New dynamic light scattering technology for high sensitivity and measurement at high concentration (NIBS)

New NIBS (Non-Invasive Back-scatter) technology extends the range of sizes and concentrations of samples that can be measured.

The sizing capability in the Zetasizer Nano S and Nano ZS instruments detect the scattering information at 173°. This is known as backscatter detection. In addition, the optics are not in contact with the sample and hence the detection optics are said to be non-invasive.

There are many advantages of using non-invasive backscatter detection:

• Sensitivity is improved
• The sample volume probed by the optics is about 10 times higher than in conventional 90 degree ‘bulk’ optics. When combined with the data collection efficiency of the NIBS optics, the sensitivity is increased by two orders of magnitude, enabling the size measurement of dilute solutions of molecules and dispersions of sub-nanometre particles
• A wider range of sample concentrations can be measured
• The laser does not have to travel through the entire sample. By measuring particles close to the cuvette wall, light passes through a shorter path length in the sample, eliminating or reducing an effect called multiple scattering, where light from one particle is itself scattered by other particles. This enables much higher concentrations of sample to be measured.
• Sample preparation is simplified
• The effects of dust are greatly reduced as contaminants such as dust scatter most light in the forward direction. Therefore, by using backscatter detection the effect of contaminating dust is minimised

The measurement position within the cuvette of the Nano S and Nano ZS is automatically set to accommodate the requirements of high sensitivity or high concentration. This position is changed by moving the focusing lens.

For small particles, or samples at low concentrations, it is beneficial to maximize the amount of scattering from the sample. As the laser passes through the wall of the cuvette, the difference in refractive index between the air and the material of the cuvette causes “flare”. This flare may interfere with the signal from the scattering particles. Moving the measurement position away from the cuvette wall towards the centre of the cuvette will remove this effect (figure a).

Large particles or samples at high concentrations scatter much more light. Measuring closer to the cuvette wall reduces the effect of multiple scattering by minimising the path length through which the scattered light has to pass (figure b).