence of ssDNA.

UV-Vis spectra of WX2-ssDNA nanosheets in solution were acquired in the range of 200– 1100 nm at room temperature (Figure 1A). Absorption peaks were observed at 630 nm (1.97 eV) and 760 nm (1.63 eV) for WS2-ssDNA and WSe2-ssDNA, respectively; this is commonly assigned as the characteristic A exciton of 2H-WX231 and corresponds to the smallest direct excitonic transition at the K point of the Brillouin zone.32 Photoluminescence (PL) spectra of WX2-ssDNA nanosheets revealed luminescence at 632 nm and 764 nm for WS2-ssDNA and WSe2-ssDNA, respectively (Supporting Information, Figure S4). DNA exhibits no PL emission, whereas pristine WS2 powder showed a lower PL emission than that of WS2-ssDNA nanosheets


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at 880 nm (1.41 eV) (Figure S4a). The PL peak of WX2-ssDNA nanosheets was consistent with the A exciton of UV-Vis spectra shown in Figure 1C (Figure S4b). PL spectra have recently been demonstrated for single-layer WS2,17, 31 which exhibits a direct band-gap at around 1.9 eV as compared to the indirect band-gap at 1.4 eV for bulk WS2. Our results are in good agreement with previous reports.17, 20, 31, 33, 34 Thus, the PL signals observed for our WX2-ssDNA nanosheets indicated the presence of single-layer WX2. A small peak corresponding to ssDNA attached to WX2 nanosheets was observed at around 260 nm in the UV-Vis spectrum. The presence of ssDNA was also detected by Fourier transform infrared (FT-IR) spectroscopy (3429 cm−1 for OH and N-H stretching; PO4− peaks at 1234, 1086, 1062, 1015, and 964 cm−1; 1188cm−1 for C-O; and 1652 cm−1 for C=O and C=N) (Supporting Information, Figure S5). Raman spectroscopy provided a simple and qualitative characterization of WX2-ssDNA nanosheets; spectra for pristine WX2 powder and WX2-ssDNA nanosheets on a SiO2/Si substrate obtained by excitation at 514 nm are shown in Figure 2A and 2B. The peaks were calibrated against the Si peak at 520 cm−1. Two typical peaks—E12g originating from the in-plane mode vibration of W-X, and A1g from out-of-plane vibrations of X atoms— were observed in both the powder and nanosheets. For the latter, E12g and A1g peaks were present at 355.8 cm−1 and 419.2 cm−1, respectively, along with another peak—labeled as 2LA(M), of second-order Raman mode—near E12g.35 E12g was in a similar position while A1g was shifted downwards compared to pristine WS2 powder (356.1 cm−1 for E12g and 420.7 cm−1 for A1g). This red-shift is in agreement with a recent report of DNA-TMD.36 The frequency difference between the two peaks was 63.4 cm−1 for WS2-ssDNA nanosheets, corresponding to two or three layers.37 The 2LA(M) peak was not present in pristine WS2 powder. For WSe2-ssDNA nanosheets, one peak with a shoulder in the region of E12g and an A1g peak at 249.7 cm−1 were detected, along with a B12g peak at 310 cm-


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associated with atomically thin layer that is inactive for bulk WSe2.38-41 In the spectrum for

pristine WSe2 powder, only one peak without a shoulder and the B12g peak were clearly seen at 251.2 cm−1 in this frequency region. As for WS2-ssDNA, the red-shift was also observed in WSe2-ssDNA nanosheets; the line width was larger than that of pristine WX2 powder. The full width at half-maximum of WS2-ssDNA and WSe2-ssDNA increased from 8.8 to 16.2 cm−1 and from 5.9 to 13.2 cm−1, respectively. This line broadening was attributed to a smaller nano size and larger defects as compared to pristine WX2 powder, consistent with previous findings using the liquid-based exfoliation method.2

Figure 2. (A, B) Raman spectra for pristine WX2 powder (black line) and exfoliated WX2ssDNA nanosheets (red line) on a SiO2/Si substrate. (C, D) High-resolution TE micrographs of exfoliated WS2-ssDNA (C) and WSe2-ssDNA (D) nanosheets.


