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Abstract Proteases, as one of the most significant kind of digestive enzymes, are closely related to a variety of physiological processes and diseases. Herein, a black phosphorus nanosheets (BPs) based sensitive fluorometric method for protease detection and inhibitor screening is proposed. The aqueous solution of perylene probe (probe 1) displays a strong fluorescence. BPs, as novel discovered two-dimensional (2D) materials, can adsorb probe 1 through electrostatic interactions, which causes fluorescence quenching of probe 1. Histone can control the interactions between the perylene probe and BPs, which can be further regulated by the introduction of a protease. Thus, the protease activity can be monitored by detecting the fluorescence intensity changes of probe 1. The method is label free, sensitive and selective. As low as 1 ng/mL trypsin can be easily detected. Graphical abstract fx1 Highlights • Black phosphorus nanosheets were used as the quencher for a fluorometric assay. • A label-free method for protease detection and inhibitor screening. • Histone controlled interactions between a perylene probe and black phosphorus nanosheets were used for signal transduction. • No covalent modifications were needed, and the assay is simple, sensitive and selective. [ABSTRACT FROM AUTHOR]

A novel sensing strategy for acetylcholinesterase (AChE) and alpha-fetoprotein (AFP) is developed, based on the perylene probe monomer to excimer fluorescence transformation induced by the in situ generation of a metal coordination polymer. In the presence of AChE, acetylthiocholine chloride was hydrolyzed to thiocholine. Ag+ and the produced thiocholine formed a positively charged metal coordination polymer, which induced the aggregation of a negatively charged perylene probe and the formation of probe excimer emission. The intensity ratio of excimer to monomer emission was proportional to the AChE concentration. A sensing method for AChE was thus established with a detection limit of 0.02 mU mL−1. The excimer emission with a large Stokes shift could avoid the interference of background fluorescence from complex biological samples, and thus achieved selective and sensitive detection of AChE. In addition, a fluorescence immunoassay strategy for AFP was then developed. Gold nanoparticles (AuNPs) co-immobilized with acetylcholinesterase and the AFP antibody as the capture and amplification probe were first prepared. In the presence of AFP, the sandwich structure was formed by immunological recognition. The hydrolysis of acetylthiocholine was catalyzed by AChE on the AuNPs, and the metal coordination polymer was then formed which resulted in the aggregation of the perylene probe and the formation of the excimer emission. The proposed sensing method offers a new strategy for the detection of other biomarkers. [ABSTRACT FROM AUTHOR]

A novel fluorescence “turn-on” assay for protease activity based on controlled aggregation of a tetraphenylethene probe is reported. A tetraphenylethene derivative (TPE-2+) with two positive charges is used in this study. TPE-2+ has no emission in an aqueous solution. Heparin is an anionic polymer, which can induce aggregation of TPE-2+. Strong aggregation-induced fluorescence emission (AIE) is observed. Histone is a cationic protein, it binds with heparin via electrostatic attractive interactions, which hinders the binding of TPE-2+ to heparin. TPE-2+ is released, and a decreased emission signal is detected. Upon the addition of a protease, histone is hydrolyzed into small fragments, which weakens its competitive binding to heparin. Free heparin induces aggregation of TPE-2+. A turn-on emission signal is recorded. An efficient and convenient fluorescence assay for protease activity is therefore established. [ABSTRACT FROM AUTHOR]

