The applications of Nanosensors and Nanofabrication process
Nanotechnology. Woah. A big, well, an intimidating word. To fully grasp the vastness of this word and what it actually means, lets first decompose it.
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The term “nano” is derived from the Greek word nanos meaning dwarf. So, its safe to assume that nanotechnology deals with or uses something small, to fix something big.
Before we dive in, take a look at how thick a single strand of your hair is (or in this case, how thin) and think of it’s diameter. It is 0.10 millimeters, or approximately 100,000 nanometers. Just keep that in mind as we go along and investigate nanosensors and nanosensor fabrication, the manufacturing process of nanosensors.
Nanosensors
So, what exactly are they?
Simply put, nanosensors are similar to the five senses of a human. They can act like the eyes and ears for an electronic device and are capable of substantial sensing capabilities on the nanoscale. They use their fine perception of their environment and ability to compute, to process new information, store it, and utilize it.
Unlike other sensors, they are sensitive, and will account for many forms of a physical stimulus, whether it be heat, light, sound or pressure. Some nanosensors have been solely developed to sense pH, oxygen, temperature, proteins, and water. They are durable, as well as lightweight. As a result of their small size, they are minimally invasive, and cause much lesser of a disturbance to their environment.
It is important to understand that nanosensors aren’t just normal sensors at a smaller scale. They are designed to use the unique properties of nanomaterials and nanoparticles to track and respond to behaviours in their environment.
Since they are so small, the applications are revolutionary, and leave an important impact on the industries they affect.
Types of Sensors
Like cells, nanosensors can be specialized (or designed) to carry out different, specific functions. Like the cells and tissues in our body.
Nanosensors are classified based on two key features. 1) Classification based on structure, and 2) Classification based on application. Here are some examples of “specialized nanosensors”;
- Optical Nanosensors - conduct optical measurement (measurement of absorption, fluorescence, phosphorescence, refraction)
- Chemical Nanosensors - sensitive enough to detect a single chemical, a biological compound, and pH concentrations
- Deployable Nanosensors - mostly used in the military and national security → e.g. the Sniffer STAR; a chemical sensor that is integrated into an unmanned aerial vehicle
- Electrometers - a nanometer-scaled electrometer
- Biosensors - capable of monitoring biomolecular processes within a single cell → consist of a biological recognition element (a bioreceptor) and a chemical sensor
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Optochemical sensors have been able to use their specific function to track and solve problems in multiple ways. In an early experiment, these sensors were used to track Na+ concentrations in the cytoplasm of a single mouse oocyte (about 0.03mm thick). The sensor measured the Na+ concentrations while the cell was in it’s growth state, as kainic acid acted as a stimulus to open and close ion channels. Measurements of Ca2+ concentrations have also been tracked through optochemical sensors. These sensors are minimally invasive, and provide great promise to understand and solve problems occuring on the cellular scale. I remember in my 8th grade science class, our teacher had us dye and examine a layer of onion skin, and compared its thickness to a single cell. How mindblowing is it, that a device can track the concentration of ions in something as paper thin and fragile as onion skin?!
Biosensors are hugely funded. This is due to the fact of their potential to accomplish endless possibilities. Biosensors are different than other sensors because they are created from synthetic polymers (dendrimers) layer by layer into a sphere less than 5 nanometers in diameter. Scientists hope to use biosensors for early cancer, disease and DNA detection. As a result of their small size, it is an aim to transmit them transdermally, through the skin. Biosignatures (a proof of past life through an element or molecule) are mostly in the liquid or vapor state which makes their concentration in parts per billion (ppb) therefore making them more difficult to detect. As an advantage of their size, many sensors can be placed on the same chip, allowing for effective and efficient readings of a variety of biosignatures.
Clark’s Oxygen Electrode
Leland C. Clark, the “Father of Biosensors” invented the Clark Oxygen Electrode in 1962, and was the first glucose biosensor (some say it was the first biosensor of any type). His device was pivotal and allowed for real time monitoring of oxygen levels in patients. This allowed for accurate and safer surgeries, impacting the healthcare industry we know today.