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Exfoliated WX2-ssDNA nanosheets were characterized by TEM. High- and low-resolution TE micrographs of electron transparent single- or multi-layer 2D-nanosheets are shown in Figure 2C and 2D and Figures S6. The nanosheets had an irregular shape with lateral dimensions of < 600 nm. Fast Fourier transform pattern of high-resolution TE images showed a hexagonal spot pattern (inset in Figure 2C and 2D), indicating that the WX2-ssDNA nanosheets were not damaged during sonication with ssDNA. Some dark spots were present in the transparent nanosheets that were attributable to ssDNA molecules, as reported for exfoliated TMD materials dispersed with other surfactants.20, 21 The chemical state of WX2-ssDNA nanosheets was further characterized by XPS (Figure 3). W peaks of WS2-ssDNA nanosheets were detected at 33.1, 35.3, and 38.5 eV, corresponding to 4f7/2, 4f5/2, and 5p3/2 for W4+ chemical state of 2H WS2. S peaks at 162.1 and 163.2 eV corresponded to S2--type 2p3/2 and 2p1/2 orbitals in WS2, respectively. W peaks of WSe2-ssDNA nanosheets were seen at 32.7 eV (W4+ 4f7/2), 34.8 eV (W4+ 4f5/2), and 38.3 eV (W4+ 5p3/2), while Se 3d peaks at 54.4 eV (Se 3d5/2) and 55.2 eV (Se 3d3/2) were consistent with Se2--type WSe2. These data are in agreement with previous reports of 2H WX2.42-45 A weak peak between 36 and 38 eV (Figure 3A) was attributed to W6+ from local oxidation of WSe2 nanosheets during water-based exfoliation. Based on the integral area of the peak, the percentage of W4+ and W6+ was about 95% and 5%, respectively. There were no traces of oxidized S or Se. We speculate that WSe2 is more readily oxidized than WS2 under aqueous conditions. Nitrogen and phosphorus are good indicators of DNA present on the WX2 surface; the N 1s and P 2p peak for WX2-ssDNA nanosheets indicated that ssDNA molecules were adsorbed onto the surface (Figure 3E and 3F and Figure S7).46 A comparison of survey and high-resolution N 1s and P 2p spectra for pristine WS2 powder and WX2-ssDNA nanosheets is shown in Figure S7.


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Figure 3. XPS spectra for W 4f, X 2p, N 1s, and P 2p of WX2-ssDNA nanosheets. (A, B) WSe2ssDNA nanosheets. (C–F) WS2-ssDNA nanosheets.

To determine the applicability of WX2-ssDNA nanosheets as an antibacterial nanomaterial, we compared the growth of E. coli on WX2-ssDNA and graphene oxide (GO) nanosheets. Bulk WX2 powder and exfoliating WX2 nanosheets without DNA caused serious aggregation in PBS buffer.


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The removal of DNA also results in restacking by van der Waals attraction between the layers. This reaggregation problem gives a great obstacle and inaccurate information for antibacterial test. GO has reported antibacterial properties47; well-dispersed GO showed a zeta potential of −47.7 mV. The well-dispersed nanosheets (80 µg/ml) were incubated with E. coli K-12 MG1655 (106 CFU/ml) in PBS at 30 °C for 5 h; PBS without nanosheets served as a control. The number of surviving bacterial colonies on the test samples relative to the number of cells in the blank sample was determined. Cell viability was decreased in the presence of WX2-ssDNA and GO nanosheets (Figure 4A). WSe2-ssDNA had higher antibacterial activity (82.3% ± 1.7% decrease in viability) than WS2-ssDNA or GO (48.2% ± 4.3% and 41.4 ± 7.3% decreases, respectively). GO/WSe2-ssDNA and rGO/WSe2-ssDNA composites also showed high antibacterial activity (81.7% ± 2.6% and 71.4 ± 4.6% decreases in cell viability, respectively) (Figure 4B). The lower value observed for the latter may be due its low dispersibility.47

Figure 4. Antibacterial properties of WX2-ssDNA vs. GO nanosheets. (A, B) E. coli cell viability was decreased by treatment with pure WX2-ssDNA and GO nanosheets (A) and GO/ or rGO/WSe2-ssDNA composite nanosheets (B). (C) Absorbance of XTT-formazan generated by


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WX2-ssDNA and GO nanosheets (80 µg/ml). XTT solution without nanosheets was used a control. (D) Loss of GSH by in vitro oxidation after incubation with WX2-ssDNA or GO nanosheets (80 µg/ml) for 2 h. H2O2 (1.0 mM) served as a positive control.

