Engineering Inside:

2014 Issue 1

The Big Wide World of the Smallest Scale

April 2014

by Robin Hegg

STM Gold

Image of surface reconstruction on a clean Gold (Au(100)) surface, as visualized using scanning tunneling microscopy.

What if you could watch atoms transfer electrons and form new molecules? Or observe a red blood cell as it travels through your vein? With the recent development of advanced tools like Scanning Tunneling Microscopes and Atomic Force Microscopes, these up-close, small-scale observations are becoming possible. Nanotechnology, or nanoscience, are the terms given to this new, exciting ability to observe, measure, and even manipulate materials at the molecular or atomic scale and it promises to change the way we manufacture everyday objects, build computers, store information, create our electronics, produce energy, and even deliver medical therapy.

”Nano” is the prefix given to a number of terms, referring to a billionth of that thing. Nanometers (length), nanoseconds (time), nanoliters (volume), and nanograms (mass) are some of the measurements used to discuss materials at this very small scale. It takes about 10 hydrogen atoms in a row to create a line 1nm in length, meaning individual atoms are less than 1 nanometer (nm) in diameter. A typical virus is about 100 nm in diameter and a bacterium is about 1000 nm from head to tail.

Nanotube Structure

Nanotube Structure

Many materials exhibit different properties when observed on the nanoscale because of changes in size and surface area. Nanotechnology involves the creation of useful materials, systems, and devices of any size through the control or manipulation of matter on the nanoscale. Nanomaterials, such as nanotubes (CNT), graphene, quantum dots, dendrimers, nanoparticles, and inorganic nanowires are already being put to use.  Research in this area is moving fast and applications have already been found that are advancing how we live, produce energy, and even receive medical care.

Carbon nanotubes are thin sheets of graphite formed into single- or multi-layer tubes with unique electronic and mechanical properties. They can behave as either a metal or a semiconductor, meaning one day electronics could be all carbon-based. They are also incredibly strong and light (one hundred times stronger than steel but one-sixth its weight). This means carbon nanotubes can be used to make objects stronger and lighter at the same time.  They can also carry current and heat, making them possible replacements for copper wires. Researchers are working to develop a stronger, lighter bulletproof vest using carbon nanotubes.

Bilayer graphene

Bilayer graphene. Credit: Peter Allen, University of California, Santa Barbara

Graphene, a one-atom thick, honey-comb shaped crystal lattice made of densely packed carbon atoms, exhibits interesting electrical, optical, mechanical, and thermal properties. It can function as a semimetal or a semiconductor and is highly opaque, blocking all but two percent of white light. Scientists are researching how graphene can be used in electronics, solar cells, energy storage, plasma displays, and chemical and biological sensors.

Dendrimers are large molecules with tree-like branches spreading out from a relatively hollow core. This core can be used to hold “guest molecules,” allowing them to be tailored for different applications. They could be used to deliver drugs, cancer therapy, or antimicrobial and antiviral agents.

luminescent porous silicon nanoparticles

Luminescent porous silicon nanoparticles. Credit: Luo Gu, Ji-Ho Park, UCSD

Because of their tiny size, nanoparticles have lots of surface area. Since most activity takes place on the surface level, nanoparticles are more active than their larger counterparts. Because they’re highly soluble, nanoparticles are used in paints, pigments, cosmetics, and medicines and because they’re highly attractive nanoparticles, they can be used in catalytic converters, water purifiers, varnishes, and adhesives. This same attractive property can also cause nanoparticles to lump together, making them less effective. Scientists are looking to find coatings that would help keep nanoparticles separate.

Quantum dots are tiny solid structures. They are so tiny that an electron inside has extremely restricted movement, meaning the electron’s kinetic energy is determined by the quantum dot’s qualities (material, size, and shape). Quantum dots also have extremely large surface-to-volume ratios, making them effective chemical and biological sensors. Quantum dots are also used in multi-colored displays, because different-sized quantum dots emit different colored lights. Quantum dots are being increasingly put to use in commercial and defense related products.

nanowire nanotrees

“Nano Trees,” a 3-D nanostructure grown by controlled nucleation of silicon carbide nanowires on gallium catalyst particles. Credit: ©Ghim Wei Ho and Prof. Mark Welland, Nanostructure Center, University of Cambridge.

Inorganic nanowires are tiny wires with diameters of 1-50 nanometers. They could be used to link tiny components into small-scale circuits and could be used to make a new generation of computer chips and memory storage devices. They may also be used for ultraviolet (UV) lasers and light emitting diodes (LEDs), and could help replace filament light bulbs.

Nanotechnology is already being put to use in our everyday lives with new applications being quickly developed. Nanoparticles have been integrated with clothing material to make stain resistant cloth, car bumpers have been enhanced with nanocrystals to make them stronger, and carbon nanotubes have been used to make products like tennis rackets and bicycle frames lighter and stronger.

Nanotechnology also holds incredible possibilities in its biomedical applications. Biosensors could be used within the body for early detection of several life threatening illnesses. Nanotechnology could also help in the development of improved drugs and dendrimers, with their hollow core, could be used to deliver drugs to targeted areas, treating sick cells and leaving healthy cells alone. Nanotechnology allows the possibility of individualized medicine based on a patient’s own genetic makeup, rather than data collected from the general population. Nanomaterials could help in the creation of stronger, more reliable prosthetics and rejection-proof donor organs. IBM recently announced that they have discovered that new types of nanoparticles can detect antibiotic-resistant bacteria like Methicillin-resistant Staphylococcus aureus (MRSA), seek it out, and destroy it by breaking down its cell wall and membrane.

Nanotechnology has the potential to make our lives better and more efficient, and the number of possible applications seems practically endless. However, there is still a lot we don’t know about nanomaterials and their possible consequences and safety issues. Some nanoparticles used in clothing have been found to wash into the water supply, damaging important bacteria in water systems. There is also concern that tiny nanofibers could pose a health problem if they were to get loose and be inhaled, or that nanoparticles might be able to be absorbed into skin. There is research that shows that under some conditions carbon nanotubes can cross membrane barriers. These are reasons that research into nanotechnology—both its possible applications and its potential dangers—is such an important and exciting field right now.

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