## 1 Introduction  
Phytohormones, which are typically present at low concentrations in plant tissues, regulate the growth and development of plants [1]. Auxins, an important group of phytohormones, were the first of the major plant hormones to be discovered. These hormones, including indole-3-acetic acid (IAA), indole-3-propionic acid (IPA), and indole-3-butyric acid (IBA), are involved in many aspects of plant growth and development [2]. IAA was the first plant hormone that was used to stimulate the rooting of cuttings. The second auxin, IBA, was discovered to also promote rooting and was determined to be even more effective than IAA [3, 4]. Due to the higher stability of IBA versus that of IAA, both in solution and in plant tissue, IBA has a greater ability to promote adventitious root formation than does IAA. The quantitative analysis of auxin is often required in agriculture and plant physiology. Various analytical techniques have been used for the analysis of auxin, mainly high performance liquid chromatography (HPLC) with different detectors such as mass spectrometer (MS) [5, 6], ultraviolet spectrophotometer (UV) [7], fluorescence [8, 9], and chemiluminescence [10]. Other techniques such as gas chromatography-mass spectrometer (GC-MS) [11, 12], capillary electrophoresis (CE) [13],and enzyme linked immunosorbent assay (ELISA) [14] were also reported. Although these methods have been successfully applied for the sensitive analysis of auxins in a variety of plants, they suffer from limitations, such as the derivatization of auxins to methyl esters in GC, the high cost of equipment for a liquid chromatography-mass spectrometer (LC-MS), and the synthesis of the antibody for auxins and the cross-reactivity of antibodies in ELISA. Therefore, the development of a simple, rapid, inexpensive, and sensitive analytical method for determining auxins in complex matrices is still of critical importance. Trace analyses of plant tissues and other complex matrices often rely on selective sample pre-treatment. Solid-phase microextraction (SPME) is a simple, time-efficient, and solvent-free sample pre-treatment technique based on the partitioning of analytes between the sample matrix and the polymer film coating on a substrate [15; 16]. Recently, SPME approaches based on the use of highly selective, adsorbent molecularly imprinted polymers (MIPs) have been found to be attractive. MIPs are the only generic synthetic polymeric materials that possess properties like those of natural receptors [17; 18]. MIPs are prepared by the co-polymerization of a cross-linker with functional monomers in the presence of a template molecule. After the removal of the target compound, binding sites are created in the polymer matrix that are capable of subsequent molecular recognition [19; 20]. The MIPs can rebind selectively with the template and its analogous structures. To date, all of the SPME techniques performed manually or automatically have been used in combination with systems such as GC [21; 22], HPLC [23], and CE [24]. In these approaches, the analyte is usually required to be desorbed from the coating by heating or dissolving for analysis. The purpose of this work was to use selective MIPs as extraction coatings for the direct detection of auxins by their intrinsic fluorescence. Quartz chips were the appropriate substrate candidates for this purpose because modification of the silica surface has been intensively studied [25], and it can also facilitate UV and fluorescence detection. The MIP coatings with satisfactory thickness were prepared through the chemically attached silyl acrylate monomer on the quartz chips using the multiple co-polymerization method, shown in Figure 1.  
The analyte was selectively retained on coatings and then quantified directly on the chip using a typical fluorescence spectrophotometer. Using this method, the high selectivity of the MIPs was combined with the high sensitivity of fluorescence detection. This combination has been observed to be favorable in previous studies [26].