Studies of the antibacterial activity of 2D graphene-based nanosheets have reported cell damage caused by oxidative stress or physical contact.28, 47 Since WX2-ssDNA nanosheets have a similar 2D structure, we examined whether these also cause oxidative stress. Oxidative stress may arise from reactive oxygen species (ROS) generation by nanosheets or via an ROSindependent mechanism, in which cell damage occurs by direct oxidation of cellular components through contact with nanosheets without ROS generation. Given that oxygen is a powerful oxidant, we first measured superoxide anion (O2•−) production by WX2-ssDNA nanosheets with the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay. XTT is reduced by O2•− to form water-soluble XTT-formazan with absorption at 470 nm. The absorbance of the solution was low and did not change in the presence of WX2-ssDNA (Figure 4C), indicating that O2•− plays a minor role in the antibacterial activity of WX2-ssDNA nanosheets. These results are consistent with the behavior of graphene-based materials.47 The 2D nanosheets were superior in terms of improving reactivity through contact owing to high surface area. We also investigated whether WX2-ssDNA nanosheets induce ROS-independent oxidative stress with the in vitro GSH oxidation assay. The GSH tripeptide contains thiol groups and is used as an oxidative stress indicator in cells. We used Ellman’s assay to evaluate the oxidation of GSH by WX2-ssDNA nanosheets, which quantifies the concentration of thiol groups in GSH based on the absorbance at 412 nm. GSH solution without nanosheets was used as a negative control, and GSH oxidation by the strong oxidant H2O2 in the absence of nanosheets served as a


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positive control. Since the negative control would not result in GSH oxidation under the experimental conditions, loss of GSH by WX2-ssDNA nanosheets was calculated from GSH absorbance of control samples at 412 nm. WX2-ssDNA nanosheets showed a capacity for oxidizing GSH, which was higher for WSe2-ssDNA than for WS2-ssDNA or GO (Figure 4D). GSH oxidation in the dark can be catalyzed by semiconductor-type tungsten chalcogenides, and can explain the antibacterial capacity of the nanosheets, which was highest for WSe2-ssDNA. Regarding the high activity of WSe2-ssDNA, the oxidation capacity of WS2 and WSe2 nanosheets may differ according to their electrical properties; it was previously reported that results for TMD field-effect transistors, MoS2 and WS2 exhibited n-type behavior18, 43, 48 while WSe2 showed p-type behavior49 . Another recent study described n-doping of MoS2 and WSe2 film using DNA.36 Although the n-doping property was enhanced by DNA molecules adsorbed on WX2 nanosheets, WS2 and WSe2 can serve as n- and p-type semiconductor nanosheets, respectively. In the dark, electron transfer is dominated by a majority carrier. Thus, n-type materials can carry out reduction, while p-type materials allow oxidation in the presence of excess holes allow oxidation. Heterogeneous electron-transfer kinetics were enhanced at p-type WSe2 semiconductors as compared to n-doped WSe2 for oxidation of Ru(NH3)62+ in aqueous solution in the dark.50 The redox potential of GSH/glutathione disulfide is −0.2 to −0.3 V at pH 6–751, which is similar to that of Ru(NH3)62+. We therefore suggest that p-type WSe2-ssDNA nanosheets have a greater positive effect than n-type WS2-ssDNA nanosheets and insulate GO for GSH oxidation under aerobic conditions. Further studies on the correlation between the catalytic oxidation reaction of WX2-ssDNA nanosheets and their electronic properties are required in order to clarify the detailed antibacterial mechanism.


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CONCLUSIONS We describe here a facile and effective exfoliation technique using ssDNA under aqueous conditions. ssDNA conferred stability and enhanced the exfoliation efficiency of WX2 nanosheets. The exfoliation yield was very high in the presence as compared to the absence of ssDNA (80%–90% vs. 2%–4%). The resultant WX2-ssDNA nanosheets had < 10 layers, with a lateral size of 65–650 nm. This method can be used to prepare single-layer or few-layer WX2 nanosheets with good aqueous dispersibility as well as potent antibacterial activity against E. coli, especially in the case of WSe2-ssDNA nanosheets (82.3% ± 1.7% loss of cell viability). This effect was associated with strong GSH oxidation capacity, suggesting that the antibacterial properties of WSe2-ssDNA nanosheets are exerted by induction of ROS-independent oxidative stress. Our exfoliation method can potentially be used for the production of semiconductors with ssDNA-stabilized WX2 nanosheets for biotechnology, sensor and nanoelectronics applications.

METHODS Materials and characterization WS2 powder (< 2 µm, 99%; Sigma-Aldrich, St. Louis, MO, USA),), WSe2 powder (10 µm, 99.8%; Alfa Aesar, Ward Hill, MA, USA) and DNA (salmon testes, 2000 base pairs, 42% G-C; Sigma-Aldrich) were used without modification. XTT (Sigma-Aldrich) and 5,5’-dithio-bis-(2nitrobenzoic acid (DNTB, Ellman’s reagent, Sigma-Aldrich) were used to examine the oxidative effect of WX2-ssDNA nanosheets. DI water with 18 MΩ cm resistivity was used in all experiments.


