State of the Art: Nanosensors
Nanotechnology… more than a concept
Nanotechnology entered the public spotlight in 2001 when U.S. President Clinton approved a $422 million budget for the US National Nanotechnology Initiative (NNI). This act implied to the public that nanotechnology is relevant to the USA economic growth and security. Nanotechnology optimizes the life cycle of materials and products, which increases economic productivity. ‘Smart’ materials at a nanoscale provide unexpected, novel properties with new functions. The vision is to create products that are high-energy intensive and less resource based. This essentially helps fulfill the dream that manufacturing can become cleaner, greener, cheaper, and more functional. Furthermore, nanotech started to show potential in other industries like healthcare, energy, environment, agriculture, and even military inventions. When it became clear to the public that nanotechnology impacts them, people started to care.
It wasn’t just the US that started to care, the world’s major economic powers committed themselves to nanoscale research. Japan, Korea, and the EU just to name a few. The EU funded €45 million annually on nanotechnology projects between 1998–2002. The US’ Fiscal Year 2019 Budget consists of nearly $1.4 billion for the NNI and a $36.5 million budget towards nanomanufacturing.
Bill Clinton describes it perfectly and simply: “There is plenty of room at the bottom! …arrange the atoms the way we want; the very atoms, all the way down!”
Nanotechnology is the manipulation of matter at a molecular or atomic level in order to produce novel, ideal materials, and devices with new extraordinary properties. The theoretical development revolves around the idea of nanoscience, which isn’t a discipline in itself. Nanoscience merges biology, physics, chemistry, medicine, and engineering into one. What’s interesting is that the basic law of classical physics no longer controls nanoscience, instead, quantum laws. This is because the drastic increase in surface area and volume ratio significantly impacts the matter’s behavior.
Nanotechnology is advancing and shows promise in the future. It’s just a matter of how and why we use it.
Within the current level of technology, nanostructured materials can already be built. Structures range from bulk to dot, wires to tubes, and powdered nanostructures. This technology is currently being integrated into everyday life beyond the lab; it’s even being extended to something as simple as bike tires. Carbon nanotubes are used on bikes to keep airless bikes in shape. Also, carbon nanosensors exist to detect tire thickness nondestructively.
Besides an advance in manufacturing quality, nanotechnologies offer more effective and precise data through nanosensors. Nanosensors are devices that convey data about the behavior/characteristics of nanoparticles, ranging from the nanoscale to a macroscopic level. The device measures physical qualities, then converts the data into electrical signals. Finally, signals are detected, transmitted and analyzed. Sensors can monitor physical parameters on a nanoscale. There are multiple types of nanosensors but their workflow to measure stays relatively the same.
Nanosensors can have nanoscale dimensions or perform nanoscale measurements. However, nanosensors don’t necessarily have to be nanosized in order to be recognized as a sensor.
So why care?
In an era of information and data, nanosensors are significant. Nanosensors radiate major potential for every industry in our future, impacting our whole quality of life, and culture. Different types of nanosensors specialize in a variety of research areas given the form of energy signals that are detected, such as physical, chemical, or biological. Here are just a few fascinating examples of how nanosensors impact our world through a lens of physical, chemical, and biological sensors:
Physical sensors measure the properties of pressure, flow, temperature, stress, strain, position, displacement, or force. The bike analogy would fall under this category. Physical sensors can provide us with data on optimizing resources, and how to make robust structures. Significantly, physical sensors can enhance the nuclear energy sector through more advanced manufacturing.
Biological nanosensors interact with biologically active substances, which is useful towards the medical or agrifood industry. Nanosensors can save you from foodborne viruses and create a more transparent food industry. In addition, sensors can detect cancer at an early age.
Chemical nanosensors can determine concentration or identity of a chemical substance/element. Data translated from these sensors would be a major contributor to environmentalism. Nanosensors can detect pollutants and remove pollutants. Metal ions and radioactive elements can be detected, and nanosensors can even absorb organic or inorganic pollutants. In addition, data retrieved can lead to discoveries on preserving energy and becoming more environmentally focused on our unnecessary waste.
From healthcare to agriculture, and from environmentalism or just the fun of science… nanosensors basically impact everyone in almost every aspect.
So how can we harvest these benefits? How can we develop a concept and integrate it into the markets- accessible to all?
The graph below depicts the evolutionary path of this technology while explaining the landscape of diversity, and beneficiary industries. There are two main analytical components to this graph.
- As research progresses, technology would become less academic and more commercialized. The graph explores the primary, secondary, and tertiary industries through commercialization. This means that the production of nanotechnology will impact different countries in different ways economically. For example, Canada is a developed country and it focuses on the secondary and tertiary industry. Whereas Bangladesh is a developing country, with primary and secondary industry as its focus.
2. Note that the “Landscape of Diversification” explores the different and increased technologies/concepts that are introduced as nanotechnology becomes more advanced. This truly proves the complexity of new technology as it develops, and what it takes for that technology to be on the market.
