SciMed Education
What is Dynamic Light Scattering (DLS) and How Does It Work?
In Summary
Dynamic Light Scattering (DLS) is a non‑destructive technique that determines nanoparticle size by analysing time‑dependent fluctuations in scattered light. It relies on Brownian motion and the Stokes–Einstein relation to convert diffusion coefficients into hydrodynamic radii.
What is Dynamic Light Scattering and why does Brownian motion matter?
DLS, also known as photon correlation spectroscopy, measures the hydrodynamic radius of nanoparticles dispersed in liquids. In a suspension, thermal agitation causes solvent molecules to constantly collide with particles, producing Brownian motion.
Smaller particles move faster, while larger particles diffuse more slowly; this size‑dependent motion directly influences the temporal fluctuations in scattered light. By monitoring these fluctuations, DLS provides a rapid, ensemble‑average measurement of particle size.
How does a DLS experiment convert motion into size?
A coherent laser beam illuminates the sample, and particles undergoing Brownian motion scatter the light. The scattered intensity fluctuates over time and is collected at a chosen angle—commonly 90° or 170°.
Autocorrelation analysis extracts characteristic decay rates that correspond to diffusion coefficients. The Stokes–Einstein equation then converts these diffusion coefficients into hydrodynamic radii, accounting for temperature and solvent viscosity.
How does DLS compare to microscopy and why does it report larger sizes?
DLS measures the hydrodynamic diameter, which includes the particle’s solid core plus its hydration layer. Techniques like transmission electron microscopy (TEM) or scanning electron microscopy (SEM) measure the dry core alone.
As a result, DLS typically reports slightly larger sizes than microscopy. This difference is especially important for soft or swollen particles, such as polymer nanoparticles and biological vesicles.
What is a correlogram and how do we interpret it?
The intensity fluctuations measured during a DLS experiment are transformed into an autocorrelation function, often displayed as a correlogram. The decay rate of this function reflects the average particle mobility: faster decay indicates smaller particles, while slower decay corresponds to larger particles.
Multi‑population samples produce multi‑exponential decays; advanced inversion algorithms convert these into size distributions.
What to do Next?
If you need to determine particle size distributions quickly and non‑destructively, our specialists can guide you to the right dynamic light scattering solution. Discover how the VASCO Kin particle size analyser provides real‑time, in‑situ DLS measurements. Speak to a SciMed product manager to see how DLS can accelerate your research and process development.
Page FAQ's
- DLS is used to measure the size of nanoparticles in liquid by analysing Brownian motion and light scattering behaviour
Brownian motion determines how fast particles move in a liquid, which directly relates to their size, with smaller particles moving faster.
It is the particle size measured including the surrounding solvent layer, not just the solid core.
- Because DLS measures the hydrated particle, whereas microscopy measures only the dry particle core.
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