We use sensors in our everyday lives. From the ones on our car that go “beep!” when you move too close to another vehicle to the ones on our washing machine that prevent water from flowing out onto the floor…but what if we shrunk their sizes down to the size of the tip of our fingertips? A molecule?What if they have the incredible power to change the world through agriculture, health and medicine, and even climate change, but all at an extremely tiny size?
These sensors are truly something special and they even have a name: NANOSENSORS.
But before I get into anything deeper, we need to first understand what nanosensors are.
Nanosensors work just like any other sensor: Their job is to detect and process signals from their surrounding environment. However, unlike the car and washing machine sensor, they are really, really, REALLY, small.
Because of this, nanosensors are typically only used to collect data about other really, really, REALLY small things such as the existence of various particles and living organisms at the nanoscale. They are capable of measuring the behavior of these things and their different visible characteristics. Once this data is collected an analyzed, the information is then converted to the macroscopic scale which can then be observed by the naked eye.
“Someday, scientists will be able to manipulate and control individual atoms and molecules.” — Richard Feynman, California Institute of Technology
But how small is this “nanoscale” exactly? How about one nanometer?
Nevertheless, I know that it’s simply hard to imagine just how small nanotechnology is. Let’s put this into perspective:
One nanometer is one billionth of a meter. The term “nano” derives from the Greek word “nanos,” meaning “dwarf.” The term itself today actually translates to “one billionth,” which you can imagine is very, very small. The nanoscale is a measurement which is used to describe anything between 1–100 nanometers and is typically used to measure extremely tiny things such as atoms, molecules or cells.
Still not able to process just how small a nanometer is? Here are a few illustrative examples that might help:
- A sheet of newspaper is about 25,400,000 nanometers thick
- A human hair is approximately 100,000 nanometers wide
- On a comparative scale, if a marble were a nanometer, then one meter would be the size of the Earth!
Nanosensors seems pretty awesome, but why should I learn more about them?
There are a whole variety of reasons.
This new technology can give us advantages like we’ve never had before…maybe enough to change the world.
After all, good things come in small packages. Here are some of the advantages of nanosensors over regular, larger sensors:
- They can operate on a much smaller scale and can gather information from places and things that are too small for other larger sensors.
- They are extremely sensitive and can give really accurate responses.
- They are incredibly effective and powerful!
Because they are so tiny, they have a very high surface area to volume ratio, in contrast to other larger sensors. This is reason why all the advantages above are true:
- They can run on lower concentrations of power, thus meaning that the nanosensor won’t have to “burn as much fuel” carrying around a larger mass if it were bigger
- Their extra surface area allows these sensors to retrieve data from more points of view on their surfaces= more accurate results
“First, because they are so tiny, nanoparticles have a very high surface area to volume ratio. You can imagine this concept by picturing a loaf of bread. The bread has a surface — the crust — that is exposed to the outside world. If you tried to spread Nutella on top of the crust, you would probably be disappointed. But now imagine slicing the bread. You still have the same amount of it in total, but because it is in smaller pieces, you have more space to slather on your favorite toast topping!” — Sustainable Nano
Because of the amazing potential that nanosensors have, they are being used by scientists and researchers worldwide to solve some of the world’s more pressing and complex issues.
Let’s take a look at how they’re making an incredible impact on today’s health care system.
Saving lives, one nanosensor at a time.
Ever heard of the rumor that dogs can smell cancer? Believe it or not, scientists are developing nanosensors that actually have the capability to “sniff out” growing cancer cells. As cancerous cells progress in maturity, the DNA and proteins in them change, which emits volatile organic compounds as a side effect. This side effect is what scientists are looking to find through using nanosensors, and is the icky stuff that dogs can smell. However, unlike dogs, nanosensors are being developed to target these compounds in extremely tiny concentrations and have been enhanced to the point where they have the capability to detect which kind of cancer an individual might have (i.e. breast, lung, colon, etc.) with only a simple breath test.
This can help us to determine whether or not a patient has cancer well before symptoms would show up as tumors or on an X-ray.
“Chad Mirkin of Northwestern University is developing nanoparticles that can diagnose and treat disease, tracking cancer at earlier stages and even determining whether hospital patients have infections.” — Popular Science
Cell personalized gene and drug deliveries:
One day, nanosensors will have the ability to deliver various genes or drugs inside of certain cells. With different shapes and chemical coatings, nanosensors can find and send these “needed items” to specific cells of a person’s choosing. They also have the capability to manipulate with these cells in a specific way. It’s like having your own mini doctors inside your body, fixing up and getting rid of all the damaging cells and turning them in healthy new ones!
This is a breakthrough in medicine as with nanosensors, we won’t have to administer unnecessary large amounts of a drug to a user, with an outcome that might not be as effective as compared to when the “wanted cells” are directly tracked down and “given a new makeover.”