How do Nanosensors work?
Generally, the main components of a biosensor include the biosensor and the transducer. When analytes (the physical substance/quality being measured) come into contact with the bioreceptor, the bioreceptor sends signals to the transducer. Bioreceptors are sensitive biological element (e.g. an antibody, tissue, or organelle) that generate an effect once they come into contact with an analyte. This effect is picked up by the transducer, converting the varying concentrations of the analyte into some form of electrical signals. These signals are amplified and sent to a signal processor where the results can be displayed.
Cantilever Sensors
Micro-fabricated cantilever array sensors are used as sensitive mechanical sensors converting biochemical and physical processes into a recordable signal. This signal is then stored in a nano-electrochemical system. When the cantilevers react to the analytes, they will react and respond to their environment. Nanocantilever-based sensors sense and detect biomolecules and the cantilevers will move and respond accordingly.
- Have been utilized for early diagnosis of Diabetes Mellitus and can monitor glucose in the blood using the ultra sensitive analytical platforms.
- These sensors have also developed to detect bacteria fungal spore and viruses
- can be engineered to bind to molecules associated on the DNA sequence (single nucleotide polymorphisms and other proteins)
Nanofabrication: The Process + The Problems
There are a few main approaches taken when producing nanosensors. These include the top-down lithography, bottom-up approach, and molecular self-assembly methods.
Top-Down Fabrication
The top-down method begins with a large section of material, and then etching or sketching the diagram for a specific circuit for a nanosensor. This allows for great waste of material. A common technique used in the top down method is nanolithography. This method is comparable to sculpting with a block of stone!
The top-down approach is quite expensive as the cost of machines and clean room environments grow exponentially as new technologies emerge. Although it is efficient and takes less time then the bottom-up approach, a major disadvantage is the cost of machines that are constantly upgrading.
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Bottom-Up Fabrication
The bottom-up method (like its name) is actually quite the opposite of the top-down approach. It begins with the moving and assembly of individual atoms or molecules into specific positions. This is usually done with an Atomic Force Microscope.
What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them?…I can’t see exactly what would happen, but I can hardly doubt that when we have some control of the arrangement of things on a small scale we will get an enormously greater range of possible properties that substances can have, and of different things that we can do. — Richard Feynman
This method of fabrication is much more cost effective than the top-down approach, but takes much more time, since each molecule is fixed individually. It is important to be precise with this method as well. To continue, it is also based off of molecular self-assembly. The key difference between the two methods is that instead of an external force assembling the molecules together, they are binding on their own. The key advantage from using this approach is that the nanostructures created are smaller than those created through the top-down approach, and they are significantly more cost efficient. However, with all this said, it is also very possible to assemble complex molecules incorrectly.
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Nanolithography
Nanolithography is the process of printing and etching patterns onto nanostructures. There are many different variations of nanolithography, such as ice lithography and photolithography. Depending on the method of lithography, the etching can be done chemically by using acids, or mechanically using ultraviolet lights and X-Rays. Most top down fabrication methods involve etching, which can be compared to building a house with building blocks!
This technique allows researchers to use many different materials, however it does produce a great amount of waste, and does not conserve energy.
How can we improve nanofabrication?
According to me, there are definitely small changes that can be made which will result in a lasting impact. Firstly, if companies are using the top-down approach, they should upgrade to a method that’s one step above them; the bottom-up approach. This way, companies will not waste the valuable material lost due to nanolithography. Companies would not have to upgrade to newer machines frequently as well. Since less material is being wasted now, it is important to invest in higher quality materials to produce better nanostructures. Through machine learning, AI might also impact the nanofabrication process to make it go by quicker. In the bottom-up method, it is crucial to be exact when creating the sensors, which gives the scientist some control. AI can assist in producing nanomaterials at a faster rate as well!
Thank you for making it to the end of this article!
Linked below, I have my resources and any other findings in case you would like to continue your study further.
