Spatial-temporal profiling of antibiotic metabolites using graphite dots-assisted laser desorption ionization mass spectrometry.

Appropriate prescription of antibiotics requires the pharmacokinetic knowledge of the drugs and their metabolites in blood, and their distribution/retention in organ tissues. Here we report that highly crystalline graphite dots (GDs) allow for quantitative profiling of antibiotic metabolites in a spatial-temporal manner, in combination with matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI). GDs matrix features an ultra-clean background base line and high efficiency in ionization of small molecules, thus enabling quantification of sulfamethoxazole (SMZ) and its metabolites with limit of detection (LOD) in the femtomole range. Distinctly different from the other MS techniques, our approach is tolerant to high levels of salt contaminants in the complexed biological samples, thus minimizing the sample purification requirements and allowing for tests in small volumes. We have demonstrated quantitative measurements of the dynamic concentration changes of SMZ (m/z 276.27) and two metabolites, N-4-hydroxy-SMZ (m/z 292.28) and N-4-acetyl-SMZ (m/z 318.31) with only 1 mu L mouse blood sample for each test. High-resolution distribution patterns of SMZ metabolites have directly been visualized a on the liver subsegments. Therefore, it allows for simultaneously acquisition of pharmacokinetic data in the blood combined with detailed hepatic zonation of SMZ metabolites for the first time. As a rapid, high-throughput platform to monitor small molecules in vivo, our approach of GDs-assisted MADLI MSI will foster the medical research on the antibiotic usage and drug development.