Abstract
Colloidal silica is an important biocompatible, inert and non-toxic material for imaging, therapy, and drug delivery biomedical applications. In this context, the evaluation of colloidal suspensions and their stabilities by a Fiber Optic Quasi-Elastic Light Scattering sensor is proposed. Two different silica nanoparticles were prepared and characterized by scanning electron microscopy and X-ray diffraction, being completely amorphous, with mean diameters of 125 and 159 nm and average specific weight of 1.94 g.cm-3. The nanoparticles were dispersed in deionized water in different concentrations ranging from 0 to 2% (m/m), resulting in suspensions with mean kinematic viscosity of 0.009157 cm².s-1. The sensor showed different sensitivities regarding concentrations and diameters, with an increase in the light intensity dispersion caused by the scattering. A decreasing tendency of the decay rate of the autocorrelation function of the light intensity signal was verified with the variation of pH, and this decay rate also showed an abrupt decrease with the enhancement of the ionic strength, detecting the limits of the colloidal stability. This work presents a simple and reliable methodology for the colloidal assessment in a low-cost and minimally invasive way, easily extendable for different chemical and biological systems.
Highlights
Colloids are metastable suspensions of particles dispersed in a base fluid (Hunter, 2004)
We demonstrated that the Fiber Optic Quasi-Elastic Light Scattering sensor was successful in showing sensitivity regarding the colloidal properties, being able to differentiate the concentrations of suspensions made of amorphous particles with different diameters
The analysis of suspension viscosities showed that there was no significant influence of this parameter on the Fiber Optic Quasi-Elastic Light Scattering (FOQELS) signal obtained for a given temperature, so it is not necessary to perform signal corrections related to this parameter
Summary
Colloids are metastable suspensions of particles dispersed in a base fluid (Hunter, 2004). The zeta-potential is the electric potential resulting from the distribution of charges around a particle, which constitute the so-called electrical double layer, and allows the indirect evaluation of the colloid stability limit (the isoelectric point) (Kirby and Hasselbrink, 2004). This technique requires sampling and operation in a controlled environment, which is not suitable for assessing dynamic phenomena like the formation, decomposition, or coalescence of the colloidal particles (Heurlin et al, 2015). Another approach is based on the absorption spectrum analysis with spectrophotometers (Zhou et al, 2009), but such methodology presents limitations in terms of sample preparation and data processing time, and again exposes the colloid to environmental effects, introducing errors in the measurements
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