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It is of great significance to establish a simple method for sensitively detecting metal ions and antibiotics for food safety. Herein, two crystalline polyimide covalent organic frameworks (COFs) were constructed via a green method, in which no organic solvents were used. Results suggested that both COF-1 and COF-2 with π-conjugated frameworks emitted strong fluorescence originating from the n−π* transition in N,N-dimethylformamide and the alkaline aqueous solution. More interestingly, both COF-1 and COF-2 showed excellent sensing performance for various metal ions and typical antibiotics. Taking COF-1 as the specific research object, the as-synthesized COF-1 exhibited noticeable turn-off fluorescence behaviors for 10 metal ions and 2 antibiotics. A high linear correlation coefficient, a wide linear range, and a low detection limit were achieved in real samples. The aggregation effect and π–π reaction were the possible fluorescence quenching mechanisms. In short, this work provides insights into the synthesis and application of fluorescent sensors based on COFs in food detection fields.

Macadamia nut contains important food allergens that potentially cause allergic reactions with severe adverse effects in infants and adults. Reliable and accurate detection of macadamia is critical to avoid allergic reactions. However, knowledge on macadamia allergen is scarce and a reliable detection method has not been reported, yet. In this study, an unbiased immunization and selection strategy was employed to select nanobodies (Nbs) recognizing specifically macadamia allergen, as well as to establish a detection method to unveil a macadamia protein contamination. An alpaca was immunized with a crude protein extract of macadamia followed by construction of a Nb library from its lymphocytes. The panning and screening of this immune Nb repertoire resulted in the selection of six target-specific Nbs. Nb-mediated immuno-capturing combined with mass spectrometry allowed us to identify the target as the macadamia vicilin-like antimicrobial peptides 2–3 (MiAMP2), a novel food allergenic protein abbreviated as Mac i 1. Later on, an immunoassay of a heterologous sandwich ELISA method based on the selected Nb-pairs was established, providing a linear response in the range of 0.442–2,800 μg/mL and with a limit of detection of 27.1 ng/mL. The dedicated immunoassay has been verified by detecting the antigen spiked in food samples. Our study provided evidence for the successful application of the unprejudiced strategy to retrieve Nbs against a priori undefined macadamia allergen. These target-specific Nbs were used to design a highly reliable and effective immunoassay.

Integration of novel bio-/nanostructures as effective sensing platforms is still of great significance for robust and rapid analysis. Herein, a novel metal−organic framework-derived NiCo 2 O 4 was synthesized via a feasible templating method. Significantly, redox couples of both Ni 3+ /Ni 2+ and Co 3+ /Co 2+ provided richer oxidation−reduction reactions, thereby leading to an enhanced catalytic activity. Furthermore, NiCo 2 O 4 as an enzyme mimic with peroxidase-like activity and oxidase-like activity could oxidize colorless thylbenzidine (TMB) to blue oxTMB in the absence of H 2 O 2 . Thus, a sensitive chromogenic sensing platform for detecting Fe 2+ , thiourea, cysteine (Cys), and epigallocatechin-3-gallate (EGCG) was proposed. The colorimetric detection methods exhibited great features of low limit of detection (LOD) and broad linear range. Owing to the complexation reaction, the chromogenic sensing system of TMB + NiCo 2 O 4 + Cys achieved effective detection of Cu 2+ and Mn 2+ with the LODs of 0.0022 and 0.0181 mM, respectively. Developed detection methods with wide linear ranges of 0.008−0.1 mM for Cu 2+ and 0.08−1 mM for Mn 2+ had excellent practical potential. Similarly, the reaction system of TMB + NiCo 2 O 4 + EGCG could achieve the colorimetric detection of Cu 2+ and Fe 3+ . The great chromogenic sensing performance for detecting Cu 2+ and Fe 3+ with a broad linear range and a low LOD could be also realized.

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