We’re a Nanometer Away from a Nano-Revolution
Nanotechnology. Smaller than life, Bigger possibilities
As countless “vertically challenged” athletes like Lionel Messi and Isaiah Thomas have proven, size doesn’t matter. This is especially proven with nanotechnology.
Nanotechnology is the manipulation of materials that measure less than 100 nanometers (a nanometer is the size of one-billionth of a meter). And Nanosensors are by far one of the greatest additions to this technology.
So, What are Nanosensors?
Nanosensors are devices that can scan nanoparticles (about 100 times the size of normal atoms) or molecules to share data about the characteristics and behaviour of its targetted substances. Sensors range in size from 10 to 100 nanometers!
Nanosensors are kicking up a storm because of the potential these sensors have to revolutionize the scientific community. One of the capabilities of nanosensors that I am fascinated by is the capability you have to control which substances nanosensors can detect. In fact, scientists at the University of California-Berkeley proved this with the use of turkey skin. As many don’t know, the skin of a turkey changes colour when the animal’s emotion changes. This is because the proteins in the skin are organized in pockets called nano-bundles. When the animal gets excited the blood vessels in the skin stretch which stretches the nano-bundles which then changes the way light reacts on the skin; therefore, changing the way we see the colour. The students at the University created a replica of a turkey’s protein arrangement in its skin using phages. They developed these phages to bind with a certain compound by developing the sensors in a specific way. The phages then formed themselves into nano-bundles. When the compound was near the phage nano-bundles, the phages bounded themselves towards it, which eventually changed the physical structure and spacing of the nano-bundles and changed the way light reacted with the surface and therefore changed the sensor’s colour.
Who knew turkeys would be a help to developing nanotechnology? So, what can we do this revolutionary information? Well, in this specific experiment in the University of California-Berkeley, researchers made the phages react to the vapour of TNT, but with the correct research, they could’ve changed what substances the phages were reactive to by altering the phages. In a real-life application, the substance the replica nano-bundles were reactive to could be changed to a more important substance that needs to be tested in certain areas like potentially, cancer cells.
So What? Why are they Important?
As stated before, Nanosensors are very important in solving problems the world is still having trouble with. They can be used to test the safety of water, pollution levels of the environment, and diseases. And because nanosensors are so small, they can be placed in objects that conventional day sensors couldn’t be. They are also known for having a large surface area to volume dimensions. This makes it easier for the sensors to detect substances at lower quantities and allow it to have more exposure to the substance it is studying.
Nanosensors have recently been used in many new medical diagnostic tools. Doctors can put a small amount of a patient’s blood in a device that can detect diseases and provide a diagnostic for said patient. Similarly, doctors can also detect diseases using the patient's saliva. Now, when testing these samples from patients, doctors would use nanosensors to detect diseases they suspect their patient may contain. By using nanosensors, doctors can get precise and accurate diagnostics than if they were to use another method. This means some diseases could be identified early on in its cycle. One can tell that Nanosensors are an important part of the future of medicine that may be implemented into healthcare systems around the world.
Not only are nanosensors smaller than standard sensors that are generally used, but nanosensors also have a faster speed of detection, better sensitivity, and are able to track multiple targets at once. Along with this, nanosensors also have a very good detection range and can lock down to the molecule of an organic, inorganic, or biological substance.
Nanosensors also have many other uses including:
- Optical Nanosensing: These nanosensors are made with non-toxic receptors and are usually used in bioimaging. This is because of how they are able to detect the fluorescence of a molecule, an important feature that can help detect many harmful substances, like tumours.
- Light Sensing: nanosensors are capable of detecting electromagnetic radiation, an important necessity when detecting light waves.
- Can be combined with other technologies: Nanosensors have recently been used as a combination with other technology. In fact, an example of this is where nanosensors were being used with microelectromechanical systems (microscopic device usually containing moving parts within it) to find traces of microorganisms in fluids.
Ok, But how do they work?
Before we get into this, it is important to know that there are two types of Nanosensors: Chemical Nanosensors and Mechanical Nanosensors.
Well, What’s the difference?
