With the goal of achieving environmentally friendly polymer synthesis strategies, enzyme-promoted polymerisation has gradually attracted people's attention. The development of hydrogel-based microfluidics provides a new carrier system for enzymatic catalysis. Here, we report a new technique for enzyme-promoted free radical polymerisation, supported on hydrogel microdots (mu HDs) within a microfluidic chip. Free radical polymerisation initiated by free horseradish peroxidase (HRP) in vials confirmed the formation of poly(N-isopropyl acrylamide) (PNiPAAm), achieving high molecular weight (500 000 Da) in 5 min. For polymerisation in microfluidics, disulphide-bearing mu HDs were mounted on a PDMS-on-glass chip. Utilising a disulphide-thiol exchange reaction, modified HRP was then captured "from the flow" through the chip, which was confirmed by fluorescence microscopy. Various polymerisation parameters were studied in the microfluidic chip, and the successful polymer formation was confirmed by copolymerisation with a fluorescent comonomer. The physical entanglement fixed the formed polymer on the mu HDs, forming a structure similar to a semi-interpenetrating network (semi-IPN). Thus, this technique provides a new direct approach to achieving semi-IPNs within microfluidic chips, showcasing the versatility in which microfluidic systems can be utilised.