Dynamic Light Scattering - Glossary

Dynamic Light Scattering (DLS) is a physics and optics method for measuring particle size and size distribution in a liquid sample. It uses laser light to observe how particles scatter light while moving randomly through Brownian motion. Smaller particles move faster, and larger particles move more slowly.

How DLS measures particle size and distribution

The instrument calculates a hydrodynamic diameter and creates a size distribution profile. It also reports a Polydispersity Index (PDI), which indicates how uniform the sample is. On a lab report, DLS is relevant because it can detect aggregation, meaning unwanted clumps of molecules that may cause adverse immune reactions or make a product ineffective.

A clean DLS result with a single narrow peak at the expected size and a low PDI is consistent with a well-dissolved, uniform sample.

Limits of DLS in lab reports

DLS has strict limitations. It cannot identify a substance chemically, distinguish between molecules of similar size, or detect small-molecule impurities, residual solvents, salts, or truncated peptide sequences.
A highly contaminated sample can still show a perfectly clean DLS peak.
DLS is commonly confused with HPLC, which measures chemical purity; Mass Spectrometry, which confirms chemical identity; and Static Light Scattering or MALS, which determines molecular weight.
If a vendor relies only on DLS to claim a product is pure or safe, that claim is not supported. Chemical analysis methods like HPLC and Mass Spectrometry are also required.

How DLS measures particle size and distribution

Limits of DLS in lab reports

Sources