Nanosensors — Changing the World Through Small Steps With BIG Impacts

8 min readMar 23, 2020

When Neil Armstrong landed on the Moon, he reported; “one small step for a man, one great leap for mankind”. Scientists today are using the same idea as they uncover the nanoworld — studying the nature of materials from 1–100 nanometers to develop technology that will provide the solution for problems in our great, big, macroscopic world. Turns out, you don’t have to go outer space to “leap” towards a brighter future after all!

Nanotechnology is the technological application of manipulating materials on an atomic or molecular scale to build microscopic technologies called nanodevices.

Welcome to the World of Nanotechnology. (Retrieved from Nanosensors a disruptive innovation in Nanotechnology — Medium)

One of these nanodevices are nanosensors — small sensors that have time and time again showed to have huge potential in every possible aspect of life. From agriculture to medicine to our beloved cell phones, nanosensors can be applied to improve our everyday lives.

So let’s jump right in to find out about this amazing little innovation!

So What Is It Exactly?

Nanosensors are, in a nutshell, chemical or mechanical sensors that can be used to detect the presence of certain chemicals and nanoparticles or to monitor physical quantities such as length, temperature, etc. all within, of course, the nanoscale. These sensors specialize in measuring chemical, mechanical and physical changes that are connected to the desired marker.

A polymeric nanosensor that has been embedded onto a piece of plastic. (retrieved from Science Direct

They can be either chemical or mechanical sensors which can be used in a variety of applications such as recognizing chemicals in gases for monitoring pollution, detecting early cancer diagnosis through identifying biomarkers which are molecules that are directly linked to certain diseases, simply monitoring various physical environmental properties such as temperature, etc. Nanosensors allow for real-time monitoring which is a better alternative to many traditional laboratory detection methods that are time-consuming and more expensive such as chromatography. With its wide range of applications, nanosensors will soon be all around us!

Okay, But How Does It Work?

Although different biosensors are designed to measure different things, their basic workflow remains the same. Every nanosensor has a selective binding of an analyte, a substance whose chemical elements are being identified and measured, causing a signal from the interaction of the nanosensor with the bio-element to be created which then finally processes the signal and converts it into useful metrics.

The workflow of some nanosensors. (Retrieved from Springer)

Compared to other sensor systems, nanosensors have higher sensitivity, specificity and thus, a better execution.

Their increased specificity comes with their teeny, tiny size. This small size is similar in scale to those of biological processes which further allows the efficient function of the nanosensor to chemical and biological molecules causing events that lead to detectable physical changes.

Their increased sensitivity comes from the high surface area to volume ratio of nanomaterials in addition to their unique physical properties that can be used as the foundation for detection. Nanosensors can also be integrated with nanoelectronics to create native processing abilities.

Hence, one-dimensional nanomaterials such as nanotubes work well with nanosensors as they can function both as transducers and wires to transmit signals. With a high surface area, larger signal changes are created after analyte binding.

Most nanosensors such as carbon nanotube-based sensors function by monitoring electrical changes within sensor materials. Within a carbon nanotube-based sensor, when a molecule of nitrogen dioxide (NO2) is detected, an electron is stripped off the nanotube — causing it to lose some of its conductivity. If ammonia (NH3) is present, it will react with water vapour to donate an electron to the carbon nanotube and make it increase its conductivity. Applying various coatings on the nanotubes allows them to increase sensitivity to certain molecules.

Carbon nanotube-based sensor (retrieved from Hindawi)

Similarly, mechanical nanosensors tend to also measure electrical changes. Within the micro-electromechanical systems that car airbags use, nanosensors are put to monitor changes in capacitance. With a weighted shaft attached to a capacitor, these systems measure changes as the shaft bend with changes in the acceleration of the car.

Diagram of different types of nanosensors (retrieved from Nanosensors the Next Step Forward -Medium)

Why Should We Care?

So why should we care about things that we can’t even see? Because it can revolutionize every single field of technology on this Earth! It can help our defence and military, our agriculture, our environment and most of all, our health care.

