By Roberta Attanasio
Nanotechnology is technology based on extremely small structures, the so-called nanostructures. How small are nanostructures? We’re talking nanoscale – about 1 to 100 nanometers. One nanometer is a billionth of a meter (there are 25,400,000 nanometers in one inch). These are the dimensions of atoms and molecules and, therefore, nanotechnology involves the manipulation of atoms and molecules.
How, then, is nanotechnology different from molecular biology (sometimes called the nanoscience of living things), physics, or chemistry? The distinction can be blurred. However, when considering nanotechnology and nanostructures, it is important to take into account that nanostructures are man-made and exhibit special size-dependent properties, in other words properties resulting exclusively from their nanoscale dimensions.
Jackie Ying, in a Nature Nanotechnology article (October 2006), gives a clear and simple definition of nanotechnology: “A toolbox that provides nanometer-sized building blocks for the tailoring of new materials, devices and systems.” In the same article, researchers, industrialists and others explain what nanotechnology means to them, providing a variety of perspectives that range from the enthusiastic to the sceptical. Peter Dobson states: “Actually, nanotechnology has been around for over a hundred years. Irving Langmuir was one of the first to truly develop the technology in the General Electric labs in the 1920s and 1930s.”
In reality, nanotechnology has been around for centuries.
The British Museum is home to the Lycurgus cup, made in Rome in the 4th century AD and known as one of the oldest nanotechnology-based marvels.
Gang Logan Liu, an assistant professor of electrical and computer engineering (University of Illinois at Urbana-Champaign), describes the cup as an “icon for inspiration” – inspiration for innovative applications of nanotechnology. Thus, inspired by the Roman cup and its optical characteristics, Liu and collaborators developed a novel, ultra-sensitive tool for the analysis of chemical compounds, DNA, and proteins. This tool is a colorimetric sensor: it “senses” (detects) the presence of specific molecules and then indicates their presence by changing color. Indeed, the ability to change color is what makes the Lycurgus cup such a marvel.
The Lycurgus cup is the only complete example of dichroic glass – glass that changes color when held up to the light. The jade-green cup turns to a glowing translucent red when light is shone through it. This dichroic effect was achieved by including in the glass plasmonic nanoparticles, in this case minutely ground gold and silver dust.
Liu and collaborators published their work at the beginning of the year in an article entitled “Colorimetric Plasmon Resonance Imaging Using Nano Lycurgus Cup Arrays”. The article appears in the the scientific journal Advanced Optical Materials and describes their nanoscale Lycurgus cup – a colorimetric device that appears green when light is shone on to it and, in absence of direct light illumination, changes its color to red. Therefore, the researchers define their device as a ‘biochemical color camera” that mimics the Lycurgus cup effect.
The colorimetric device is fabricated on a transparent plastic substrate (about the size of a postage stamp) and consists of about one billion nano Lycurgus cups organized in an array with subwavelength opening. The nano Lycurgus cups are decorated with metal nanoparticles on the side walls and are the results of nanoplasmonics research – the study of optical phenomena in the nanoscale vicinity of metal surfaces. Liu and his team are particularly excited by the extraordinary characteristics of the material, yielding 100 times better sensitivity than any other reported nanoplasmonic device.
Colorimetric sensors based on Nano Lycurgus Cup Arrays can be used for both qualitative and quantitative analysis and will have applications in drug discovery, diagnosis of diseases and identification of chemical compounds. These sensors can be included in low-cost, portable, handheld test systems – for example test systems to detect infectious microorgansims in biological samples (urine or blood). Being colorimetric, these test systems provide simple-to-understand results.
Sometimes, the future can be found by looking at the past.