Nanotechnology and Human Health

Manipulation of Nanoparticles

Now that you understand how really small the nanoscale is, you might be asking yourself how on earth does someone manipulate atoms when you can't see or touch them to build from the bottom up. There are two ways atoms and molecules are manipulated at the nano level. They can be physically manipulated through the use of the microscopes or guided into position through the process of self-assembly.

How is Physical Manipulation Accomplished?

A lot of progress has been made regarding nanoscale manipulation. Some of the more significant advances involve electron microscopes including computer-controlled SPM, optical tweezers, and nanomanipulators. Real-time, hands-on manual nanoparticle manipulation can be accomplished through computer-controlled scanning probe microscopy. These computer-controlled SPMs are still in a rudimentary state but basically provide a virtual environment, similar to a virtual reality game, whereby researchers have virtual surface accessibility. Optical tweezers use a focused beam of light directed onto a particle in liquid. The light's force is strong enough to keep the particle relatively still. If it moves the light will push it back in place toward the center of the focus. Nanomanipulators are used in conjunction with SEMs and TEMs and use a type of crystal tip that has the ability to generate a voltage in response to mechanical energy. Nanomanipulators are useful in testing the newest electronic circuit boards and integrated circuits. ¹⁷

What is Self-Assembly of Molecules?

Self-assembly can be defined as the ability of atoms and molecules under specific conditions to spontaneously arrange and organize themselves into a structure or pattern without specific clearly defined control from an outside force. ¹⁸ The conditions that make self-assembly work are:

1. The right combination of ingredients (nanoparticles or base elements like phosphate, sodium, chlorine that exist in certain substances)
2. The appropriate environment, like water or oil, for the ingredients
3. Reversible binding force
4. A driving force or catalyst to start the self-assembly process. (Note: See the Activity 'Experiencing Self-Assembly' in the Classroom Activities section as a way to introduce the concept of Self-Assembly).

How do we use Self-Assembly?

When the topic of self-assembly arose I questioned whether the concept of self-assembly, as it relates to nanotechnology, is really new. The concept is not new, but what is new, is the ability to see what is happening at the nanoscale. Basic food preparation involves nanotechnology employing the process of self-assembly at some level. I'll explain how.

One way to take advantage of self-assembly to manipulate matter and create nanoparticles is first to create an emulsion. Making emulsions is not a foreign concept and is something many of us have done. Examples of emulsions that we can relate to include: mayonnaise, peanut butter, and salad dressing. An emulsion is defined as a suspension of small drops of one liquid into a second liquid within which the first liquid does not mix. A common illustration of two liquids that would result in an emulsion is oil and water. To illustrate this idea if you take the yolk of an egg, lemon juice, and oil and create mayonnaise you are taking the first step a nanotechnologist takes to create nanoparticles, in a very crude sense. Measuring and gathering the egg yolk, lemon juice and oil is the ingredient step of self-assembly, putting all the ingredients in a bowl establishes the environment, using the electric mixer to blend the ingredients provides the driving force, and the weak intermolecular interactions that occur within the mixture takes care of the reversible binding forces. Blend the solution until there is a cloudy mixture. This emulsified mixture is composed of the dispersed droplets of oil and lemon juice suspended in the egg yolk.

The process is explained in nano terms here. The oil is comprised of individual phospholipid molecules. These structures have a hydrophilic (water soluble) part and a hydrophobic (water insoluble) part. They arrange themselves into two layers that surround or encase the water, or in this example the lemon juice. The hydrophobic parts arrange themselves facing away from the lemon juice and the hydrophilic parts arrange themselves facing the lemon juice creating a liposome encapsulating the lemon-juice. Nanoparticles are created using a similar process with a few additional steps. An emulsion is created with the liposomes encapsulating the intended drug suspended in the emulsion. The emulsion is then lyophilized, which is a process that involves freeze-drying and evaporation. Once the liquid has dissipated, what remains are nanoparticles containing the drug or other intended substance.

(An activity that I recommend to engage students in visualizing the concept of self-assembly is to make homemade bubbles. Follow this activity up with the information provided in Issue 6 of Nanooze 2008 starting on pages 4-5. This contains illustrations and a detailed explanation of the process of self-assembly.)