At first, the depletion capability of PAANY was investigated. To this end, different concentrations of PAANY in borate buffer (pH 9.0, 200 mM) were added to a solution of silica microspheres (1.15•10 8 # colloids/mL) to construct an aggregation calibration curve (Figure ). From this curve, it becomes clear that at least 0.5 mM PAANY should be used to have a significant depletion effect. In contrast to our previous work , for these colloidal experiments borate buffer of pH 9.0 was used as colloidal silica was found to stick to the glass wall of the capillary at lower pH. In the absence of the anhydride fuel the colloids form a stable dispersion with PAANY acting as a depletant. Subsequently, different concentrations of PAANY (0.5/0.6/0.7 mM) were used in fuel cycles with acetic anhydride (chemical fuel), pyridine (catalyst forward reaction) and imidazole (catalyst backward reaction) (Figure and Figure ). With lower pyridine concentration (0.7 mM) only 50% of PAANY is acetylated at its maximum (Figure -UV-VIS conversion) and the colloid (dis)assembly response is less strong (Figure ) compared to the optimized conditions (Figure and Figure ). With more pyridine present (1.75 mM) almost 90% of the NY groups on the polymer are acetylated (Figure -UV-VIS conversion) and the colloidal assembly cycle is more pronounced (Figure and Figure ). In Figure the colloid aggregation (%) as a function of time is shown for the optimized conditions (0.7 mM PAANY with 2.5 equivalents of pyridine and imidazole). Initially, the colloids are 55% aggregated due to effective depletion interactions with PAANY. After addition of 20 equivalents of the anhydride fuel, the colloid clusters immediately disassemble and an aggregation of only 30% can be observed with mostly dimer structures present (Figure -microscopy image 5 min). Hence, the polymer in its globule state with is not able to deplete the colloids anymore at this concentration and the large clusters disassemble. During the fuel cycle the colloidal aggregation increases again and microscopy images after 90 min and 180 min show the reappearance of the larger colloidal clusters (Figure ). This can be attributed to an increase in the depletion interactions as the polymer is deacetylated back and in its random coil conformation again. The colloidal clusters from the reference microscopy images of the starting sample can be viewed in Figure (high and low magnification), overall corresponding to an average aggregation percentage of 54.5 ± 5.78%. Microscopy images of colloidal assembly over the course of a full fuel cycle are presented in Figures (high and low magnification).