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UV-Vis spectra for dispersed WX2-ssDNA and composite GO/ or rGO/WSe2-ssDNA were obtained using a S-3100 Photodiode Array UV-Vis spectrophotometer (Scinco, Seoul, Korea). A quartz cell with a path length of 1.0 cm was used for absorbance or transmittance. Zeta potential and size distribution of the WX2-ssDNA dispersion were measured by DLS using a Zetasizer Nano ZS instrument (Malvern Instruments, Malvern, UK). An XPS elemental analysis was carried out using a K-Alpha XPS analyzer with a micro-focused monochromatic Al Kα X-ray source (Thermo Scientific, Waltham, MA, USA). Spectra were fitted using a GaussianLorentzian peak shape after baseline correction. Raman spectra were obtained at 514 nm with a Jobin Yvon LabRAM-HR instrument (Horiba Scientific, Edison, NJ, USA). The silicon peak at 520 cm−1 was used to calibrate absolute peak position. FT-IR spectra were recorded using a KBr pellet (Perkin Elmer, Billerica, MA, USA) and CD spectra were obtained using a Jasco-815 spectropolarimeter (Jasco, Easton, MD, USA). AFM measurements were performed using a D3100 a Digital Instruments Dimension AF microscope (Veeco, Plainview, NY, USA). TEM was carried out with a JEM 2100F microscope (JEOL, Tokyo, Japan) using holy carbon grid. AFM and TEM, samples were prepared by drop-casting a small volume of dilute dispersion on a substrate, which was dried under ambient condition.

Aqueous dispersion of WX2-ssDNA nanosheets DNA was dissolved in DI water (1.5 mg/ml) and the solution was heated at 95°C for 2 h to obtain ssDNA. WX2 bulk powder (1.0 mg/ml) was added and the mixture was sonicated for 3 h using a tip sonicator (Sonosmasher-LH700S; Ulsso Hitech Co., Chungwon, Korea) at 40% amplitude of 700 W with pulse operation (2 min on/2 min off). A control experiment was carried out in parallel without DNA under the same conditions. After sonication, the dispersion was


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centrifuged at 1000–13,000 rpm for 20–40 min to remove unexfoliated WX2 flakes and unreacted DNA (Combi-514R, Hanil Science Industrial Co., Incheon, Korea). The yield for WX2 exfoliation was estimated from the sediment volume after centrifugation at 2000 rpm. The dispersion was washed three times with DI water and dialyzed to remove residual free DNA. The color of the resultant dispersions was dark green for WS2 and dark Indian-pink for WSe2; the dispersions were stable for a few days (i.e., did not aggregate).

Cell preparation E. coli K-12 MG1655 was grown in Luria-Bertani (LB) medium at 30°C and harvested at the mid-exponential growth phase (i.e., optical density, OD = 0.5). Cells were centrifuged at 8000 rpm for 1 min and the pellets were washed three times with 1× PBS. The final pellet was resuspended in PBS and OD was measured on a UV spectrometer at 600 nm, then diluted to 106 CFU/ml in PBS.

Antibacterial test A 10-µl volume of E. coli (106 CFU/ml) was added to 1 ml PBS containing GO and WX2ssDNA nanosheets (80 µg/ml). After shaking the mixture for 5 h at 30°C with 360° rotation, 100 µl of the suspension were spread on an LB agar plate, which was incubated overnight at 30°C. As a control, cells in PBS without GO or WX2-ssDNA nanosheets were prepared in the same manner. Colonies were counted and cell number was calculated relative to the control sample. All experiments were carried out in triplicate and repeated at least twice.

Oxidative stress test


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To assess O2•− generation, XTT-formazan absorption was measured at 470 nm. XTT (0.27 mg/ml) solution and WX2-ssDNA dispersion (80 µg/ml) were prepared in PBS (pH 7.0). A 1-ml volume of WX2-ssDNA in PBS was added to 1 ml of XTT solution, and the mixture was incubated at 37°C for 5 h in the dark. WX2-ssDNA nanosheets were removed from the mixture with a 0.25-µm polyethersulfone syringe filter. Filtrates (800 µl) were transferred to a 25-well plate for absorbance measurements. A control sample was prepared consisting of XTT solution without WX2-ssDNA nanosheets. The effect of WX2-ssDNA nanosheets on GSH oxidation was assessed by Ellman’s assay. WX2-ssDNA dispersion (80 µg/ml ) and GSH solution (0.8 mM) were prepared in 50 mM bicarbonate buffer (pH 8.7) and mixed in equal volumes (225 µl). The mixture was shaken at room temperature for 2 h in the dark, before adding 50 mM Tris-HCl (785 µl) and 100 mM DNTB solution (15 µl). The solution (yellow color) was filtered with a 0.25-µm polyethersulfone syringe filter. Filtrates (800 µl) were transferred to a 25-well plate for absorbance measurements at 412 nm. GSH solution without WX2-sDNA nanosheets was used as a negative control and GSH oxidation by H2O2 (1 mM) served as a positive control. Oxidation levels are expressed as a percentage of GSH reduction relative to the control sample. All samples were tested in triplicate.

