Fig. 2. Single exponential plasma clearance term, k_clear, estimated for metal NPs, molecular tracers and protein drugs of different sizes. Open circles: k_clear for molecular tracers and proteins; data obtained from ref. 55. The identity of some proteins is shown as example. Solid line calculated with eqn (5). Green triangles: glutathione-coated NPs of different core compositions (entries 1–4 in Table S1†). k_clear was estimated as CL/V_d using pharmacokinetic data from ref. 38. Blue circles: glutathione- and PEG-coated gold NPs (entries 5–6 in Table S1†). k_clear was estimated as [C₀]/AUC using data from ref. 28. Brown diamonds: atomically precise glutathione-coated gold NPs (entries 7–10 in Table S1†). k_clear was estimated as CL/V_d using data from ref. 42. Orange squares: glutathione-coated gold NPs administered under different doses (entries 14–16 in Table S1†). k_clear was estimated as CL/V_d using data from ref. 18. Purple inverted triangle: glutathione-coated gold NPs (entry 17 in Table S1†). k_clear was estimated as [C₀]/AUC using data from ref. 57. Red star: PEG/MBA-coated gold NP. k_clear was estimated as [C₀]/AUC using data from ref. 58.