## 1 Introduction  
Foodborne pathogens contamination is one of the main sources of food safety problems [1]. Among the genus _Listeria_, _Listeria monocytogenes_ and _Listeria iwanovii_ have been classified as important human and animal pathogens and are widely distributed in food [2]. Human infections are caused by \(L\). _monocytogenes_ and \(L\). _iwanovii_ mainly through eating contaminated food [3], such as meat products [4], vegetables [5], dairy products [6], and seafood [7], while animal infections are caused by the ingestion of organisms through contaminated vegetation. Human infection with pathogenic _Listeria_ spp. can cause severe symptoms including sepsis, meningitis, and miscarriage [8], mainly affecting the elderly, pregnant women, newborns, and immunocompromised people [9], with a high fatality rate (about 20%) [10, 11]. Some countries, such as EU member states (e.g., Germany, France, and The Netherlands), tolerate a contamination limit of 100 CFU/g of \(L\). _monocytogenes_ in ready-to-eat foods during their shelf life, while other countries, including the US and Italy, apply a zero-tolerance policy and require an absence of \(L\). _monocytogenes_ in 25 g of foodstuff [12; 13]. In order to effectively reduce the harm of _L. monocytogenes_ and _L. Ivanovii_, it is particularly important to improve the detection sensitivity of pathogenic _Listeria_ spp. in foodstuffs. Sensitive and rapid screening for these two pathogenic _Listeria_ spp. to prevent outbreaks is therefore needed. Polymerase chain reaction (PCR) and its derivatives are widely used methods for bacterial identification and detection, including real-time PCR, nested PCR, and multiplex PCR (mPCR) [14]. Among them, mPCR allows the simultaneous identification and analysis of multiple bacteria in a single reaction tube [15]. Many methods based on mPCR have been reported for simultaneous analysis and screening of pathogens. For example, [PERSON] et al. [16] reported an mPCR assay for the concurrent screening of _Escherichia coli_ O175:H7, _Salmonella_ spp., and _L. monocytogenes_ in liquid whole eggs with a detection limit of 10 cells/25 g after overnight pre-enrichment. However, although mPCR methods were capable of identifying and analyzing multiple pathogens at the same time with high sensitivity [17], the long pre-enrichment process is still necessary and is not suitable for rapid screening and diagnosis of bacterial infection. To enhance the detection sensitivity and shorten the screening time, it is particularly important to improve the sampling technology of low-level target pathogens and reduce or eliminate the interfering components in the food matrix. The enrichment strategy based on magnetic nanoparticles (MNPs) can effectively separate the target from complex samples [18]. Among them, the immunomagnetic enrichment strategy has been generally used in pathogen separation due to its advantages of high specificity. An impedance biosensor was established by [PERSON] et al. [19] for rapid detection of _L. monocytogenes_ in lettuce, where the limit of detection (LOD) was 30 CFU/mL after immunomagnetic enrichment for 47 min. However, the expensive, unstable, and difficult-to-store properties of antibodies limit their application in underdeveloped regions. Therefore, a number of low-cost, stable antibody alternatives have been developed for simultaneous recognition and separation of multiple bacteria, such as antibiotics [20], lectins [21], aptamer [22], and polymers [23]. Studies have shown that the bacterial surface is rich in lipopolysaccharide, tichoic acid, and other components, which make the bacterial surface negatively charged [24]. Among many bacterial recognition reagents, polymers are a class of synthetic reagents that can be customized to contain different functional groups. Therefore, MNPs modified with positively charged polymers can bind to bacterial surfaces through electrostatic interactions. Compared with other interaction modes, charge-based interactions usually have faster response speed and broader target binding capacity.