Check out this image. Cancer, the abnormal growth of cells, is the leading cause of death worldwide â not because of cancer being completely uncurable, but because of people discovering cancer when itâs too late to be cured. Most of the time, cancer initially starts off as asymptomatic. By the time symptoms come to the surface, the condition will have spiraled out of control, making it far harder to cure and remove. đ«
According to medicalnewstoday, the detection of cancer at early stages can âsignificantly improveâ a personâs chances of being cured. This is especially the case when the cancer did not spread yet, so doctors can isolate and treat it much more effectively. This is where these ânanosensorsâ come in to play. Oversimplified, when detecting low pH, a trait of some cancers, the nanosensors lights up the tissue, as in the picture above, allowing for early diagnosis. The tiny, minuscule scale of these nanosensors makes this even more amazing! Most nanosensors are between 10 and 100 nanometers wide â merely a tenth of a red blood cell, the 2nd smallest cell in the body.
Imagine the number of lives saved from such technology! As a non-invasive and safe procedure, which is far less is harmful than some current cancer detection procedures, many would benefit from using nanosensors for cancer detection. Itâs both hard and wondrous to believe that something so small can make a difference so big. Here is a laymanâs guide to Nanosensors, one of the smallest oxymorons of the Technological World. đ
What in the world are they?
They detect signals, ranging from the presence of cancer to how fast it is accelerating to the concentration of Nitrogen Dioxide, on the nanoscale (a billionth of a meter). They are so small, you can only see them under a microscope! đ
Each Nanosensor, due to its size, is designed and specialized to detect specific signals, for example, the interaction between molecules or the physical changes of the nanosensor. Such data is collected and analyzed through many methods, i.e emitting fluorescence (as in the first image) or sound that can be detected. Nanosensors generally have their own electrical source (capacitors) to generate these detection signals once the stimuli was sensed. They typically have some sort of simple electronics system with a signal producer.
Some Nanosensors have transducers that convert energy from one type to another, which can potentially transform the energy from the stimuli (if it is in some form of energy) to the signal. This does not require the capacitor/electronics system entirely! (how amazing is that đŻ)
How do they work?
This largely depends on what the sensor is sensing, split into Chemical and Mechanical stimuli. However, to trigger a signal, both types mostly rely on a change in electrical conductivity due to the stimuli. Once the conductivity is above/below a specific threshold, current can flow through and the signal is released.
Chemical Stimuli:
Once the chemical stimuli were detected, because of binding or absorbing a chemical molecule (i.e Antigen binding to Antibody), a nanomaterialâs structure can change. This can, in turn, alter its electrical conductivity. So, the nanomaterial is connected to the electronics system.
For example, if ammonia (NO3) wants to be detected, because of how it reacts with water vapor, it would donate an electron to the carbon nanotube (connected to the electronics system) coated with water vapor. This would make the nanotube more conductive. Once it surpasses a threshold, current flows to the producer and a signal is released.
Mechanical Stimuli:
Once the physical stimuli were detected, like above, they have nanomaterials that change their electrical conductivity. However, in order to do this, the nanomaterial generally has physical properties i.e being easily bendable to an external force (cantilever). In this case, the change in conductivity as a result of bending could have a relationship with the force experienced. This can then be used to detect the force on the nanosensor.
Generally, to detect mechanical stimuli, the nanomaterials might involve specialized designs that require an object moving in it due to the stimuli. How the object moves would alter the electrical conductivity, i.e a rotating mechanism as below that detects velocity.
Why SIZE matters.
The beauty of all of how nanosensor works is their size. By relying on the properties of special nanotubes or devices, as well as activating the production of signals through changing electrical conductivity, the size can be limited to merely about 100 hydrogen atoms wide. This size creates immense potential far beyond traditional sensors:
- Measures on the Molecular Level (highly sensitive to small, trace amounts that are hard to detect on a large scale)
- Real-Time Monitoring (so small it can stay inside organisms or places without interfering its operations, while continuously sensing stimuli and producing signals detectable outside)
- Travels to places HARD to access (travels through blood/water across the organism, to places that are hard to access, i.e Bone blocks X-Ray signals)
- Is generally noninvasive (their small size can cause minimal or no damage to our bodies, and naturally leave or stay our system)
What are they used for?
These UNIQUE and EXCLUSIVE properties allow for nanosensors to be used in fields we never could have done before.
Medical Diagnosis and Monitoring đ
Imagine a FitBit not for your wrist, but for your organs or blood. It sounds weird, but nanosensors can attach themselves to specific places or travel through your bloodstream or digestive tract. They can detect bacteria, viruses, antigens or cancer, and more, from places hard to access or not testable using traditional methods (i.e behind tissue). Furthermore, the nanosensors are noninvasive not requiring surgery, as well as can track real-time changes, which is great for essential places like our brain or heart. Such factors make nanosensors the ideal solution for monitoring our bodies, which can prove highly beneficial for detecting diseases early, like cancer. In real-time, nanosensors can offer a much-needed warning for situations like spikes in cholesterol, blood sugar, pressure which can forecast strokes or heart attacks. Such monitoring can be very useful in agricultural industries as well to monitor the disease or health of animals on a large scale, simply by injecting the nanosensors into them.
Environmental Monitoring
The highly sensitive nature of nanosensors allows them to detect very small amounts of substances, such as bacteria, metals or toxins in the environment. This is crucial due to how even trace amounts, to the molecular scale, of these in our air, water, food or soil would potentially damage or kill organisms. Apart from that, they can monitor minuscule physical changes like vibrations or pollutants, which can forecast disasters like earthquakes or sandstorms.