However, it’s sometimes a bit challenging to allow cells to “open up” to these “suspicious” new nanosensors which carry new DNA. Scientists have been coming up with certain strategies that can help them “trick” the DNA components of various cells which are designed to “block invasion”:
- Coating the nanosensor with viruses (this is the most frequent way)
- Rearranging DNA molecules on the nanosensor into a circle! (this is a new way that has been recently discovered)
“You arrange a simple molecule in a spherical form, and it naturally enters cells better than anything known to man!” — Chad Mirkin from Northwestern University
However, the second method still is a bit tricky. It is still not confirmed that every type of cell will simply accept different types of DNA arranged in a spherical shape to enter. It like having to find a universal sneaky disguise to let you into almost every forbidden place. Except, in this case, the nanosensors are sneaking in for good to potentially save the life of a sick patient.
Now, nanosensors don’t work magically— so how do they really function?
To be honest, this is a complicated question. There are countless different types of nanosensors, which are all used to measure different things (the small world is extremely large after all), and there are so many more to come and new discoveries to be made. However, I can tell you one similarity that ultimately lies true among all the nanosensors: They work by measuring electrical changes.
Here’s an overview of how they work:
- Nanosensors are mainly used to monitor the electrical changes of a material, otherwise called a nanomaterial.
- Many nanomaterials have incredibly high electrical conductivity, which can often cause a movement/any sort of physical change → is something detectable that can be measured with a nanosensor.
- Nanosensors are what detect change on its external surface, and this change is reported to other internal parts called nanocomponents.
Furthermore, nanosensors can be classified into two different categories:
- Chemical nanosensors
- Mechanical nanosensors
Because of the high conductivity of many nanomaterials, this will cause a binding (when molecules/atoms stick together due to exchanged or shared electrons) or absorption of a molecule, atom, or electron which is then measured using a chemical nanosensor.
For example, let me show you how chemical carbon nanotube-based sensors work:
Essentially, carbon nanotubes are large molecules of pure carbon that are long and thin and shaped like cylinders.
When a molecule of of nitrogen dioxide (NO2) is present, it will take an electron away from the nanotube, which will cause the tube itself to be less conductive. Vise versa, if the nitrogen dioxide was ammonia (NO3), it then will react with water vapor and give away an electron to the carbon nanotube, therefore increasing its electrical conductivity.
So overall, by treating these nanotubes with various coating materials (made from a variety of compounds and elements), they can be made sensitive to certain molecules, and immune to others.
Mechanical nanosensors also work by detecting electrical change, but unlike chemical nanosensors, it gathers data from another object/itself after it has been manipulated by the electrical change.
There are several different types of mechanical nanosensors, including the MEM nanosensors which can be found in car airbags:
This system works by having a minuscule weighted shaft attached to a capacitor (a device that stores electrical energy in an electrical field). The shaft is affected by the movement of the car by bending to various degrees and this is measured as the changes in potential electrical energy or capacitance. By using this method, the machine inside the car’s airbags will know when to set off the airbags due to the sudden change in acceleration and thus capacitance.
Pretty cool right?
But how it is possible to create such TINY things? There must be a way.
Well, of course there’s a way or else the term “nanosensors” would simply be something unreal and that wouldn’t be great.
In fact, this building process has it’s own unique name: NANOFABRICATION
Nanofabrication is the manufacture of nanotechnology with nanometer dimensions.
There are several ways that nanofabrication might be done:
- The Top Down strategy
- The Bottom Up strategy (includes self and molecular assembly)
The Top Down process:
Top-down lithography is the manner in which most integrated circuits are now made. It involves starting out with a larger block of some material and carving out the desired form. — Wikipedia
Donatello was a top-down artist, he used this method to create The Bronze David from one large block of stone. Slowly, he used his knife to carve out the negative spaces until his sculpture was the size and shape that he wanted it to look, reducing the size of the block by at least half and leaving behind a ton of waste.
We also use this method to create these incredibly minuscule nanosensors. Often, this strategy is used especially to carve out nanometer scale patterns on the sensor’s surface. This is called nanoimprint lithography (NIL). It’s an incredibly simple process that can create extremely high resolution results in a short amount of time. Ultimately, it’s like making imprints on a piece of clay using different tools to carve away different pieces in certain areas. Fun right?
The Bottom Up process:
This process is the exact reverse of top down strategies: instead of taking away material from a larger piece, material is added on bit by bit to create a structure.
Typically, atoms are stacked together on top of one another by other nanotechnology into a specific shape and size with application of tools such as chemical synthesis, quantum dots, plasmonically active particles, carbon nanotubes, metallic nanowires, and other multifunction particles. Often using this strategy, nanosensors can be produced in large quantities through a nanofactory system (in other words, an extremely, EXTREMELY, small factory where packages of food or things are replaced with singular carbon and hydrogen atoms).
