What Are Nanomaterials?

Nanomaterials are substances in which at least one dimension falls between approximately 1 nm and 100 nm, a scale at which surface area-to-volume ratios become very large and quantum effects begin to govern physical and chemical behavior. Unlike bulk versions of the same material, nanomaterials can display dramatically different optical, magnetic, electrical, and catalytic properties. The field draws from chemistry, physics, and materials science to produce, characterize, and apply these substances across sectors from medicine to energy to electronics.

Types of Nanomaterials

Nanomaterials are commonly classified by geometry and composition. Zero-dimensional nanoparticles include metal nanoparticles such as gold and silver colloids, whose localized surface plasmon resonances produce intense, tunable colors. Quantum dots are semiconductor nanoparticles with size-dependent optical band gaps. One-dimensional forms include nanowires and carbon nanotubes (CNTs): single-walled CNTs exhibit either metallic or semiconducting behavior depending on their chiral angle and are among the strongest known materials by tensile strength. Two-dimensional materials are exemplified by graphene, a single atomic layer of carbon arranged in a hexagonal lattice. Graphene combines exceptional electron mobility (up to 200,000 cm2 V-1 s-1), near-optical transparency, and mechanical stiffness. A foundational account of its electronic properties appears in Nature.

Nanocarriers form a distinct functional category: engineered nanoscale containers such as liposomes, polymeric nanoparticles, and dendrimers designed to encapsulate and release therapeutic payloads with spatial or temporal control.

Properties That Distinguish Nanomaterials from Bulk

At the nanoscale, a large fraction of atoms reside at or near the surface, where coordination is incomplete and reactivity is high. This surface effect is responsible for the extraordinary catalytic activity of platinum and gold nanoparticles compared with their bulk counterparts. Quantum confinement becomes important when a particle's dimensions approach the de Broglie wavelength of its charge carriers: energy levels discretize, absorption edges shift, and fluorescence wavelengths change with size. Magnetic nanoparticles below a critical diameter become superparamagnetic, losing remanence at room temperature, which is essential for safe biomedical imaging agents.

Size-dependent melting points also have practical consequences. Gold nanoparticles of 2 nm diameter melt near 300 degrees C rather than the bulk 1064 degrees C, enabling low-temperature sintering of conductive inks. The National Cancer Institute's Alliance for Nanotechnology in Cancer has documented how these tunable properties underpin targeted drug delivery and diagnostic imaging.

Synthesis and Characterization

Nanomaterials are produced by two broad strategies. Top-down approaches, such as ball milling, laser ablation, and lithographic etching, subdivide bulk material into nanoscale fragments. Bottom-up approaches, such as chemical vapor deposition, colloidal synthesis, and atomic layer deposition, assemble nanostructures atom by atom or molecule by molecule.

Characterization requires techniques sensitive to atomic-scale features. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) resolve individual atomic columns. X-ray diffraction quantifies crystallite size through peak broadening analyzed by the Scherrer equation. Dynamic light scattering measures hydrodynamic diameter in suspension. Safety assessment of engineered nanomaterials also demands careful physicochemical characterization, as the NIST Center for Nanoscale Science and Technology has established reference nanomaterials and measurement protocols to support standardization.

Applications

• Drug delivery: Liposomal and polymeric nanocarriers improve the bioavailability and tumor targeting of chemotherapeutic agents, reducing systemic toxicity.
• Electronics: Carbon nanotubes and graphene serve as channel materials in transistors and as transparent conductive electrodes in touchscreens.
• Catalysis: Platinum and palladium nanoparticles on oxide supports catalyze automotive exhaust conversion and hydrogen evolution reactions with far less precious metal than bulk catalysts.
• Energy storage: Silicon nanowire anodes and nanostructured cathode materials increase the specific capacity and cycle life of lithium-ion batteries.
• Antimicrobial coatings: Silver nanoparticles embedded in textiles or surface coatings release ions that inhibit bacterial growth in medical and consumer applications.
• Sensors: Gold nanoparticle-based lateral flow assays and quantum dot fluorescent probes enable rapid, sensitive detection of pathogens and biomarkers.