ASSOCIATED CONTENT Supporting Information. Electronic Supplementary Information (ESI) available: Preliminary test for MoS2 exfoliation using commercial short- and long-DNA, Photographs for the effect of exfoliation with and without ssDNA and WX2-ssDNA dispersions, CD spectra of ssDNA and WX2-ssDNA dispersions, AFM analyses of the WS2-ssDNA nanosheets, UV-Vis


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and PL spectra of WX2-ssDNA dispersions, and XPS and FT-IR spectra of WX2-ssDNA nanosheets are included. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Phone: +82 42 350 7427. Fax: +82 42 350 7283. E-mail: [email protected] Author Contributions #

These authors contributed equally to this work.

Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS We acknowledge financial support from Nano-Material Technology Development Program (2012M3A7B4049807), Basic Research Program of ETRI (15ZE1110), and LG Display Co., Ltd. We thank Dr. Il-Suk Kang of National Nanofab Center for DLS analysis and Danim Ihm of KAIST for performing GO synthesis.

REFERENCES


18

Page 19 of 27

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


1.

Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S., Electronics and

Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides. Nat. Nanotechnol. 2012, 7, 699-712. 2.

Bang, G. S.; Nam, K. W.; Kim, J. Y.; Shin, J.; Choi, J. W.; Choi, S.-Y., Effective Liquid-

Phase Exfoliation and Sodium Ion Battery Application of MoS2 Nanosheets. ACS Appl. Mater. Interfaces 2014, 6, 7084-7089. 3.

Cao, L.; Yang, S.; Gao, W.; Liu, Z.; Gong, Y.; Ma, L.; Shi, G.; Lei, S.; Zhang, Y.; Zhang,

S.; Vajtai, R.; Ajayan, P. M., Direct Laser-Patterned Micro-Supercapacitors from Paintable MoS2 Films. Small 2013, 9, 2905-2910. 4.

Chen, R.; Zhao, T.; Wu, W.; Wu, F.; Li, L.; Qian, J.; Xu, R.; Wu, H.; Albishri, H. M.; Al-

Bogami, A. S.; El-Hady, D. A.; Lu, J.; Amine, K., Free-Standing Hierarchically Sandwich-Type Tungsten Disulfide Nanotubes/Graphene Anode for Lithium-Ion Batteries Nano Lett. 2014, 14, 5899-5904. 5.

Ratha, S.; Rout, C. S., Supercapacitor Electrodes Based on Layered Tungsten Disulfide-

Reduced Graphene Oxide Hybrids Synthesized by a Facile Hydrothermal Method. ACS Appl. Mater. Interfaces 2013, 5, 11427-11433. 6.

Zhu, C.; Mu, X.; Aken, P. A. v.; Yu, Y.; Maier, J., Single-Layered Ultrasmall Nanoplates

of MoS2 Embedded in Carbon Nanofibers with Excellent Electrochemical Performance for Lithium and Sodium Storage. Angew. Chem. Int. Ed 2014, 53, 2152-2156.


19


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

7.

Page 20 of 27

Huang, J.-K.; Pu, J.; Hsu, C.-L.; Chiu, M.-H.; Juang, Z.-Y.; Chang, Y.-H.; Chang, W.-H.;

Iwasa, Y.; Takenobu, T.; Li, L.-J., Large-Area Synthesis of Highly Crystalline WSe2 Monolayers and Device Applications. ACS Nano 2014, 8, 923-930. 8.

Lee, Y.-H.; Yu, L.; Wang, H.; Fang, W.; Ling, X.; Shi, Y.; Lin, C.-T.; Huang, J.-K.;

Chang, M.-T.; Chang, C.-S.; Dresselhaus, M.; Palacios, T.; Li, L.-J.; Kong, J., Synthesis and Transfer of Single-Layer Transition Metal Disulfides on Diverse Surfaces. Nano Lett. 2013, 13, 1852-1857. 9.

