In mice, they then tracked how the particles traveled through and interacted with various components of the kidney. “Cell membranes are mainly negatively charged, but the degree of the negative charge may vary depending on the type of cell. On the other hand, treating kidney disease requires stronger nanoparticle interactions with the kidneys. Using the nanoparticles as probes allowed the researchers to understand which component of the kidney’s complex structure is most negatively charged. Now we finally figured out the charge barrier, which is much more complicated,” Zheng said.