The accumulation of partially degraded waste material in astrocytes is increasingly recognized as contributing to age-dependent neurodegenerations, and increased pH of the lysosomal lumen is a likely cause. Acidic nanoparticles are predicted to lower the lysosomal pH and reduce this accumulation; their ability to be internalized to lysosomes and non-toxic to astrocytes makes this a potentially long-term solution. In order to track nanoparticle delivery to lysosomes and optimize their incubation conditions, fluorescent-labeled nanoparticles are necessary. Here, we describe an improved method for fluorescent labeling of acid nanoparticles to determine their delivery to lysosomes. We synthesized nanoparticles from polymers in which 502 H PLGA was covalently bonded to the fluorescent dye Cyanine3. These stable fluorescent nanoparticles enabled detection of colocalization between lysosomes and nanoparticles in astrocytes, with retention up to two weeks. The time course and concentration of nanoparticles had a significant effect on their delivery efficiency. We also examine the ability of acid nanoparticles to recover lysosomal pH or functions. In summary we developed an improved method to label acid nanoparticles which gave enhance detection of delivery to lysosomes.