Materials Science and Technology of Polymers at the University of Twente


The impact of the spatial confinement of polystyrene-block-poly (acrylic acid) block copolymer (BCP) vesicles on the reactivity of encapsulated enzymes, such as bovine pancreas trypsin, were studied (Fig 1).



                                            Figure 1: Enzymatic reactions in the confinement of block copolymer vesicles.
                                                             The liberation of fluorescent molecules allows one to monitor reaction kinetics.


Enzymes, as well as small molecules, were encapsulated with loading efficiencies up to 30% in the vesicles which exhibited internal vesicle diameters between 30 nm to 250 nm, obtained by manipulating the vesicle preparation conditions (Fig 2 and 3).




                            Figure 2: A transmission electron micrograph                                    Figure 3: AFM image of tightly packed
                                             of block copolymer vesicles.                                                                  block copolymer vesicles.


The kinetics of the trypsin-catalyzed reaction of a fluorogenic substrate inside and outside the vesicles is quantitatively estimated using fluorescence spectroscopic analyses in conjunction with the use of a selective quencher for non-encapsulated fluorophores (see scheme). The values of the catalytic turnover number obtained for reactions in differently sized nanoscale reactors show a significant increase with decreasing vesicle volume, while the values of the Michaelis-Menten constant decrease. The observed corresponding increase in enzyme efficiency by two orders of magnitude compared to bulk solution is attributed to an enhanced rate of enzyme-substrate and molecule-wall collisions inside the nanosized reactors, as predicted in the literature on the basis of Monte Carlo simulations.


Publication: Chen, Q., Schönherr, H., Vancso, G.J., Block-copolymer vesicles as nanoreactors for enzymatic reactions (2009) Small, 5 (12), pp. 1436-1445.