Increasing the Nanoparticle Size Detection Sensitivity of Dynamic Light Scattering using Wavelength Dependent Excitation

We report on the development of homebuilt Dynamic Light Scattering (DLS) instrumentation to measure the size of monodisperse (MD), spherical nanoparticles (NPs) of gold. HeNe and Ar-ion lasers constitute the excitation sources for the scattering experiment, while an avalanche photodiode detects the scattered light, and an autocorrelation card analyzes the resulting signal to provide a measurement of the translational diffusion coefficient, which allows for the determination of NP diameter. We characterized our instrumentation using commercially-produced gold NPs with diameters ranging from 10nm to 200nm in aqueous solution. The strong wavelength λ dependence of the scattered light intensity (1/λ⁴) provides increased sensitivity for smaller excitation wavelengths. We present DLS measurements on gold NPs using excitation from both a HeNe laser (λ = 632.8nm) and a tunable Argon laser (457nm < λ < 515nm). The increased scattering from the shorter wavelengths should increase our sensitivity to smaller particles.