Two-dimensional cancer theranostic nanomaterials: Synthesis, surface functionalization and applications in photothermal therapy

In recent years, novel two-dimensional (2D) nanomaterials are of great interest for diverse potential applications such as device fabrication, energy storage, sensing and theranostics because of their superlative physical features namely, large surface area, minimal thickness, tunable composition and easier surface modification methods. Rapid exploration in design and fabrication of 2D nano-structures have opened new avenue for cancer theranostics as it can encapsulate group of cancer cells and inflict major damage with great specificity in a non-invasive manner. Among the reported 2D materials such as graphene and its derivatives, metallic compounds, transition metal dichalcogenides (TMDC), black phosphorous and MXenes (e.g., carbides, nitrides, or carbonitrides), 2D nanomaterials based on graphene and TMDCs have gathered most of the limelight in this field due to their easily tunable properties. In this review, we summarize recent progress in the design of 2D theranostic nanomaterials, functionalization methods and their applications in photothermal therapy (PTT) as well as synergistic cancer therapy. We have also addressed the different modes of cellular entry of 2D nanomaterials into tumor cells based on their unique structural properties and investigated different methodologies to enhance PTT effect by optimizing the physico-chemical properties of the 2D sheets. Recent progress on in vitro and in vivo short and long term biocompatibility, immunotoxicity and excretion of the decorated structure is also highlighted. Investigation of the interaction of 2D nanomaterial with hematological factors such as RBC and WBC is of paramount importance as they are key indicators in in vivo responses, and this investigation will give a better solution for overcoming direct inflammation and infection related issues of the animal system. Besides, investigations on addressing the ways to incorporate polymer linkers and drug conjugates on to the surface of 2D materials, multiplexing capability, and the influence of surface functionalization on PTT effect is vital for future developments in clinical level diagnosis and cancer therapy. Finally, we conclude our opinion on current challenges and future prospective on meeting the various demands of advanced cancer imaging and therapies.