Nanosensors and Nanofabrication — Sensing the Future
What if sensing love, and giving it a numerical value was possible? The idea seems impossible and straight out of a fiction novel, but with nanosensors, the fine line between the possible and impossible almost disappears.
The notion of, “I love you to the moon and back,” seems so vague. How much love exactly is that? With nanosensor technology, scientists are now able to detect the dopamine in the brain, which directly connects to romantic love.
The goal with this discovery is to apply a second function to the nanosensors, detecting the concentration of this chemical component and transferring it to quantitative data.
Sensors will help us better understand the world we live in.
Nanosensors are beginning to unlock big opportunities for such minuscule technology
To give you an idea of how small the sensors are, a single strand of hair is 80,000 - 100,000 nanometers wide, meanwhile the sensor or distance between the sensor and the substance being observed is 10 - 100 nanometers. A common misconception is, nanosenors must have nanoscale dimensions, however they may also serve the purpose of observing substances at a nanoscale distance, while harbouring larger dimensions.
Classifying the Sensors
Nanosensors are classified according to the energy signal they detect: physical, chemical, optical or biological. Each class can be further divided into various other sensors with similar purposes.
- Physical nanosensors: Measure properties including, pressure, force, mass, and displacement
- Chemical nanosensors: Determine concentration/identity of a chemical substance
- Optical nanosensor: Best for analytical purposes; can continuously monitor chemical or biological processes and convert information into signals for vital data.
- Biological nanosensors: Monitor biomolecular processes such as antibody/antigen interactions, DNA interactions, enzymatic interactions or cellular communication processes.
Why Nanosensors?
First let’s touch on how these sensors actually work.
An analyte, sensor, transducer and detector are parts of a sensor system, with feedback from the detector transferring to the sensor. Sensitivity, specificity and ease of the execution are the main goals in designing a sensor. Nanosensors in particular, generally function by monitoring electrical changes in sensor materials.
For example, when a molecule of nitrogen dioxide is present in a carbon nanotube-based sensor, it will strip an electron from the nanotube, making the nanotube less conductive. The detector then picks up this electrical change and sends signals back to the sensor. Another example is if ammonia is present, the molecule reacts with water vapour and donates an electron to the carbon nanotube, making it more conductive. By treating nanotubes with numerous coating materials, they can be made sensitive to certain molecules and immune to others.
Now let’s get back to, why nanosensors?
In comparison to today’s mainstream sensors, nanosensors provide greater efficiency overall. A single nanosensor can achieve multiple functions, resulting in higher sensitivity, therefore higher accuracy. A key difference that sets apart nanosensors is the smaller sample sizes required for the same data, if not more. With smaller sample sizes, there is little, to no disturbance to the observed material or process.
Nanosensors play a vital role in atmospheric environmental testing. They offer important advantages over conventional methods and cater the need for portable analytical tools with features of higher selectivity and stability. The sensors provide opportunities to observe and work at the nanolevel effectively.
As nanosensors posses the ability to sense substances at a molecular level, they can be applied to early cancer detection and monitoring. The use of nanomaterials in sensors to extract and detect tumour specific biomarkers, circulating tumour cells, or extracellular vesicles shed by the tumour holds promise to detect cancer much earlier thus, improving the long-term survival of patients.
Daniel Roxbury: Monitoring Cancer from your Smartphone
Daniel Roxbury, Ph.D. Roxbury is a researcher at the Sloan-Kettering Institute for Cancer Research in New York. Although he is currently working out how the technology would play out in humans, he envisions doctors inserting the nanosensor by a gel-like substance underneath the skin through a minimal interference procedure. The patient would then posses an external device such as a smart watch or smart phone that could read signals from the nanotube sensor and track the levels of cancer biomarker in the patient’s blood — similar to how a heart monitor works. The patient could then be able to monitor for the presence of the markers whenever they like.
If you are able to detect biomarkers in the blood at a low concentration, so many lives can be saved. As the problem lies in detecting cancer later on, when it is difficult to treat, the importance of nanosensors becomes key as it can solve this problem with ease.
You may ask yourself: If this technology is so beneficial and efficient in comparison to our every day sensors, why are they not being applied everywhere? The answer is: because of the complicated and intricate manufacturing process, nanofabricating.
Nanofabrication: Building Nanosensors
Nanosensors can be built using two methods; top-down and bottom-up. At first they sound pretty simple, but it gets pretty complicated when self-assembling nanostructures are thrown into the mix.
