Cytotoxicity of exfoliated transition-metal dichalcogenides (MoS2 , WS2 , and WSe2 ) is lower than that of graphene and its analogues.

Studies involving transition-metal dichalcogenides (TMDs) have been around for many decades and in recent years, many were focused on using TMDs to synthesize inorganic analogues of carbon nanotubes, fullerene, as well as graphene and its derivatives with the ultimate aim of employing these materials into consumer products. In view of this rising trend, we investigated the cytotoxicity of three common exfoliated TMDs (exTMDs), namely MoS2 , WS2 , and WSe2 , and compared their toxicological effects with graphene oxides and halogenated graphenes to find out whether these inorganic analogues of graphenes and derivatives would show improved biocompatibility. Based on the cell viability assessments using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-8) assays on human lung carcinoma epithelial cells (A549) following a 24 h exposure to varying concentrations of the three exTMDs, it was concluded that MoS2 and WS2 nanosheets induced very low cytotoxicity to A549 cells, even at high concentrations. On the other hand, WSe2 exhibited dose-dependent toxicological effects on A549 cells, reducing cell viability to 31.8 % at the maximum concentration of 400 μg mL(-1) ; the higher cytotoxicity displayed by WSe2 might be linked to the identity of the chalcogen. In comparison with graphene oxides and halogenated graphenes, MoS2 and WS2 were much less hazardous, whereas WSe2 showed similar degree of cytotoxicity. Future in-depth studies should be built upon this first work on the in vitro cytotoxicity of MoS2 and WS2 to ensure that they do not pose acute toxicity. Lastly, nanomaterial-induced interference control experiments revealed that exTMDs were capable of reacting with MTT assay viability markers in the absence of cells, but not with WST-8 assay. This suggests that the MTT assay is not suitable for measuring the cytotoxicity of exTMDs because inflated results will be obtained, giving false impressions that the materials are less toxic.

[1]  Nancy A. Monteiro-Riviere,et al.  Challenges for assessing carbon nanomaterial toxicity to the skin , 2006 .

[2]  R. Tenne,et al.  Improved orthodontic stainless steel wires coated with inorganic fullerene-like nanoparticles of WS(2) impregnated in electroless nickel-phosphorous film. , 2008, Dental materials : official publication of the Academy of Dental Materials.

[3]  Andras Kis,et al.  Stretching and breaking of ultrathin MoS2. , 2011, ACS nano.

[4]  Lain‐Jong Li,et al.  Large-area synthesis of highly crystalline WSe(2) monolayers and device applications. , 2014, ACS nano.

[5]  Lain‐Jong Li,et al.  Synthesis of Large‐Area MoS2 Atomic Layers with Chemical Vapor Deposition , 2012, Advanced materials.

[6]  Peter Wick,et al.  The reliability and limits of the MTT reduction assay for carbon nanotubes-cell interaction , 2007 .

[7]  A. Splendiani,et al.  Emerging photoluminescence in monolayer MoS2. , 2010, Nano letters.

[8]  M. Pumera,et al.  The toxicity of graphene oxides: dependence on the oxidative methods used. , 2013, Chemistry.

[9]  S. Morrison,et al.  Single-layer MoS2 , 1986 .

[10]  Hongzheng Chen,et al.  Graphene-like two-dimensional materials. , 2013, Chemical reviews.

[11]  A. Ivanisevic,et al.  Inorganic material coatings and their effect on cytotoxicity. , 2012, Chemical Society reviews.

[12]  H. Zeng,et al.  Two-dimensional semiconductors: recent progress and future perspectives , 2013 .

[13]  Zhiyuan Zeng,et al.  Metal dichalcogenide nanosheets: preparation, properties and applications. , 2013, Chemical Society reviews.

[14]  Youngki Yoon,et al.  How good can monolayer MoS₂ transistors be? , 2011, Nano letters.

[15]  Christy L Haynes,et al.  Cytotoxicity of graphene oxide and graphene in human erythrocytes and skin fibroblasts. , 2011, ACS applied materials & interfaces.

[16]  Lev Rapoport,et al.  Self-lubricating coatings containing fullerene-like WS2 nanoparticles for orthodontic wires and other possible medical applications , 2006 .

[17]  Liang Cheng,et al.  Drug Delivery with PEGylated MoS2 Nano‐sheets for Combined Photothermal and Chemotherapy of Cancer , 2014, Advanced materials.

