*2.2. Instruments*

Scanning electron microscopy (SEM, SU1510, Hitachi, Tokyo, Japan), transmission electron microscopy (TEM, JEOL-2010 FEF, Tokyo, Japan), Fourier transform infrared (FT-IR) spectrophotometry (Tensor 27, Bruker, Karlsruhe, Germany), and fluorescence spectrometry (Lumina, Thermo Scientific, Waltham, MT, USA) were used to characterize the polymers.

#### *2.3. Bacterial Strains and Cultivation of Strains*

*Listeria monocytogenes* strain ATCC 19111, *S. aureus* strain ATCC 25923, *E. coli* O157:H7 strain ATCC 35150, and *Salmonella* strain ATCC 14028 were obtained from the American Type Culture Collection (ATCC). All bacteria stains were cultivated in Luria-Bertani (LB) broth at 37 ◦C with shaking overnight. The bacterial cells were suspended in phosphate bu ffer solution (PBS bu ffer) under gentle vortex mixing [33].

For the Pickering emulsion polymerization, the *L. monocytogenes* were cultivated to an OD600 (the optical density was measured at 600 nm by a UV spectrophotometer) of about 0.6 to 0.8. After centrifugation at 5000 rpm for 5 min, the bacteria cells were collected and washed three times with PBS bu ffer. Finally, the bacteria were resuspended in PBS and adjusted to a QD600 of 2, this being the template in Pickering emulsion polymerization.

#### *2.4. Synthesis of CdTe QDs*

The CdTe QDs were synthesized following the method given in [34]. Briefly, 53.2 mg of Cd(CH3COO)2·2H2O was dissolved into 50 mL of deionized water in a 100 mL flask. Then, 18 μL of TGA was added and the pH value was adjusted to 10.5 witha1M NaOH solution. After stirring for 5 min, 50 mL of 0.2 mg ml−<sup>1</sup> K2TeO3 solution and 80 mg of NaBH4 were successively added to the solution. Next, the reaction proceeded for another 5 min, and the flask was attached to a condenser and refluxed for 1 h at 100 ◦C. After cooling to room temperature, the CdTe QDs with an emission peak at 556 nm were obtained and stored at −4 ◦C for subsequent experiments.

#### *2.5. Preparation of N-Acrylchitosan (NAC) and NAC-QD Complex*

A NAC preparation method was followed according to the literature with slight modifications [23]. Here, 1.61 g of chitosan was dispersed in 40 mL of DMAC and named solution A. Solution A was stirred for 12 h at room temperature, purged with argon gas for 10 min at 0 ◦C, and treated with 600 μL of triethylamine under continuous stirring. Solution B was prepared by adding 322 μL of acryloyl chloride to 5 mL of DMAC. This was then added dropwise into solution A. The mixture was stirred at 0 ◦C for 4 h followed by stirring at 25 ◦C for 20 h, and successively washed in DMAC, dichloromethane, and methanol. Finally, the NAC powder was collected by filtration and dried in a vacuum chamber.

The NAC-QD complex was prepared as follows: 1.5 mg of NAC was dissolved in 5 mL of acetic acid solution (0.03%). Then, 5 mL of CdTe QDs and 5 mg of EDC were separately added dropwise to the above solution and stirred overnight at room temperature.

#### *2.6. Synthesis of MIPs by Pickering Emulsion Polymerization*

Bacterial-stabilized Pickering emulsions were prepared using a method similar to that described by Shen et al., except that the NAC-QD complex was used to replace NAC to form a bacteria-pre-polymer complex [23]. First, 900 μL of the NAC-QD solution and 300 μL of the *L. monocytogenes* PBS suspension (OD600 = 2) were mixed; the mixed solution was set aside for 30 min to form the NAC-QD bacteria network, which was used as the water phase in the Pickering polymerization. Second, 0.6 mL of TRIM, 0.6 mL of DVB, 6.2 mg of BPO, and 31.3 μL of DMA were added in another 5 mL tube as the oil phase. Subsequently, the two phases were mixed by vigorous hand shaking for 10 min, such that a stable Pickering emulsion was established. The Pickering emulsion was stabilized via the NAC-QD-bacteria network and was kept still for 24 h at room temperature without agitation. To remove the template, the resulting polymer beads were successively washed with 10% acetic acid, 1% SDS, water, and methanol. After drying in a vacuum chamber, MIPs with specific binding sites for *L. monocytogenes* were obtained.

