Durability of ZnONP in artificial lysosomal fluid (ALF, pH 4.5) and artificial interstitial fluid (Gamble's solution, pH 7.4). ZnONP were incubated at 37°C for 24 h with gentle shaking. (A) Gross picture taken by digital camera. The photographs were taken before centrifugation. (B) Percentage of mass compared to initial mass (50 mg). Values are mean ± S.D. n = 3.