[18]  R. Tenne,et al.  Recent Progress in the Study of Inorganic Nanotubes and Fullerene-Like Structures , 2009 .

[19]  Zhiyuan Zeng,et al.  Single-layer semiconducting nanosheets: high-yield preparation and device fabrication. , 2011, Angewandte Chemie.

[20]  M. Pumera,et al.  Cytotoxicity of halogenated graphenes. , 2014, Nanoscale.

[21]  Rong Yang,et al.  Biocompatible inorganic fullerene-like molybdenum disulfide nanoparticles produced by pulsed laser ablation in water. , 2011, ACS nano.

[22]  Kostya S. Novoselov,et al.  Two-dimensional crystals: Beyond graphene , 2011 .

[23]  Hua Zhang,et al.  The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. , 2013, Nature chemistry.

[24]  H. Tributsch.  Photoelectrochemical behaviour of layer-type transition metal dichalcogenides , 1980 .

[25]  E. Makovicky.  Crystal Structures of Sulfides and Other Chalcogenides , 2006 .

[26]  Andre K. Geim,et al.  Two-dimensional atomic crystals. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[27]  R. Tenne,et al.  Medical applications of inorganic fullerene-like nanoparticles , 2011 .

[28]  Reshef Tenne.  Fortschritte bei der Synthese anorganischer Nanoröhren und Fulleren‐artiger Nanopartikel , 2003 .

[29]  Martin Pumera,et al.  Layered transition metal dichalcogenides for electrochemical energy generation and storage , 2014 .

[30]  R. Tenne,et al.  Recent progress in the research of inorganic fullerene-like nanoparticles and inorganic nanotubes. , 2010, Chemical Society reviews.

[31]  J. Shan,et al.  Atomically thin MoS₂: a new direct-gap semiconductor. , 2010, Physical review letters.

[32]  H. Krug,et al.  Oops they did it again! Carbon nanotubes hoax scientists in viability assays. , 2006, Nano letters.

[33]  Ib Chorkendorff,et al.  Molybdenum sulfides—efficient and viable materials for electro - and photoelectrocatalytic hydrogen evolution , 2012 .

[34]  R. Shamberger.  Selenium in the environment. , 1981, The Science of the total environment.

[35]  J. Wilson,et al.  The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties , 1969 .

[36]  R. Tenne.  Inorganic Nanotubes and Fullerene-Like Nano-particles: From the Lab to Applications , 2013 .

[37]  T. Mosmann.  Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays. , 1983, Journal of immunological methods.

[38]  Sanjeev Kumar,et al.  Vitamin A as an enzyme that catalyzes the reduction of MTT to formazan by vitamin C , 2000, Journal of cellular biochemistry.

[39]  S. Miyake,et al.  Tribological characteristics of WS2/MoS2 solid lubricating multilayer films , 2003 .

[40]  R. Tenne.  Advances in the synthesis of inorganic nanotubes and fullerene-like nanoparticles. , 2003, Angewandte Chemie.

[41]  Andres Castellanos-Gomez,et al.  Elastic Properties of Freely Suspended MoS2 Nanosheets , 2012, Advanced materials.

[42]  C. Koshland,et al.  Particle-induced artifacts in the MTT and LDH viability assays. , 2012, Chemical research in toxicology.

[43]  Lain-Jong Li,et al.  Large-Area Aiming Synthesis of WSe2 Monolayers , 2013, 1304.7365.

[44]  Qing Hua Wang,et al.  Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. , 2012, Nature nanotechnology.

[45]  Charge density wave, superconductivity, and anomalous metallic behavior in 2D transition metal dichalcogenides. , 2000, cond-mat/0012147.

[46]  Can Ataca,et al.  Stable, Single-Layer MX2 Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure , 2012 .

[47]  Changgu Lee,et al.  Frictional Characteristics of Atomically Thin Sheets , 2010, Science.

[48]  Gang Liu,et al.  PEGylated WS2 Nanosheets as a Multifunctional Theranostic Agent for in vivo Dual‐Modal CT/Photoacoustic Imaging Guided Photothermal Therapy , 2014, Advanced materials.

[49]  H. Tributsch,et al.  Low temperature chemical preparation of semiconducting transition metal chalcogenide films for energy conversion and storage, lubrication and surface protection , 1988 .

[50]  Hao‐Li Zhang,et al.  A mixed-solvent strategy for efficient exfoliation of inorganic graphene analogues. , 2011, Angewandte Chemie.