Fabrication and Characterization of Poly(2-Hydroxyethyl Methacrylate) Microparticle Sensors

Optical biosensors are desired for the monitoring of various biochemical markers, which are relevant indicators in the treatment and diagnosis of diseases. Specifically, luminescence sensors are favorable for optical interrogation since they are highly sensitive to analyte changes and may be implemented in lifetime or intensity-based systems. In order to develop particle-based fluorescent sensors, poly(2-hydroxyethylmethacrylate) (HEMA) microspheres have been fabricated via membrane emulsification and characterized to evaluate the emulsion method and the overall process of tailoring properties to synthesize spheres of specific mean sizes. A pH-sensitive indicator seminaphthorhodafluors-4F 5-(and-6)-carboxylic acid (SNARF) was immobilized within the microspheres, and resulting sensor particles were exposed to various pH buffers to obtain a pH calibration curve based on intensity measurements.

PolyHEMA microparticles were fabricated in a systematic study with measured mean sizes ranging from 8-21 um. Optical and scanning electron microscopy images revealed the formation of spherical, porous particles, which were additionally stabilized with polymer coatings. The lowest coefficient of variation value achieved was 50%, indicating the inability to produce monodisperse particles due to the dispersity of pore sizes in the membrane. SNARF was immobilized within the polyHEMA spheres, and fluorescence was observed when exposing the sensors to different pH buffers on a fluorescence microscope. Ratiometric intensity measurements for the sensor particles were obtained on a spectrofluorometer while flowing pH buffers over the immobilized spheres in a reaction chamber. The peak intensity ratio of the microparticle sensors exhibited a change in 0.9 units when decreasing the pH from 8.4 to 5.5. In the future, these pH sensing particles may be implanted alongside glucose sensing materials in order to provide valuable pH information in understanding the immune response to specific biomaterials and sensing components.