Let’s break it down!
Top-Down: Sculpting
Think of this method as similar to sculpting from a block of stone. The base material is eventually eroded until the desired shape is achieved, starting from top to bottom. This can be done chemically using acids or mechanically using ultraviolet light, x-rays or electron beams. This method can be seen in the manufacturing of computer chips.
A common technique practised in this method is, lithographic patterning. We’ll be touching on nanoscale imprinting, stamping and molding more specifically.
Getting technical with lithographic patterning — The goal of nanoscale imprinting, stamping and molding is making a master “stamp” by electron-beam lithography — the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film — and then applying this stamp, or multiple layers of it to a surface to create the pattern.
Plasma etching is then used to remove the thin layer of the masking material under the stamped regions. Any residual polymer is removed, a nanoscale lithographic pattern is left on the surface. Smaller features are obtained by using scanning probes to deposit or remove thin layers.
Bottom-Up: Building
While top-down is similar to sculpting, this method can be closely compared to building a brick house. However instead of using bricks, atoms and molecules are placed from bottom to top until desired nanostructure is achieved
This method requires a lot of time and is tedious work, which introduces self-assembling.
Behind the Iron Man suit- but smaller, much smaller with self-assembling nanostructures — These nanostructures use the abilities of certain molecules and polymers to organize into 2D or 3D nanostructures. The specific structure and type of molecule used produce different properties and characteristics. This idea is inspired by biological systems, where nature harnesses chemical forces to create basically all the structures needed by life. Researchers hope to replicate this ability.
An example of self-assembly is the growth of quantum dots. Indium gallium arsenide dots can be formed by growing thin layers of indium gallium arsenide on gallium arsenide so that repulsive forces caused by compressive strain in the indium gallium arsenide layer results in the formation of isolated quantum dots. After the growth of multiple layer pairs, a fairly uniform spacing of the dots can be achieved. This growth can be directed into different formations and structures.
DNA assisted assembly is another common technique for this process. By using this strategy, it is possible for molecules on surfaces to control attachments between objects in fluids. Polymers made with complementary DNA strands would be treated as “adhesive tape” by attaching only when there is a correct pairing. This process can be paired with electrical fields to help locate these attachment sites, followed by more-permanent attachment approaches, like electrodeposition and metallization.
Fabrication is awesome, but it is not perfect… yet
- Top-down; it works well at the microscale (at millionths of a metre), however it is increasingly difficult to apply them at nanoscale dimensions. This method involves planar techniques, which means structures are created by the addition and subtraction of patterned layers (deposition and etching), so three-dimensional objects are difficult to construct.
- Bottom-up; it is time consuming if not self-assembled. On the other hand, there is lack of research in self-assembly, as it is fairly new. Therefore currently, there are scarce methods.
- Expense; Products containing nanosensors range from $0.6 billion to $2.7 billion, as it is new technology.
How can we resolve these problems?
A few of my ideas include:
- More research in different materials and substances that can grow quantum dots, to increase resources.
- Investing more into nanoscale imprinting and stamping, and working towards making the stamps more accommodating for 3D construction. This process is also cheaper and can be done in a regular laboratory, therefore, investing in research and popularizing this technique can potentially decrease the overall expense of nanofabrication.
The nanosensor market is expected to reach $1,321.30 million by 2026, which is still expensive but manageable in comparison to $0.6–$2.7 billion. Following some of my ideas may lead to the prices further decreasing eventually. In the end, the key reason for this expense is that nanosensors are so new and are not yet popularized. I believe with time and marketing, nanosensors will be easily accessible for all.
My Personal Note
The fast progress made in nanotechnology and nanosensors is impressive to me. The research and time invested into nanosensors is mindblowing and I believe something as out of this world as Iron Man’s self-assembling suit can one day be made possible. Nanosensers’ application to cancer research also deeply intrigued me and I hope to contribute to research in monitoring cancer at the early stages. The efforts of the scientists I read about taught me that anything can be made possible with an idea and perseverance.
And hopefully, in the near future we can truly find out exactly how much love “I love you 3000,” is.
If you are interested in nanosensors like me, here are some resources where you can learn more and develop your inquiry-based mindset:
- Treating Cancer with Nanosensors
- Nanotechnology and Functional Materials for Engineers
- Nanopolyemers
- Applications of Nanotechnology
- Early Cancer Detection and Therapeutic Drug Monitoring
Have fun and keep learning!
