The origins of nanoparticles

Around 1960, Richard Feynman proposed a revolutionary idea at the time, making machines even smaller. Perhaps Richard Feynman’s idea fueled the fascination with nanoparticles. However modern nanotechnology only really started to gain traction in the 1981s with the invention of the scanning tunneling microscope, designed to map images of surfaces at the atomic level. But was that the start?

The fascination with division has always been there. In ancient Greece, Democritus theorized that matter is continuous and could be infinitely divisible. Meanwhile, the Greeks coined the term “atomos” meaning “indivisible,” however, we now know that even an atom can be split. Perhaps there are even more types of divisions yet to be discovered. Nano on the other hand has a reference in Greek as a prefix meaning “dwarf.” The American Society for Testing and Materials (ASTM) has set a global standard for nanoparticles to be three-dimensional and have to be between 1 and 100 nm in size to be defined as a nanoparticle. It is possible in the coming decades to come, that smaller particle sizes will be defined, perhaps even redefining existing ones.

Nanoparticle continuous formation
Moving forward, nanotechnology and particle science have sparked a lot of interest and have created a deeper understanding and potential over the last four decades in industries such as energy, aerospace, electronics, pharmaceuticals, food, and biotech sectors. The potential end benefits of nanoparticle technology and integration in the products we use daily, both internally and externally, are unlimited. Presently, you could define two origins or sources of nanoparticles. One is from naturally occurring phenomena and the other from anthropogenic sources. Natural nanoparticles are formed naturally by the elemental interactions in nature due to chemical, material friction, and biological processes such as physical fragmentation of natural elements like earthquakes, erosion, biochemical weathering of minerals, photo-oxidative chain reactions, oxidation-reduction reactions, gas-solid nucleation in our atmospheric layers such as the thermosphere, mesosphere, etc., and precipitation. Large amounts of particles undergo continuous cycles of nucleation, sorption, aggregation, precipitation, chemical reactions, and transportation through water, earth, and air.

As previously mentioned, natural nanoparticles are a part of the environment and have existed since the earth was formed. The cycle of physical fragmentation of solid material due to natural emissions is an ongoing continuous process. Examples include spray from ocean/sea water or waterfalls, Sahara sand/dust storms, volcanic activity forming ash plumes, nanoparticle formation in clouds due to nucleation, and iron oxidation. Microorganisms such as viruses, bacteria, fungi, algal, and yeast cells even can transport metals from their environment and convert them to nanoparticles which are either accumulated and stored within the organism or secreted back into the environment.

Anthropogenic nanoparticles
Anthropogenic nanoparticle sources, on the other hand, are man-made or indirectly caused by human activities that interfere with and add to natural nanoparticle cycles. There are two main categories of anthropogenic nanoparticles. The first category began during the industrial revolution and has grown exponentially in its use and exposure. These nanoparticles are produced from combustion particulates such as petrol, LPG, diesel exhaust gases, soot, carbon black, welding fumes, and bituminous coal ash, among others. They mostly have mixed chemistry and range in size from 1 to 5 nanometers (nm), with larger soot particles between 10 to 100 nm.

The second category of anthropogenic nanoparticles is specifically engineered in laboratories and industrially manufactured and produced, such as dendrimers, nanotubes, micelles, quantum dots, titanium dioxide coatings, and several others. Their abundance is increased through human use of products containing nanoparticles, which eventually will be released into the environment through either their initial production, industrial processes, consumer use, or landfills. This results in the absorption of a diverse array of nanoparticles in animals, other organisms, and the environment. While the emissions of these particles still pose health risks and contribute to global ground, water, and atmospheric pollution, it is still unclear what their long-term biological and environmental impact could be.

Although the exact number is unknown, it is safe to assume that a large volume of nanoparticles is knowingly and unknowingly being released into the environment. The reason for this is due to their smaller size and unique properties, the particles are being incorporated with great success into manufacturing processes and implemented into the products we use daily. For example, nanoparticles are being used in a diverse array of products such as surface or particle coatings, in fossil and biofuels, as additives in paints and many other liquids and powders, and in pesticide formulations, fertilizers, foods, medications, and feeds. Additionally, nanoparticles are also being formed, as by-products due to combustion reactions of fossil fuels, bio-energy, and bio-fuels in engines, turbines, and many industrial manufacturing processes.

