ABSTRACT
We demonstrate a total internal reflection-based method that detects, for the first time to the best of our knowledge, directly without any sample dilution or special sample preparation, the presence of aggregates in highly turbid aqueous suspensions of polystyrene nanospheres. Aggregation is induced by changing either the sample pH or ionic strength. The polystyrene mass density in our samples is two orders of magnitude higher than previously reported polystyrene aggregation studies. In cases when aggregates have formed but do not yet occupy a significant fraction of the sample volume, our sensor outperforms state of the art techniques such as dynamic light scattering in terms of sensitivity. Conversely, when the sample volume is dominated by aggregates, our sensor is not as effective.
ABSTRACT
We demonstrate, to the best of our knowledge, a first accurate empirical model for reflectance measurements from highly turbid media over the full range of incident angles, i.e., for reflectivity values going from unity in the total internal reflection regime to nearly zero when almost all the light is transmitted. Evidence that our model is accurate is provided by extraction of the particle size, followed by independent verification with dynamic light scattering. Our methodology is in direct contrast with the prevalent approach in turbid media of focusing on only the critical angle region, which is just a small subset of the entire reflectance data.
