Active ester surfmers are polymerizable monomers with a reaction centre for interaction with biomolecules. These molecules enable for the preparation of nanoscale polymer beads (surfmer nanoparticles) via emulsion polymerization of styrene (St) or methyl methacrylate (MMA). The reactivity of such fabricated surfmer nanoparticles was determined by immobilization of remazol-brilliant blue and streptavidin. The interaction of a p-(11-(acrylamido)undecanoyloxy)phenyldimethylsulfonium methylsulfate (AUPDS) and the surfmer nanoparticle (poly(St-co-AUPDS)) with remazol-brilliant blue was monitored by isothermal titration calorimetry (ITC). The binding properties and hydrolysis stability of surfmer nanoparticles was quantified via (ITC). The enthalpy of the reaction of AUPDS with remazol-brilliant blue amounts to -32.1 kJ mol(-1), the enthalpy of the reaction of poly(St-co-AUPDS) with remazol-brilliant blue to -38.8 kJ mol(-1). Time and temperature dependence investigations of the surfmer nanoparticles displayed their long-ranging storage stability at 6degreesC in aqueous solution. The faster hydrolysis of the surfmer nanoparticle surface is the reason for the long-term instability at room temperature. (C) 2003 Elsevier B.V. All rights reserved.