Dynamic Light Scattering (DLS) also known as Photon Correlation Spectroscopy (PCS) works by first measuring the scattered light intensity at one angle.
The intensity of light scattered in a particular direction by dispersed particles tends to periodically change with time.
These fluctuations in the intensity versus time profile are caused by the constant changing of particle positions brought on by Brownian motion. DLS instruments obtain, from the intensity versus time profile, a correlation function.
This exponentially decaying correlation function is analyzed for characteristic decay times, which are related to diffusion coefficients and then by the Stokes-Einstein equation, to a particle radius.

DLS has several advantages over other laser light scattering technologies available today. First, it is an absolute measurement, where knowledge of the composition of the suspended particles is not needed. This can be helpful if the optical properties of the suspended particles are not known or if the suspension is made up of particles with different optical properties. Second, DLS can size particles down to 1 nm, which is ideal for making measurements on proteins or other types of nanoparticles. 





2. SPOS - Single Particle Optical Sensing -  AccuSizer

The method of single-particle optical sensing (SPOS), also called optical particle counting (OPC), was originally developed for the field of particulate contamination analysis.
Particles in gas or liquid suspension flow through a small "photozone" -- a narrow, slab-like region of uniform illumination, produced by light from a laser diode or incandescent bulb.

The particle suspension is sufficiently dilute when the particles pass, one at a time, through the illuminated region, avoiding coincidences. The passage of a particle through the sensing zone causes a detected pulse, the magnitude of which depends on the mean diameter of the particle and the physical principle of detection -- light scattering or obscuration (blockage). 


 
A particle size distribution (PSD) is constructed one particle at a time, by comparing the detected pulse heights with a standard calibration curve, obtained from a set of uniform particles of known diameters.
The SPOS technique possesses several characteristics that make it ideal for measuring the PSD of a wide variety of particle suspensions, emulsions and dispersions. These include exceptional resolution, wide dynamic range and high sensitivity.

The AccuSizer 780 Optical Particle Sizer has refined the SPOS technique for general use in particle size analysis. Through the addition of a proprietary dilution method, called Autodilution. and significant innovations in hardware and software design, this important technology is attractive for a variety of applications.
Samples of arbitrary concentration can be measured quickly and automatically, without sacrificing any of the essential advantages inherent in the SPOS method.

The High-end Dispersion Analyzer LUMiSizer® of L.U.M. GmbH is your complete dispersion lab, all in one instrument. The quick characterization of any demixing phenomena, consolidation and the calculation of the velocity distribution in the centrifugal field as well as of particle size distribution make the LUMiSizer® the instrument of choice for research, development and QA/QC.

Applying the patented STEP™-Technology the instrument determines demixing processes of dilute or concentrated suspensions/emulsions for up to 12 different samples simultaneously. Even different sample cell types and physical references can be measured at the same time.

The stability testing can be accelerated by up to 4500x compared to traditional test tube tests. Fast stability ranking and shelf-life determinations of undiluted dispersions in original concentration are done in minutes/hours instead of months/years.

The multy-sample analytical centrifuge is ideally suited for characterization and optimization of dispersion properties. It quantifies particle- particle-interactions, the compressibility of particles, flocs, gels and the elastic behavior of sediments.

The concentration, viscosity, complexity and particle size of a wide range of dispersions are easily analyzed. Many applications in research and development as well as in industry benefit from the LUMiSizer®.

SEPView™ is a comprehensive database driven software solution coming with the Dispersion Analyzer LUMiSizer®. It controls the instrument and provides functions for data management, visualization, analysis and result documentation. The application welcomes the operator with an intuitive and user friendly graphical user interface. This enables new users to become familiar with the features necessary for the daily work in a short time.

All information (calibration data, programmed measurement methods, comments, transmission profiles, settings etc) is stored in one database, no file management required. Fast access to validation and measurement results and sample information is guaranteed. Comparison of sample data from different measurements is easily achieved.

Different program components are provided for the qualitative and quantitative analysis of the samples, e.g. for the clarification the Integral Transmission; for settling, creaming & consolidation the Front Tracking and the PSA-module for the calculation of the particle size distribution.

The included animation tool displays the recorded measurement data with programmable playback parameters for easy recognition & identification of complex separation phenomena.

Standard database functions like import & export of measurements and results, filtration of database content by various criteria, user and database administration are supported by SEPView™. The program supports different languages and different systems of units.

The modular and object oriented design of the software provides easy extension and customizing opportunities on customer's request, i.e. for special R&D or QC tasks.

SEPView™ complies to CFR 21 Part 11.

The new AccuSizer FX sensor combines the high resolution and sensitivity of particle counters with the ease of use of light scattering methods. A proprietary signal can resolve complex multi-modal distributions and is cable of sizing and counting small numbers of particles in the tail of a submicron distribution.

FX stands for Focused Extinction. This sensor employs a tightly focused laser beam to greatly increase the measurement concentration compared to conventional light obscuration without sacrificing the sensitivity and resolution.