By the middle of the 20th century, the effects of wide-scale pollution were beginning to be noticed in countries around the world, with only a  minor global population estimated at 2.5 billion consuming resources and using products.  Since then, aside from the continuous natural nanoparticle cycles in nature, human industry, and consumer goods have increased exponentially in the past decades, the occurrence of anthropogenic particles in the environment, has therefore also continuously increased due to the industrial expansion and the increased human activity. Moving forward to 2022 with a global population of around 8 billion, it is evident that anthropogenic particle pollution will rise considerably and pose a significant threat to the environment and health of all animals on the planet if not properly understood and addressed.

For example, nanoparticles are vigorously being researched and patented for use in the agriculture, food industries, and various consumer products. However, many studies have already shown that nanoparticles could be toxic to humans and animals, but there are currently few regulations governing their use and production. Another important factor is that nanoparticles are also more difficult to detect than regular particles, they show low mass concentrations but exhibit a higher overall concentration, because of their smaller particle size. Despite this, their use in various industries continues to be explored and implemented. Therefore there is a growing need to create experimental protocols for synthesizing nanoparticles that are reliable, nontoxic, clean, eco-friendly, and green. Meanwhile working on formulating a deeper understanding and some kind of regulation, concerning nanoparticles and their potential environmental risks.

Nanoparticle synthesis
As could be imagined nanomaterials are the fundamental principle of nanoscience and nanotechnology applications and can be designed to form specific shapes and sizes while being synthesized through various methods, Because of their smaller size, nanoparticles have a  higher surface energy and an increased reactivity due to their relative larger surface area to volume ratios. These unique properties can make nanoparticles useful in various materials such as ceramics, polymers, metals, and biological molecules and also function as catalysts, drug delivery systems, or as sensors.

There are several ways to produce metal and other nanoparticle materials. For example, nanoparticles can be synthesized through chemical synthesis whereby chemical reactions are used such as to produce nanoparticles from precursor materials. Like, the reduction of metal ions by a reducing agent, through the precipitation of metal salts. This method can be used to synthesize a wide range of nanoparticles, including metals, ceramics, and polymers. Another synthesis method is physical vapor deposition which involves the evaporation of a selected material and its condensation on a substrate, which then forms a thin film of desired material such as metals and ceramic nanoparticles. Other methods for synthesizing nanoparticles include laser ablation, electrochemical synthesis, template-assisted synthesis, self-assembly, and even biosynthesis of nanoparticles using bacteria.

Nanoparticle properties
Nanoparticles are of interest for applications due to their unique characteristics mentioned previously. Being smaller in particle size than the same material on a larger scale makes nanoparticles useful in various applications. Some of the characteristics of nanoparticles include the aforementioned higher surface area to volume ratio resulting in higher surface energy and more reactivity compared to the larger particle of the same material. nanoparticles also exhibit improved electrical conductivity, enhanced thermal stability, more versatile mechanical strength, better-sintering characteristics, and enhanced catalytic activity, which makes them ideal in catalytic reactions and function as catalysts in chemical processes. Their smaller size also enables bioengineers to design nanoparticles to function and be used as drug carriers, allowing for the targeted delivery of drugs to specific cells or tissues in the body. Furthermore, the small size of nanoparticles can also lead to improved sintering behavior, which helps the process of forming a solid mass from a powdered material without really melting it. Nanoparticles also possess unique optical properties, such as enhanced light absorption or scattering, which can be utilized in optoelectronic and photonic applications. The benefits of nanoparticles are clearly of great interest and usefulness in producing the products and technologies we use.

In summary
Nanotechnology is a positive direction for technology to advance into. It is not a stretch to believe that nanotechnology will be the future, considering the trend of technological hardware has become smaller and smaller in the past century. Research, innovation, and advancements in various industries have improved production methods, increase global awareness, and enhanced the technology available to us. The advancements in technology can be seen across all sectors, bringing us closer to equilibrium on a global scale. The progress humanity has made in the past decades, including both successes and failures, has led us to where we are today. It is important to find a balance between technological advancement and the environment, as tipping the scale in either direction is detrimental. Ultimately, technological integration is inevitable and will eventually lead to sustainability in all areas of our daily lives.