# Applications of Nanomaterial Coatings in Solid-Phase Microextraction (SPME)
## 7 Recent Advances in the Type of Fiber Material Used in SPME  
In the food, environmental, and medicinal industries, solid-phase microextraction (SPME) is frequently used to preconcentrate and remove trace amounts of harmful and beneficial substances from natural goods. High efficiency, minimal resource use, ease of use, and speed are some of its main advantages. A key factor in improving extraction efficiency and selectivity is the sorbent material selection. Graphene (G), graphene oxide (GO), functionalized carbon nanotubes (CNTs), metal-organic frameworks (MOFs), covalent organic frameworks (COFs), molecularly imprinted polymers (MIPs), and other inorganic nanomaterials are all popular materials because of their large surface areas, tunable structures, high porosity, and chemical stability. Furthermore, because of their effectiveness and selectivity, environmentally friendly sorbents such as carbon black, aerogels, and zeolites have become more popular [133]. In this review, we did not look into MOFs as sorbent materials because the application of MOFs to SPME is another subject matter on its own, which we might look at separately in the future. Also, while MOFs have broad applicability, many suffer from water instability, degrading upon contact, which poses challenges for preparing water-based biological samples. Additionally, issues like recycling, waste management, and scalable production require further improvement [134]. In designing SPME fiber coatings, two key principles must be considered: the coating material should strongly and specifically interact with analytes to achieve effective enrichment, and it must be easily and securely immobilized on a supporting substrate. The evolution of SPME fiber coatings, as illustrated in Figure 5, highlights three key components: the coating material (blue dot), support material (green dot), and coating method (red dot). While the timelines show progress in certain areas, such as the shift from silica to metal fibers for better mechanical and chemical stability, other aspects have seen less development. The transition to metallic supports has improved the durability and lifespan of fibers due to their toughness and rigidity, replacing the more brittle silica fibers [45]. [PERSON] et al. demonstrated the progress of SPME fibers by creating a new substance specifically designed for the analysis of benzene series in oilfield wastewater. Through the use of an ionic liquid-assisted wet spinning process, metal-organic framework development, and pyrolysis, they modified graphene fibers with ordered mesoporous carbon nanotube arrays (CNTAs) to generate a unique fiber structure. Due to the crumpled graphene fiber stem and CNTAs acting as \"hairs\", the resulting \"hair-brush-like\" microfiber design greatly improves extraction efficiency. Verified by gas chromatography-mass spectrometry, this novel architecture provides a large surface area, a large number of binding sites, and remarkable enrichment capabilities for toluene, m-xylene, p-xylene, benzene, and ethylbenzene. In terms of extraction efficiency, the fibers outperformed commercial fibers thanks to their wide linear detection ranges (0.2-600 \(\upmu\)g L\({}^{-1}\)), low detection limits (0.005-0.03 mg L\({}^{-1}\)), and exceptional repeatability (3.2-5.5% for one fiber, 2.1-6.7% for fiber-to-fiber) [39]. To measure nicotine and six metabolites in different parts of the rat brain, [PERSON] et al. developed a new hydrophilic-lipophilic SPME probe employing benzene diimine triazine benzodioxane-methylbenzoyliodoxane (BDTB-MBD), a nitrogen-rich porous polymer coating. According to their findings, the coating material had balanced hydrophilic and hydrophobic qualities, a large surface area of 1001.7 m\({}^{2}\)/g, an ideal pore diameter of 5.28 nm, and outstanding stability.