Nitric Oxide Radical-Based Nanoparticles as Magnetic Resonance Imaging Probes for Ascorbic Acid Quantification

Ascorbic acid (AsA) is intravenously administered as a drug for disease therapy, fatigue recovery, antiaging, and cancer therapies. However, the traditionally quantitative AsA detection needs blood draws followed by mainly hyper-pressure liquid chromatography utilizing diluted samples. Meanwhile, NO radical-based nanoparticles (NONPs) have been widely used in biomedicine and as functional materials. This study demonstrated the quantitative detection of AsA by using NONPs as probes for magnetic resonance imaging (MRI). Simply organic NO radicals such as 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PROXYL), which form as a monomer in solutions, promptly react with AsA and diminish the paramagnetic property during the MRI time scale (several minutes to several tens of minutes), yielding difficulty in the acquisition of MRI images. In contrast, NONPs consisted of the designed organic radicals, which are based on an amphiphilic PROXYL framework, maintained the paramagnetic property with appropriate decay during the MRI time scale, yielding AsA-dose-dependent MRI images. This facilitated the direct measurement of AsA concentrations upon probe addition, thereby realizing in vitro quantitative AsA detection via MRI. In the future of AsA therapy, noninvasive diagnosis of the diseases via the MRI will be a promising method. Furthermore, this method reduced patient burden by eliminating the need for blood draws, facilitating quick and cost-effective medical examinations for wider generations.