Wageningen Food Safety Research 1 article published in JoVE Chemistry Nanoparticle Tracking Analysis of Gold Nanoparticles in Aqueous Media through an Inter-Laboratory Comparison Sophie M. Briffa1, Jo Sullivan2, Agnieszka Siupa2, Pauline Carnell-Morris2, Michele Carboni2, Kerstin Jurkschat3, Ruud J. B. Peters4, Carolin Schultz5, Kang Hee Seol6, Sook-Jin Kwon6, Sehee Park7, Tae Hyun Yoon6,7, Colin Johnston3, Stephen Lofts8, Eugenia Valsami-Jones1 1School of Geography, Earth and Environmental Sciences, University of Birmingham, 2Malvern Panalytical, 3Department of Materials, University of Oxford, 4Wageningen Food Safety Research, 5UK Centre for Ecology & Hydrology, 6Institute for Next Generation Material Design, Hanyang University, 7Department of Chemistry, College of Natural Sciences, Hanyang University, 8UK Centre for Ecology & Hydrology The protocol described here aims to measure the hydrodynamic diameter of spherical nanoparticles, more specifically gold nanoparticles, in aqueous media by means of Nanoparticle Tracking Analysis (NTA). The latter involves tracking the movement of particles due to Brownian motion and implementing the Stokes-Einstein equation to obtain the hydrodynamic diameter.