Derivatized, swellable polymer microspheres for chemical transduction Original Research Article

Derivatized lightly cross-linked polymer microspheres that swell and shrink as a function of analyte concentration are useful chemical transduction elements that can be coupled to a variety of readouts, including methods based on changes in refractive index, physical displacement and electrical properties. We are preparing 0.3 to 3 μm diameter microspheres in one step by dispersion polymerization. To introduce porosity sufficient to allow analyte access to the interior of our microspheres, we are using polymer systems with hydrophilic backbones or using the particles prepared by dispersion polymerization as seed particles for two-step seeded emulsion polymerization which allows us to incorporate a porogenic solvent in the second step. Much of our work to date has been performed with pH-sensitive polymers, either aminated polystyrene or poly(4-hydroxy-3-nitro)styrene. More recently, we have incorporated ionophores into poly(4-hydroxy-3-nitro)styrene microspheres and demonstrated that ion binding accompanied by loss of a proton causes the polymer to swell. This provides a generic approach for incorporating ionophore selectivity into swellable polymer microspheres. We have been particularly interested in optical transduction with swellable polymer microspheres entrapped in a hydrogel. The measured parameter is the change in optical properties of the gel that accompany swelling. This can be measured in the near infrared using technology developed for fiber optic communications.