Immunochromatographic assay (ICA) is widely applied in various fields. However, severe matrix interference and weak signal output present major challenges in achieving accurate and ultrasensitive detection in ICA. Here, a polydopamine (PDA)-mediated magnetic bimetallic nanozyme (Fe 3 O 4 @PDA@Pd/Pt) with peroxidase-like activity was synthesized and used as a probe in ICA. The magnetic property of Fe 3 O 4 @PDA@Pd/Pt enabled effective magnetic enrichment of targets, thereby reducing the matrix interference in the sample. PDA coating on the magnetic bimetallic nanozyme was employed as a mediator and a stabilizer. It improved the catalytic ability and stability of the magnetic bimetallic nanozyme by providing more coordination sites for Pd/Pt growth and functional groups (−NH and −OH). In addition, the Pd/Pt bimetallic synergistic effect could further enhance the catalytic ability of the nanozyme. A method was developed by integrating Fe 3 O 4 , PDA, and Pd/Pt into Fe 3 O 4 @PDA@Pd/Pt as a probe in ICA. With the proposed method, human chorionic gonadotropin and Escherichia coli O157:H7 were successfully detected to be as low as 0.0094 mIU/mL in human blood serum and 9 × 10 1 CFU/mL in the milk sample, respectively. This method may be readily adapted for accurate and ultrasensitive detection of other biomolecules in various fields.

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Conventional fluorescent microspheres (CFMs) have the disadvantages of low photoluminescence intensity (aggregation-caused quenching) and poor antibody conjugation. Herein, we achieved the improved performance of lateral flow immunoassay (LFIA) based on the high-fluorescent property of aggregation-induced emission fluorescent microspheres (AIEFMs) and biofriendly antibody coupling strategy of the polydopamine (PDA) layer. Although the PDA layer quenches the fluorescence intensity of AIEFM by Förster resonance energy transfer (FRET), quenching can be effectively controlled by ingenious adjusting of the thickness of the PDA. The PDA-coated AIEFM (AIEFM@PDA), which not only retained the strong fluorescence of AIEFM but also improved the antibody coupling efficiency and reproducibility of LFIAs, was successfully applied in sandwich and competitive LFIAs for the highly sensitive detection of pathogenic bacteria (Escherichia coli O157:H7) and antibiotics (enrofloxacin). In comparison with the CFM method, the proposed AIEFM@PDA-LFIA for the detection of E. coli O157:H7 and enrofloxacin could enhance the sensitivity by 40 times and 20 times, respectively. In addition, AIEFM@PDA-LFIA was further used for the detection of E. coli O157:H7 in river water, apple juice, and milk with satisfactory recoveries from 82.24 to 123.02% and enrofloxacin in pork, chicken, fish, and beef with satisfactory recoveries from 75.67 to 120.89%. The proposed AIEFM@PDA-LFIA showed excellent potential in rapid detection applications.

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