The nervous system coordinates sensing, internal processing and responses through networks of neurons and supporting cells. Its organization connects rapid electrical signals with chemical communication. The central nervous system and peripheral nervous system describe major anatomical divisions.

Structures and processes that acquire and transform information about external or internal conditions, including receptors, transduction and downstream neural processing.

Interacting neurons and connections supporting a defined processing or behavioural function.

Retention and later use of information acquired through experience. Behavioural tests distinguish retention from immediate sensory responses and continuing access to external cues.

Photolithography transfers a pattern defined by light into a photosensitive photoresist coating. After exposure and development, the remaining photoresist forms a relief pattern that can protect selected regions during etching or another material-transfer step.^[ref]

A photomask can place bright and dark regions in the projected optical image. A positive photoresist develops more rapidly where exposed, so sufficiently exposed regions are removed; a negative photoresist retains the exposed regions instead. The final geometry depends jointly on the optical image and the material response. In particular, diffraction limits the image delivered by the optics, while photoresist contrast determines how a gradual variation of exposure is converted into a material boundary. Photolithography therefore connects wave optics, photochemistry and semiconductor device fabrication.

Film deposition through chemical reactions of gas-phase precursors at a surface. Surface kinetics and delivery through a boundary layer can separately limit growth.

Deposition through physical release and transport of material, including evaporation and sputtering.

A gold nanoparticle is a small particle of gold whose optical and surface chemistry depend on its geometry and surroundings. A dispersion of such particles can appear red or purple rather than resembling a piece of bulk gold.^[ref]

In 1857, Michael Faraday described ruby-coloured fluids containing finely divided gold. He compared the transmitted colour of these fluids with coloured glass and observed changes toward blue or violet under conditions that altered the dispersed particles. These observations established a striking connection between the physical state of gold and its interaction with light.^[ref]

A modern explanation involves localized surface plasmon resonance: the collective response of conduction electrons to an incident electromagnetic field changes absorption and scattering. The resulting spectrum depends on particle shape and the surrounding dielectric, as well as size. Thus colour alone is not a universal measure of nanoparticle diameter.

Experiments on gold nanorings show how geometry changes the response: varying the ratio of ring thickness to radius shifts the localized surface plasmon resonance. This is evidence for control through particle shape rather than a change of chemical element.^[ref]

A nanoscale, approximately spherical carbon structure. Surface oxidation and grafting can change dispersion without requiring any biological processing.

Removal of material with a focused ion beam, for example to prepare a thin transmission electron microscopy specimen. Implantation, amorphization and redeposition can require a low-energy finishing step.

A crystalline particle with nanoscale dimensions. Its shape and growth kinetics depend on exposed interfaces, defects and material supply, not just its bulk crystal structure.

An elongated structure with nanoscale transverse dimensions. Crystal structure, growth direction, sidewall facets and surface chemistry determine its properties and morphology.

Patterned material removal by chemically reactive plasma species and directional ion bombardment.

A nanoparticle is a particle whose external dimensions lie on the nanoscale. Its behaviour can depend strongly on its size, shape and surface chemistry, even when its overall chemical chemical composition is fixed.

For a sphere of radius $r$, the ratio of surface area to volume isHalving $r$ therefore doubles the surface area exposed per unit volume. At fixed total volume, making many smaller particles exposes more material to the surrounding medium. This helps explain why surface reactions and attached molecules can have a large effect on nanoparticles.^[ref]

The size of an individual nanoparticle also differs from the size of an particle aggregate containing many particles. Reports of particle size consequently need to identify what was measured. Gold nanoparticles provide a visible example: their interaction with light can differ markedly from bulk gold.

A nanostructure has structural features on the nanoscale. The relevant dimension may be the thickness of a thin film, the diameter of a nanowire, or the overall size of a nanoparticle. A material can therefore be macroscopically large while containing nanostructures internally.

The geometry matters because it changes the relative importance of surfaces, the distances over which charge carriers move, and sometimes the allowed quantum states. A thin film and a nanoparticle made from the same chemical material need not have the same properties: their quantum confinement dimensions and exposed surface areas differ. Characterizing a nanostructure requires specifying which dimensions are small, its shape and its chemical chemical composition, rather than reporting a single size alone.^[ref]

Organization of interacting building blocks into a structure through their own dynamics under specified environmental conditions. A useful description states the components, interactions, environment and reversible transport/rearrangement mechanisms. A favourable thermodynamic equilibrium structure can still fail to form if aggregation or glassy arrest prevents defect correction.

Replication of a patterned master into a deformable or curable material to define nanoscale features. A subsequent filling, etching or transfer step can turn the replicated geometry into a functional structure. Master defects, residual layers, shrinkage and release damage must be controlled in repeated large-area fabrication.

Fabrication of small structures from deposited, patterned surface films. A structural layer can be built on a sacrificial layer and released by selective removal of that support while retaining anchors. Film thickness sets a vertical dimension; residual stress, access to the sacrificial material and release-induced stiction require separate control.

The size of an organism, operationalized through a measure such as mass or a specified linear dimension. Comparative measurements require consistent definitions and allowance for growth.

Study of relationships between organismal form and ecological performance or resource use.