(599bg) Characterization of the Key Properties of Optically Diffracting Hydrogels for Biosensing Applications

Protein kinases are a critical family of enzymes that modulate virtually all cellular processes and have been implicated in a myriad of diseases, making kinases among the most important targets for therapeutic molecules. However, kinases are inherently difficult to assay due to the lack of measurable signal and there is a lack of robust, high-throughput screening methods available for kinase inhibitors and activators. To address this problem, we have developed a novel biosensor that is based on a kinase-responsive polymer hydrogel, which enables label-free screening of kinase activity via changes in optical properties. The optical response of the sensor is dependent not only on the kinase activity but also (i) the materials properties of the hydrogel, (ii) the immobilized charge distribution in the hydrogel, and (iii) the ionic character of the surrounding environment. A model of swelling in ionic polymer networks elucidates these dependencies, allowing for quantification of the extent of phosphorylation and enzyme kinetics. The model was used to predict methods for increasing sensitivity, such as eliminating extraneous charges immobilized in the hydrogel, decreasing the elastic restoring force upon swelling, and increasing the driving force for polymer-solvent mixing. It was found that extent of swelling, and therefore sensor response, is highly sensitive to the type and concentration of immobilized charges in the hydrogel and the magnitude of the polymer-solvent interaction parameter and less sensitive to changes in the Young’s modulus of the hydrogel. Enhancing understanding of the parameters that most affect the extent of swelling allows for the development of more sensitive, robust photonic crystal biosensors for assaying the activity of kinases and other enzymes that catalyze post-translational modifications.