Two-dimensional (2D) materials are a special class of materials having a wide range of applications due to their various advantages like high aspect ratio, high surface to volume ratio, improved mechanical/ optical properties, etc., than those of their bulk counterparts. After the discovery of graphene in 2004, other layered materials like hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDC) attracted significant interest to the scientific community. Different exfoliation techniques like mechanical exfoliation, ball milling, liquid-phase exfoliation (LPE), gas-phase exfoliation, etc have been employed to obtain graphene-like nanosheets. Immediately, these exfoliated materials find their utility in a large number of applications. One of these application sectors is bioelectronics which is growing rapidly over the past few years because of its wide range of applications like sensing, point-of-care monitoring, wearable devices, implants, etc.
To use 2D materials in these applications, the processing steps have to be environment-friendly and safe. The processing solvent preferably has to be water. This is the most important criterion to use those materials in bioelectronics. However, obtaining water dispersion of 2D materials is really a challenging task since most of these materials are hydrophobic in nature. Although, there are numerous reports in the literature, describing the methods of obtaining aqueous dispersions of 2D materials. However, in most of the reports, surfactants/additives were used to obtain aqueous dispersion. This is an old-school technique to make hydrophobic material hydrophilic. Most often complete removal of surfactants is impossible which ultimately degrades the device’s performance. Therefore, obtaining additive-free aqueous dispersion of 2D materials remains challenging. Recently, our paper published in Chemistry-A European Journal (10.1002/chem.202005491) solves all these problems.
Here, employing a simple pre-processing step makes our life easier. Firstly, h-BN and TMDC (e.g. MoS2, MoSe2, WSe2) are liquid phase exfoliated in an organic solvent. Secondly, the dispersions are dried to obtain powders which are subsequently ultrasonicated for few minutes in water to obtain water dispersion. The obtained aqueous dispersion is found to be well stable for a reasonable duration of time.
In this paper, we also studied the glial cell compatibility and enzymatic degradation of these 2D materials (h-BN and MoS2). Cytocompatibility and biodegradation studies are indispensable parts of bioelectronics because these materials should degrade automatically after finishing their intended task for a definite period of time. Also, the degradation byproduct has to be non-toxic for safe use inside the human body as well as for the environment. Biodegradation of h-BN and MoS2 has been confirmed through Raman spectra and transmission electron microscopy. Besides, it is observed that these 2D materials are safe for glial cells up to 100 μg/mL. The whole paper can be summarized through the following schematic.
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