Nanotechnology is the understanding and control of matter at dimensions between approximately 1 and 100 nanometers. At this tiny scale, unique physical, chemical, and biological properties can emerge that may be substantially different from those of bulk materials and single atoms or molecules. By being able to understand and manipulate matter on such a small scale, scientists aim to revolutionize virtually every industry and area of society.
A Definition of Nanotechnology
The term "nanotechnology" refers specifically to the technical ability and engineering processes involved in manipulating matter at the nanoscale. A nanometer is one-billionth of a meter – about the width of 3-5 atoms lined up next to each other.
To put that tiny size into perspective:
- A human hair is around 80,000-100,000 nanometers wide
- A red blood cell is approximately 7,000-8,000 nanometers wide
- A water molecule is almost 0.3nm wide
So when we talk about nanotechnology, we‘re dealing with extraordinarily tiny structures – individual molecules, atoms, and supramolecular structures typically between 1-100nm in size.
The reason size matters so much is that when materials are engineered and structured at such minuscule dimensions, they start to exhibit remarkable traits that don‘t conform to the physics and chemistry that governs macroscopic objects we interact with in our everyday lives.
The Unique Properties of Nanomaterials
Nanomaterials can display vastly different optical, structural, and electronic behavior compared to their bulk counterparts. This is because nanoscale particles have an extremely high surface area to volume ratio.
In macroscopic materials, the majority of atoms are located within the bulk of the material, while only a relatively few inhabit the surface. However in nanomaterials, a much higher percentage of the total atoms are located on the surface. This allows interactions at the materials interfaces to dominate over bulk interactions, drastically altering many physical properties.
Additionally, quantum mechanical effects start to dominate at the nanoscale. Properties such as conductivity, thermoelectric behavior, optical absorption and emission, and chemical reactivity can become heavily influenced by quantum effects arising from confinement of electrons and phonons inside minuscule structures.
This interplay between surface phenomena and quantum effects gives rises to many exceptional optical, electronic, and structural traits in nanomaterials that allow them to far surpass the functionality of their bulk counterparts in a range of applications, as we will explore throughout this article.
Categories of Nanomaterials
There are many different varieties of nanomaterials, but most can be grouped into four main categories:
Carbon-Based Nanomaterials
Carbon is capable of forming a range of fascinating nanostructures due to its ability to adopt different hybridization states and bond with itself in multiple ways. Carbon nanomaterials include nanoparticles like quantum dots, along with allotropes such as fullerenes, graphene, and carbon nanotubes.
Fullerenes are sphere, ellipsoid or tube-shaped molecules composed entirely of carbon. Spherical fullerenes are also referred to as buckyballs, named after Buckminster Fuller whose architectural creations the molecules resemble.
Graphene is a flat, single layer of carbon atoms tightly packed into a 2D honeycomb lattice structure. It is extremely strong, conducts heat and electricity efficiently, and has interesting optical properties.
Carbon nanotubes can be visualized as rolled up sheets of graphene. These cylindrical tubes have unique thermal, structural, and electronic properties with a broad range of potential applications.
Metal-Based Nanomaterials
Nanoparticles composed of metals exhibit distinctive optical, magnetic, electronic, and chemical properties compared to their bulk metal counterparts. Common examples include gold nanoparticles and quantum dots formed from semiconducting materials.
Quantum dots (QDs) are semiconducting nanocrystals just a few nanometers wide. Their electronic properties can be precisely tuned by changing the size of the dots during production. This enables their optical and electronic properties to be optimized for different applications.
Gold nanoparticles (Au NPs) have specialized optical, electronic and molecular recognition properties with applications in biomedicine, catalysis, electronics and imaging. Their optical properties originate from localized surface plasmon resonances of conduction band electrons inside the nanostructure.
Dendrimers
Dendrimers are repetitively branched molecules that adopt a spherical three-dimensional morphology. The size and shape of a dendrimer molecule can be meticulously controlled during the synthesis process. This allows spaces inside the sphere to be used to transport drugs or other molecules.
Nanocomposites
Nanocomposites consist of nanoparticles embedded in or mixed with larger bulk-type materials such as other solid metals or polymers. This combines the favorable properties of nanoscale particles with the advanced features of the bulk matrix around them.
Examples include polymer matrix nanocomposites reinforced with nanoscale carbon filler materials, and ceramic matrix nanocomposites strengthened with nanoparticles and nanotubes.
Methodologies for Nanomaterial Synthesis
A variety of sophisticated techniques have emerged for controlling matter precisely at the smallest scales to produce nanomaterials with tailored properties. Generally these syntheses methods fall into either "bottom up" or "top down" approaches.
Bottom-up Approaches
In bottom-up syntheses, nanoscale structures are built up from individual atoms or molecules that assemble themselves chemically. This involves sequentially adding molecular precursors together in careful reaction conditions.
Chemical synthesis: Nanoparticles can be grown in specialized chemical baths where atomic clusters initially nucleate out of solution then grow by accretion of atoms or molecules from the surrounding bath. Reaction conditions tightly control final size and geometry.
Molecular Beam Epitaxy: A form of physical vapor deposition that allows materials to be grown as stacked atomically flat planes only a few nanometers thick using ultra high vacuum techniques. This permits very precise control over thickness, composition and doping structure.
Top-down Approaches
By contrast, top-down methods carve, etch, mold or pattern bulk materials into nanostructures. Lithographic techniques are often employed.
