Graphene: Properties, Biomedical Applications and Toxicity

TANDABANY C. DINADAYALANE, DANUTA LESZCZYNSKA AND JERZY LESZCZYNSKI

1.1 Introduction

Among numerous commercial endeavors, nanotechnology is regarded as the key technology of the 21st century. It provides novel products and facilitates applications of innovative techniques in medicine, pharmacy, computer technology, and sensing. Therefore, it holds promise for potential global socioeconomic benefits. In 2011, there were about 1100 commercial products that include nanomaterials. It is a common belief that nanotechnology could assist in solving many global problems that society faces. These include environmental and health concerns of the fast-growing human population, as well as access to clean water and affordable energy. The quickly growing applications of nanomaterials are due to their unique properties which offer advantages over conventional materials.

The variety of various nanomaterials is too big to cover in a single chapter. Therefore, we decided to focus on one particular class of species and discuss in details its characteristics and applications. Since the 2010 Nobel awards validate the importance of graphene not only in basic research but also in various commercial applications, we selected this nanomaterial as the main subject of our chapter.

The demand for carbon nanostructures, particularly carbon nanotubes (CNTs) and graphene, is increasing rapidly in electrical, mechanical, and biomedical applications. This is due to their outstanding thermal, electrical, mechanical, optical and other unique properties. Although the intense interest and continuing experimental success of graphene-based devices facilitate their various applications, the reliable production of high quality samples of graphene on a large scale is very difficult. At present, great efforts have been made toward the preparation of graphene nanosheets. Among them, the chemical reduction of exfoliated graphene oxide (EGO) is the most commonly used approach due to its low cost for large-scale production. In the case of carbon nanotubes, closely related to graphene, controlling their size and diameter is still very challenging. The availability of carbon nanotubes, both in quality and quantity, has stimulated the worldwide pursuit of carbon nanotubes for technological applications. Nevertheless, carbon nanotubes (especially single-walled carbon nanotubes (SWCNTs)) are still quite expensive. To assist experimental studies, the structures, reactivities, and functionalization of defect-free and Stone–Wales defective SWCNTs have been investigated by our group, using quantum chemical calculations.

The morphology of graphene is different from that of CNTs; for example, the length of CNTs influences their toxicity but graphene and graphene oxide (GO) do not have a "length". An important similarity between these carbon nanomaterials is that both graphene/graphene oxide and carbon nanotube structures vary according to the synthetic processes employed. Such processes can also change their physical properties, including dispersity, surface functionality, and their toxicity. In the materials science world, carbon nanostructures such as fullerenes, carbon nanotubes and graphene are famous for their small dimension and unique architecture, and several possible applications in diversified areas. In addition to these carbon nanostructures, scientists now produce a plethora of carbon-based nanoforms such as 'bamboo' tubes, 'herringbone' and 'bell' structures. Figure 1.1 shows a "family tree" of carbon nanoforms that were obtained by applying various transformations to graphene (details of operations are provided in the figure). Though the diagram is non-exhaustive (primarily for clarity), this chart is useful to classify the nanoforms by morphology and provides a first step towards a standardized nomenclature.

The research involving graphene has grown at a spectacular pace in the last few years. Several potential applications have been proposed for graphene. These include conductive and high-strength composites, energy storage and energy conversion devices, sensors, field emission displays and radiation sources, hydrogen storage media, and nanometre-sized semiconductor devices, probes, and interconnect (Scheme 1.1). Impressive advances have been made in realizing some of the applications of carbon nanotubes and graphene. Graphene is a possible replacement material in applications where carbon nanotubes are presently used. A recent study has revealed that graphene-based liquid crystal devices (LCDs) showed an excellent performance with a high contrast ratio. Thus, LCDs might be the first realistic commercial application of graphene. Like carbon nanotubes, the unique properties of graphene offer a wide range of opportunities and application potential for biology and medicine (Scheme 1.1). Bioapplications of carbon nanotubes and graphene have attracted much attention recently.

Significant recent development and progress in the use of graphene-based materials for biosensors, drug and other delivery systems, and bioimaging have generated much excitement...