Basics of Dynamic Light Scattering (DLS)

The first webinar in our latest series introducing the fundamentals of Dynamic Light Scattering (DLS) - whether you’re new to light scattering or just need a refresher. In this 30-minute session, Dr Ben Lynch explains how Brownian motion maps to hydrodynamic diameter via the Stokes-Einstein equation, how to read a correlogram (and what slope, intercept, and baseline really tell you), and what measurement conditions set you up for reliable, repeatable measurements. You’ll also see practical guardrails for concentration and viscosity inputs, plus application snippets from liposomes to quantum dots.

Key moments

• 6.26 - Small particles move faster; dispersant viscosity and temperature set the pace.
• 7.45 - From diffusion to diameter: extracting the translational diffusion coefficient via the Stokes-Einstein equation
• 11.50 - Reading the correlogram: decay = size, slope = polydispersity, baseline = quality of the sample and whether larger particles are present
• 14.45 - Sample success checklist: clean, non fluorescent dispersant (at 633 nm), correct viscosity, and no dissolution/aggregation.
• 18.20 - When concentration bites: spotting multiple scattering and using backscatter positioning to widen the window.
• 19.00 - Applications: liposome stability trending over 48 hours; getting reliable sizes for fluorescent quantum dots with a narrow band optical filter.
• 22.00 - Q&A hits: pigments and absorption, managing fluorescence, inline monitoring realities, PDI expectations, and why “it depends” for concentration.

Key takeaways

• DLS measures motion. You capture translational diffusion and convert to hydrodynamic diameter—which includes solvated layers and anything that codiffuses with the particle.
• Environment matters. Viscosity and temperature directly influence via the Stokes-Einstein equation. Ionic strength compresses the electrical double layer, shifting the apparent size.
• Correlogram = truth table.
  • Faster decay → smaller size
  • Steeper slope → more monodisperse
  • Elevated baseline → large contaminants/aggregates
  • Low intercept → unsuitable concentration
• Mind the dynamic range. Intensity scales ~ d⁶, so tiny particles need enough concentration and refractive index contrast; very large or dense particles risk sedimentation. Typical practical range is ~1 nm to ~1 μm (sample dependent).
• Tactics that help. Non-invasive backscatter positioning reduces multiple scattering at higher concentrations. A narrowband optical filter can suppress fluorescence so you measure size, not glow.

What do our customers say?

“DLS is a non invasive technique; the particles we measure should be the same after the measurement as they were before.”

“Small particles diffuse rapidly; large particles diffuse slowly.”

“We aim for the correlation intercept as close to one as possible.”

Tools & technologies mentioned

• Zetasizer Advance 
• Dynamic Light Scattering (DLS)
• Non-invasive backscatter (NIBS)

Resources & further learning

• Explore the full series, Mastering Light Scattering Techniques: Essential Concepts for 2025 
• ISO guidance for Dynamic Light Scattering 
• Visit our Zetasizer content hub