Nanosensors — Thinking Small is Thinking Big

Nanotechnology. What is it?

The word nano itself means very small or minute. This might lead one to think that this is indicative of the capabilities of nanotechnology when in reality, that is far from the truth. Nanotechnology has already been making large strides in the world today in several subfields. From nanomedicine and nanobiotechnology to nanoart and of course, nanosensors. The capitalization of this revolutionary field of technology could mean significant boosts to production at a noticeably reduced cost. Products of this field of research (such as nanosensors) require less energy, fewer materials, will be lighter, smaller, and despite all this be much more functional and helpful for specific specializations that could change the way we live our lives. Though there is one small detail I left out. Everything that is manufactured under the nanotechnology umbrella also refers to its size being 10–100 nanometers.

I guess you could say it’s no big deal!

Just to illustrate how small I’m talking about…

One nanometer is a billionth of a meter.

• 1 sheet of paper has a thickness of about 100,000 nanometers
• 1 cm (about the width of a fingernail) has 10 million nanometers

“The impact of nanotechnology on the health, wealth, and lives of people. It will be at least the equivalent of the combined influences of microelectronics, medical imaging, computer-aided engineering and man-made polymers developed in this century.” — Richard Smalley (Nobel Laureate in Chemistry)

The History Behind Nanotechnology

The term was coined in 1974 by Japanese scientist Norio Taniguchi.

The invention of the scanning tunneling microscope in 1980 allowed the viewing of a foreign atomic level. This enhanced research at the nanoscale.

During 1990–2000 nearly every industrialized nation made nanotechnology initiatives

Now that you have a basic understanding of the nanotechnology field and the nanoscale, let’s get to a specific specialization within the nanotechnology field and what you came here for.

Nanosensors. What is it?

Nanosensors are small sensors (10–100 nm) that are tasked to convey info about the nanoscale to the macroscopic world by analyzing the nanoparticles. Different variations of the nanosensor can detect many different things such as health and chemical abnormalities, electrical and physical signals and more. These sensors could have a very large impact on our world.

Nanosensors measure physical qualities and from there, turns them into electrical signals. For example, physical (mechanical) nanosensor (1 of the types of nanosensors) work because when it is moved, it results in the change of electrons. This affects the electric capacitance and when a change is detected, you can be sure the sensor will know and send a signal. Those signals are received which can then be further analyzed.

Rather than just being cheaper to manufacture nanosensors are also more precise, reliable and their size allows them to reach places that have not been analyzed before.

Examples of use:

1. Detect change in temperature
2. Detect various chemicals concerning pollution monitoring
3. Detect types of organic molecules

The 4 different types of nanosensors

Biological Nanosensors

These sensors can detect protein, antigens, DNA strands, and other biologically active substances. As one could imagine, this could prove useful in several crucial industries such as finding viruses within the food and treating patients by checking for abnormalities in the blood.

Physical Nanosensors

The physical sensors can detect mass, pressure, and force at the nanoscale. These sensors, for example, can be used to create surfaces with very high sensitivity and accuracy. These sensors can greatly contribute to more advanced manufacturing and testing of products.

Chemical Nanosensors

The chemical nanosensors can determine the amount of a substance or element. These sensors could be used in the environment for detecting pollution or radioactivity that might be present. These have the potential to be used in the lab or in the environment in very beneficial ways.

Optical Nanosensors

Proximity nanosensors detect the motion of various appliances, electronics, and more. The Ambient Light nanosensors can detect the intensity of light from various items (such as a TV).

Okay, but so what?

Right about now you might be thinking that nanotechnology is no big deal (pun intended) but that is the opposite of the truth. In this day and age, all we do is collect information and numbers. And when one takes a look around a major city in 2020, it will be evident that sensors are everywhere. From our cars to even walking through doors, sensors have become heavily involved in our everyday lives. Just imagine the capabilities if we were able to incorporate an incredibly accurate sensor at the nanoscale. The possibilities are limitless and there is a conceivable use of them in almost every field!

The advances in the medicinal field with nanosensors include the ability of nanosensors to be injected into the bloodstream and blood vessels to detect abnormalities.

Advances in the agriculture industry can ensure our safety for years to come. The process of food packaging is where the most foodborne illness contaminants spread. Nanosensors can help detect the presence of harmful chemicals and pathogens.

The space industry is always advancing. Imagine if we could send a sensor to another planet via a probe and find out whether the planet is habitable or not. Using nanosensors could also provide more safety for astronauts by monitoring their health for example.

