Optical Fiber-Based Nanoporous Molecularly Imprinted Polymer Sensors for the Detection of Acute Kidney Injury Biomarkers Quinolinic Acid and Tryptophan

The urinary quinolinic acid (QA)/l-tryptophan (T) ratio is a noninvasive prognostic biomarker for the early detection of acute kidney injury (AKI). We describe a rapid, sensitive, robust, and cost-effective detection tool in the form of a disposable optical fiber sensor for potential AKI testing based on molecularly imprinted polymers (MIPs). AKI is a sudden and life-threatening deterioration of kidney function. It occurs in >50% of intensive care patients and is associated with multiple organ damage. Thus, AKI is a sign of severity, requiring urgent care. AKI is often rapidly reversible at its early stage; however, the current markers for AKI provide late diagnosis, and they are not suitable for continuous monitoring. Therefore, the implementation of point-of-care tests in clinical settings would foster early assessment so as to trigger a rapid treatment and save numerous lives. Herein, nanoporous MIP layers, endowed with a fluorescent naphthalimide reporter monomer, were synthesized on the surface of optical fiber waveguides via in situ evanescent wave photopolymerization, initiated by a visible-light-sensitive photoiniferter. The photoiniferter allowed for further coating of the MIP with polyethylene glycol brushes, which served as an antifouling polymer layer for enhanced sensing performance of the waveguide in urine samples. The MIP-coated optical fibers exhibited specific fluorescence enhancement when binding QA and T in spiked urine. MIP binding was also selective, as no recognition was observed with dipicolinic acid and d-tryptophan, which are very close structural analogues of QA and T, as well as with urea and creatinine, the major constituents of urine.