Wang, X.; Feng, H.; Wu, Y.; Jiao, L., Controlled Synthesis of Highly Crystalline MoS2

Flakes by Chemical Vapor Deposition. J. Am. Chem. Soc. 2013, 135, 5304-5307. 10. Zande, A. M. v. d.; Huang, P. Y.; Chenet, D. A.; Berkelbach, T. C.; You, Y.; Lee, G.-H.; Heinz, T. F.; Reichman, D. R.; Muller, D. A.; Hone, J. C., Grains and Grain Boundaries in Highly Crystalline Monolayer Molybdenum Disulphide. Nat. Mater. 2013, 12, 554-561. 11. Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A., Ultrasensitive Photodetectors Based on Monolayer MoS2. Nat. Nanotechnol. 2013, 8, 497-501. 12. Yin, Z.; Li, H.; Li, H.; Jiang, L.; Sh, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H., Single-Layer MoS2 Phototransistors. ACS Nano 2012, 6, 74-80. 13. Cheng, L.; Liu, J.; Gu, X.; Gong, H.; Shi, X.; Liu, T.; Wang, C.; Xiaoyong Wang , G. L., Huaiyong Xing , Wenbo Bu , Baoquan Sun , and Zhuang Liu, PEGylated WS2 Nanosheets as a Multifunctional Theranostic Agent for in vivo Dual-Modal CT/Photoacoustic Imaging Guided Photothermal Therapy Adv. Mater. 2014, 26, 1886-1893.


20

Page 21 of 27

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


14. Yong, Y.; Zhou, L.; Gu, Z.; Yan, L.; Tian, G.; Zheng, X.; Liu, X.; Zhang, X.; Shi, J.; Cong, W.; Yin, W.; Zhao, Y., WS2 Nanosheet as a New Photosensitizer Carrier for Combined Photodynamic and Photothermal Therapy of Cancer Cells. Nanoscale 2014, 6, 10394-10403. 15. Xi, Q.; Zhou, D.-M.; Kan, Y.-Y.; Ge, J.; Wu, Z.-K.; Yu, R.-Q.; Jiang, J.-H., Highly Sensitive and Selective Strategy for MicroRNA Detection Based on WS2 Nanosheet Mediated Fluorescence Quenching and Duplex-Specific Nuclease Signal Amplification. Ananl. Chem. 2014, 86, 1361-1365. 16. Zhu, C.; Zeng, Z.; Li, H.; Li, F.; Fan, C.; Zhang, H., Single-Layer MoS2-Based Nanoprobes for Homogeneous Detection of Biomolecules. J. Am. Chem. Soc. 2013, 135, 59986001. 17. Eda, G.; Yamaguchi, H.; Voiry, D.; Fujita, T.; Chen, M.; Chhowalla, M., Photoluminescence from Chemically Exfoliated MoS2. Nano Lett. 2011, 11, 5111-5116. 18. Coleman, J. N.; Lotya, M.; O’Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V., Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, 568-571. 19. Zeng, Z.; Yin, Z.; Huang, X.; Li, H.; He, Q.; Lu, G.; Boey, F.; Zhang, H., Single-Layer Semiconducting Nanosheets: High-Yield Preparation and Device Fabrication. Angew. Chem. Int. Ed 2011, 50, 11093-11097.


21


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

Page 22 of 27

20. Smith, R. J.; King, P. J.; Lotya, M.; Wirtz, C.; Khan, U.; Sukanta De; O’Neill, A.; Duesberg, G. S.; Grunlan, J. C.; Moriarty, G.; Chen, J.; Wang, J.; Minett, A. I.; Nicolosi, V.; Coleman, J. N., Large-Scale Exfoliation of Inorganic Layered Compounds in Aqueous Surfactant Solutions. Adv. Mater. 2011, 23, 3944-3948. 21. Guardia, L.; Paredes, J. I.; Rozada, R.; Villar-Rodil, S.; Martinez-Alonso, A.; Tascon, J. M. D., Production of Aqueous Dispersions of Inorganic Graphene Analogues by Exfoliation and Stabilization with Non-ionic Surfactants. RSC Adv. 2014, 4, 14115-14127. 22. Yuan, Y.; Li, R.; Liu, Z., Establishing Water-Soluble Layered WS2 Nanosheet as a Platform for Biosensing. Anal. Chem. 2014, 86, 3610-3615. 23. Ge, J.; Tang, L.-J.; Xi, Q.; Li, X.-P.; Yu, R.-Q.; Jiang, J.-H.; Chu, X., A WS2 Nanosheet Based Sensing Platform for Highly Sensitive Detection of T4 Polynucleotide Kinase and Its Inhibitors. Nanoscale 2014, 6, 6866-6872. 24. Zhao, J.; Ma, Y.; Kong, R.; Zhang, L.; Yang, W.; Zhao, S., Tungsten Disulfide Nanosheet and Exonuclease III co-assisted Amplification Strategy for Highly Sensitive Fluorescence Polarization Detection of DNA Glycosylase Activity. Analytica Chimica Acta 2015, 887, 216-223. 25. Heckl, W. M.; Smith, D. P. E.; Binnig, G.; Klagges, H.; Hansch, T. W.; Maddocks, J., Two-Dimensional Ordering of the DNA Base Guanine Observed by Scanning Tunneling Microscopy Proc. Natl. Acad. Sci. USA 1991, 88, 8003-8005. 26. Li, Y.; Zhu, H.; Shen, F.; Wan, J.; Lacey, S.; Fang, Z.; Dai, H.; Hu, L., Nanocellulose as Green Dispersant for Two-Dimensional Energy Materials. Nano Energy 2015, 13, 346-354.