Although nanosensors are still under research and development for military purposes, they can be used for chemical detection, decontamination and forensics. Nanosensors can be used to detect explosive or toxic gases as since gas molecules are identified based on mass if it is absorbed in the surface of the detector, the frequency of the resonance caused by crystal changes within can be measured as changes in electrical properties. Furthermore, nanosensors can be applied to military clothing as nanoparticles with polymer and other receptor layers will change colour when in contact with analytes like dangerous gases.

A graphene-based sensor for toxic gases (retrieved from Advanced Science News)

The agricultural field will be revolutionized with nanosensors as well. Nanosensors will improve various sub-area in food and environment including food processing and air and water quality. These sensors will allow us to rapidly analyze products for the detection of food contaminating particles. Nanosensors can also be used to detect food odours to determine the freshness of foods by the detection of atmospheric gases.

Applications to food production. (Retrieved from Nanosensors for Dummies -Medium)

Currently, nanosensors are being established to detect pollutants within the environment. Quantum dot surfaces can be integrated with antibodies that bind to pollutants.

When it comes to health care, the applications of nanosensors are just as vast as the field itself. A notable usage involves using cadmium selenide quantum dots’ fluorescence properties to detect tumours within the human body. However, due to their high toxicity within the body, researchers are trying other alternatives that have the same effect. Another application would be using silicon nanowires in IV lines to monitor organ health. These nanowires are sensitive and detect trace biomarkers that diffuse into the IV line through the blood and can aid with monitoring kidney or organ failure. A final notable application of nanosensors would be its usage in detecting contamination within organ implants. The nanosensor is put within the implant and will detect contamination in the surrounding cells of the implants via electric signals that are sent to the clinician. With this technology, the nanosensor can detect whether the cells are healthy, inflammatory or contaminated.

Nanosensors will help relay information on cells to health care professors through electric signals. (Retrieved from Nanosensors for Dummies -Medium)

How Is It Made?

Nanosensors seem really promising, right? But, what kind of magic does it take to make these? Nanosensors are made by a process called nanofabrication. There are three general ways of nanofabrication: top-down lithography method, bottom-up self-assembly and molecular assembly.

Top-down lithography or optical lithography is a nanofabrication procedure that is used heavily for semiconductors. To understand lithography you need to think of it as sculpting and how a sculptor etches patterns on a piece of rock until almost half the mass of the slab is gone. How this happens is special chemicals are added to a nanostructure and precise waves of light pierce through the chemical and make patterns on the nanostructure.

Sculpting is kind of like top-down lithography because you etch in details in both.

Bottom-up self-assembly is kind of like the opposite because instead of subtracting parts of the nanostructure, you build it up by adding atoms and molecules. It is kind of like constructing a building you don’t carve it out you build it up with different materials. Unlike top-down lithography, this saves a lot more money because you aren’t wasting resources when you carve out the structure.

Bottom-up self-assembly is like building a house with bricks you don’t shave off things, you build using different particles

Molecular assembly is more of an idea at this moment, it also implies the bottom-up approach but it is more of a natural process where the molecules bond together naturally to make a nanosensor. It is similarly economic but, it takes more time. Scientists hope to understand and control this process better in the future.

What are the problems with nanofabrication?

You might be asking why nanosensors are not largely accessible to the public. Its because it has some issues with making it. Lithography has the problem of cost and you can create smaller structures with self-assembly. For self-assembly, the main problems are that forming complex structures can be harder. Molecular Assembly could take more time and it is still theoretical.

In top-down lithography, since you are wasting so many resources etching out the patterns you are wasting a lot of money. Also, you can make smaller structures with self-assembly.

In bottom-up self-assembly, you can’t make structures more precise than lithography because in lithography you can etch it out. This will make the nanosensor less precise.

How to fix these problems:

I believe it is easy to say that bottom-up self-assembly would be a better method of nanofabrication. This is why large manufacturing companies should lean towards self-assembly because you can make smaller and more cost-effective nanosensors. Now many companies are not using the self-assembly technique and they are only using lithography that’s why I believe companies should change their technique to make nanosensors accessible to everyone — so that everyone can take this leap to the future together.

References:

Nanosensors — Changing the World Through Small Steps With BIG Impacts

Written by Iffat Iqbal