Introduction
Polymer Nanoparticles
Polymer nanoparticles have been widely studied as possible drug delivery systems due to their ability to control the release of drug contained within them and due to their biocompatibility [1,2]. They are relatively easy to produce with their drug release profiles dependent upon polymer structure. Some of the important characteristics of polymer nanoparticles for drug delivery applications include their particle size and surface chemistry. Typically, they range in size from 10 to 1000nm in diameter allowing them to transverse cell membranes.
There are a variety of ways in which delivery of encapsulated drug from polymer nanoparticles can be controlled [1]. These include physical (e.g. sonorphoresis), chemical (e.g. pH, salt concentration), biochemical (e.g. enzyme) and environmental (e.g. temperature) mechanisms. The influence of these mechanisms on the size of the polymer nanoparticles can be investigated using dynamic light scattering (DLS).
Dynamic Light Scattering
Dynamic light scattering is a non-invasive technique for measuring the size of colloidal dispersions and molecular solutions. In the technique, a sample is contained in a suitable cuvette and illuminated with a laser beam. The resulting scattered light fluctuates in intensity due to the random, Brownian motion of the particles. An analysis of these intensity fluctuations through autocorrelation allows for the determination of the diffusion coefficients, which in turn yield the particle size through the Stokes-Einstein equation [3-5].Experimental
A sample of polymer nanoparticles dispersed in water was measured on a Zetasizer Nano ZS using a temperature range of 50 to 90oC at 1oC intervals. A delay time of 5 minutes was used at each temperature to ensure that the sample viscosity was equilibrated before the measurements were taken. The Zetasizer Nano ZS uses a 4mW He-Ne laser operating at a wavelength of 633nm with a detection angle of 173°. The detection angle of 173o allows for size measurements of concentrated, turbid samples.
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