As a control, non-imprinted polymer (NIP) beads were also prepared using the same procedure, with the exception of the absence of *L. monocytogenes*.

#### *2.7. Analysis of Bacterial Binding Properties*

Adsorption kinetic data were tested as follows: 5 mg of theMIPs was added to 1 mL *L. monocytogenes* PBS solution (1.0 × 10<sup>5</sup> colony forming unit (CFU) mL−1). The supernatant was removed after gently shaking for di fferent periods of time (0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, and 7 h) and allowing the sample to settle for 3 min. The target bacteria absorbed on the polymer beads were eluted with 1 mL PBST (PBS containing 5 mL L−<sup>1</sup> Tween 20) solution, and the number of bacteria in elution was analyzed by viable cell counting. The binding amount was calculated as followed:

$$Q = \frac{C\_s}{M} \times V$$

Here, *Q* (CFU mg<sup>−</sup>1) is the adsorption capacity and *C*s is the bacteria concentration in the elution. *V* (mL) is the volume of bacterial suspension and *M* (mg) is the adsorption weight.

For the static adsorption testing, 5 mg of MIPs/NIPs were weighed into 1 mL PBS bu ffer with di fferent concentrations of bacterial suspension (7.5 × 101, 1.6 × 102, 7.6 × 102, 1.5 × 103, 7.5 × 103, 1.5 × 104, 3.8 × 104, 7.5 × 104, 1.6 × 105, and 7.5 × 10<sup>5</sup> CFU mL−1). After shaking for 2 h, the supernatant was removed and the binding amount of *L. monocytogenes* was recorded.

The selectivity study was conducted using two strategies depending on purpose. For visual studies, 5 mg of MIPs were incubated in 1 mL *L. monocytogenes* and *S. aureus* for 2 h under the same conditions, respectively. After removing the supernatant and Gram staining the MIPs, *L. monocytogenes* and *S. aureus* assembled on the polymer beads were directly observed by optical microscope. For a detailed evaluation, 5 mg of MIPs or NIPs were suspended in a 2 mL mixture containing *L. monocytogenes*, *E. coli*, *Salmonella*, and *S. aureus* (each 4.0 × 10<sup>4</sup> CFU mL−1). The amounts of *L. monocytogenes*, *E. coli*, *Salmonella*, and *S. aureus* binding on the polymer beads were recorded via the plate-coating method.

#### *2.8. Aplication to Real Samples*

Here, 1 mL of milk was directly inoculated with *L. monocytogenes* at final concentrations of 1.0 × 10<sup>3</sup> and 1.0 × 10<sup>5</sup> CFU mL−1. After adding 5 mg of MIPs, the mixture was thoroughly shaken for 2 h and sedimented for 3 min. After removing the supernatant, the residual MIPs were dried in a vacuum chamber and the fluorescence was directly observed via a fluorescence microscope.

One gram of pork was inoculated with 5 mL of 1.0 × 10<sup>3</sup> and 1.0 × 10<sup>5</sup> CFU mL−<sup>1</sup> of *L. monocytogenes* and set aside overnight at 4 ◦C. Afterwards, 5 mL of the sample solution was collected and mixed with 5 mg of the MIPs. After thoroughly shaking for 2 h and sedimenting for 3 min, the fluorescence color of the residual MIPs was observed using a fluorescence microscope.