But to understand how nanosensors can be placed on the market, it is important to understand how they are made. So we can optimize its benefits and minimize its flaws.
How are nanosensors made?
Nanosensors are made through nanofabrication. Nanofabrication ensembles numerous technologies to fabricate small structures from 1 to 100 nm. The designs and engineering of these structures should be specifically targetted towards a given application. The main aspect of nanofabrication involves pattern formation. Sensors are built through a lithography process, then through a pattern transfer process.
In the general process of any type of lithography, they follow the same typical process. The process can be summarized as:
i. A substrate is coated with an irradiation-sensitive polymer layer, which is referred to as the resist.
ii. The resist is exposed across the process of light, electrons or ion beams.
iii. The resist image is developed with a suitable chemical.
To be more specific, the lithography process diverges into two methods of conventional and nonconventional.
Conventional lithography methods are top-down. Its methods can be compared similarly to carving a statue out of stone because they are both subtractive methods.
Conventional methods:
- Electron beam lithography
- Focused ion beam lithography
- Optical projection
- Extreme UV
- X-Ray
- Electron and ion projection
Non-conventional methods are a bottom-up assembly, which involves self-assembly, self-organization, and nano-manipulation. Essentially, molecular building blocks would link together to form nanostructures. The idea is similar to building a complex Lego structure piece by piece. Comparatively from conventional lithography, nonconventional techniques are low cost, and more accessible.
Nonconventional methods:
- Nanoimprint lithography
- Near-field optical lithography
- Proximity probe
- Chemical and biological approaches
- Miscellaneous technologies that aren’t as fleshed out as others, such as holographic lithography.
After lithography, the next step is pattern transferring from the resist to subtract. Pattern transfers are achievable with various techniques, such as doping through open space of the resist using diffusion or implantation.
Performance and quality for lithography rely on resolutions, throughput, pattern placement, and over-lay alignment accuracy. But most importantly, control of critical dimensions and microscopic properties of individual nanostructures. Although nanofabrication has advanced over the last years, they are still several problems and prone flaws.
Nanofabrication problems and ideas to solve!
Conventional lithography is expensive because the material is wasted as the product is being etched. Conclusively, it is rigid to develop out of the traditional microelectronics industry. Given the unavoidable waste to subtractive methods, scientists have been focusing on improving bottom-up fabrication methods instead.
When it comes to bottom-up fabrication, the issue is a thin-film deposition. Thin film deposition refers to the application a thin film of material to a substrate surface, or onto an existing deposited coating to form more layers. The application is between a few nanometers. The problem is that bottom-up fabrication can’t adhere properly onto the substrate due to residual stress, stoichiometry, defects, impurity, and nonhomogeneity. To accommodate this problem, engineers can improve the thin film deposition process through better quality control and steps. In addition, it is a matter of temperature, humidity control, and choice of materials: a design for manufacturability.
Nanofabrication can learn from doors’ seasonal affective disorder, a silly yet accurate term. Doors like other matter expand in humidity and contract in cold, dry air. Those in the door industry have found solutions such as changing the material or adjusting the door throughout seasons to adapt to its changes. Different elements have differential thermal expansion coefficients. For example, wood has a lower rate than metals. Therefore, it is more practical to use wooden doors. Or even better, fiberglass doors barely change shape. This same principle of choosing optimal materials can apply to address the thin-film deposition problem. When more research is conducted, discoveries such as the carbon nanotubes pay off.
Another thought is to develop a 3-D nanofabrication printing technology, where the fabrication requires the input of energy as it involves the addition, modification, or removal of material in a controllable manner within single equipment. This will standardize nanofabrication while creating efficient manufacturing.
Bullet-Point Take-Aways
- Nanosensors change the game through advancements in collecting and managing data such as efficiency and sensitivity.
- Nanosensors are built by either conventional or nonconventional nanofabrication methods. These methods ensemble numerous other technologies in its techniques, and are interesting to look into.
- However, problems still exist in nanofabrication. Nanofabrication processes’ problems translate into its product: nanosensors (in this case).
- Conventional methods are too expensive and nonconventional methods struggle with Thin Film Deposition.
- Solution: focus on nonconventional methods. Then, research optimal materials to reduce residual stress.
- 3D nanofabrication printing techniques should be developed if we want to move onto the next step of commercialization.
Bibliography
So Why Care?
Published Books:
Kenneth David, Paul B. Thompson. 2008. What Can Nanotechnology Learn From Biotechnology? Academic Press.
Charles P. Poole Jr., Frank J. Owens. 2003. Introduction to Nanotechnology. Wiley Interscience.
Jurgen Schulte. 2005. Nanotechnology Global Strategies, Industry Trends and Applications. Wiley.
Academic Journal:
Yong Chen, Anne Pépin. 2001. Nanofabrication: Conventional and nonconventional methods. Electrophoresis, issue 22, page 187–207.