To make things more complicated, there are two ways to use the bottom up fabrication method:
The Self-Assembly method:
This is the natural process how things assemble in existence without human manipulation. Here are some examples below:
- Protein folding and packaging within a cell
- Dust and other particles that turn into galaxies
- Different weathers
However, things can get a bit hard because if this process if to be controlled, the components which are to be naturally assembled must be designed in a specific way (i.e. the particles characteristics). It’s like trying to chemically merge paper and water by simply stirring…you just can’t! However, if you mix milk and vinegar, these substances will turn into a solid substance on their own because of the special interaction between milk and vinegar particles.
The Molecular Assembly method:
I guess you could say that this it the “man’s way” of assembling things. It’s different from the “self-assembly” method as it is more mechanical and specially controlled. The vision is that everything is in a factory-like system where atoms are physically put together piece by piece through various other nanotechnologies (in other words, they are factories at the nano-scale!).
Click here to watch an amazing animation of the molecular assembly nanofabrication process!
Nanofabrication seems really cool, but it’s still not perfect…yet.
There is still a long way left to go in our journey of developing nanosensors; we are still in the early stages of developing this nanotechnology and its various applications. There are still many exciting problems left to solve and many more to come on the way!
It’s almost like trying to become a black belt kung fu master in one day…it’s literally impossible…at least for now.
Currently, there are major issues in today’s different nanofabrication processes that we have yet to find a solution for. Here are some of the issues in the methods that I have mentioned so far:
Issues with Top Down methods:
Once you carve out your own Bronze David, you’ll see that you’ll have a huge pile of broken stone behind you → you would have wasted a lot of valuable material that you could have made another sculpture with!
Same goes for nanosensors. After carving out a nanosensor, there is wasted material, which often cannot be recycled to make new nanosensors.
Additionally, the specific nanotechnology used to carve patterns on the surfaces of these nanosensors is extremely expensive and is an automatic wallet drain.
Issues with Bottom Up methods:
Although these methods don’t typically need expensive tooling, the process is not as effective as the top down methods and it takes much longer to create the nanosensors, especially because they are manufactured in greater quantities at a time through this method.
So it’s either you have to spend all the money in your pockets or you wait for a longer period of time, generating poorer quality results → neither of them are good! We will have to continue working on developing better nanofabrication processes, or in other words, better ways that we can use to build various nanosensors.
Some of my own advice
After looking into the broad topic of nanosensors, nanofabrication, and the issues with nanofabrication, it has inspired me to think about my own ways of how I might approach the arising issues in the development of nanotechnology and the efforts in how we can make the manufacturing process more effective. It’s not just the super smart scientists that try and solve these problems, you can help too!
Here are some of my own creative suggestions for improvement:
- We should move away from the common top-down and bottom-up processes, let’s experiment with something new! We’ve already seen that there are issues with prices and efficiency with these current methods, so let’s brainstorm together to come up with a new strategy. It might even work! Who knows?
- Remember the self-assembly methods? Maybe we should focus more on those.
I know that it might be slightly tricky to be able to design and retrieve the desired components for the natural assembly to happen but in the end, these methods can save us a lot of time and money as we won’t need to purchase various equipment to do the processes for us. Everything will do it by itself like magic! Also the process will overall be much more effective and produce better quality nanosensors!
Once you know how certain nanoparticles behave and what properties they possess you can use this knowledge to deliberately create structures with desired properties. This is a better way than trying to throw a bunch of compounds in a cement mixer in a more or less arbitrary way based on guesses and see what materials you get and then try and figure out what you can do with them. — Encyclopedia Britannica
We still have a lot to learn about this specific method, as we have been focusing more on the other ones, but it’s really cool and may change the way nanosensors are made for good!
Want to learn more? Here’s something interesting to look into!
Recently, as of 2020, scientists have found a way to use nanosensors to detect aquatic toxins in water! Led by Dr. Jonathan Claussen, ISU researchers are using a specifically designed nanosensor that can detect damaging chemicals called organophosphates (which can be found in herbicides and pesticides) at levels 40 times smaller than the U.S. Environmental Protection Agency (EPA) recommendations!
When we thought that we got rid of enough…turns out nanosensors can help us save even more lives! Even the smallest of pollutants that enter our bodies can still be damaging.
Additionally, the same sensor is currently being developed to have various other functions and do other tasks:
“The sensors could be designed to detect pathogens in food processing facilities to prevent food contamination. They could also be used to monitor cattle diseases, for example, before physical symptoms are present. This technique could really be a game changer for a variety of in-field sensing applications that require low-cost but highly sensitive biosensors.” — Nanoscale Horizons (Research Paper)
Well there you have it! Now you know about nanosensors more than you did before! Nevertheless, it is evident that nanosensors are on a path to change the world from healthcare, to agriculture, to climate change, to society as a whole. It can help us solve complex issues on a global scale which are affecting large masses of the world’s population and are causing extremely negative impacts. Using this new nanotechnology we can learn more about this “invisible” dimension of Earth which the world is built upon, atom by atom. Who knows what else we can find using nanosensors or other ways that we can apply it to human life? After all, the future of nanosensors is still yet to be uncovered.