Abstract We report a proof-of-concept micro-spectroscopy, stochastic dynamics, and optical trapping study of a well-known reaction for methylene blue photodegradation catalyzed by titanium dioxide aggregates and nanotubes. Photocatalysis is performed under a high concentration of reactants and catalyst loading to characterize the fundamental chemical kinetics and dynamics aspects of this reaction under in operando conditions. We also report the effect of substrate concentration, light intensity, and substrate/catalyst ratio on the kinetic profiles. Optical imaging is used to quantify how spatial and concentration variations affect the reaction kinetics. To study the dynamics of individual nanoparticle catalysts under in operando conditions, we use optical trapping to characterize the stochastic dynamics of single TiO2 nanotubes. Overall, the results presented here indicate that the setup can be used to monitor photocatalytic degradation of methylene blue with simultaneous measurements of images and spectra while also monitoring the catalyst Brownian motion at the single-particle level.