## 1 Introduction  
As an efficient sample preparation technique, solid-phase microextraction (SPME) can integrate sampling, preconcentration, extraction, and sample injection into one step [1, 2]. At present, it has been widely applied in the field of environmental analysis, drug monitoring, food testing, and biological analysis in order to remove impurities and enrich the trace target compounds in real samples [3, 4, 5, 6]. It uses the adsorption of a sorbent to extract analytes from a sample matrix; these analytes are then desorbed from the sorbent and directed into an analytical instrument, such as gas chromatography (GC), high-performance liquid chromatography (HPLC), etc. [7; 8; 9; 10]. The material used in the extraction coating is an important factor because the extraction process is achieved through a distribution equilibrium between the target compounds in the sample solution and the extraction coating. At present, most commercial SPME fibers are made of fused silica, which is not only expensive, but also easy to break and swell in organic solvents [11; 12]. Therefore, it is urgent to find a kind of fiber with thermal, chemical, and mechanical stability, excellent selectivity, and high sensitivity to overcome these problems. In the past two decades, many studies have focused on high-strength metal substrates, such as aluminum wire [13], silver wire [14], zinc wire [15], platinum wire [16], copper wire [17], and stainless steel wire [18], that were modified with different kinds of organic, inorganic, and hybrid coatings, which exhibited good bending properties and chemical and mechanical stabilities. Titanium dioxide (TiO\({}_{2}\)) has been comprehensively studied and used in various fields due to its chemical and thermal stability, biocompatibility, anti-polluting nature, and high corrosion resistance due to its photoelectrochemical activities [19]. Some studies have found that nanostructured TiO\({}_{2}\) is an excellent adsorbent for organic compounds in SPE and SPME [20; 21]. Moreover, it is an import smart material for many practical applications, including self-cleaning, solar cells, lithium-ion batteries, pollutant photodegradation, and oil/water separation [22; 23; 24; 25]. In situ fabrication of a TiO\({}_{2}\)-nanotube coating on the surface of chemically oxidized Ti wire with hydrogen peroxide solution has been used for SPME of dichlorodiphenyltrichloroethane and its degradation products [26]. [PERSON] et al. fabricated TiO\({}_{2}\) nanotube arrays on the surface of Ti wire for use in the SPME of PAHs. Their results showed that TiO\({}_{2}\) nanotube arrays are capable of extracting PAHs, but the very thin nanotube walls make the coating very fragile and easy to destroy when carrying out SPME [27]. The [PERSON] group presented a simple and rapid anodic method for the in-situ fabrication of a novel fiber consisting of Ti wire coated with rod-like TiO\({}_{2}\). It was used for the concentration and determination of trace PAHs and phthalates (PAEs) by SPME, coupled to HPLC with UV detection [28]. The [PERSON] group prepared a core-shell TiO\({}_{2}\)@C fiber for SPME, which was carried out by the simple hydrothermal reaction of a titanium wire, followed by the coating of amorphous carbon. It was successfully used for the determination of PAHs in the Pearl River water with higher GC responses than commercial PDMS and PDMS/DVB fibers [29]. Although different metal wires have been widely used as the sorbent instead of conventional fragile silica fibers by many researchers, various sorbent coatings were always required in conjunction with the metal wire for SPME in previous reports. The Yan group fabricated a stainless steel wire etched with hydrofluoric acid for SPME [30]. Although the pristine wire had almost no extraction capability toward the tested analytes, the etched wire did exhibit a high affinity to the tested PAHs, with a high enhancement factor in the range of 2541-3981, but no extraction ability to hydrophilic phenol, butanol, and aniline was found.