Turbidity Spectroscopy for Characterization of Submicroscopic Drug Carriers, Such as Nanoparticles and Lipid Vesicles: Size Determination

To apply UV/Vis spectrometry for characterization of submicroscopic drug carriers, such as nanoparticles and lipid vesicles. We first investigated theoretically, within the framework of the Rayleigh-Gans-Debye approximation (RGDA), parameters affecting turbidity spectrum, tau(lambda), of nanosized light scatterers. We then analyzed, within the framework of the RGDA, experimental turbidity spectra (lambda = 400-600 nm) of extruded unilamellar vesicle (70 nm a parts per thousand currency signaEuro parts per thousand 2r a parts per thousand currency signaEuro parts per thousand 110 nm) suspensions to derive vesicle size, using dynamic light scattering results for comparison. We similarly studied the preparations polydispersity and lamellarity and monitored vesicle size changes. Turbidimetry suffices for accurate, fast, and viscosity-independent characterization of submicroscopic particles. Analysis of turbidity spectra, or more precisely wavelength exponent spectra (derivatives of logarithmic turbidity spectra), yielded similar average radii (r = 54.2 +/- 0.2 nm; 46.0 +/- 0.2 nm; 35.5 +/- 0.1 nm) as dynamic light scattering (r = 55.9 +/- 1.5 nm; 46.1 +/- 0.4 nm; 36.1 +/- 0.4 nm). Both methods also revealed similar suspension polydispersity and cholate-induced vesicle size changes in a few nanometer range. Despite its experimental simplicity, the widely accessible turbidimetric method provides accurate size values and is suitable for (continuous) monitoring size stability, or sameness, of submicroscopic drug carriers.