Graphene oxide (GO) is a two-dimensional carbon nanomaterial derived from graphene. It is chemically modified to possess unique, highly versatile properties. Understanding the material’s interaction with the human body is necessary due to its potential for widespread use. This article examines the structure of GO, its pathways of exposure, its biological fate, and the specific adverse effects observed in controlled studies, providing an overview of safety considerations.
Graphene Oxide: Structure and Potential Applications
Graphene oxide is a single layer of carbon atoms arranged in a hexagonal lattice, similar to graphene. The fundamental difference is the presence of oxygen-containing functional groups, such as hydroxyl, epoxy, and carboxyl groups, attached randomly to the sheet’s surface and edges. These groups disrupt the carbon lattice, making the material less electrically conductive than pure graphene, but they make it hydrophilic. This hydrophilicity allows GO to disperse easily in water and biological fluids.
Scientists are exploring GO for numerous applications due to its high surface area, mechanical strength, and chemical tailorability. In biomedicine, GO is being developed as a nanocarrier for targeted drug and gene delivery. Its properties are also being investigated for use in biosensors, tissue engineering scaffolds, and various consumer products, increasing the likelihood of human contact.
Pathways of Human Exposure
Graphene oxide can enter the human body through several recognized pathways, based on its current and anticipated uses in manufacturing and biomedical research.
- Inhalation: This is a primary route for workers handling GO in powder or aerosolized forms, as airborne particles can deposit deep within the respiratory tract.
- Ingestion: This occurs if the material is incorporated into food contact materials, packaging, or accidentally swallowed in occupational settings.
- Dermal exposure: This happens when the material contacts the skin, such as during manufacturing or through products like cosmetics.
- Direct administration: This is a deliberate route in clinical or research settings, typically via intravenous injection.
Biological Interactions and Biodistribution
When graphene oxide enters the body, its initial interaction is with proteins in biological fluids. These proteins rapidly coat the GO surface, forming a “biomolecular corona,” which determines how the body recognizes and processes the foreign material. Immune cells, particularly macrophages, attempt to engulf the GO sheets through phagocytosis to clear the material.
The material’s ultimate fate, or biodistribution, depends heavily on its physical characteristics, such as size, shape, and surface functionalization. Smaller GO sheets are more readily excreted, while larger sheets tend to accumulate. GO accumulates in organs with high blood flow and filtering functions, including the liver, spleen, and lungs. This accumulation leads to long biopersistence, meaning the material remains in these tissues for extended periods, raising concerns about long-term health effects.
Specific Mechanisms of Toxicity and Adverse Effects
The adverse effects of graphene oxide are linked to its ability to induce cellular damage through several specific mechanisms observed in non-human studies. One major mechanism is the generation of Reactive Oxygen Species (ROS), which leads to a state of oxidative stress within cells. This excess ROS damages essential cellular components, including lipids, proteins, and DNA, leading to cellular dysfunction and reduced cell viability.
Graphene oxide sheets can also cause direct physical damage to cellular structures. The sharp edges of the material physically disrupt the integrity of cell membranes, leading to leakage of intracellular contents and cell death.
The body’s response to the material is often an inflammatory reaction. GO exposure can trigger the release of pro-inflammatory signaling molecules (cytokines), leading to inflammation and, in the lungs, potentially resulting in chronic fibrosis or the formation of granulomas. Genotoxicity is also a concern, where GO exposure has been shown to cause direct damage to DNA strands. The observed toxicity is dose-dependent, and the current understanding of these side effects is predominantly derived from controlled in vitro and animal models.