# Applications of Nanomaterial Coatings in Solid-Phase Microextraction (SPME)
## 1 Introduction
Metal-organic frameworks (MOFs), carbon fiber, graphene, polypropylene, polydimethylsiloxane (PDMS), polyacrylate (PA), Carbowax, polydimethylsiloxane-divinylbenzene (PDMS-DVB), and carboxen-polydimethylsiloxane (CAR-PDMS) are examples of common coatings. Despite their widespread use, polymer coatings have significant drawbacks, including low heat resistance, swelling when organic solvents are present, and limited extraction efficiency. To tackle these problems, scientists have looked into nanomaterials, which have benefits like a large surface area, mechanical strength, and special chemical and physical characteristics. Materials including nanofibers, nanoparticles, and nanotubes have greatly improved SPME fiber extraction efficiency and capacity. They successfully surpass the restrictions placed by the small diameter of conventional fibers thanks to their large surface area and large number of active adsorption sites. The continuous creation of new coatings, such as molecularly imprinted polymers, polymeric ionic liquids, and other nanomaterials, is still a key area of SPME research. By strengthening the technique's selectivity, sensitivity, and adaptability, these developments hope to make it possible to use it in more challenging analytical situations [10; 11; 12; 13; 14; 15]. Nanotechnology enables the design of materials with exceptional properties [16]. Nanomaterials with remarkable chemical and physical attributes are gaining significant attention in the field of separation science. Nanomaterials are now being used in extraction procedures because they have tiny pores and high surface areas that make them more efficient at extracting substances. These materials are also used as SPME coatings because they can withstand high temperatures. Future reviews on SPME coatings and nanomaterials in analytical sample preparation should focus on the use of nanomaterials for SPME coatings [17; 18]. In order to obtain the necessary results, an analytical procedure usually consists of several steps, such as sample preparation (including sampling), chromatographic methods (LC or GC), capillary electrophoresis, detection, and data processing. SPME has become a useful technique for sample preparation because of its ease of use, effectiveness, and capacity to combine extraction and preconcentration in a single step. The enhancement of SPME and other sample preparation methods is greatly aided by nanoparticles. Their physical characteristics and chemical characteristics, like sorption capacities, are frequently advantageous. In order to simplify procedures and make it possible to analyze very small sample volumes, nanoparticles--or chemically modified variants--are utilized for sample cleanup and analyte preconcentration. This development is especially helpful for performing studies with small sample amounts or for investigating novel sample matrices where the sample amount is minimal [19]. The objective of this review is to evaluate the performance of various nanomaterials used in SPME fibers, with a particular emphasis on sensitivity, selectivity, durability, and suitability for detecting specific analytes. The assessment seeks to determine which materials and production techniques have exhibited the best overall performance across a variety of applications. In this review, we focus on the different applications of nanomaterials as coatings on SPME fibers. We also review the different types of nanomaterials that could be used as coatings, for example, metal oxide nanoparticles, carbon nanoparticles, metal nanoparticles, and others. We conclude the review by looking at the performances of the different types of nanomaterials as SPME coatings.