Both of these types of nanosensors work similarly to one another. Mechanical and Chemical Nanosensors both work by determining the alteration of the electrical conductivity of a substance. Chemical Nanosensors generally have high electrical conductivity which then decreases when its target binds with them. This change is what chemical nanosensors measure to sense whether the targetted substance is present. An example of chemical nanosensors are the 1-dimensional objects, nanotubes and nanowires. Physical nanosensors work a little differently. Physical nanosensors induce a change in their electrical conductivity when they are physically manipulated which causes a detectable change in the sensor that sometimes can be determined using a capacitator.
*Some people consider biological nanosensors as a category of nanosensors as well. Biological nanosensors detect changes in biomolecular systems such as cellular communication.
Nanosensors can also be either passive or active. An active nanosensor can have information gathered from it remotely. An example of this is when a nanosensor is placed in a lake. There it can remotely communicate that there is a dangerous substance in this body of water. A passive nanosensor is when the nanosensor can be recognized through changes in its colour, fluorescence, or opacity.
So how are these made?
Nanosensors are made through the process of nanofabrication. This is the process of creating nanomaterials. There are generally two ways to make nanosensors, top-down or bottom-up. The most common method of performing top-down nanofabrication is lithography, specifically photolithography.
PHO-TO-LI-THOG-RA-PHY: Definition: The process of transfer of geometric shapes onto a silicon wafer using lights. When translated from its Greek meaning photo means light, litho means stone, and graphy means to write, so all together photolithography means, printing with light.
To understand this process of creating nanosensors, people use the analogy of Michelangelo sculptings. Michelangelo created his sculptures starting from the top of the marble block to the bottom of it. He would generally use half the block to create his sculpture and would leave the rest as the waste product. This represents the way photolithography works where you break down the nanosensor until you have the wanted size and shape.
In the picture of above, you see the steps for photolithography. In the second step, a layer of metal is placed on the silicon wafer as a masking strip. The photoresist is spun evenly to the metal layer in step 3. In step 4, UV light is directed down through a mask onto the resist to induce a chemical change. In step 5, parts of the layer that are soluble are removed. In the etching process, a chemical removes the metal layer to make the silicon wafer exposed to areas not covered by the metal layer. In the final step, the resist layer is stripped off.
Unfortunately, there are many issues with the way this is done. Firstly; this process produces a lot of waste, secondly; toxic chemicals are usually needed for this type of nanofabrication, thirdly; this a very slow and tedious process, and finally; it is very difficult to recreate a specific nanosensor used previously. Along with this, this method also poses other problems such as cost, difficulty, contamination control, particle detection, and dependability.
The other method of nanofabrication is the bottom-up method. There are two submethods of bottom-up nanofabrication. The first is self-assembly. This is where nanosensors self-organize themselves. They are commonly found in nature. The other submethod is molecular assembly which isn’t even yet classified as a scientific theory let alone performed. This process is where nanosensors are assembled through machinery process lines. It relates to the idea of self-replicating machinery.
Unfortunately, self-assembly is difficult to maintain on a larger measure and is not yet fully understood by the scientific community. Molecular assembly on the other hand, is an idea that could potentially work if the correct research and effort are put into the method.
Well, how can Nanofabrication Improve?
Because photolithography is the most commonly used method of nanofabrication, it is only right I have some ideas to talk about my ideas to fix the problems it poses. One of the problems of nanofabrication that can be fixed is the cost. Instead of using a silicone-based wafer, a cheaper material like aluminum or boron could be used. Each type of material could be used for varying uses of nanosensors depending on the situation as they have different electrical conductivity.
Although this isn’t a very technical idea, in my opinion, to improve the process of nanofabrication molecular assembly has to be put into standard nanofabrication procedures across the world. Molecular assembly, which was already briefly talked about in this article, is where nanomaterial are specifically chosen that are capable of interacting and combining with other nanomaterials to create shapes. Because the interaction between nanomaterials cannot be controlled by scientists, they had to influence these particles in another way to create nanosensors. This is by determining the direction in which the interaction takes place (chemical control) and the temperature in which they do as well (entropic control). Scientists have recently developed a simulation to better understand the effects of entropic and chemical controls. By using machine learning and encoding the information from this simulation, researchers are now able to predict the final product of molecular assembly quite well. With the information we now have about this method of nanofabrication, companies will not only save money and materials by implementing it but also revolutionize the way nanosensors are used in the world.
