Monitoring the fate of small silver nanoparticles during artificial digestion

•SAXS is useful for determination of particle size distributions in digestion fluids.•Silver nanoparticles without food components aggregate strongly during digestion.•Sizes of silver nanoparticles are constant in saliva and stomach but particles were etched in the intestine.•Milk powder is an excellent colloidal stabilizer and prevents aggregation and etching during digestion.

We report on the results of an in vitro digestion study of silver nanoparticles in presence and absence of food. The particles were poly(acrylic acid) stabilized ultra-small silver nanoparticles with a radius of 3.1 nm and a relative size distribution width of 0.2. As food components oil, starch, skimmed milk powder and a mixture thereof were chosen. Aggregation of the particles was quantified with small-angle X-ray scattering in terms of log-normal radii distributions. Complete aggregation of the primary particles was determined in the absence of food. In contrast, the presence of oil and starch initiates a disaggregation in the intestine. Only small aggregates of 6 nm radii and aggregation numbers of 7 were found in the presence of milk powder. It prevents primary particles from etching in the gastric and intestinal juice. Our results indicate that the silver nanoparticles can pass the digestion process in a nanoscale form but undergo a strong and food-dependent transformation in their state of aggregation.

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