Nanosensors — small, but mighty.
At some point in our lives, we have come in contact with sensors. Whether if it’s at the grocery store when the automatic door slides open or when you’re scrolling through your phone on Instagram, sensors are everywhere. They are an essential part of current society and allow us to live in a more advanced civilization. However, have you ever seen a nanosensor? Probably not with the naked eye! Even conventional light microscopes can’t view these small, but mighty devices. Yet, you’ve probably come across them in your own home. Can you think of one?
When we say things are ‘nano’, we say things are very small. As small as one billionth of a meter! The term nanometer literally means ‘dwarf meter’ in Greek. To put that into perspective, a honeybee is about 20 million nanometers, the width of a human hair is about 100,000 nanometers, and a red blood cell is about 7,000 nanometers. But, these nanosensors are even smaller than red blood cells. We’re talking 1–100 nanometers. Now that’s small! Nanosensors are devices that can record behaviours and characteristics of other nanoparticles. In other words, nanosensors are sensors on a ‘nano’ scale. Now, how could something so small actually help us? Won’t their effects be useless because of their microscopic size? I wouldn’t recommend underestimating these little guys. Today, they help us detect carbon monoxide in our homes, find dangerous bacteria such as certain strands of E.coli in our foods, and measure the temperature inside living cells and other nanofluids. To really understand nanosensors, let’s take a look at some applications of nanosensors.
Importance of Nanosensors
Without nanosensors, life would suck. We would be breathing in harmful air, potentially eating dangerous foods, and drinking lead-poisoned water all without knowing it. Luckily for us, they exist! And, they exist in many different situations. Healthcare, food safety and quality, and the environment are only a few of the countless industries that use nanosensors. Here are a few examples of how nanosensors help us live our lives today.
- Air Quality: a new approach to air sampling comes from using nanosensors to detect pollutants in the air for better air quality. For example, we can detect the smallest bits of mercury in any medium through the use of dandelion-like Au/polyaniline (PANI) nanoparticles combined with surface-enhanced Raman spectroscopy (SERS) nanosensors. Additionally, researchers from the University of Southampton have developed a graphene-based nanosensor that detects individual CO₂ molecules and volatile organic compound (VOC) molecules at a very low cost. VOCs can be harmful to our health and are linked to multiple diseases like asthma, chemical sensitivity, and sick-building syndrome (SBS). They are found in homes, specifically from furniture, walls, and other interior materials.
FUN FACT! Nanosensors have been found useful during the 2008 Beijing Summer Olympic Games for assessing air pollution.
- “Smart Pipe”: a prototype built using nanosensors to monitor water quality and water distribution by the Environmental Protection Agency. Characteristics of water such as flow rates, slow flow sections, pipe pressures, pipe leakage, backflow, and stagnant points are measured using this technology. Another innovation called Au-TA-DNS was designed at the Central Mechanical Engineering Research Institute (CMERI) in Durgapur, India that essentially detected extremely low concentrations of lead and copper ions (Pb²+ and Cu²+) using nanosensors and paper strips. Using this technology, detecting lead-poisoned water can be easier than ever.
- Food Safety and Quality: not only can nanosensors be used for detecting foodborne pathogens, toxins, and other unwelcome substances in specifically raw foods, but they can also aid in food storage, transportation, display, and freshness. Smart packaging can help reduce food waste by monitoring multiple physical attributes of food (humidity, pH, light exposure, temperature), gas mixtures, the presence of pathogens, and existing decomposition. So, now we can reduce the risk of getting multiple foodborne illnesses like salmonella and reduce food waste by having smart storage methods.
- Agriculture: nanotechnology can help revolutionize the agricultural industry, making it more efficient, and sustainable than traditional farming.
How do nanosensors work?
Okay, hold up. We now know that nanosensors can do all sorts of detecting and monitoring, but how do they really work? Different types of nanosensors work very differently from each other. But, they all have a few things in common. All nanosensors detect changes in the environment, specifically electrical changes in the particles they are sensing. For example, remember when we looked at a graphene-based nanosensor that detected pollutants in the air? Well, that sensor detected changes in electrical resistance which identified the pollutants. Let’s break it down. The components of nanosensor include:
- an analyte (the material being measured);
- a sensor;
- a transducer (a device that converts some form of energy into electrical signals);
- and a detector.
Firstly, the detector detects the analyte. Then, the sensor senses the attributes such as temperature or pressure of the material that must be measured. Then, these physical attributes are converted into electrical signals using the nanosensor’s transducer.
How are nanosensors built?
