AgNPs modulates mitochondrial transmembrane potential. Changes in mitochondrial transmembrane potential (MTP) was determined using the cationic fluorescent indicator, JC-1. Fluorescence images of control A549 cells (without silver nanoparticles (AgNPs)) and cells treated with biologically synthesized AgNPs (bio-AgNPs) (25 μg/ml) and chemically synthesized AgNPs (chem-AgNPs) (70 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.