Nanoparticle tracking analysis of gold nanoparticles in aqueous media through an inter-laboratory comparison by Briffa, SM, Sullivan, J, Siupa, A, Carnell-Morris, P, Carboni, M, Jurkschat, K, Peters, RJB, Schultz, C, Seol, KH, Kwon, S-J, Park, S, Yoon, TH, Johnston, C, Lofts, S, Valsami-Jones, E