LAUSR

There is a need to develop at-home phenylalanine (Phe) test kits, analogous to home glucose meters, for phenylketonuria patients who must measure their blood Phe levels frequently to adjust their diet. Unfortunately, such test kits are not available yet due to the lack of simple and inexpensive Phe-sensing elements. With the goal of developing a Phe-sensing element, we fabricated 2D photonic crystal (2DPC) hydrogels that quantify human serum phenylpyruvate (PhPY), which is the product of the reaction be-tween Phe and the enzyme phenylalanine dehydrogenase. The PhPY-sensing hydrogels have oxyamine recognition groups that link PhPY to the hydrogel polymer network via chemoselective oxime ligation. This structural modification induces the hydrogel to swell, which then increases interparticle spacings within the embedded 2DPC. The PhPY-induced particle spacing changes are measured from light diffraction and used to quantify PhPY concentrations. The estimated limit of detection of PhPY in human serum for a detection time of 30 min is 19 μM, which is comparable to the minimum blood Phe concentrations of healthy people. Besides the potential application for developing Phe-sensing elements, this new hydrogel sensing approach via chemoselective oxime ligation is generalizable to the development of other chemical sensors working in complex biological environments.