Commercial Monitoring
For commercial products, nanosensors can play a pivotal role in the manufacturing and quality control process. Some products might not be able to have impurities at all or must be kept at a specific temperature/pressure during transportation. By attaching nanosensors to continuously monitor a batch, it would an effective way to ensure its quality. Any damage or alterations could be alerted as a result. In products crucial to safety, for example, airbags or parachutes, the sensitivity of nanosensors are essential for ensuring quality and safety.
I want one! How do I make one?
Sadly, you canât make them at home. đ„ Not with ordinary scissors and tape. We need to use something called nanofabrication, which uses specialized equipment and materials. This falls under two types:
- Top-Down: Carving out the patterns out of the resist (top layer) on top of the substrate (base). This is like a sculptor who chisels away marble to form a statue.
- Bottom-Up: Adding devices or particles to the substrate (base). This is like a bricklayer who lays bricks one by one to build a structure.
Top-Down Nanofabrication
In the nanotechnology industry, to remove parts of a material out, there are several most commonly used methods for achieving this.
RIE (Reactive-Ion Etching): Pumping Plasma that react and carve away the surface of the material, and a mask is placed on areas not wanted to be etched
SPL (Scanning-Probe Lithography): Using a sharp tip to make patterns on a surface. The tip can be heated to high temperatures and vaporize the material
Photolithography: Placing a mask over a light-sensitive material and hitting the mask with a light beam, causing areas not covered by the mask to erode
Bottom-Up Nanofabrication
Assembling components at the nanoscale is a very difficult task, requiring the manipulation of specific properties of materials for it to work. The most common methods of Bottom-Up nanofabrication are as follows.
CVD (Chemical Vapor Deposition): When atoms are vaporized, they can be deposited on a surface where the atoms decompose to form patterns.
Block Copolymers (a form of self-assembly): In some polymers chemically bound together, when given energy, they reconfigure and assemble in a pattern based on the polymerâs properties and shape
Nucleation Growth (a form of self-assembly): Based on thermodynamic principles of entropy and phase changes, like how crystals grow, particles can nucleate and aggregate together into a fairly predictable pattern
Which is better? đ€
According to the Brookhaven National Laboratory,
(Top-Down Nanofabrication) is generally fasterâand more reliably produces the designed structuresâbut requires expensive, complex tools
(Bottom-Up Nanofabrication) is often slower and less predictive but it is inexpensive and can be easier.
While there are many great things about nanosensors, you might have asked: Why havenât I seen nanosensors in my life yet? (unless you were fortunate enough to have tried out these marvelous devices before)
Despite our current technology, there are many obstacles and flaws in nanofabrication preventing from nanosensors dominating our world right now. Here are some of the most troublesome ones:
- Precision VS Efficiency:
Yes. The decade-long question of quality vs quantity. In order to produce nanosensors with high resolution to work well, generally, top-down methods are ideal. However, technology such as electron beams, though quick, are very expensive and complex to operate. Photolithography, while fairly inexpensive, comes with the expense of resolution because of exposure or focusing problems. At the same time, relatively cheaper self-assembly mechanisms are random with no guarantee that it assembles the way desired.
- Very HIGH Barriers of Entry
When people talk about nanotechnology, mostly talk about it like it is something advanced and high-tech, with a reason. Access to the nanomaterials or equipment needed for nanosensors or doing nanofabrication is not widespread, with high costs and lots of research required in order to be successful. All nanofabrication techniques require lots of experimentation and testing, limiting factories around the world from doing nanofabrication themselves and making nanosensors widespread.
What can we do? đŻ
Fear not! What researchers need to do is simply getting the best of both worlds, of Top-Down and Bottom-Up Nanofabrication, and develop a precise, efficient, quick and cheap solution. This might seem unrealistic, but researchers at the Brookhaven National Laboratory have begun experimenting with directed self-assembly.
What is directed self-assembly?
Basically, a combination of Top-Down and Bottom-Up approaches. How, you might ask? One solution is to order self-assembly nanomaterials inside a lithography (top-down) patterned template (reusable). This produces a pattern from self-assembly materials guided by lithography. This not only allows the self-assembly materials to take more patterns but also makes them more precise and predictable. How the template is reusable without using the top-down equipment multiple times also keeps the cost down.
This is just only one implementation of directed self-assembly, with others that attempt to use chemicals like in RIE to control the self-assembly process.
Other Solutions?
I have many ideas for improving nanofabrication, that have no scientific evidence and are merely thoughts open for discussion.
- Involve Magnetic or Electric Fields in some form to direct atoms or molecules into a specific order. Then, the particles can be merged together using chemicals
- Involve Machine Learning to detect flaws or errors in the end products of Nanotechnology
- Create bigger microdevices that can behave like factories to produce or piece together nanodevices
Final Words
As Dr. Seuss once said,
Think and Wonder.
Wonder and Think. đ
It is always wise to question current processes and think if something can be improved. I am grateful for TKS for giving me an opportunity to get to learn about amazing nanosensors but also thinking about the flaws of current methods and how to enhance it. Looking into the future, nanotechnology is a burgeoning field that would soon take a key part of our lives. Imagine seeing this nanotechnology in our bodies, in our phones, even in our food!
I know, for certain, that this day would come very, very soon. And as always, stay curious and stay innovative! đ
Enoch
For more reading (if you are interested):
https://www.azonano.com/article.aspx?ArticleID=5106
https://www.sciencedirect.com/science/article/abs/pii/S2211285519304677
