Microparticle

Microparticles are particles between 0.1 and 100 $\mu$m in size. Commercially available microparticles include those made of glass, latex, polystyrene, various metals (carbon, silver, copper, etc.), and various magnetic materials. One can encounter microparticles everyday, such as pollen, very fine sand, and dust.

Microparticles have a much larger surface-to-volume ratio than at the macroscale, and thus their behavior can be quite different. For example, metal microparticles can be explosive in air.

Microspheres are spherical microparticles, and are used e.g. as carriers of pharmaceutical substances.

Microparticles in diagnostic medical tests

Most people are familiar with home pregnancy testｓ - a color appears if the test is positive. These tests make use of gold microparticles.

Alternative definitions for size

Although the generally accepted definition of 0.1 to 100 $\mu$m compliments the size definition of nanoparticles, there are other ways to define the size.

Mathematical: as the term "micro" refers to $10^{-6}$, the range for micro would then be $10^{-7.5}$ to $10^{-4.5}$, or roughly 31.6 nm to 31.6 micrometers. However, general acceptance considers particles smaller than 100 nm nanoparticles.

Rounding: rules of rounding in mathematics provide an alternative for the definition. Anything larger than 0.5 $\mu$m and anything smaller than 0.5 mm is considered microparticles.

Convenient/popular: Very often particles with dimensions more than 100 nm are still called nanoparticles. The upper range may be between 300 to 700 nm, so this would give a size definition for microparticles of 0.3 to 300 $\mu$m or 0.7 to 700 micrometers.