Stabilized graphene nanohybrids: magnetism and cancer therapy

The thesis conceives few important contemporary problems that are faced by graphene researchers, through its title, “Stabilized Graphene Nanohybrids: Magnetism and Cancer Therapy”. Even though, the experimental realization of graphene challenged the Mermin-Wagner theorem, graphene continues to be at the centre of research world by surprising the research community with its established astonishing attributes and mesmerising with scientific developments from time to time. The thesis revolves about the understanding of the intriguing magnetism of graphene and designing a suitable nanohybrid for cancer treatment applications. This is achieved through synthesizing graphene and its derivatives by novel techniques. Further, the origin of magnetism is explored. Finally, we demonstrate ways to tackle few generic issues of this wonder material for potential applications. There are seven chapters in the thesis. The first chapter clearly expresses the aim, motivation and the highlights of the project undertaken. The second chapter gives a brief review of the literature in concerned areas that is necessary to comprehend the mid-chapters, thereby contributing to the growth of it. However, specific literature survey could also be found in the introduction of every chapter. The third chapter gives a novel method to synthesize luminescent graphitic quantum dots by exposing the size reduced graphene oxide to UV radiation. These quantum dots showed defect mediated ferromagnetic behavior. The chapter four reports the production of bi- and tri-layered graphene solution by liquid phase exfoliation of graphite at high temperature and pressure. The bi- and tri-layered graphene were found to be twisted and with lesser defects due to the oxidation or reduction free synthesis. These types of twisted graphene are potential candidates for spintronics applications. Further, the origin of magnetism and deconvolution of the mixed magnetism in exfoliated graphite is discussed. The mixed magnetism in exfoliated graphite is deconvoluted using low field-high field hysteresis loops at different temperatures. The strength of the interactions among the edge states (intra- and inter-zigzag), the external field and the temperature play important roles in deciding the final magnetic state of the system. The chapter five solves a serious problem of reduced graphene oxide pertaining to its dispersion stability that has impaired its use in several commercial applications. The reduced graphene oxide is stabilized using cross-linking polymers, thereby improving its bio-compatibility. The dispersion follows an electrosteric stabilization mechanism. Also, various theoretical models were adopted to understand this enhanced stability by estimating the potential barrier for agglomeration, surface free energy and Hansen solubility parameters of the dispersion. The chapter six combines few of the above synthesis techniques to produce a polymer stabilized iron oxide-graphene nanohybrid that has good response to the thermo-chemotherapy of cancer. The synthesis procedure is simple and easy to commercialize for large scale production due to its one-pot approach. The nanohybrid is found to have a good colloidal stability and is also biocompatible even at higher concentrations (2.5 mg/ml) by virtue of cross-linking polymers. The bio-compatibility of the composite is tested using HeLa cell lines by computing the percentage of the reactive oxygen species. The composite has the ability to load and release both hydrophobic and hydrophilic drugs with a good loading efficiency and capacity. Under an AC magnetic field, it takes less than 16 min to reach the stable hyperthermia temperature, suggesting it as a good anticancer material. A time-dependent cellular uptake of doxorubicin-conjugated composite has been studied to optimize the parameters for thermo-chemotherapy of cancer. The synergetic effect of both, the drug and hyperthermia is observed in the killing of the cancerous cells-verified by computing the cell apoptotic population using a flow cytometer. However, it has been noticed that, even in the absence of chemotherapy, the composite shows good antiproliferative activity with thermotherapy alone. Finally, the chapter seven summarises the thesis and outlines any future prospects. The thesis have produced five international journal articles (Carbon, RSC Advances, Applied Physics Letters, Journal of Physical Chemistry C, and ACS Applied Materials & Interfaces). The thesis winds up with a gratefulness to the persons who have directly or indirectly contributed for its existence. Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia.