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[Display omitted] • A colorimetric sensor for S. aureu s detection based on HCR and G-quadruplex DNAzyme. • Cascade amplification was successfully used to detect S. aureu s in milk samples. • Combining the sensor with the APP we developed, on-site detection can be achieved. • Providing a new reference for the detection of pathogens in milk. • Expanding the application of HCR combined with G-quadruplex in pathogens detection. As a foodborne pathogen, Staphylococcus aureus (S. aureus) poses a serious threat to the dairy industry. A colorimetric sensor based on hybridization chain reaction (HCR) and G-quadruplex for the detection of S. aureu s is reported. The aptamer of S. aureus was hybridized with the target probe and fixed on the magnetic particles. When S. aureus was present, aptamers preferentially coupled with S. aureus. The released target probe triggered the HCR to form long-chain DNAs with multiple G-quadruplex. S. aureus can be quantitatively detected by measuring the catalytic signal of G-quadruplex. Cascade amplification enabled rapid and sensitive detection of S. aureus with a detection limit of 4.4 cfu·mL−1. Meanwhile, combining this method with the smartphone application (APP) developed by us can achieve on-site detection. In addition, the sensor has a good performance in the detection of S. aureus in milk samples. This method provides a new reference for detecting pathogens in milk and expands the application of HCR combined with G-quadruplex in pathogens detection. [ABSTRACT FROM AUTHOR]

• A ratiometric colorimetric method for AA based on analyte-triggered AgNPs aggregation was established. • The proposed method exhibited a wide AA detection range from 1 μM to500 μM, and a low detection limit of 0.7 μM. • AA can be easily detected in various fruit juices with 10 min employing the proposed one-step method. A simple, fast, one-step method is described for ratiometric colorimetric detection of ascorbic acid (AA) based on 4-mercaptophenylboronic acid (4-MPBA) and silver nanoparticles (AgNPs). In the presence of AA, the aggregation process of AgNPs can be triggered and accelerated, due to the interaction between 4-MPBA and the cis 1,2-diol moieties of AA through a reversible esterification, resulting in a distinguish color change from yellow to brownish red. The AA concentration-dependent color change can be quantified by the bare eyes or a UV–Vis spectrometer. The whole AA detection procedure was able to complete in 10 min with an excellent linear relationship (1–500 μM) and a low limit of detection (0.70 μM). The proposed approach was also used to accurately evaluate AA levels in orange juice. In our perception, this assay is rapid, sensitive, and specific, which demonstrates its potential on constructing biochemical and clinical sensors. [ABSTRACT FROM AUTHOR]