**1. Introduction**

Multifunctional polymers with special physical and chemical properties (such as optical, electrical, thermal, chirality, and magnetic characteristics) have drawn increasing attention due to their potential application in numerous areas [1–4]. As a kind of luminescent nanomaterial, quantum dots (QDs) have high quantum yields, excellent photostability, broad excitation and narrow symmetric emission spectrum, and a size-dependent band gap, therefore, they have attracted considerable attention [5,6]. On the other hand, magnetic nanoparticles (MNPs), which are used as an important magnetic nanomaterial, have grea<sup>t</sup> potential applications in magnetic resonance imaging (MRI), drug delivery, catalysis, chemo/biosensors, and medicine diagnosis [7–10]. MNPs have a large surface area and high mass transference based on their size, which enables them to promote fast electron transfer [11–13]. Moreover, MNPs can be directly separated; this facilitates ultra-trace analyte enrichment without going through centrifugation and filtration steps in bioassay, and improves the detection efficiency and sensitivity.

By combining quantum dots with magnetic nanocrystals, an advanced nanocomposite polymer with excellent functionalities can be prepared, which simultaneously integrates the optical and magnetic properties [14,15]. A magnetic nanoparticle coupled with quantum dots can be directly separated and is then able to generate readable optical signals for analysis. The ability to combine the purification process with the detection procedure in one step means that magnetic quantum dot polymers have a promising future and novel applications in bio-detection, biomedicine, drug delivery, and environmental monitoring [16–18]. However, when dealing with a complex matrix, the synthesized magnetic quantum dots demonstrate nonspecific binding in the separation process, which results in high level background fluorescence response and restricts their specificity and sensitivity for analysis. To enhance the specificity and sensitivity of magnetic quantum dots, a molecular imprinted polymer (MIP) layer can be loaded on the surface of the magnetic quantum dot nanocomposite to tailor the selectivity of analytes using molecular imprinting technology [19–22].

Molecular imprinting is a well-established technique to design an artificial molecular recognition unit that involves polymerizing functional monomers in the presence of template molecules [23]. MIPs exhibit excellent selectivity and a ffinity with the template molecules [24]. The MIP layer coated on the surface of magnetic quantum dots will introduce the selectivity recognition sites to the nanocomposites and prevent interfering molecules from binding with the nanocomposites. MIPs have been introduced as promising recognition elements with high selectivity for detecting trace analyte. Zhang et al. developed imprinted polymer coating CdTe quantum dots for specific recognition of BHb [25]. Zhao et al. prepared ZnS QDs-based molecularly imprinted polymer composite nanospheres for fluorescent quantification of pesticides [26]. Zhao et al. used molecularly imprinted water-soluble CdTe QDs for Listeria monocytogenes detection in food samples [27]. As CdTe QDs su ffer from bio-compatibility issues, ZnS QDs based MIPs with low biotoxicity are preferable [28]. Furthermore, magnetic nanoparticles involving fluorescent multifunctional nanoparticles can facilitate magnetic separation, also the fluorescent response is quicker because the magnetic nanoparticles promote faster electron transfer. So together with MIPs' selectivity, this novel multifunctional sensor is expected to demonstrate improved properties for trace target detection.

In this work, an innovative magnetic fluorescent sensor based on FeOx/ZnS@MIPs was prepared for the separation and detection of trace BPA in complex samples. Bisphenol A (2,2-bis(4-hydroxyphenyl)propane) is an estrogenic endocrine disruptor. It is a common chemical that has been extensively used in the manufacture of polycarbonate plastics and epoxy resins for the linings of food, beverage packaging, and other consumer products [29]. Increasing evidence indicates that BPA can migrate from containers into foods and beverages, and trace residue levels of BPA can be released into environmental water through di ffusion or degradation, which carries a high risk of causing adverse effects on human reproductive health and the ecosystem [30,31]. Because of BPA's ubiquity in nature and its potential implications in human health and the ecological environment, various analytical methods have been developed for monitoring or detecting BPA [32–41]. However, many of those analytical techniques for BPA need sophisticated instrumentation, and the procedures involve pre-concentration, extraction, purification or derivatization [42–44]. Those methods are costly and time-consuming, and require well trained and experienced personnel to guarantee the accuracy of results. Therefore, it would be highly advantageous to develop a low-cost, selective method for the convenient and rapid separation and detection of BPA. The prepared FeOx/ZnS@MIP enables fluorescence analysis and the e fficient separation of BPA without any expensive instruments or time-consuming procedures. Based on the fluorescence quenching being proportional to the concentration of the target molecule, FeOx/ZnS@MIP was successfully applied to the direct fluorescence sensing of BPA without any further pretreatment. Notably, FeOx/ZnS@MIP has the advantage that it can be easily recycled and rapidly removed from the trace contaminant in the environment. The FeOx/ZnS@MIPs could specifically bind and magnetically enrich trace BPA, which avoids interfering substances in complex matrices and enhances the detection e fficiency and sensitivity. Additionally, the proposed methods for the

preparation of FeOx/ZnS@MIPs exhibits promising potential to isolate and detect proteins and other target molecules in biology detection applications.

#### **2. Materials and Methods**
