Detect of Polymeric Nanoparticles Size Using Laser Speckle Interferometry Technique

A new double aperture laser speckle interferometry technique is presented for detecting the size of polymeric nanoparticles, namely chitosan polymer. The optical setup uses a He-Ne laser for the source together with a lens to expand the laser beam and double apertures illuminating through both of them the same scattering surface. CCD camera provides images of the two superimposed speckle fields through the double apertures, interference fringes are formed within the speckle pattern, where the images of the two apertures overlap. Thus a periodic grid structure is introduced within each speckle .A first exposure was taken with the absence of the specimen and a second one after introducing the chitosan polymer sample in the way to the rough surface. By simple subtraction of the two digital pictures, we obtain a moire nano fringe pattern that gives us information about the polymeric Nanoparticles size. The laser speckle interferometry technique is use to investigate the effect of moire' fringes on the particle size. TEM micrograph showed that the particle size of the samples is agreements with the results of Auto diluter submicron Particle sizer. The final dimension of the speckle grain size is controlled by the optical set-up. For samples with particle size smaller than the speckle grain size, the double aperture speckle interferometry should be used. The least measurable samples are the samples with particle size equal to the grid spacing formed within the speckles.