Polymersomes: Small 10/2009

The cover picture illustrates how the activity of enzymes encapsulated in polymersome nanoreactors (≈300–500 nm) can be probed using flow cytometry, a powerful technique that is routinely used for high-throughput fluorescence-activated cell sorting. Carboxyfluorescein diacetate, which is converted to the fluorescent carboxyfluorescein by the enzyme/Candida antarctica/lipase B, is used to assess the activity of CalB inside porous PS-PIAT polymersomes. To prevent diffusion out of the polymersomes of the fluorescent product, a trapping agent is co-encapsulated with CalB. This polycation traps the negatively charged carboxyfluorescein product molecules and thus co-localizes their fluorescent signal with active catalysts only. These highly fluorescent nanoreactors can then be separated from others using flow cytometry, resulting in completely active populations of bioreactors. The same principle is also demonstrated for encapsulated fluorescent markers such as GFP and DsRed. For more information, please read the Communication “Sorting Catalytically Active Polymersome Nanoreactors by Flow Cytometry” by J. J. L. M. Cornelissen, J. C. M. van Hest, et al. beginning on page 1138.