black phosphorus is a new class of two-dimensional materials that exhibits exceptional physio-chemical, electronic and optical properties. It has strong light matter interactions, high carrier mobility, tunable band gap and anisotropic physical characteristics. These attributes contribute to its excellent biomedical applications like photonic/photoacoustic/photodynamic therapies, diagnostic imaging (including cancer imaging), biosensing, drug delivery, tissue engineering etc.
Unique layered structure and layer dependent band gap of BP is one of the major features that has drawn immense attention from the scientific community recently. Unlike other group IV elemental layered materials such as graphene and silicene, BP is composed of only phosphorus atoms with each phosphorus atom having five outer shell electrons resulting in zig-zag and armchair crystalline structures.
Compared with other 2D materials such as graphene, WSe2, MoS2 and h-BN, BP possesses better biocompatibility in its nanodot or monolayer form, which makes it eligible for various biomedical applications. In addition, it shows higher in vivo biodegradability and less cytotoxicity when compared to graphene and molybdenum disulphide.
Chemical sensing with BP is another unique feature that has attracted a lot of attention in recent times. BP shows very selective response to NO2 gas, whereas other chemical gas sensors such as WSe2, graphene, MoS2 show no response to oxygen functionalized analytes. Hence, BP is a good choice for chemical gas sensing application due to its selectively tunable band gap and non-toxic biodegradability.
Various synthesis methods for few layer BP have been developed in recent years to synthesize this material in atomically thin sheets at a wafer scale. However, adsorption of organic solvents on the surface of as-exfoliated nanosheets is still a major problem which can be overcome by utilizing surface stabilization assisted hydrothermal exfoliation.