Food safety is paramount to all of us. Aflatoxin B1 (AFB1) is a secondary metabolite produced by Aspergillus flavus(Wang et al. 2021). The fungal mycotoxin is the most toxic mycotoxin known, with mutagenic(Zavala-Franco et al. 2020), teratogenic(Oliveira et al. 2021), immunosuppressive(Myndrul et al. 2021) and carcinogenic effects( Azaiez et al. 2014; Rushing and Selim 2019). AFB1 is classified as a Group I carcinogen by the International Agency for Research on Cancer( He et al. 2019). Low-cost, stable, and large-scale technology that directly detects AFB1 in food samples is needed to realize real-time monitoring and control of AFB1 contamination of food. Current methods to detect AFB1 include liquid chromatography-tandem mass spectrometry (LC-MS/MS), high-performance liquid chromatography, and enzyme-linked immunosorbent assays (ELISA) (Zhang et al 2018). The latter is the most commonly used detection method for AFB1 because of its convenience and highly sensitive detection capability(Lei et al. 2020; You et al. 2021). The enzymatic process of ELISA permits signal amplification(Jiang et al. 2020). Natural enzymes have high catalytic efficiency(Shen et al. 2022) and specificity under physiological conditions(Li and Head-Gordon 2021). However, disadvantages that include high production and purification costs and variability limit their applications.
Nanozymes are nanomaterials with intrinsic enzyme-like characteristics. Nanozymes that include metals(Yu et al. 2019), metal compounds(Lin et al. 2021), and metal-organic framework (MOF)(Shen et al. 2022) have better stability and lower cost than natural enzymes. In addition, other unique properties of nanomaterials can endow nanozymes with more functions(Xu et al. 2020). Therefore, The nanozyme linked immunosorbent assay (NLISA) has attracted increasing attention for analytical detection due to its excellent specificity and low-cost. Among the various types of nanozymes, porous materials like MOFs possess many active sites, and high specific surface areas(Gorle et al. 2021; Li et al. 2021), and have excellent potential for catalysis(Huang et al. 2021). Therefore, MOFs can serve as an ideal nanozyme to improve the detection stability of NLISA(Wang et al. 2022). Recently, our group used the MIL-88 MOF to replace natural enzymes, such as horseradish peroxidase (HRP), to create an MOF-linked immunosorbent assay (MOFLISA)(Xu et al. 2021a). However, most MOF crystals have a strong tendency to aggregate in solution. Their poor dispersion(Lee et al. 2019; Xu et al. 2021b) hampers their detection reproducibility(Zhao et al. 2015). Therefore, a strategy to improve the sensitivity and stability of NLISA for direct detection of AFB1 in foods is imperative.
Inspired by previous work, we found that acid modulators can alter the surface potential of MOFs with carboxyl ligands(Jiang et al. 2019), which enhances dispersion(Prabhu et al. 2019). Herein, we describe a strategy that uses acetic acid modulation. The inhibited deprotonation of iron-porphyrin linkers increases the surface potential, thereby enhancing the dispersion of the traditional PCN-223(Fe). The novel NanoPCN-223(Fe) has excellent peroxidase activity and colloidal stability. An enhanced dispersion MOFFLISA (Ed-MOFLISA) based on NanoPCN-223(Fe) nanozyme catalysis was successfully achieved to improve the detection reproducibility of AFB1. The findings indicate the suitability of the novel NanoPCN-223(Fe) nanozyme in food safety control.