22

Page 23 of 27

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


27. Li, Q.; Mahendra, S.; Lyon, D. Y.; Brunet, L.; Liga, M. V.; Li, D.; Alvarez, P. J. J., Antimicrobial Nanomaterials for Water Disinfection and Microbial Control: Potential Applications and Implications. Water Research 2008, 42, 4591-4602. 28. Zhang, Y.; Ali, S. F.; Dervishi, E.; Xu, Y.; Li, Z.; Casciano, D.; Biris, A. S., Cytotoxicity Effects of Graphene and Single-Wall Carbon Nanotubes in Neural Phaeochromocytoma-Derived PC12 Cells. ACS Nano 2010, 4, 3181-3186. 29. Patil, A. J.; Vickery, J. L.; Scott, T. B.; Mann, S., Aqueous Stabilization and SelfAssembly of Graphene Sheets into Layered Bio-Nanocomposites using DNA. Adv. Mater. 2009, 21, 3159-3164. 30. Rosa, M. n.; Dias, R.; Miguel, M. d. G.; Lindman, B. r., DNA-Cationic Surfactant Interactions Are Different for Doubleand Single-Stranded DNA. Biomacromolecules 2005, 6, 2164-2171. 31. Zhao, W.; Ghorannevis, Z.; Chu, L.; Toh, M.; Kloc, C.; Tan, P.-H.; Eda, G., Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2. ACS Nano 2013, 7, 791-797. 32. Coehoorn, R.; Haas, C.; Dijkstra, J.; Flipse, C. J. F.; Groot, R. A. d.; Wold, A., Electronic Structure of MoSe2, MoS2, and WSe2. I. Band-Structure Calculations and Photoelectron Spectroscopy. Phy. Review B 1987, 35, 6195-6202. 33. Elıás, A. L.; pez, N. s. P.-L.; Castro-Beltrań, A. s.; Berkdemir, A.; Lv, R.; Feng, S.; Long, A. D.; Hayashi, T.; Kim, Y. A.; Endo, M.; Gutie´rrez, H. R.; Pradhan, N. R.; Balicas, L.; Mallouk, T. E.; pez-Urıás, F. L.; Terrones, H.; Terrones, M., Controlled Synthesis and Transfer of Large-Area WS2 Sheets: From Single Layer to Few Layers. ACS Nano 2013, 7, 5235-5242.


23


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

Page 24 of 27

34. Frey, G. L.; Elani, S.; Homyonfer, M.; Feldman, Y.; Tenne, R., Optical-Absorption Spectra of Inorganic Fullerenelike MS2 (M= Mo, W). Phy. Review B 1998, 57, 6666-6671. 35. Zhao, W.; Ghorannevis, Z.; Amara, K. K.; Pang, J. R.; Toh, M.; Zhang, X.; Kloc, C.; Tane, P. H.; Eda, G., Lattice Dynamics in Mono- and Few-Layer Sheets of WS2 and WSe2. Nanoscale 2013, 5, 9677-9683. 36. Park, H.-Y.; Dugasani, S. R.; Kang, D.-H.; Jeon, J.; Jang, S. K.; Lee, S.; Roh, Y.; Park, S. H.; Park, J.-H., n- and p- Type Doping Phenomenon by Artificial DNA and M-DNA on TwoDimensional Transition Metal Dichalcogenides. ACS Nano 2014, 8, 11603-11613. 37. Benameur, M. M.; Radisavljevic, B.; Heron, J. S.; Sahoo, S.; Berger, H.; Kis, A., Visibility of Dichalcogenide Nanolayers. Nanotechnology 2011, 22, 125706 (125705pp). 38. Luo, X.; Zhao, Y.; Zhang, J.; Toh, M.; Kloc, C.; Xiong, Q.; Quek, S. Y., Effects of Lower Symmetry and Dimensionality on Raman Spectra in Two-Dimensional WSe2. Phy. Review B 2013, 88, 195313-195311-195313-195317. 39. Terrones, H.; Corro, E. D.; Feng, S.; Poumirol, J. M.; Rhodes, D.; Smirnov, D.; Pradhan, N. R.; Z. Lin; Nguyen, M. A. T.; Elıás, A. L.; Mallouk, T. E.; Balicas, L.; Pimenta, M. A.; Terrones, M., New First Order Raman-active Modes in Few Layered Transition Metal Dichalcogenides. Sci. Rep. 2013, 4, 4215. 40. Yamamoto, M.; Dutta, S.; Aikawa, S.; Nakaharai, S.; Wakabayashi, K.; Fuhrer, M. S.; Ueno, K.; Tsukagoshi, K., Self-Limiting Layer-by-Layer Oxidation of Atomically Thin WSe2. Nano Lett. 2015, 15, 2067-2073.