A fluorescence turn-on assay for alkaline phosphatase (ALP) activity is developed through the controlled release of polyethyleneimine-capped copper nanoclusters (PEI-capped CuNCs) from the MnO nanosheets. In an aqueous solution, the positively charged PEI-capped CuNCs could be adsorbed onto the surface of the negatively charged MnO nanosheets. Such adsorption through favorable electrostatic interactions could efficiently quench the nanocluster fluorescence emission via resonance energy transfer from the PEI-capped CuNCs to the MnO nanosheets. 2-Phospho- l-ascorbic acid (AAP) could be hydrolyzed to l-ascorbic acid (AA) in the presence of ALP. AA could reduce MnO into Mn and trigger the disintegration of the MnO nanosheets. As a result, the CuNCs were released and the quenched fluorescence was recovered efficiently. The detection strategy is simple, inexpensive, sensitive, selective, with low toxicity, and has better biocompatibility. The newly fabricated biosensor for ALP activity will potentially make it a robust candidate for numerous biological and biomedical applications. [ABSTRACT FROM AUTHOR]

[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]

Bis(difluoroboron)-1,2-bis[(1H-pyrrol-2-yl)methylene]hydrazine (BOPHY) is a new class of highly fluorescent organoboron compound. The new symmetric structural motif, the unusual absorption and emission properties, and better photostability have attracted considerable attentions for the development of various functional chromophores. In the present work, a novel BOPHY derivative (BOPHY-NNBOH) for the selective sensing of Cu 2+ was synthesized. BOPHY-NNBOH shows very weak fluorescence. However, it displays significant fluorescence enhancement in the presence of Cu 2+ . The method is sensitive and selective, and sensing of Cu 2+ ions in HeLa cells is also demonstrated. To our knowledge, the present work is the first application of BOPHY derivatives in bioanalysis. [ABSTRACT FROM AUTHOR]

Fluorescence spectroscopy is widely used in basic research, disease diagnosis, environmental monitoring, and the development of novel bioanalytical techniques. We mainly focus on the changes in fluorescence signal originated from the controlled self-assembly of small molecule probes, including aggregation caused quenching, aggregation induced emission, controlled turn-on of probe monomer emission, and the tunable monomer–excimer transition. Recent developments in the related bioanalytical techniques have been reviewed. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI) is one of the most studied conducting polymers. It could adopt a number of chemical forms depending on the redox states of the assay solution. It was observed that the emeraldine base form of PANI could be reduced by common antioxidants (such as glutathione and ascorbic acid), which resulted in clear changes of the solution color and the UV–vis absorption spectra. In addition, it was observed that the fluorescence of CdTe quantum dots could be efficiently quenched by PANI, and the fluorescence quenching could not take place by the addition of antioxidants. The intensity of the quantum dots fluorescence could be directly related to the amount of antioxidant added to the assay solution, thus a sensitive fluorescent turn-on sensor for antioxidant was established. The detection limits for glutathione and ascorbic acid were estimated to be 50 nM and 100 nM, respectively. Our assay is simple, sensitive, and label-free, we envision it could facilitate the antioxidant sensing related applications. [ABSTRACT FROM AUTHOR]

In this work, a fluorescence turn-on method for copper(II) detection is reported. A molecular beacon (MB) was designed as a template. Cu 2+ was reduced to Cu + in the presence of a reductant (ascorbic acid). Two short single-stranded oligonucleotides one was labeled with a 5′-alkyne and the other with 3′-azide group, proceeded a template-dependent chemical ligation through the Cu(I)-catalyzed azide-alkyne cycloaddition. The newly generated click-ligated long chain oligonucleotide, which was complementary to the MB, opened the MB hairpin structure and resulted in a turn on fluorescence. The increase in fluorescence intensity is directly proportional to the amount of Cu 2+ added to the assay solution. The present assay is quite sensitive and allows the detection of 2 nM Cu 2+ . The described assay also exhibits high selectivity over other metal ions. [ABSTRACT FROM AUTHOR]

