Background Loop-mediated isothermal amplification (LAMP) is a simple, low-cost, and instrument-free assay, which is highly adaptable for the detection of foodborne pathogens. However, current methods have a high background, making it difficult to achieve sensitive on-site detection. Results Herein, LAMP-CuNCs assay with a low background signal was established. LAMP amplicons were used as the templates for the synthesis of copper nanoclusters (CuNCs), and LAMP results were determined by the fluorescence intensity of the amplicons-CuNCs. The stability of LAMP amplicons templated CuNCs was improved by the addition of 1.5 g/mL fructose, which effectively prolonged the fluorescence lifetime. The detection limit of Salmonella DNA was 756 pg/μL, and the sensitivity and specificity of this method were 12/12 and 12/12, respectively. This method could detect Salmonella at a minimum concentration of 1910 CFU/mL in spiked salmon samples. Significance The study provided a method that can quickly obtain results within 16 min for detection of genomic DNA and visual inspection under a 365 nm UV flashlight. In addition, this method could also be used to detect Listeria monocytogenes , Vibrio parahaemolyticus , and Escherichia coli .
pH sensors based on up-conversion nanoparticles (UCNPs) are widely studied due to their effective elimination of background signals. However, ratiometric pH measurement depending on blue and red luminescence under NIR irradiation has been seldom reported for the lack of simultaneous strong blue and red emissions for traditional UCNPs. In this work, we designed NaGdF4:Yb,Tm@NaYF4:Yb,Eu@NaYF4:Yb,Nd@NaYF4 core–triple shell (CTS) UCNPs as fluorescent materials to realize blue/red ratiometric pH measurement. On the basis of Gd3+-mediated interfacial energy transfer and Yb3+-mediated energy migration, CTS particles present intense luminescence and a high red/blue (615 nm/450 nm) peak intensity ratio of 0.47 at 808 nm excitation. Composed of these particles and pH indicator bromocresol green, the pH sensor exhibits ratiometric responses in a pH range of 4–7 according to blue/red luminescence intensity ratios, avoiding the common errors as well as potential mutual fluorescence signal interference. Owing to strong overall luminescence and additional red emission of CTS UCNPs distinctly improving the signal-to-noise ratio, this ratiometric sensor reveals high sensitivity. Moreover, the employed excitation wavelength of 808 nm can not only eliminate autofluorescence signals, but also alleviate severe temperature rise in biosamples under continuous irradiation, ensuring accurate pH determination. More intriguingly, a CCD RGB camera serves as a collector to record luminescence signals, further promoting commercial feasibility. The successful application of CTS UCNPs on sensors indeed realizes blue/red ratiometric measurement towards pH under 808 nm irradiation, also pointing out a novel way for pH sensors with high sensitivity and accuracy.
危险品化学品经营许可证（带存储）