Development of Molecularly Imprinted 2D Photonic Crystal Hydrogel Sensor for Detection of L-Kynurenine in Human Serum.

l-Kynurenine (KYN) is a metabolite of the Kynurenine pathway and is a known potential marker of immune suppressant disorders and cancer. Here, we present a molecularly imprinted two dimensional (2D) Photonic crystal (PC) hydrogel sensor for the detection of L-KYN in human serum. The sensor utilizes polystyrene-based 2D PC colloidal arrays (2D PCCA) hydrogel with methacrylic acid as the functional monomer which can imprint the L-KYN template by hydrogen bonding. After removal of the template, the resulting nanocavities in the hydrogel can selectively bind and recognize L-KYN in the serum samples. The binding is selective for L-KYN, which is revealed by shrinkage of the hydrogel volume and decrease in the particle spacing that can be easily monitored through changes in the Debye diffraction ring diameter using a LASER pointer. The sensor demonstrates visible red to green color shift upon binding to L-KYN. The 2D PC sensor demonstrates the limit of detection (LOD) of 50  nM, linear relationship of particle spacing versus L-KYN concentration range (50-1000  nM) with the analytical recovery of up to 92 % in the spiked serum samples. The sensor can distinguish between L-KYN and D-KYN and is re-usable up to five times. The sensor is available for the rapid and quantitative detection of L-KYN in the human serum.