Dynamic Light Scattering

The Nicomp 380 Submicron Particle Size Analyzer uses the principle of Dynamic Light Scattering (DLS) to obtain the partcile size distribution of colloidal systems whose sizes range from 0.5 nanomters to 6 microns. DLS works by illuminating a group of particles in suspension with a focused laser beam which gives rise to many scattered light waves. These waves interfere with each other and produce a net scattered intensity that fluctuates as a function of time at some distant detector. Diffusion, or Brownian motion, of the particles causes random variations in the phases of the individual waves, resulting in a fluctuating light intensity. The particle size distribution can be obtained by analyzing the time behavior of these fluctuations using an autocorrelator. The autocorrelation function for a single uniform size distribution is a decaying exponential function where particle diffusivity is easily obtained from the decay time. Finally the particle radius can easily be calculated using the Stokes-Einstein relationship.

In general most samples are not uniform instead they are quite often polydisperse, having a range of particle sizes. The autocorrelation function then consists of a combination of decaying exponential functions, each having a different decay time and the analysis of the autocorrelation function is no longer quite simple. The instrument using varying deconvolution algorithms must invert the raw data in order to arrive at the best estimate of the true particle size distribution. The Nicomp excels at characterizing these difficult particle size distributions by utilizing a group of unique deconvolution algorithms ranging from a simple Gaussian approximation to a proprietary high resolution multi-modal deconvolution analyses called the “Nicomp Distribution".

Some of the unique features found on Gaussian analysis mode is a baseline adjust parameter which provides aggregate compensation that excedes the sensitivity found on most other instruments which employ a dust or dirt factor. The Gaussian analysis mode also allows for the user to specify a solid or vesicle weighting mode for analysing thin walled colloidal systems like liposomes. The Nicomp Analysis Mode is a proprietary high-resolution deconvolution algorithm that was first introduced over 25 years ago. It has historically proven its ability to accurately analyze even the most difficult closely spaced bimodals (e.g. 2:1 apart) and even certain trimodal distributions. This is extremely useful in finding the native peak of the aggregate distribution.

The standard Nicomp 380 is equipped with a 12 mW laser diode and PMT detector with an optical fiber set to 90°. Sample is introduced with drop-in cells.

The 380 is the only Dynamic Light Scattering Instrument designed using a modular approach. Its capabilities may be enhanced by adding one or more modules:

Autodilutio

This patented module eliminates the need for manual dilution of concentrated sample. Autodilution makes particle size analysis quick and easy, with no training required. Results are highly reproducible.

380/HPLD High Power Laser Diodes

PSS offers an array of high power laser diodes to meet the needs of our most demanding applications. Higher power lasers are needed to extend the lower limit of our instrument by providing adequate scattering from small particles. They are also useful when measuring large particles such as dextrans, which yield insufficient scattering intensity because of index of refraction properties. The result is a more versatile instrument, ideal for sizing microemulsions, surfactant micelles, proteins and other macromolecules. It can even estimate the extent of aggregration of biopolymers after reconstitution, without chromatographic separation.

Avalanche Photo Diode (APD) Detector

The Nicomp 380 can be equipped with various high-powered lasers as well as a high-gain Avalanche Photo Diode Detector (APD which provides approximately seven times the gain of a conventional photomultiplier tube. The APD is used to increase signal-to-noise and sensitivity in systems that do not scatter light well. Proteins, micelles, other macro-molecular-based systems, and nanoparticles are often dilute (1 mg/ml or less) and are made of atoms that do not scatter light well. The Avalanche Photo Diode coupled with a nominally higher powered laser diode module offers a low cost solution for accurately analyzing nanoparticles in a short period of time.

380/MA Multi-angle Goniometer

Particles larger than 100 nm do not scatter light isotropically in all directions. It is possible to make DLS measurements more sensitive to certain sized particles by changing the angle of detection. The Nicomp 380 can be equipped with a mini-goniometer that moves the optical fiber between 12° and 175° by 0.9° increments.