AgNPs modulate mitochondrial transmembrane potential. Changes in mitochondrial transmembrane potential (MTP) was determined using the cationic fluorescent indicator, JC-1. Fluorescence images of control A549 cells and L132 cells (without silver nanoparticles (AgNPs)) and cells treated with AgNPs (30 μg/ml).The changes of mitochondrial membrane potential by AgNPs were obtained using fluorescence microscopy. JC-1 formed red-fluorescent J-aggregates in healthy A549 cells with high MTP, whereas A549 cells exposed to AgNPs had low MTP and, JC-1 existed as a monomer, showing green fluorescence. L132 cells exposed to AgNPs shows healthy and had high MTP.