24

Page 25 of 27

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


41. Tonndorf, P.; Schmidt, R.; Böttger, P.; Zhang, X.; Börner, J.; Liebig, A.; Albrecht, M.; Kloc, C.; Gordan, O.; Zahn, D. R. T.; Vasconcellos, S. M. d.; Bratschitsch, R., Photoluminescence Emission and Raman Response of Monolayer MoS2, MoSe2, and WSe2. Opt. Exp. 2013, 21, 4908-4916. 42. Mao, X.; Xu, Y.; Xue, Q.; Wang, W.; Gao, D., Ferromagnetism in Exfoliated Tungsten Disulfide Nanosheets. Nanoscale Res. Lett. 2013, 8, 430-435. 43. Morrish, R.; Haak, T.; Wolden, C. A., Low-Temperature Synthesis of n-Type WS2 Thin Films via H2S Plasma Sulfurization of WO3. Chem. Mater. 2014, 26, 3986-3992. 44. Yan, Y.; Xia, B.; Li, N.; Xu, Z.; Fisherc, A.; Wang, X., Vertically Oriented MoS2 and WS2 Nanosheets Directly Grown on Carbon Cloth as Efficient and Stable 3-Dimensional Hydrogen-Evolving Cathodes. J. Mater. Chem. A 2015, 3, 131-135. 45. Wang, H.; Kong, D.; Johanes, P.; Cha, J. J.; Zheng, G.; Liu, N.; Cu, Y., MoSe2 and WSe2 Nanofilms with Vertically Aligned Molecular Layers on Curved and Rough Surfaces. Nano Lett. 2013, 13, 3426-3433. 46. Lee, C.-Y.; Gong, P.; Harbers, G. M.; Grainger, D. W.; Castner, D. G.; Gamble, L. J., Surface Coverage and Structure of Mixed DNA/Alkylthiol Monolayers on

Gold:

Characterization by XPS, NEXAFS, and Fluorescence Intensity Measurements. Anal. Chem. 2006, 78, 3316-3325. 47. Liu, S.; Zeng, T. H.; Hofmann, M.; Burcombe, E.; Wei, J.; Jiang, R.; Kong, J.; Chen, Y., Antibacterial Activity of Graphite, Graphite Oxide, Graphene Oxide, and Reduced Graphene Oxide: Membrane and Oxidative Stress. ACS Nano 2011, 5, 6971-6980.


25


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

Page 26 of 27

48. Ovchinnikov, D.; Allain, A.; Huang, Y.-S.; Dumcenco, D.; Kis, A., Electrical Transport Properties of Single-Layer WS2. ACS Nano 2014, 8, 8174-8181. 49. Pradhan, N. R.; Rhodes, D.; Memaran, S.; Poumirol, J. M.; Smirnov, D.; Talapatra, S.; Feng, S.; Perea-Lopez, N.; Elias, A. L.; Terrones, M.; Ajayan, P. M.; Balicas, L., Hall and FieldEffect Mobilities in Few Layered p-WSe2 Field-Effect Transistors. Sci. Rep. 2015, 5, 8979. 50. Horrocks, B. R.; Mirkin, M. V.; Bard, A. J., Scanning Electrochemical Microscopy. 25. Application to Investigation of the Kinetics of Heterogeneous Electron Transfer at Semiconductor (WSe2 and Si) Electrodes J. Phys. Chem. 1994, 98, 9106-9114. 51. Millis, K. K.; Weaver, K. H.; Rabenstein, D. L., Oxidation/Reduction Potential of Glutathione J. Org. Chem. 1993, 58, 4144-4146.

SYNOPSIS. Aqueous exfoliation of Tungsten dichacogenides (WX2, X = S, Se) using singlestranded (ss)DNA of high molecular weight and their antibacterial effect. High molecular-weight ssDNA provided enhanced the exfoliation efficiency and a high degree of stabilization of WX2 nanosheets. WSe2-ssDNA nanosheets had a high antibacterial activity against E coli K-12 MG1655 cells.


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DNA-Assisted Exfoliation of Tungsten Dichalcogenides and Their

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