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[Display omitted] • KEEP detects inorganic mercury ions based on fluorescence quenching response. • KEEP detects organic mercury based on fluorescence enhanced response. • KEEP-Hg2+ can detect hydrogen sulfide through fluorescence reproduction. • KEEP achieved fluorescence imaging of Hg2+ and H 2 S in living cells. Mercury species, including inorganic and organic mercury, are extremely harmful to organisms and the environment. Therefore, it is of great significance to rapidly and selectively detect and distinguish inorganic mercury ions and organic mercury. This study reports peptide sequences that can act as inorganic mercury ions and organic mercury ligands. The peptide fluorescent probe KEEP ((Dansyl-Glu-Glu) 2 -Lys-NH 2) can detect mercury species by its coordination with the side chain of glutamic acid. Hg2+ can be detected by the "turn-off" fluorescence mode, while CH 3 Hg+ and PhHg+ can be detected by the "turn-on" fluorescence mode. This probe with different fluorescence response to inorganic and organic mercury is very rare, which makes it possible to distinguish between Hg2+, CH 3 Hg+ and PhHg+. KEEP-Hg2+ can also detect hydrogen sulfide (H 2 S) through fluorescence reproduction. KEEP can detect these three analytes without interference from other substances due to excellent selectivity. KEEP also has good biocompatibility and low biotoxicity, and can successfully monitor the accumulation of Hg2+ and S2- in living cells. This probe provides a new approach for the detection of inorganic mercury and organic mercury. [ABSTRACT FROM AUTHOR]

Mercury is an anthropogenic toxic heavy metal found in the environment. It is highly desirable to develop a fluorescence probe that can selectively and sensitively detect mercury ions using a turn-on response. This paper reports the successful development of a peptide fluorescence probe, TP-2 (TPE-Trp-Pro-Gln-His-Glu-NH 2), which uses aggregation-induced emission effects and high selectivity to detect Hg2+. After fluorescence was activated, Hg2+ was efficiently detected using the change in fluorescence intensity. The detection limit for Hg2+ in the buffer solution was 41 nM (R2 = 0.9952). Owing to its high sensitivity, high cell permeability, and low biotoxicity, the probe could perform live cell imaging under biological conditions. This study demonstrated that TP-2 can detect Hg2+ in complex biological environments. [Display omitted] • The peptide fluorescence probe based on AIE can obtain 30-fold fluorescence enhancement. • Highly selective response to Hg2+ among various biological relevant metal ions. • The side chains of Trp, Gln, His, and Glu are used as Hg2+ coordination sites, making the probe highly specific. • This probe can be used for detecting and imaging Hg2+ in live cells. [ABSTRACT FROM AUTHOR]

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]

Sensitive and efficient monitoring of food-borne bacteria is of great importance for food safety control. Herein, a novel biosensor for highly sensitive detection of Staphylococcus aureus (S. aureus) was constructed by combining hybridization chain reaction (HCR) and nicking enzyme. Different from the upstream-downstream based circuit, the proposed biosensor integrated HCR circuit and three-way DNA junction nicking enzyme assisted signal amplification (3WJ-NEASA) into a virtuous circle of promotion. In the HCR-mediated 3WJ-NEASA sensing strategy, target DNA of S. aureus initiated the self-assembly between HCR hairpins (H1 and H2), which exposed the gap to capture molecular beacon (MB) and construct the 3WJ structure. Meanwhile, MB increased the stability of HCR nanowires and enhanced the efficiency of the HCR circuit, and thus more 3WJ-NEASA circuits were generated in HCR nanowires. Benefiting from the synergistic amplification coupling HCR and 3WJ-NEASA, this isothermal biosensor can detect as low as 6.7 pM of target DNA in one step within only 30 min. Furthermore, the HCR-mediated 3WJ-NEASA assay has been applied in the detection of S. aureus with a limit of detection (LOD) as low as 1.2 × 101 cfu mL−1, and has exhibited reliable practicability in spiked milk. It is the first time that a DNA biosensor combining HCR and 3WJ-NEASA for dual signal amplification was developed and has been adopted to the sensitive analysis of food-borne bacteria. Additionally, this strategy can serve as a universal platform for monitoring other analytes, and therefore possesses broad application prospects in food safety and environmental monitoring. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent nanozyme with catechol oxidase activity was studied. • The nanozyme combines functions of catechol recognition and signal output. • Catechol sensing based on the nanozyme without addition of other agent. • The method is facile and shows good selectivity. Nanozymes, an unusual category of nanomaterials possessing enzymatic properties, and have generated considerable interest regarding their application feasibilities on several important fronts. In the present work, an innovative sensing device for catechol was established ground on a fluorescent nanozyme (Cu-BDC-NH 2) that exhibited catechol oxidase activity. The fluorescent nanozyme combines both functions of catechol recognition and response signal output, and can realize the sensing of catechol without the addition of other chromogenic agents. In the existence of Cu-BDC-NH 2 , catechol can be oxidized efficiently to produce quinones or polymers with strong electron absorption capacity, which immediately results in efficient fluorescence quenching of Cu-BDC-NH 2. However, other common phenolic compounds, such as phenol, the other two diphenols (hydroquinone and resorcinol), phloroglucinol, and chlorophenol, do not result in efficient fluorescence quenching of Cu-BDC-NH 2. The method shows a nice linear relationship between catechol concentration prep the fluorescence intensity of Cu-BDC-NH 2 in the scope of 0–10 μM, with a detection limit of 0.997 μM. The detection of catechol in actual water samples has also achieved the satisfactory consequences, which provides a new strategy for the convenient and selective detection of catechol. [ABSTRACT FROM AUTHOR]

