Two-Dimensional Nitrogen-Doped Carbon Nanosheets Derived from g-C3N4 /ZIF-8 for Solid-Phase Microextraction in Exhalation of Esophageal Cancer Patients

Here, two-dimensional (2D) nitrogen-doped carbon nanosheets (CNSs) were prepared through carbonizing MOFs (ZIF-8) in-situ grown using graphitic carbon nitride (g-C3N4) as a template. The developed ZIF-8 CNS was then used as solid-phase microextraction (SPME) fiber coating for beneficiation of five biomarkers in exhalation of patients with esophageal cancer and in gas chromatography-mass spectrometry (GC-MS) for determination. The ZIF-8 CNS fiber exhibits satisfactory enrichment factors (3490-5631), wide linearity (5-1000 μg L-1), and low detection limits (0.26-0.96 μg L-1). The relative standard deviations (RSDs) for six replicate extractions of the same ZIF-8 CNS fiber were between 2.0-3.9% (intra-day) and 2.8-5.2% (inter-day). The reproducibility of three fibers prepared by the same approach was in the range 6.8-12.3% (RSD). The developed ZIF-8 CNS fiber can persist in 120 SPME cycles with no prominent loss of extraction efficiency and precision. The high enrichment factors of the 2D ZIF-8 CNS coatings are attributed to the high specific surface area, ultrathin thickness, and nano-pore or interlayer channels; moreover, nitrogen doping also endows the π system with a strong electron absorption ability, which will enhance the π-π interaction between the ZIF-8 CNS and the aromatic ring. Ultimately, the self-made ZIF-8 CNS-coated SPME fiber was applied to the analysis of exhaled breath samples. The recoveries of spiked analytes are between 84 and 105%.