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The Zetasizer Nano ZSP from Malvern Pananalytical is a high performance particle characterization system that can be used for the measurement of particle and molecule size, electrophoretic mobility and zeta potential of nanoparticles and surfaces and the microrheology of protein and polymer solutions. In addition, the system enables the measurement of the second virial coefficient of macromolecules (A2), and the DLS interaction parameter (kD). Its high performance makes it a very suitable choice for the characterization of proteins and nanoparticles as highest sensitivity is needed for the measurement of size and zeta potential of those.
The instrument is equipped with an autotitrator (pH-monitored), which allows the titration of samples and their automated measurement.
Irene Schaffner PhD, Jakob Wallner BSc
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Methods & Expertise for Research Infrastructure
Particles or molecules in suspension under Brownian motion scatter light at different intensities. Small particles diffuse rapidly, whereas large particles move slowly. Dynamic Light Scattering (DLS) measures the time dependent fluctuations in the scattering intensity and converts it to size and size distribution using Stokes-Einstein relationship. By the incorporation of NIBS (Non-Invasive Back Scatter) technology, sensitivity is increased, enabling size measurement from 0.3 nm to 10 µm in diameter. The DLS interaction parameter, kD, is determined as a function of size and concentration.
When applying an electric field to a particle in solution, a potential is build up at the slipping plane within the particle´s electric double layer. This potential is called zeta potential. In electrophoresis, this phenomenon is used to move charged particles towards the electrode of opposite charge. The velocity of a particle in an electric field is dependent on the strength of the electric field, the dielectric constant and the viscosity of the medium and the zeta potential. Laser Doppler Micro-electrophoresis (LDE) uses light scattering techniques to measure the movement of charged particles in an electric field. If a laser beam is passed through a sample, light scattered from a moving particle experiences a frequency shift. A second beam, called the reference beam, is routed around the cell and combined with the scattered light beam, creating a fluctuating signal intensity where the rate of fluctuation is proportional to the speed of the particles. From the resulting frequency spectrum information about electrophoretic mobility and hence the zeta potential can be obtained.
Static Light Scattering (SLS) is used to determine the molecular weight of proteins and polymers. Similar to DLS, particles in a solution are illuminated by a light source but instead of measuring the time dependent fluctuations in scattering intensity, SLS makes use of an averaged intensity of scattered light over a certain period. From this, not only the molecular weight of proteins but also the second virial coefficient A2 can be determined, a parameter describing the interaction strength between particles and solvent. The applicable molecular weight measurement range of the Zetasizer Nano ZSP is from a few hundred g/mol to 500,000 g/mol for linear proteins and over 20,000,000 g/mol for non-spherical proteins and polymers. Zetasizer Nano ZSP measures the intensity of scattered light of the samples at various concentrations and compares it with the scattering intensity of a standard (Toluene). This gives the so-called Debye plot and allows the determination of both the absolute molecular weight and the second virial coefficient.