Nanoparticle

A nanoparticle is a microscopic particle of matter that is generally defined as being between one and one hundred nanometers in size. A nanometer is a unit of measurement corresponding to one billionth of a meter. For reference, a nanometer is about 25.4 millionths of an inch or one hundred thousand times smaller than the thickness of a sheet of paper. The size of nanoparticles allows them to exhibit unique properties. Nanoparticles are governed by the same fundamental physical laws as larger materials, but their small size causes quantum and surface effects to influence their behavior more strongly. Nanoparticles can occur naturally or be manufactured. Their distinct properties were first noticed more than a thousand years ago and used to make stained glass windows and exceptionally strong sword blades. Nanoparticles are used in everyday items such as electronics and sunscreen and aid in medical science to detect and treat disease.

Early History

While they did not understand the concept of nanoparticles, ancient cultures in China and Egypt had discovered a substance known as soluble gold as early as the second millennium BCE. Soluble gold, also called colloidal gold, consists of tiny gold nanoparticles suspended in a liquid solution. Around the beginning of the fourth century CE, Roman artisans were using gold and silver nanoparticle substances to create a form of glass that changed properties depending on the direction of a light source. The only intact surviving example of this glass is the Lycurgus Cup, a drinking vessel made around 325 CE. The cup appears green and opaque when light shines on it from the outside, but turns red and transparent when the light is placed on the inside. This occurs because the small size of the gold and silver nanoparticles confines the movement of the electrons in their atoms. As a result, the nanoparticles react differently to light than do larger particles.

Nanoparticle substances were also used to create the vivid colors of medieval stained-glass windows. Glassmakers discovered that by adding specific amounts of gold and silver substances to the glass, they could change its physical characteristics. For example, adding a gold substance to the glass produced a distinct red color, while adding silver made a yellow color. Adjusting the type and amount of the substances produced different shades. From the thirteenth to the eighteenth centuries, bladesmiths developed a process using carbon nanoparticle tubes to create a durable substance known as Damascus steel. Swords made with this steel became legendary for their strength.

Topic Today

It was not until the twentieth century that scientists were able to better understand nanoparticles. The earliest microscope that allowed scientists to see at the level of nanoparticles was invented in the 1930s. The term nanotechnology was coined in 1974 by Japanese scientist Norio Taniguchi to describe working with materials at the atomic and nanoparticle scale. Further scientific advancements allowed researchers to see individual atoms and manipulate nanoparticles in the 1980s. Beginning in the early twenty-first century, scientists developed nanoparticle-based materials for applications ranging from lightweight composites and electronics to energy storage, medicine, and environmental technologies. These are used in numerous consumer products, such as automobile bumpers, tennis rackets, and golf balls. Silver nanoparticles are added to some fabrics because their antimicrobial properties help reduce odor-causing bacteria. Nanoparticles are also infused into sunscreen, making it clear upon application while keeping its protective capabilities. In electronics, they are used to make improved digital displays in televisions and cell phones and to increase computer memory. Quantum dots, which are semiconductor nanoparticles that emit specific colors of light, are used in high-resolution television displays and are being studied for medical imaging.

In the medical field, nanoparticle technology is used in a variety of ways to help in preventing illness and diagnosing and treating diseases. Because of their small size, nanoparticles can be placed more easily in targeted areas and help improve scans taken through magnetic resonance imaging (MRI), a process that uses magnetic waves to view inside the body. Particles known as perfluorocarbon emulsion nanoparticles have a high acoustic reflectivity and can be used to enhance ultrasound images in fields from obstetrics to oncology.

Because gold nanoparticles can be engineered to interact safely with biological tissues under certain conditions, researchers are studying their potential use in cancer imaging and targeted therapies. Cancer is the abnormal and uncontrolled growth of cells in the body. The difficulty in treating cancer is that methods used to kill cancerous cells also harm healthy ones. Using particles such as gold nanoparticles or carbon nanotubes, doctors can target specific cancer cells and coordinate treatment with the nanoparticles. The particles coating the cells can be irradiated with short pulses from a laser to create small shockwaves that destroy the cancerous cells, while leaving healthy cells intact. A similar method involves using nanoparticles with magnetic properties to target cancer with magnetic waves. The waves heat the nanoparticles and cause enough damage to kill the cells. The particles can also be used to determine if a potential cancer treatment is working, allowing doctors the ability to continue or alter treatment more quickly. Some nanoparticle-based drug delivery systems are used in cancer treatment to help medicines reach tumors more effectively while reducing damage to healthy tissue.

Researchers have developed mRNA lipid nanoparticle (LNP) vaccines, such as several created in response to the COVID-19 global pandemic in 2020. These vaccines offer several advantages over traditional vaccine development and production, notably the variables that may be developed and the speed with which the vaccines can be manufactured.

One of the reasons nanoparticles are so effective is that despite their smaller size, they actually have more surface area than larger objects with the same mass. This can be illustrated with a six-sided cube with each side measured at one centimeter. The total surface area of the cube would be six square centimeters. If that same cube were to be turned into one thousand millimeter-sized cubes, each of those smaller cubes would have a surface area of six square millimeters or sixty square centimeters. While the total mass of the cube did not change, it would now have a greater total surface area. A larger surface area means that more of the particles can come into contact with the surrounding material, increasing their reactive ability. Scientists are studying how nanoparticles released into air, soil, and water may affect ecosystems and human health.

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