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Enhanced Exfoliation of Biocompatible MoS Nanosheets by Wool Keratin Xiangyu Xu, Jianyang Wu, Zhaohui Meng, Yanran Li, Qiaoling Huang, Yue Qi, Yufei Liu, Da Zhan, and Xiang Yang Liu ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00788 • Publication Date (Web): 24 Sep 2018 Downloaded from http://pubs.acs.org on September 25, 2018
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Enhanced Exfoliation of Biocompatible MoS2 Nanosheets by Wool Keratin iaoling Huang,, Xiangyu Xu,† Jianyang Wu, † Zhaohui Meng,† Yanran Li,† Qiaolin g Huang han,,*† Xiang Yang Liu*†‡ Yue Qi,† Yufei Liu,§ Da Zhan †Research
Institution for Biomimetics and Soft Matter, Fujian Key Provincial
Laboratory for Soft Functional Materials Research, College of Materials & College of Physical Science and Technology, Xiamen University, Xiamen, 361005, PR China E-mail:
[email protected] ‡Department
of Physics, National University of Singapore, 2 Science Drive 3,
Singapore 117542, Singapore. E-mail:
[email protected] §Key
Laboratory of Optoelectronic Technology & Systems (Chongqing University),
Ministry of Education, Chongqing, 400044, China
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ABSTRACT: The unique properties of thin-layer transition metal dichalcogenides (TMDs) materials have been extensively investigated for both fundamental studies and practical applications in recent years. To develop the TMDs for medical engineering and bioelectronics in practical applications, the exfoliation and stabilization of TMDs using naturally biocompatible protein agents are highly demand. However, such strategies are far from being thoroughly studied. In this article, we present that wool keratin can assist exfoliation of MoS2 in aqueous solutions under sonication. And, the wool keratin exfoliation of 2D material is systematically verified by molecular dynamics calculations and a series of experimental data observations. Moreover, compared with the traditionally used naturally biocompatible BSA under the same experimental conditions, wool keratin has been deemed to have an obvious better performance in exfoliating bulk MoS2. Relevant theoretical analysis indicates that high sulfur-containing functional groups on wool keratin molecules could provide sufficient possibility for the effective adsorption at the edges of MoS2 nanosheets. This discovery ensures that wool keratin biomolecules can provide superior colloidal stability for high concentration dispersion. The related investigations indicated that the biocompatibility of WK-MoS2 films can also be demonstrated well on the basis of cell proliferation and viability assays. We also proved that wool keratin has a universal property for exfoliation of other types of two-dimensional materials. This discovery offers some new ways and opportunities for exfoliation of MoS2 and its biological applications.
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KEYWORDS: wool keratin, two-dimensional (2D) material, transition metal dichalcogenides (TMDs), liquid-phase exfoliation, nanosheets 1. INTRODUCTION Since the discovery of graphene in 2004,1-2 two-dimensional materials have begun to become one of the focuses for scientists in physics, chemistry, and biology. Although the two-dimensional (2D) materials possess the chemical composition as same as their counterpart bulk forms, they show obvious different properties in physics and chemistry.3-7 Transition metal disulfides (TMDs) are a category of bulk layered materials, which can be exfoliated into 2D state with extraordinary electronic properties to be potentially applied practically in next generation of flexible nanoelectronics. Among all TMDs, molybdenum disulfide (MoS2) is most representative and has been widely studied in the fields of field effect transistor,8-9 optoelectronic
devices,10-11
biosensors,12-13
new
energy14-15
and
bioimaging
technologies16-17 in recent years. To date, the preparation methods of MoS2 nanosheets fall into two categories, one is bottom-up, the other is top-down.18 The former methods including hydrothermal synthesis19 and chemical vapor deposition,20 can produce large-area ultrathin film, but usually require harsh reaction conditions and complicate post-treatment. The later one, including the most simple method tape exfoliation,8 can produce the very good crystalline quality nanosheets for fundamental research but cannot be applied practically due to the extremely low yields. To compromise the cost and efficiency, the liquid phase exfoliation has been rapidly developed due to its advantages of low manufacturing cost and mass production.21-23 3
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To summarize, most of the solvents used in the liquid phase exfoliation are limited to surfactants or organic solvents.22, 24-30 And it is usually considered that surfactants provide layered materials colloidal stability through adsorption of their hydrophobic section onto the layered surface, whereas their hydrophilic head is usually oriented towards the water molecules. Furthermore, the structural transformations of the surfactant in the adsorbed layer would be associated with changes in the stabilized ability of this kind of layered materials and the dispersed concentrations.31 Despite the fact that they can be fulfill the industry applications in various areas, however, most of these surfactants are derived from synthetic origin, which raises concerns as regards the high cost, environmental pollution and the bio incompatible property with living tissues, greatly restricting their development in biomedical field.32 In order to broaden the applicability of 2D materials obtained by direct liquid-phase exfoliation, biomolecules have received increasing attention as dispersants for 2D materials in recent years, as they can greatly improve the biological/environmental performance over more conventional, synthetic dispersants. Successful exfoliation and stabilization of 2D materials by biomolecules benefit from the amphiphilic character of the biomolecules themselves. In recent years, research in this area has developed rapidly, including various biomolecules such as proteins,33-38 nucleic acid39-40 and polysaccharides24, 41. Guan et al.35,
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reported that the functional groups of BSA
protein were preferentially bound to MoS2 through hydrophobic interaction, which successfully exfoliated the stable MoS2 to nanosheets in aqueous solutions while maintaining good biocompatibility. Sim et al.36 reported that hydrogen bonding 4
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between the O-H groups on the protic polar solvent molecules and the polar side groups of silk fibroins contribute to stabilization of the MoS2 dispersion. Although there are many other biocompatible protein materials available, the published studies on the effective exfoliation and stabilization of TMDs are still underexposed. In this work, we present wool keratin (WK) assisted exfoliation of MoS2 in aqueous solutions. By introducing the effects of high sulfur-containing functional groups on wool keratin in detail, it is revealed that the using WK gives rise to higher efficiency for exfoliation of MoS2 nanosheets (the WK assisted exfoliation for other 2D materials is also demonstrated), while it also performs a good biological compatibility.
2. EXPERIMENTAL 2.1. Materials Molybdenum sulfide (MoS2) (99.5% metals basis,
