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With the rapid development of animal husbandry, animal food safety issues are increasingly exposed. Detecting pathogenic bacteria and residual antibiotics in animal food is of great significance for the early detection and regulation of harmful substances that threaten food safety. However, developing a fluorescent sensor that can detect both pathogenic bacteria and antibiotics is challenging. In this study, an interesting dual-channel ratiometric nanoprobe (CDs-Eu) based on europium-functionalized carbon dots was developed to realize the visual detection of Bacillus anthracis marker (DPA) and tetracycline antibiotics (TC) in a water environment under different excitation channels. This method had high sensitivity, comprehensive response range, anti-interference ability, and visualization for detecting DPA and TC. Combined with intelligent phone color scanning applications, a portable agarose gel nanosensor was designed to achieve multicolor on-site assessment of DPA and TC. In addition, an advanced three-to-six logic gate analysis method was also developed, which was expected to achieve intelligent sensing of DPA and TC in food safety. • A dual-channel ratiometric nanoprobe based on europium and carbon dots. • Realization of TC and DPA visual sensing through two channels. • Combined application of gelled detection device and intelligent APP. [ABSTRACT FROM AUTHOR]

• A novel multicolor probe based on Zif-8 and rare earth. • Realization of TC visual detection with high recognition. • Ultrafast POCT detection of TC in various water and food samples. • Combined application of gelled detection device and intelligent APP. In this work, a high-precision visual and point-of-care testing (POCT) ratiometric fluorescent nanosensor for TC was constructed by embedding fluorescein (FL) into l -histidine modified ZIF-8 (LZIF-8) and chelating with rare earth citrate complex. Upon exposure to TC, the coordination and energy transfer between Eu3+ and TC make Eu3+ sensitized emission characteristic red fluorescence, while without prejudice to the emission peak intensity of FL. This ratiometric fluorescent probe with stable reference signal had the characteristics of high sensitivity (ultralow LOD = 5.99 nM) and selectivity and fast response kinetics (within 20 s). The high-bright fluorescence emission was beneficial to human eye recognition and it can realize semi-quantitative detection of TC in eggs, meeting the requirements of household use. In addition, the color can be read and analyzed quickly with the help of smart phone color analysis APP, and the semi-quantitative concentration of TC can be determined more conveniently. [ABSTRACT FROM AUTHOR]

Based on a novel signal amplification strategy by catalytic hairpin assembly and displacement of G-quadruplex DNA, an enzyme-free, non-label fluorescent aptasensing approach was established for sensitive detection of four tetracycline veterinary drugs in milk. The network consisted of a pair of partially complementary DNA hairpins (HP1 and HP2). The DNA aptamer of four tetracycline veterinary drugs was located at the sticky end of the HP1. The ring region of HP1 rich in G and C could form a stable G-quadruplex structure, which could emit specific fluorescence signal after binding with the fluorescent dye and N-methylmesoporphyrin IX (NMM). When presented in the system, the target analytes would be repeatedly used to trigger a recycling procedure between the hairpins, generating numerous HP1-HP2 duplex complexes and displacing G-quadruplex DNA. Thus, the sensitive detection of target analytes was achieved in a wide linear range (0-1000 μg/L) with the detection limit of 4.6 μg/L. Moreover, this proposed method showed high discrimination efficiency towards target analytes against other common mismatched veterinary drugs, and could be successfully applied to the analysis of milk samples.Schematic of target analyte detection based on catalytic hairpin assembly reaction and displacement of G-quadruplex [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative hydrostable perovskite-europium hybrid fluorescence sensor was designed and prepared. • The perovskite-europium nanosensor can realize TC sensing in various water samples. • The sensor had a good linear response in the range of 0–25 μM, and the LOD was 11.15 nM. • With a color-scanning application, the real-time intelligent detection of TC was realized. The development of real-time and efficient visual tetracycline sensors is helpful to evaluate the pollution status of tetracycline antibiotics in the environment. Considering the unique fluorescence properties of perovskite and rare earth elements, an innovative water-stable perovskite-europium hybrid fluorescence sensor MAPbBr 3 @PbBr(OH)@SiO 2 -Cit-Eu was fabricated. The introduction of tetracycline resulted in the increase of the fluorescence intensity of Eu complex, while the fluorescence intensity of perovskite quantum dots decreased slowly, accompanied by visual green-red switching. The sensor had good linear response in the range of 0–25 μM, and the detection limit was 11.15 nM. With the help of color analysis software in smart phones, the real-time intelligent detection of TC was realized. In addition, the wearable glove sensor obtained by fixing the nanosensor in the gel can realize the qualitative and semi-quantitative visual sensing of TC on the surface of many foods (eggs, apples, bananas, pears and oranges). It is believed that this work will open a new avenue for perovskite-europium hybrid nanosensors in intelligent sensing fields. [ABSTRACT FROM AUTHOR]