Enzymatic Biodegradability of Pristine and Functionalized Transition Metal Dichalcogenide MoS2 Nanosheets

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com (1 of 12) 1605176 in air and aqueous media. Indeed, the stability of such nanomaterials can influence their behavior in the different types of envisaged uses.[3–5] MoS2 is considered relatively chemically inert in ambient conditions. However, its chemical stability, optical and electrical properties are dependent on its crystalline phase. The most common crystalline phase of MoS2 is the trigonal prismatic (2H phase). In this phase, MoS2 acts as semiconductor, while in the orthogonal phase (1T phase) MoS2 acts as metal.[6] MoS2 in 1T phase is more reactive than in 2H phase, the latter being inert toward most of the chemicals. Indeed, the difference in their electronic states dictates the chemical reactivity of these two crystalline forms of MoS2. Although metastable, it has been shown that 1T phase of MoS2 can be stabilized by insertion of Li+ ions into its crystal lattice, and recently covalent functionalization resulted also effective in stabilizing this phase.[7] Earlier, Voiry et al. reported a simple and efficient route for covalent functionalization of MoS2 sheets facilitated by electron transfer between electron-rich metallic 1T phase and organohalides leading to semiconducting MoS2. Covalent functionalization of MoS2 sheets was also achieved by exploiting the reactivity of surface and edge defects.[8] The defects on the lattice of MoS2 were modified, for example, by functionalization with thiols leading to MoS2 sheets with tuned electronic properties.[8] Alternatively, electron transfer characteristics of MoS2 can be altered by complexation between MoS2 layers and optoelectronically active molecules like phthalocyanines.[9] Besides the development for electronics, optoelectronics, and catalytic applications, to mention few of them, biomedical applications of exfoliated TMDCs are increasingly attracting the attention as promising alternatives to graphene. This is mainly due to their high biocompatibility compared to other nanomaterials and strong contrast properties because of the presence of heavy elements like Mo, W, Bi, etc.[3] In this context, TMDCs showed high potential in drug delivery, cancer theranostics, antimicrobials, bioimaging, and biosensing.[3,10–12] Near-infrared light-mediated multimodal cancer theranostics based on TMDCs seems to be more promising for biomedicine due to higher photothermal conversion ability as well as stronger contrasting nature over carbon nanomaterials.[3] However, a limited number of data on toxicity are available, while Enzymatic Biodegradability of Pristine and Functionalized Transition Metal Dichalcogenide MoS2 Nanosheets