GO can undergo significant physicochemical transformation in two simulated lung fluids–Gamble’s solution and artificial lysosomal fluid (ALF), as the organic acids in lung fluids cause reduction of GO. Biotransformation markedly inhibits the endocytosis of GO by scavenging macrophages. Notably, alterations in Gamble’s solution enhance the aggregation of GO in a layer-to-layer manner, resulting in GO precipitation and reduced interaction with cells, whereas changes in ALF lead to edge-to-edge aggregation of GO, enhancing the adhesion of large sheet-like GO aggregates on plasma membrane without cellular uptake.