Dynamic Light Scattering
Dynamic Light Scattering (DLS) · Also known as: DLS, photon correlation spectroscopy, particle size measurement
Dynamic Light Scattering (DLS), also known as Photon Correlation Spectroscopy (PCS), is an analytical technique for determining the size and size distribution of particles suspended in fluids by analyzing the time-dependent intensity fluctuations of scattered laser light. Developed by Robert Pecora in 1964, DLS exploits the Brownian motion of particles: smaller particles move faster, causing faster intensity fluctuations; larger particles move slower, causing slower fluctuations. By correlating intensity over time, particle size is deduced. DLS is rapid, non-destructive, and requires minimal sample volume, making it the standard technique for characterizing nanoparticles, proteins, colloids, and emulsions.
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When to use it
DLS is ideal for measuring particle size in the nanometer range (1-1000 nm) in dilute suspensions. Most applicable to spherical or near-spherical particles. For polydisperse samples, DLS gives number-weighted average size. Works best on transparent or translucent samples; opaque samples require modifications. Combine with complementary techniques (TEM, SEM) for morphology confirmation.
Strengths & limitations
- Rapid measurement: size determination in seconds to minutes
- Non-destructive and requires minimal sample (~1 mL) and no sample modification
- Sensitive to small particles (1-10 nm) where other methods (optical microscopy) fail
- Automated instruments provide high-throughput capability for quality control
- No absolute calibration required; relative measurements are reliable
- Assumes spherical particles; non-spherical particles give equivalent spherical diameter, not true dimensions
- Large aggregates scatter too strongly, saturating detector; samples must be diluted carefully
- Multiple scattering (in concentrated suspensions) invalidates single-scattering theory; limited to ~10% volume fraction
- Size distribution resolution poor for very broad distributions; number-weighted versus intensity-weighted size differs significantly
- Cannot measure particles below ~1 nm or above ~10 micrometers reliably with standard DLS
Frequently asked
Why is DLS size different from TEM size?
DLS measures hydrodynamic radius (size including hydration shell); TEM measures dry particle core. For hydrophilic nanoparticles, DLS sizes are 10-50% larger. DLS is number-weighted; TEM is often intensity/intensity-weighted, giving different averages for broad distributions.
What scattering angle should I use?
90° scattering angle is most common and avoids forward-scattering complications. Larger angles (120°-173°) reduce multiple-scattering artifacts but lower signal. Angle choice depends on particle size and concentration.
How do I measure size distribution, not just average?
DLS-derived size distributions rely on fitting the autocorrelation decay to a model (usually assuming lognormal or Gaussian). Resolution is limited; CONTIN or cumulants analysis provides better distribution resolution than simple fitting.
Can I measure non-spherical particles?
DLS measures the hydrodynamic radius of particles equivalent spheres. For rods or disks, this gives an effective size but not true dimensions. Use complementary techniques (TEM, AFM, SAXS) for shape determination.
Sources
- Pecora, R. (1964). Spectral distribution of scattered light from a suspension of particles. Physica, 30(11), 2055-2070. link ↗
- Berne, B. J., & Pecora, R. (1976). Dynamic Light Scattering: With Applications to Chemistry, Biology, and Physics. John Wiley & Sons. link ↗
- Bushell, G. C., Yan, Y. D., Woodfield, D., Raper, J., & Amal, R. (2002). On techniques for the measurement of the mass fractal dimension of aggregates. Advances in Colloid and Interface Science, 95(1), 1-50. DOI: 10.1016/s0001-8686(00)00078-6 ↗
How to cite this page
ScholarGate. (2026, June 3). Dynamic Light Scattering (DLS). ScholarGate. https://scholargate.app/en/materials-science/dynamic-light-scattering
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