Lithography: This uses radiation beams, electrons, ions, stamping or embossing tools to pattern nanoscale devices and structures onto surfaces. Nanoimprinting lithography uses molds to stamp patterns into polymers. In dip-pen nanolithography an atomic force microscope tip acts as a pen depositing molecules as ink onto substrates.
Thin film deposition: Techniques like chemical vapor deposition, sputtering, atomic layer deposition and molecular beam epitaxy allow structural layers just 1-100 atoms thick to be deposited onto surfaces which can then be etched into precise nanoscale patterns.
Applications of Nanotechnology
Owing to the many exceptional thermal, mechanical, optical, catalytic, and electronic properties possible with nanomaterials, they enable enhanced functionality and miniaturization across virtually every technological application and industry:
Medicine: Nanoparticles and nanocomposites are enabling precision drug delivery systems, advanced imaging agents, early diagnostic sensors, tissue engineering scaffolds, antimicrobial materials and medical devices. Gold nanoparticles and quantum dots have allowed breakthroughs in cancer imaging and sensing assays for early-stage diagnosis.
Electronics: Semiconducting quantum dots have led to displays with vastly improved color performance, lower power demands and simpler manufacturing compared to previous technologies. Carbon nanotubes are enhancing performance and energy efficiency in circuits and computer chips.
Energy Storage & Generation: Nanomaterials like graphene and nanotubes can drastically increase charge capacity and voltage handling in battery electrodes. Nanocomposite membranes are increasing efficiency of fuel cells. Quantum dot solar cells can extract more energy across the solar spectrum through tuning of optical absorption properties.
Catalysts: The morphology of many nanomaterials greatly increases reactive surface area to allow more efficient and selective heterogeneous catalysis. Nanoparticles of titanium dioxide, silver, nickel and gold display very high catalytic activity. Their catalytic properties can also be optimized by altering nanoparticle size and shape.
Filtration & Separation: Nanoporous graphene membranes offer opportunities to highly efficiently filter or purify water through size-selective sieving of contaminant particles and emulsions at the molecular scale. This also shows promise for purification and separation in chemical and manufacturing processes.
Anti-Microbial Materials: Silver nanoparticles have natural biocidal properties allowing them to powerfully combat bacteria growth. When embedded into polymer nanocomposites and woven into textiles, this allows clothing with antibacterial functionality.
The Future of Nanotechnology
Many of the nanotechnology applications existing today essentially amount to improving existing technologies through harnessing nanoscopic phenomena. But the most transformative technological paradigm shifts are expected still to emerge – where nanotechnology doesn‘t just enhance existing processes, but completely alters the way technologies are conceived.
Quantum computing is one such field where macroscopic computational architectures may be abandoned completely in favor of radically different nanoscale hardware architectures that can solve problems classically intractable machines cannot.
Molecular nanotechnology – the concept of engineering functional robotic systems, motors, and even whole factories out of nothing but carefully structured compounds on the molecular scale – suggest more radical departures still from modern technological paradigms may emerge in future.
The limits remain unknown for now, but what is clear is that nanotechnology will radically shape the capabilities of almost every technological field in the years ahead.
Health and Environmental Considerations
The small size and high surface reactivity of many types engineered of nanoparticles has raised concerns over their environmental and health impact as nanotechnology becomes widespread across consumer industries.
Nanoparticles introduced into the environment or the human body have a tendency to penetrate further compared with larger particles. This means they may reach and interact with biological tissues, organs and cellular function deeper inside organisms. Physiochemical interactions of some nanoparticles with cell membranes may induce adverse effects through mechanisms such as inducing inflammation, free radical formation, physical damage to membranes, organelles, and DNA.
However, toxicity depends enormously on the exact composition, size, shape, surface chemistry and physicochemical environment the particles inhabit. These parameters dictate how easily nanoparticles can aggregate, their ability to generate free radicals through surface interactions, where they localize inside the body upon exposure, how readily the body can clear them through filtration organs like the kidneys and liver, and whether protective protein coronas form around particles in biological fluids.
While some nanoparticles appear innately non-toxic, legislative bodies and regulators face the significant challenge of implementing appropriate labeling directives and environmental exposure limits on the huge variety of nanoparticles and nanomaterials towards ensuring human safety without suppressing innovation. It remains an ongoing debate.
Careful surface coatings to reduce reactivity to biological tissues, along with functionalization to improve compatibility and clearance inside the body are important considerations for engineering safer nanoparticles where medical and other direct exposure applications are envisioned. But ultimately nanotoxicology requires extensive further research for us to better elucidate the breadth of particle attributes resulting in detrimental effects, along with realistic exposure thresholds likely to trigger such effects, encompassing the broad spectrum of nanomaterials being developed across areas spanning electronics, textiles, cosmetics, microelectronics, medicines and more.
The word "nano" refers to structures ranging in size from just 1-100 nanometers. At such tiny scales unique quantum properties kick in allowing carefully engineered nanomaterials to exhibit exceptional optical, electronic, mechanical and chemical traits vastly different from bulk materials. Diverse varieties of nanoparticles, nanocomposites, allotropes like graphene and carbon nanotubes have enabled innovations across virtually every technological field – from electronics, computing and medicine through to catalysis, filtration and imaging. Safety and labeling requirements to protect human health remain ongoing considerations surrounding the increasing pervasiveness of engineered nanomaterials entering commercial products and processes. But used judiciously and safely, nanotechnology overall promises to revolutionize capabilities in every sphere of application its applied to for decades to come.
