To reach these aims, we utilized a Bayesian Optimizer with the Expected Improvement (BOEI) algorithm. This combination enables a closed-loop optimization process specifically tailored for the precise targeting of assembled particle sizes. Figure illustrates a flowchart detailing the algorithm and explains the underlying principles governing the construction of the size targeting algorithm. Initially, the BOEI algorithm randomly selected four sets of total flow rates, volume fractions, and concentrations from a predefined parameter space. In the following, these were total flow rates spanning from 1 to 8 ml/min, water volume fractions ranging from 0.6 % to 0.98 %, and concentrations varying between 0.5 and 5 mg/ml. Subsequently, online DLS measurements were conducted for each of these initial points automatically without user intervention being required beyond provision of a polymer stock solution. The colour scalebars are both aligned to 300 nm to make the plots easier comparable, even though b) reaches sizes above 1000 nm.