A nanoparticle based assay for monitoring chemical reactions in real-time, ion concentrations in solution, and oxidation potential of ions in solution is describe. The assay is based on use of photoluminescent perovskite nanoparticles with the composition XYZ3. The XYZ3 nanoparticles are added to a reaction or a solution to be analyzed, and the optoelectronic response of the nanoparticle is proportional to the chemical kinetics of the reaction or concentration of target. The resulting color changes can be qualitatively monitored by eye or quantitatively by spectroscopy. The assays may serve as a compliment or replacement for routine chemical analysis performed over the course of a reaction.