Gold Nanoparticle-Enabled Fluorescence Sensing of Gadolinium-Based Contrast Agents in Urine

Gadolinium-based contrast agents (GBCAs) are commonly used in magnetic resonance imaging (MRI). Concerns about the retention of gadolinium in the body and its potential toxicity have highlighted the need for detection methods to monitor its urinary excretion after MRI procedures. This study presents a fluorescence-enhanced assay for detecting GBCAs in urine using gold nanoparticles (AuNPs) functionalized with a chelator [3,4,3-LI(1,2-HOPO)] and europium, which together act as a fluorophore. The higher binding affinity of the chelator for gadolinium over europium constitutes the analytical principle of this competition assay. AuNPs enhance the assay sensitivity by amplifying europium fluorescence through near-field enhancements and plasmonic hotspots. Assay performance was demonstrated for two clinical GBCAs, i.e., gadopentetic acid and gadodiamide, in synthetic as well as real patient urine samples. By adjusting the concentration of the nanosensor, the dynamic range and detection limit could be adjusted to cover clinical concentration ranges. Importantly, the assay does not require sample digestion and shows higher accuracy than mass spectrometry, which is the gold standard technique (average quantification error of 3.6 vs 11.8%, respectively). Taken together, this method offers a sensitive and adaptable approach for quantifying gadolinium in urine after MRI, advancing GBCA monitoring capability, and improving patient safety.