Synthesis and photografting of highly pH-responsive polymer chains

Here, we describe the construction of pH sensitive surfaces via the synthesis and controlled photografting of pH sensitive, fluorescent tethers from the surface of a reactive polymeric substrate. The living radical photografting technique presented makes use of dithiocarbamate-functionalized polymer to graft synthetic poly(ethylene glycol) acrylate succinyl fluorescein. Fluorescence intensity of grafted chains is analyzed as a function of photografting reaction time, graft length, buffer solution pH, and cycling sensors from acidic to basic conditions for optical switching. The graft fluorescence response occurs rapidly in a basic environment and grafted functionalities do not cleave or dramatically deplete (up to 72 h later) upon initial exposure to high or low pH buffers. This behavior is a result of the increased stability when introducing the PEG spacer into the structure of the fluorescein. Ultimately, the pH sensitive grafts developed here demonstrate rapid response times, are easy to produce, and are readily integrated onto a fully polymeric microfluidic device using photolithographic techniques and spatially controlled living radical photografting chemistry. Once integrated, sensors such as these could be useful in monitoring pH changes when mixing, reacting, or introducing new chemicals onto a microdevice like the one presented.