A variety of other techniques have been employed to characterise the mucin polymer matrix in CF sputum, including atomic force, scanning electron or confocal imaging microscopy55, fluorescence recovery after photobleaching56, rheology (to measure viscoelastic properties)57 and multiple particle tracking (MPT; to assess the microstructure of mucus and matrix pore size using nanoparticle diffusion)58. The gene discussed is MUC5AC; the disease is cystic fibrosis.