Polymer Microarrays for Surface Plasmon Resonance Based Sensors

Surface plasmon resonance spectroscopy (SPR) is used to detect pH changes in acidic solutions. SPR is an optical, label-free method for highly sensitive detection of refractive index changes. A microarray of pH-sensitive polymers, using poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP), as recognition elements, is investigated on a gold surface. Swelling and protonation of the polymers lead to refractive index changes at the sensor surface. For the first time, a polymer microarray in a microfluidic channel is used to detect pH values smaller than 5 by SPR in aqueous hydrochloric acid and buffered solutions of different ionic strength. Every polymer has a distinct pH range where it shows its highest pH sensitivity. pH measurements are performed in a range between pH 0.75 and 5. The ionic strength influences the swelling behavior and the pH sensitivity of the polymers. The applied polymers are pH-selective in the used buffers containing sodium, phosphate, citrate, potassium and chloride ions.