Salmonella can cause serious foodborne diseases, which is a major concern for global public health. The sensitive and fast analysis of Salmonella is of importance for food safety. Herein, we developed a fluorescence sensing array based on photonic crystals (PCs) and recombinase-aided amplification (RAA) for high-throughput and high-sensitive analysis of Salmonella in foods. In this assay, RAA was employed for powerful amplification of the target DNA of Salmonella , and the generated dsDNA amplicon was embedded with nucleic acid dye SYBR Green I (SGI), emitting fluorescence. Furthermore, the fluorescence signal was physically enhanced by PCs array; meanwhile, the high-throughput and sensitive detection was realized by microplate reader. Because of the isothermal reaction and lyophilized regent of RAA, the proposed array possessed gentle operation and stable amplification performance. Besides, a small volume of loading samples with 2 μL was required on the PCs array for powerful fluorescence enhancement. Due to the synergistic signal amplification effect of RAA and photonic crystals, a low limit of detection (LOD) of 10 CFU/mL was achieved. Besides, the proposed array exhibited excellent performance with 100% accuracy in 20 spiked food samples. Therefore, the proposed method with the advantages of sensitivity and high throughput showed great application potential. • A fluorescent biosensor based on RAA and PCs was engineered for sensitive detection of Salmonella. • RAA with SYBR Green I has rapid, isothermal and cheap features without need of complex instruments. • PC array was employed to achieve rapid, simultaneous and high-throughput detection. [ABSTRACT FROM AUTHOR]

SARS-CoV-2 isolation from cold-chain food products confirms the possibility of outbreaks through cold-chain food products. RNA extraction combined with RT-PCR is the primary method currently utilized for the detection of SARS-CoV-2. However, the requirement of hours of analytical time and the high price of RT-PCR hinder its worldwide implementation in food supervision. Here, we report a fluorescence biosensor for detection of SARS-CoV-2 N protein. The fluorescence biosensor was fabricated by aptamer-based conformational entropy-driven circuit where molecular beacon strands were labeled with graphitic carbon nitrides quantum dots@Zn-metal-organic framework (g-CNQDs@Zn-MOF) and Dabcyl. The detection of the N protein was achieved via swabbing followed by competitive assay using a fixed amount of N-48 aptamers in the analytical system. A fluorescence emission spectrum was employed for the detection. The detection limit of our fluorescence biosensor was 1.0 pg/mL for SARS-CoV-2 N protein, indicating very excellent sensitivity. The fluorescence biosensor did not exhibit significant cross-reactivity with other N proteins. Finally, the biosensor was successfully applied for the detection of SARS-CoV-2 N protein in actual cold-chain food products showing same excellent accuracy as RT-PCR method. Thus, our fluorescence biosensor is a promising analytical tool for rapid and sensitive detection of SARS-CoV-2 N protein. • An aptamer-based sensor could detect of SARS-CoV-2 in food products within 30 min. • Conformational entropy-driven circuit was designed for signal amplification. • g-CNQDs@Zn-MOF was utilized to improve stability and reproducibility of biosensor. • This strategy unlocks a route for the development of sensitive analytical tools. [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]