Humans are physically incapable of building nanosensors. We are just too darn big! But, using the help of nanofabrication, we can build nanosensors that help us in our everyday lives.
Nanofabrication — the process of creating nanomaterials for various contexts
This definition can be quite broad. But, as we get into the types of nanofabrication and some examples of nanofabrication, you’ll get a better understanding of how nanosensors are built.
There are 2 main approaches to nanofabrication:
Michelangelo was a top-down artist. He started his sculptures with a large block of Carrara marble and shaved his way down to a work of art.
The top-down approach is a type of nanofabrication where engineers work with larger materials that are scaled down to create nanodevices — just like how Michelangelo scaled his block of marble down to his sculpture. This seems pretty straightforward, but it isn’t the best method for creating nanodevices. When Michelangelo sculpted, he had to chip away large chunks of marble to earn the desired shape. In terms of nanofabrication, this is called nanolithography — the etching, writing, and printing on nanostructures. But with etching and sketching on sculptures, Michelangelo created lots of wasted pieces of marble. Similarly, nanofabrication produces a significant amount of waste and is very time-consuming, energy-consuming, and dangerous due to certain chemicals that need to be used. Plus, it is very difficult to create extremely small devices with the top-down approach since you are starting with a larger object.
What’s the opposite of the top-down approach? You guessed it! The bottom-up approach starts from the smallest units of matter (atoms and molecules) and assembles them together to create components of nanostructures. Take a look at the animation below. It takes us through the process of the bottom-up approach.
With this method of nanofabrication, we can create the smallest nanosensors at relatively lower costs than the top-down approach. Bottom-up is much more reliable, adaptable, and flexible. The bottom-up approach is tackled in two ways:
- Molecular assembly (man-made)
- Self-assembly (nature’s way)
Molecular assembly is exactly what the animation above illustrates. Man-made nanodevices put together by man-made factories. We haven’t reached this point in the future yet, but when we do, nanotechnology will revolutionize the world.
Self-assembly is very different from molecular assembly. It’s basically letting nature do its thing and create its own nanodevices, sometimes with the help of humans. We can input specific stimuli into the equation that helps us get the desired nanodevice. It’s literally a chemistry experiment! All we need to know is how to control and initiate the process of how specific molecules assemble, then we can build amazing devices atom by atom.
Nanofabrication isn’t perfect.
There are many setbacks and flaws to nanofabrication that make it a bit of a painful process. As mentioned with the top-down approach, nanofabrication can use up a lot of resources, time, and energy, making it an expensive process. Also, since we’re working on such a tiny scale, several methods of nanofabrication can be prone to errors. But, don’t fret! Nanotechnology is a new industry and we’re only at the beginning of a technological revolution.
Some types of nanofabrication are much more efficient than others. For example, the top-down approach is the most straightforward but has the most barriers and setbacks. Rather than solving these setbacks, we can shift our focus to other alternatives like the bottom-up approach, specifically self-assembly. Self-assembly is the most efficient type of nanofabrication because external forces are barely needed to acquire the desired result. We let nature do its job and we’re done (kind of…)!
Why can’t we use regular-sized sensors instead?
It may seem like regular-sized sensors can do the job just as well as nanosensors. Plus, they are easier to make. But, there are actually many advantages to using nanosensors, mainly because of their size:
- Responses are faster
- Data collected is more accurate
- More data can be stored in a smaller storage space
- Less interference to the materials and substances being measured
- 💾 Nanosensors are super small sensors.
- 🌾 They’re important because they help humanity thrive in many situations.
- ⚡ They work by detecting electrical changes in the environment.
- 🏗️ They are built using a process called nanofabrication.
- 🚧 Nanofabrication has two types: top-down and bottom-up
- 💸 Nanofabrication can be expensive, time-consuming, and resource-consuming.
- 🛑 We should stop doing the top-down method as often because it is very inefficient. Rather, do self-assembly!
Further Reading + Sources
Nanotechnology is the future. How can you contribute to its growth? Learn more by clicking on the links below!
What are Nanosensors? How and Where are They Used?
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Nanofabrication and nanomanufacturing - what is it, what it is used for
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Graphene-based sensor detects harmful air pollution in the home
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Nanosensors: Definition, Applications and How They Work
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The next generation of carbon monoxide nanosensors
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Smart gold nanosensor for easy sensing of lead and copper ions in solution and using paper strips …
DOI: 10.1039/C5RA14886C (Paper) , 2015, 5, 69024-69031 Received 27th July 2015 , Accepted 3rd August 2015 First…