Nanosensors: Minuscule Machines with Massive Potential
If so, that’s pretty cool. But don’t pat yourself on the back just yet, because to at least one dimension of a nanosensor, that text you just read is larger than Mount Everest.
What are nanosensors?
Nanosensors are minuscule devices that collect and transfer information on the nanoscale. This data allows us to identify dangers and to better understand the world we live in, ultimately helping us better react to the world around us.
Still, how can something so small be so important?
The benefits of nanosensors
Nanosensors have defining characteristics that set them apart from any other form of data collection. Evidently, they are small. To be considered a nanosensor, at least one of its dimensions must be smaller than 100 nm. That’s about 750 times the diameter of a human hair! Their microscopic size allows us to obtain information on processes that occur on the nanoscale.
Also, nanosensors are highly sensitive; their ability to detect single molecules allows for optimal precision and reduces the necessary sample size for a study. This will vastly prevent disturbances and modifications in the observed environment.
The sensors return information promptly; having a low response time provides us with the information necessary to react to dangers immediately or study processes in real-time.
What they can do — Some applications of nanosensors
Good things come in small packages. Nanosensors can help us to:
- Detect pollutants or toxins in the environment
- Detect bacteria and viruses
- Detect cancers in the body
- Detect contaminants in food
- Monitor physical parameters such as temperature, displacement, and flow
- Monitor plant signalling and metabolism
- Study neurotransmitters in the brain
How do they do it?
The sensitivity of the nanotube is a fundamental characteristic in relation to the function of the nanosensor. Nanosensors work by monitoring electrical changes in the sensor materials. They are layered with various coating materials that react differently based on the molecules they interact with.
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The sensor system has three main components:
- Analyte: the substance that is being identified or measured
- Receptor: material with a special coating that reacts uniquely with the analyte
- Transducer: uses the interaction between the analyte and receptor to create an electrical signal
Let’s look at an example to better understand this process.
Nitrogen dioxide (NO₂) is a chemical that causes an inflammation of the lining of the lungs when inhaled for extended periods of time, which can lead to problems such as wheezing, coughing, colds, flu, and bronchitis.
When a carbon nanotube-based sensor comes into contact with a molecule of NO₂, it will be stripped of an electron, ultimately reducing the conductivity of the nanotube. But in the presence of NO₃, the nanotube’s reaction with water vapour causes it to gain an electron, leading to an increase in conductivity.
Because of its sensitive coating, chemical nanosensors send different signals based on the molecule they are in contact with; by monitoring these small, electrical changes, they can help us to detect the presence of harmful gas in our environment.
Nanofabrication — How it’s made
There are two main categories of nanofabrication: top-down and bottom-up. It’s exactly what it sounds like. Top-down involves starting with a larger block of material and carving down to the desired shape and size, whereas the bottom-up method uses atoms and molecules to assemble the sensors from scretch.
Even within top-down and bottom-up nanofabrication, there are numerous different manufacturing techniques used to make nanosensors.
Top-down techniques
- Lithography:
Lithography is a common top-down nanofabrication process that begins with a larger block of some material that is carved out into the desired form.
It uses focused radiant energy to create precise patterns in silicon wafers. First, a wafer is coated with a light sensitive layer called a photoresist. A mask is applied to parts of the photoresist, and like a stamp, UV light removes the exposed areas, carving a sensor with the remaining material.
- Chemical etching:
Chemical etching is a method of engraving that uses an acidic spray and metal nanoparticles to remove material, resulting in a permanent etched shape in metal. Similar to how one would spray paint using a stencil, a protective mask helps ensure that material is removed selectively to obtain the desired shape.
Bottom-up techniques
- Molecular self-assembly:
This technique is the automatic assembly of molecules to form the sensors. The structure of the sensor is built using a combination of molecules that have specific shapes and properties. Having the molecules assemble independently from any outside influence results in more efficient nanofabrication and can lead to new, otherwise unattainable nanostructures.
A good example of molecular self-assembly occurs between sulfur and gold atoms. By pouring over a gold surface a solution containing organic molecules that have a sulfur atom on one end, the sulfur atoms bond to the gold atoms autonomously. It’s all about building new structures by taking advantage of existing molecular characteristics.
Challenges with nanofabrication
Nanofabrication is not a perfect process. If it were, there’d be a lot more of it out there. Let’s revert to the typical pros and cons list in comparing both top-down and bottom-up nanofabrication.
Nanofabrication is still in its infancy; there remain many challenges with cost, efficiency, and reliability. However, with more experimentation, this technological domain has the potential to make impactful change in pretty well every industry.
Key Takeaways
- Nanosensors are miniscule devices that collect and transfer information on the nanoscale
- They are small, highly sensitive, and accurate
- They provide us with the information necessary to detect dangers, monitor parameters, and study processes that occur on a molecular level
- Nanosensors work by monitoring electrical changes caused by the interaction of the sensor materials with the molecule in observation
- There are two main methods of nanofabrication: top-down, which involves carving a material down to nano-size, and bottom-up, consisting of building nanosensors out of smaller atoms and molecules
- With more experimentation, nanosensors will continue to make positive impactful change in countless industries
