Quantitative Analysis of Macrophage Uptake and Retention of Fluorescent Organosilica Nanoparticles

This study investigates the uptake and retention of stable fluorescent organosilica nanoparticles by macrophages, which play a vital role in scavenging environmental nanoparticles and nanomedicine within the body. We used rhodamine 6G-loaded fluorescent organosilica nanoparticles (SiNP-R6G) synthesized from a thiol-functionalized organosilane precursor. Our primary objective was to establish a quantitative relationship between fluorescent measurements and nanoparticle tracking analysis, enabling the precise "counting" of nanoparticles taken up by macrophages under kinetic measurement conditions. Our kinetic study demonstrated a concentration-dependent, saturable internalization of nanoparticles in a model macrophage (RAW 264.7 cells), with a maximum uptake rate (Vmax) of 7.9 x 104 nanoparticles per hour per cell. The estimated number concentration of nanoparticles for half-maximum uptake was approximately 0.8 trillion nanoparticles per milliliter, and a significant portion ([~]80%) of internalized SiNP-R6G remained entrapped within the cells for 48 hours, indicating the sustained particle retention capacity of macrophages. These findings highlight the successful development of a methodology to accurately "count" the cellular uptake of nanoparticles in macrophages, providing valuable insights into the kinetics and retention capabilities of macrophages for nanoparticles.