Graphene-like Metal-Free 2D Nanosheets for Cancer Imaging and Theranostics

Cancer is a group of complicated diseases that are difficult to cure due to their rapid proliferation, malignant migration, and easy recurrence. It is important to develop new multifunctional materials to promote advanced cancer theranostics systems at early disease stages. 2D nanomaterials with huge planar structures are emerging as superstar materials to provide new perspectives for cancer theranostics. The integration of multimodality imaging and therapeutic approaches contributes to precise early diagnosis and synergistic therapy with significantly enhanced efficiency. Forming heterostructures or composites by building 2D nanomaterial blocks or hybridizing pristine 2D nanomaterials with other materials facilitates their complementary properties. The great success of graphene has driven the discovery and development of new 2D nanomaterials with different optical, electrical, and thermal properties. Compared with other graphene-like 2D nanomaterials, metal-free 2D nanomaterials hold great potential in biomedical applications since they exhibit much better biocompatibility and biosafety. We give an overview of some rapidly emerging graphene-like metal-free 2D nanomaterials including black phosphorus, hexagonal boron nitride, and graphitic carbon nitride, as well as 2D organic polymer-based nanomaterials, and highlight their impressive advances for bioimaging and cancer theranostics in recent years. The challenges and some thoughts on future perspectives in this field are also addressed. The great success of graphene has driven the discovery and development of new 2D nanomaterials with different optical, electrical, and thermal properties. Compared with other graphene-like 2D nanomaterials, metal-free 2D nanomaterials hold great potential in biomedical applications since they exhibit much better biocompatibility and biosafety. We give an overview of some rapidly emerging graphene-like metal-free 2D nanomaterials including black phosphorus, hexagonal boron nitride, and graphitic carbon nitride, as well as 2D organic polymer-based nanomaterials, and highlight their impressive advances for bioimaging and cancer theranostics in recent years. The challenges and some thoughts on future perspectives in this field are also addressed. a membrane composed of endothelial cells tightly bound together, preventing harmful molecules from damaging the brain. the appearance of nanoparticles, such as shape, size, dimension, and other properties. a biomedical imaging modality where nonionizing laser pulses irradiate biological tissues. The tissues absorb the energy and convert it to heat, resulting in ultrasonic images. a process where a nontoxic photosensitizer generates reactive oxygen species, which activate the cellular apoptosis pathway and destroy subcellular organelles under the irradiation of specific wavelengths. one form of luminescence; the process of reradiating photons after a substance has absorbed photons. a noninvasive approach to induce the death of cancer cells or ablation of tumor tissue assisted by agents with high photothermal conversion efficiency. the ratio of utilized photons to total absorbed photons, representing the utilization rate of light quanta in photochemical reactions. a new concept that represents a combination of diagnostic imaging and therapy. polymers that generally consist of π-conjugated backbones that show light absorption and emission as well as hydrophilic side chains that enable the polymer to dissolve in aqueous solution.