Nearly every field of science is affected by this tiny device. Nanosensors have the capability to impact everyone and can ultimately redirect humanity.

That’s cool and all, but how do they work?

All nanosensors work by detecting a change in their respective fields. After detecting a change, a signal is sent to a processor which can then further analyze what the heck is going on. There are many ways to detect change within a nanosensor. For example, say some sort of molecule made contact with a chemical carbon tube sensor. When it comes into contact, it will attach carbon bonds to them, which creates resistance in the circuit. After receiving the information that there is resistance, the sensor will send a signal that is further analyzed. Another example of this is with a nanocantilever-based sensor. There is a switch on the sensor that when moved, sends a signal to the processor for translation and interpretation.

How do you build something this small?

In order to build a nanosensor, and other nanostructures, a process called nanofabrication is used. Overall, there are 2 methods in which one can go about the process of nanofabrication.

The two methods are:

1. Top-Down Lithography (Conventional)
2. Bottom-Up Lithography (Unconventional)

Firstly in lithography, a substance is covered with an irradiation sensitive layer. Then it is exposed to light or electron beams. Then finally it is developed with a suitable chemical.

Top-Down (Conventional)

When this method is used, it is starting from something and breaking it apart. It is going from big to small. This can be compared to carving a statue, where you start off with a block of marble to make what you want and then ends up smaller to reach the product. The most common form of top-down lithography is nanolithography. This is where the material that is required is covered by a mask and the excess is etched off.

Some other examples of Top-Down Lithography:

• Focused Ion Beam Lithography
• Electron Beam Lithography
• X-Ray

Bottom-Up (Non-Conventional)

When this method is used, it can be thought of as playing a game of Jenga or building LEGO because you build it from the bottom up. The molecular blocks come together to form the nanostructures. This usually incorporates self-assembly and self-organization which is where the atoms and molecules can rearrange themselves into structures.

Some examples of Bottom-Up Lithography:

• Nanoimprint lithography
• Near-field optical lithography
• Proximity Probe

Top-Down & Bottom-Up Lithography

There are a couple of things that ensure quality and performance for lithography:

• Resolution is very important in lithography and for better resolution, requires better tools
• The control of the critical dimensions and the properties of the nanotechnology and the structures
• Pattern placement and over-lay alignment accuracy

As you can see, nanofabrication is great.. but there’s a catch

Problems with Nanofabrication

Though nanofabrication lets us do things we have not been able to before, there are setbacks. When using the top-down fabrication method, it is fast and more efficient than the bottom-up method, but it is extremely expensive. The equipment is more expensive and more material is being wasted since you are carving away from a bulk.

Bottom-up fabrication is more cost-effective and can give high precision when building at such a small scale and help create complex structures. But, it is unconventional and takes a much longer time than the top-down method. Another problem with the bottom-up method is something called thin-film deposition. This refers to a thin film of material depositing and creating more layers due to adhesion problems that come from stress and defects.

Other Problems:

• Heat dissipation becomes a problem
• There are physical boundaries to lithography. It is incredibly difficult to create an immensely detailed nanotech.
• Keeping the lab clean is vital and the cost grows with newer technology
• In conventional top-down methods, shavings can potentially build-up and deteriorate the quality of the nanosensors
• Stitching: this is the misalignment of the pattern and is caused by problems during the development process

How do you solve these problems?

With the problems listed, it comes into view that nanosensors and nanotechnology are just not completely viable yet.

A possible method would be to manufacture a 3-D printer that would be able to handle nanofabrication. Of course, this would not just be an ordinary printer as it would need to have an incredible amount of accuracy. Though, if something like this were to be made, it would make manufacturing much easier and efficient.

Another way to prevent some problems is the choice of material and equipment. With problems such as thin film deposition, it is imperative to have the right equipment for the job and making sure that everything is in tip-top shape (clean, right temperature etc.)

With continuous research in the field, our knowledge of this subject matter will continue to evolve. In the future, there could be a method that combines the strengths of both top-down and bottom-up lithography methods. Only time will tell if we might be able to create something revolutionary for the future of nanofabrication.

Final Thoughts

Nanotechnology has just begun its take on the world and will constantly develop. There are an incredible amount of usability for nanotechnology and nanosensors in so many fields. If we were able to capitalize and make the process of nanofabrication more efficient, this technology would revolutionize how we live our lives. I can assure that we will run into many errors but when we fail, we are bettering ourselves and learning more. Besides, where’s the fun without a challenge?

The future is smaller, so don't think too big.