Optical Detection of Nanoaggregates in highly Concentrated strongly Absorbing Colloids without Sample Dilution

The ability tomonitor the flocculation, aggregation and settling of micro and nano-sized particles is important for many environmental, chemical, biological and biomedical processes. However, standard approaches such as dynamic light scattering or absorption spectroscopy require sample dilution for characterization of highly concentrated samples. In this model study a new method using total internal reflection (TIR) is demonstrated to directly detect aggregates in highly-concentrated, strongly-absorbing samples of aqueous gold nanoparticles without sample dilution or pretreatment. Aggregation of the gold nanoparticles is induced by changing solution pH or by increasing ionic strength. Results obtained using the new sensor with no dilution agree with the post-dilution results obtained by absorption spectroscopy, dynamic light scattering, and zeta potential measurements. This validation of the sensor by standard methodologies is important because earlier work with sensitive detection of aggregates in non-absorbing polystyrene nanoparticles precluded the use of standard methodologies. Published by Elsevier B. V.