# Applications of Nanomaterial Coatings in Solid-Phase Microextraction (SPME)
## 4 Advances in the Adsorbent Type Used in the Extraction Phase of the SPME Fiber
### SPME Based on Nanoparticles
#### 4.1.1 Metal Nanoparticles in SPME  
Metallic nanoparticles, particularly those containing metals such as silver and gold, have unique visual, physical, chemical, and biological properties that make them useful in a variety of applications. Their high affinity for both inorganic and organic mercury species enables them to be used efficiently in mercury extraction methods. These nanoparticles can also help separate heavy metals, organic chemicals (including pyrene, olefins, and methylene blue), and gaseous species (like NO and SO\({}_{2}\)) [51]. Metal nanoparticles (MNPs) are crucial for the effective and selective extraction of analytes from various matrices. The application of metal nanoparticles in SPME has focused significantly on gold nanoparticles, due to the special properties they possess as an adsorbent material. Figure 3: Advances in materials chemistry for the fabrication of different materials for use in SPME fibers. Printed with permission from [45]. Copyright 2022, John Wiley and Sons. Gold Nanoparticles as Sorbent Material in SPME  
Gold nanoparticles (AuNPs) are particularly notable due to their strong affinity for binding organic compounds with thiol groups and their effectiveness with other functional groups. AuNPs can spontaneously adsorb biomolecules containing thiol (SH) or amino (NH\({}_{2}\)) groups, resulting in the formation of self-assembled monolayers. Despite their extensive surface area for interactions with analytes and column surfaces, research on AuNPs within separation science is limited. Their high surface-to-volume ratio, long-term stability, ease of synthesis, and favorable chemical modification properties make AuNPs promising candidates for diverse applications [48; 52]. In a work by [PERSON] et al., gold nanoparticles (AuNPs) were in situ coated on ordered mesoporous carbon (OMC) to generate an SPME covering with better extraction capacity and aniline selectivity. The researchers discovered that this composite significantly improved extraction efficiency, with enrichment factors for anilines ranging from 1143 to 3420, while such factors for alcohols and phenols ranged from 45 to 845 and 86 to 545, respectively, indicating notable aniline selectivity due to strong interactions between gold and amino groups. The approach quantified four anilines using gas chromatography and flame ionization detection, with limits of detection ranging from 0.072 to 0.18 \(\upmu\)g/L and good precision (1.9% to 3.8% RSD). The technique was successfully applied to river and drinking water samples, with recoveries ranging from 83.9% to 107.7% for river samples and 94.0% to 113.1% for drinking water. The authors concluded that the AuNP/OMC composite fiber outperformed individual AuNPs, OMC, and commercial coatings in terms of extraction efficiency, emphasizing its potential for preconcentrating trace anilines in environmental samples and its strong affinity for thiol-containing compounds due to gold interactions [53]. In another study, [PERSON] et al. developed a poly(3,4-ethylenedioxythiophene)@Au nanoparticle (PEDOT@AuNP) coating for SPME using a self-assembled monomer on AuNPs that was electropolymerized on stainless steel. They described the coating as having a cauliflower-like microstructure with exceptional heat stability (up to 330 \({}^{\circ}\)C) and durability, able to withstand over 160 extractions without losing performance. Because of its hydrophobic interactions with PEDOT affinity for AuNPs, the coating has a high extraction capacity for polycyclic aromatic hydrocarbons (PAHs). The researchers used gas chromatography (GC) to obtain low detection limits (2.5-25 ng/L) and high repeatability, with recovery rates ranging from 89.9% to 112% in a variety of environmental water samples. [PERSON] et al. found that the PEDOT@AuNP coating is an effective, long-lasting solution for PAH analysis in environmental settings [54]. An SPME coating based on gold nanoparticles was designed by [PERSON] et al. to detect organochlorine pesticides in ambient water samples.