Nanoparticle synthesis methods and applications

Nanoparticles are particles between 1 and 100 nanometres in size. At this scale, materials behave differently from their bulk counterparts: they have a higher surface area relative to their volume, different optical properties and, in some cases, entirely new functional characteristics. This article explains how nanoparticles are made, which synthesis methods are used and where they are applied in industry and medicine.

What makes nanoparticles different from bulk materials?

The properties of a material change significantly at the nanoscale. A bulk piece of gold is yellow and chemically inert. Gold nanoparticles are red or purple depending on their size and absorb light in the visible range due to surface plasmon resonance. Iron oxide in bulk form is a brown powder. Iron oxide nanoparticles are superparamagnetic and used in magnetic resonance imaging and targeted drug delivery.

This change in behaviour comes from two factors: the high surface area relative to particle volume, and quantum mechanical effects that become relevant at small sizes. Both make nanoparticles interesting for applications where bulk materials would not perform.

The three main approaches to nanoparticle synthesis

Nanoparticle synthesis methods are divided into three broad categories: physical methods, chemical methods and biological methods. A comprehensive review published in PMC covers all three approaches in detail, including their advantages and limitations across different materials and applications.

Physical methods

Physical synthesis methods break bulk materials down into nanoparticles, a top-down approach. The starting material is reduced in size through mechanical or thermal processes until nanoparticles are formed.

Ball milling is one of the most common physical methods. A bulk material is placed in a rotating drum with hard balls. The repeated impact and friction break the material into progressively smaller particles. Ball milling is used for metals, ceramics and composite materials and can produce particles in the low nanometre range, though size distribution is often broad.

Gas condensation is a physical method used for metal nanoparticles. The metal is vaporised in an inert gas atmosphere, typically argon or helium, and the vapour condenses into nanoparticles as it cools. This vapour phase process produces particles with a narrow size distribution and high purity, but requires specialist equipment and works best for metals with relatively low melting points.

Physical methods are generally scalable and do not introduce chemical contamination, but they offer less control over particle size and shape than chemical methods.

Chemical methods

Chemical synthesis methods create nanoparticles from molecular precursors, a bottom-up approach. Chemical reactions in solution or in the gas phase assemble atoms and molecules into nanoparticles with controlled size and shape.

Sol-gel processes are among the most widely used chemical methods for oxide nanoparticles. A metal precursor dissolved in a solvent undergoes hydrolysis and condensation reactions to form a gel, which is then dried and calcined to produce nanoparticles. Sol-gel processes are used to make silica, titania and other metal oxide nanoparticles for coatings, catalysts and optical applications.

Colloidal synthesis is used for many different types of nanoparticles including gold nanoparticles, silver nanoparticle, iron oxide and quantum dots. The precursor is reduced or decomposed in a solvent in the presence of stabilising ligands that control particle growth and prevent agglomeration. The result is a stable colloidal suspension of nanoparticles, also known as colloidal nanoparticles, with a narrow size distribution.

Chemical vapour deposition (CVD) is a vapour phase chemical method used to deposit thin films and nanoparticles on surfaces. The precursor is introduced as a gas and reacts at the substrate surface to form a solid layer. CVD is used for carbon nanotubes, semiconductor nanoparticles and hard coatings.

Chemical methods give the best control over particle size, shape and composition, but often involve solvents and chemical reagents that need to be handled and disposed of carefully.

Biological methods

Biological synthesis methods, also called green synthesis, use plant extracts, microorganisms or enzymes to reduce metal ions into nanoparticles. A solution of metal salt is combined with a plant extract, and the natural compounds in the extract act as both reducing and stabilising agents.

Green synthesis produces metal nanoparticles such as silver nanoparticles and gold nanoparticles without the need for harsh chemicals. It is studied as a more environmentally friendly alternative to conventional chemical methods. The main limitation is less precise control over particle size and shape compared to colloidal synthesis.

Metal boride nanoparticle synthesis

Metal boride nanoparticles, including lanthanum hexaboride (LaB₆), are synthesised using a solid-state reaction. The synthesis involves the reduction of a boron precursor at high temperatures to elemental boron particles, which react with a metal halide to form the metal boride nanoparticles. No solvent is involved in the process.

The resulting nanoparticles are between 5 and 20 nm in size and can be formulated directly into a stable ink. This ink is part of a patented platform (WO2025063847) that allows functional coatings to be applied at temperatures below 90°C, without the need for high-temperature sintering or vacuum equipment. For more on how this works, visit our LaB₆ nanoparticles page.

Applications of nanoparticles in medicine

Nanoparticles are used in many different medical applications. Their small size allows them to interact with biological systems in ways that bulk materials cannot.

Drug delivery

Nanoparticle-based drugs are used to deliver active pharmaceutical ingredients to specific tissues. Targeted drug delivery uses nanoparticles coated with molecules that bind to specific cell receptors, concentrating the drug where it is needed and reducing side effects elsewhere in the body. This is particularly relevant in cancer treatment, where conventional chemotherapy affects healthy tissue alongside tumour cells.

mRNA vaccines

Lipid nanoparticles are used as delivery vehicles for mRNA vaccines. The lipid nanoparticle protects the mRNA from degradation and helps it enter cells where the mRNA can be translated into protein. This technology became widely known through its use in COVID-19 vaccines and is now being studied in clinical trials for cancer treatment and other applications.

Magnetic resonance imaging

Iron oxide nanoparticles are used as contrast agents in magnetic resonance imaging (MRI). Their magnetic properties improve image contrast in soft tissue and can be used to visualise tumours and other structures that are difficult to see with standard MRI.

Immune response modulation

Nanoparticles are studied for their ability to modulate the immune response. Some nanoparticle-based formulations stimulate immune activation, which is useful in vaccine development. Others suppress immune responses, which is relevant in autoimmune disease treatment.

Applications of nanoparticles in industry

Coatings and surface treatment

Nanoparticles are used in functional coatings for glass, metals and polymers. Hydrophobic coatings use silica or titanium dioxide nanoparticles to repel water. Hard coatings use metal boride or metal carbide nanoparticles to resist wear. Infrared absorbing coatings use LaB₆ or cesium tungstate nanoparticles to block near-infrared radiation in automotive and architectural glass.

Electronics and energy

Carbon nanotubes are used in electronics for their exceptional electrical conductivity and mechanical strength. Quantum dots are semiconductor nanoparticles used in display technology and solar cells. Silver nanoparticles are used in conductive inks for printed electronics.

Catalysis

Metal nanoparticles such as platinum, palladium and gold are used as catalysts in chemical reactions. Their high surface area makes them more reactive than bulk catalysts at the same mass of material. Nanoparticle catalysts are used in fuel cells, automotive catalytic converters and chemical production.

Nanotechnology in construction and materials

Silica nanoparticles are added to cement and concrete to improve strength and durability. Titanium dioxide nanoparticles in building coatings provide photocatalytic self-cleaning properties. This makes them useful in infrastructure projects where durability and reduced maintenance matter.

Frequently asked questions about nanoparticle synthesis

Summary

Nanoparticles are synthesised through physical, chemical and biological methods. Physical methods such as ball milling and gas condensation break bulk materials into nanoparticles. Chemical methods such as colloidal synthesis and sol-gel processes build nanoparticles from molecular precursors with precise size control. Biological methods use plant extracts or microorganisms for greener production. Nanoparticles are used in medicine for drug delivery, mRNA vaccines and imaging, and in industry for coatings, electronics, catalysis and construction. Metal boride nanoparticles such as LaB₆ are produced by a solid-state reaction and formulated into functional inks for low-temperature coating applications.