In this blog post, we will examine the exceptional properties of nanomaterials, along with the risks they pose to human health and the environment—including carbon nanotubes—issues related to exposure during production and use, and the biomolecule-based detection techniques developed to identify them.

Why Have Nanomaterials Opened Up New Possibilities?

It is often said that if the 20th century was the century of the “micro,” the 21st century will be the century of the “nano.” One nanometer—equivalent to one-billionth of a meter—is about the size of three to four atoms lined up side by side, making it much smaller than a cell or a virus. The reason the scientific community has recently been focusing on nanomaterials is due to the unique phenomena that occur in the nanoscale world. The exceptional mechanical, electrical, and optical properties that arise from the arrangement of atoms at the nanoscale are opening up new possibilities for devices and materials across various fields. As a result, the use of nanoparticles has expanded significantly over the past few decades, and research and applications of nanomaterials continue today in diverse fields such as electronics, energy, the environment, and medicine. However, many scientists are also warning about the risks associated with nanomaterials, which are like a double-edged sword. Let’s take a closer look at the risks of nanomaterials and the methods to address them.

Why can carbon nanotubes be hazardous?

Of course, advances in nanotechnology have dramatically expanded the boundaries of what we can achieve. For example, they are opening up possibilities for solving problems that were once considered intractable, such as selectively eliminating cancer cells or developing new superconducting materials. Carbon nanotubes, among the most widely used nanomaterials, are utilized in various fields—including composites, electrical and electronic engineering, energy, the environment, and biotechnology—due to their extremely light weight and high mechanical strength. However, studies on the environmental and human health hazards of carbon nanotubes have pointed out that, because of their very small diameter, they can become airborne or be inhaled during work processes, and they are difficult to remove or recover from aquatic environments. In particular, it has been reported that some carbon nanotubes cause inflammation in the lungs when inhaled, and prolonged or repeated exposure may lead to problems such as pulmonary fibrosis or granuloma formation. However, it is also important to consider that the toxicity of carbon nanotubes does not manifest identically across all types; it can vary depending on factors such as length, diameter, surface properties, agglomeration state, impurities, exposure levels, and exposure routes.

Can gold nanoparticles and silver nanoparticles be considered safe?

The issue is not limited to carbon nanotubes. Even in the case of gold nanoparticles and silver nanoparticles—representative nanomaterials that are relatively well-known to the general public—research has shown that, due to their high surface reactivity and physicochemical properties at the nanoscale, they may cause effects related to reactive oxygen species (ROS) production or cellular-level oxidative stress when introduced into the body. In particular, the biological effects of silver nanoparticles can vary depending on the release of silver ions, particle size, and surface properties, and research on their toxicity to cells and tissues is ongoing. Similarly, the behavior and toxicity of gold nanoparticles within the body can vary depending on their size, shape, and the substances bound to their surfaces. Given that the scale of use of these metal and metal oxide nanomaterials has expanded significantly compared to the past, it is difficult to ignore the potential biological and environmental risks posed by the development and use of products containing nanomaterials.

How are nanomaterials released into the environment during production and use?

Are these nanomaterials, for which such risks have been raised, being thoroughly managed during their production and use? It is difficult to say that this is entirely the case at this point.
Studies examining the entire life cycle of nanomaterials have raised concerns that nanomaterials may be released into the workplace, the atmosphere, or aquatic environments during research, production, processing, use, and disposal. In processes involving nanomaterials, a significant portion of the raw materials may not be converted into the final product but may remain as byproducts or waste; furthermore, some nanomaterials may be released into the environment during cleaning or wastewater treatment processes. In particular, because nanomaterials are extremely small and have unique surface properties, it is difficult to assume that they behave in the same way as ordinary particles. In some cases, it is difficult to produce uniform nanomaterials during the manufacturing process; furthermore, if the produced nanomaterials are not fully converted into the final product within a completely sealed environment, the unused material undergoes disposal or cleaning processes. During these processes, some nanoparticles may be released into the atmosphere or aquatic environments. The behavior of nanoparticles released into the environment varies depending on the type of material, its surface properties, and the surrounding environment; some substances do not degrade easily and may remain in the environment or bind to other substances and migrate. Therefore, when assessing environmental exposure to nanomaterials, it is necessary to consider not only the production stage but also the entire life cycle, from production through use to disposal.

Why Has It Been Difficult to Detect Nanomaterials?

One reason why nanomaterials are difficult to manage—despite their potential to cause serious environmental and biological problems—is their size. Because they are extremely small—measuring one-billionth of a meter—it has been difficult to accurately determine their presence, concentration, size, shape, and surface properties using conventional physical and chemical analytical methods, let alone through visual observation. However, as our understanding of the various physical and chemical reactions occurring in the nanoscale world has recently deepened, diverse analytical and detection techniques for identifying and quantifying nanomaterials have been developed. Among these, methods that utilize interactions between biomolecules and nanomaterials have emerged as an important area of research. While it is difficult to replicate the various chemical reactions that occur within living organisms exactly in a laboratory setting, simulating and applying molecular-level interactions found in nature can lead to the development of new methods for detecting nanomaterials. For example, in the case of carbon nanotubes, sensors and detection systems can be developed by utilizing the property whereby biomolecules, such as DNA, interact with the surface of carbon nanotubes. DNA bases can bind to the surface of carbon nanotubes through π-π interactions, and by utilizing this property, it is possible to detect specific substances by measuring the structural, electrical, and optical changes formed by the interaction between DNA and carbon nanotubes. In other words, this approach detects nanoscale substances—which were previously difficult to identify using conventional analytical methods—by leveraging interactions at the level of tiny, invisible molecules. In fact, research on sensors utilizing the binding of DNA to carbon nanotubes has led to the development of highly sensitive analytical methods capable of detecting target substances at extremely low concentrations. This approach has the potential to be applied not only to carbon nanotubes but also to the detection and analysis of various metal and metal oxide nanoparticles, and related research continues today in the fields of nanobiosensors and nanosensors.

How should the advancement of nanotechnology and risk management go hand in hand?

As science advances, the scope of human curiosity has shrunk to the atomic level while simultaneously expanding to the scale of the solar system. Although the benefits of advanced civilization make daily life more convenient for many people, it is by no means a desirable attitude to simply enjoy these benefits while ignoring the problems that may arise as a result. The acceptance of nanotechnology is an indispensable milestone for future scientific progress. Even now, numerous computer circuits, new materials, and medical technologies are being researched based on nanoscience, and the scope of nanomaterial applications continues to expand. However, the risks that nanomaterials pose to the human body and the ecosystem vary depending on the type and characteristics of the material, as well as the route and level of exposure, and there are still aspects that have not yet been fully elucidated. Therefore, before using nanoparticles, we must thoroughly assess the risks they pose to living organisms and the environment and ensure they can be used safely within manageable limits. There is a saying that nature knows the answer. In the case of nanoparticles, we are seeking breakthroughs by understanding the molecular-level interactions found in nature and learning how to harness them. Rather than pursuing only the benefits gained through indiscriminate development, we must also pay attention to identifying and resolving the risks that may arise during that development process. The true advancement of nanotechnology will not stop at creating new possibilities; it will begin with understanding and managing the risks that those possibilities may bring.