Due to increasing food‐safety issues, exploiting efficient approaches for food quality assessment and instrumentation has attracted concerns worldwide. Herein, a smart evaluation system based on a fluorescent metal–organic framework (MOF) is developed for real‐time visual monitoring of food freshness. Via post‐synthetic modification, a ratiometric fluorescent MOF probe is constructed by covalently coupling fluorescein 5‐isothiocyanate (5‐FITC) with NH2‐rich lanthanide MOF. The probes exhibit a dual‐emissive‐responsive to biogenic amine, resulting in an increase in FITC emission along with a decrease in Eu3+ emission accompanied by a clear distinguishable color transition from orange red to green. After doping the probes on a flexible substrate, the obtained MOF composite film can be integrated with a smartphone‐based portable platform easily. It is proved that this smart evaluation system can be used for on‐site inspection of the freshness of raw fish samples. This work develops a fluorescent MOF‐based smart evaluation system as a novel platform for application in food monitoring, which not only has enormous economic value but also holds great public health significance.

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Antibiotics abuse has caused various problems threatening human health and ecological environment. Monitoring antibiotics residual levels is of great significance, yet still challenging for quantitative point-of-need testing with high-sensitivity and visual capability. Here we developed a competitive lateral flow immunoassay (CLFIA) platform with flexible readout for enrofloxacin (ENR), a regularly added antibiotic. To overcome the limitation of low sensitivity of traditional colloidal gold-based CLFIA, the three-dimensionally assembled gold nanoparticles (AuNPs) within dendritic silica scaffold were fabricated as signal reporters. The assembly structure effectively retained the intrinsic absorption features of hydrophobic AuNPs and greatly enhanced the light extinction ability of a single label for signal amplification. The obtained CLFIA strips can not only achieve qualitative screening of ENR at a very low concentration by naked eye (cutoff value: 0.125 ng/mL), but also enable ultrasensitive quantification of ENR by an optical scanner (limit of detection: 0.00195 ng/mL) or a smartphone (limit of detection: 0.0078 ng/mL). Moreover, to elaborate the visual inspection degree of CLFIA against traditional yes/no interpretation, a novel multirange gradient CLFIA strip was prepared for visually semiquantitative identification of ENR with four concentration ranges. The novel CLFIA platform demonstrated sensitive, specific, and reliable determination of ENR with flexible signal readout and provides a potential and invigorating pathway to point-of-need immunoassay of antibiotics.

Immunological detection of small molecules in a point-of-care (POC) format is of great significance yet remains challenging for accurate visual discrimination and quantitative analysis. Here, we report a novel hue recognition competitive fluorescent lateral flow immunoassay (HCLFIA) strip that allows both visual and quantitative detection of aflatoxin M1 (AFM1). The HCLFIA strip works on the basis of the ratiometric change of emission, arising from the overlap of fluorescence signals of two nanocomposites tagged with probe antibodies and coated antigens. A visually discernible orange-red-to-green fluorescence color change allows the naked eye semiquantitative readout of AFM1 around the threshold concentration (0.05 ng mL–1), yielding a visible detection limit of 0.02 ng mL–1. Moreover, using a custom smartphone-based device and color chart analysis, ultrasensitive quantitative detection of AFM1 can be achieved with a low limit of detection at 0.0012 ng mL–1, which is considerably better than those of the previously reported colorimetric and fluorescent strips. The accuracy performed in spiked milk samples ranged from 97.91 to 113.12% with a coefficient of variation below 7.8%, showing good consistency with the results from isotope dilution liquid chromatography–tandem mass spectrometry. Thanks to the unique hue recognition scheme, the HCLFIA strip holds great potential for POC detection of small molecules.

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