An ultrasensitive dihydroxybenzene (DHB) quantitative detection method was developed based on the fluorescent graphene quantum dots (GQDs). In the presence of H 2 O 2 and horse radish peroxidase (HRP), DHB could be oxidized to the corresponding benzoquinone which could efficiently quench the fluorescence of GQDs. The fluorescence intensity ratio of GQDs ( I / I 0 ) was proportional to the concentration of o-dihydroxybenzene (o-DHB), m-dihydroxybenzene (m-DHB) and p-dihydroxybenzene (p-DHB) in the concentration ranges of 0.5–250, 1–120, and 0.5–90 nM, respectively. The detection limits are 2.0 × 10 −10 mol/L, 8.0 × 10 −10 mol/L and 3.0 × 10 −10 mol/L, which were much more sensitive than previous reports. In addition, the present method could be used for DHB sensing in rainwater and tap-water samples, and had a potential application for detecting various analytes which can be translated into benzoquinone in aqueous solution. [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]

Abstract: The catalytic behavior of the mesoporous sieve supported potassium nitrate KNO3/MCM-48 for the synthesis of dipropyl carbonates (DPC) by transesterification of dimethyl carbonate (DMC) with propanol was investigated. The catalysts were characterized by the techniques of X-ray diffraction (XRD), CO2 temperature-programmed desorption (CO2-TPD), FT-IR spectroscopy, N2 adsorption and X-ray fluorescence (XRF). The XRD results indicated that the structure of MCM-48 was gradually deformed with the increase in the KNO3 loading, whereas the framework of MCM-48 was basically retained until the loading of KNO3 was over 18%. IR spectra showed that KNO3 was gradually decomposed with increasing calcination temperature. The CO2-TPD showed two new types of basic site were generated, which have higher catalytic ability for the synthesis of DPC. Effects of the loading amount of active components, the calcinatory temperature, the catalyst dosage and the reaction conditions on the catalytic activity were investigated in detail and the optimized reaction conditions were acquired. [Copyright &y& Elsevier]

Cysteine-capped ZnS nanometer-sized fluorescent particles were produced by a colloidal aqueous synthesis. The functionalized nanoparticles are water-soluble and suitable for biological application. A synchronous fluorescence method has been developed for the rapid determination of DNA with functionalized nano-ZnS as a fluorescence probe, based on the synchronous fluorescence enhancement of cysteine-capped nano-ZnS in the presence of DNA. When Δλ=190 nm, maximum synchronous fluorescence is produced at 267 nm at pH 5.12. Under optimum conditions, the synchronous fluorescence intensity is proportional to the concentration of nucleic acids in the range 0.1–1.2 μg ml-1 for calf thymus DNA, 0.1–0.6 μg ml-1 for fish sperm DNA. The corresponding detection limit is 32.9 ng ml-1 for calf thymus DNA and 24.6 ng ml-1 for fish sperm DNA. This method is simple, inexpensive, rapid and sensitive. The recovery and relative standard deviation are satisfactory. [Copyright &y& Elsevier]

A novel fluorescence turn-on strategy for glucose sensing is demonstrated. The fluorescence of a perylene probe could be quenched by the silver nanoparticles (Ag NPs). The Ag NPs could be etched by H2O2 generated from the enzymatic oxidation of glucose. And efficient probe fluorescence recovery was detected. [ABSTRACT FROM AUTHOR]

• A sensor array for the discrimination of metal ions and drinking waters. • Two novel functionalized fluorescent perylene probes were utilized. • The sensor array is based on perylene monomer-excimer emission transition. A new type of sensor array is developed for the highly efficient differential sensing of metal ions and drinking waters. Two functionalized fluorescent perylene probes (Pery-1 and Pery-2) were employed. These probes could interact with metal ions via electrostatic and coordinate bonding interactions. As a result, the probe monomer fluorescence was quenched, and the appearance of distinct excimer emission was observed. Depending on the metal ion used, various degrees of quenching of probe monomer fluorescence, and the generation of excimer emission were observed. For example, quenching of monomer fluorescence was observed when Cu2+ and Fe3+ ions were tested. However, quenching of monomer fluorescence and generation of excimer fluorescence were both observed when Pb2+, Zn2+ and Al3+ ions were employed. And it was also observed that Ni2+, Mn2+ and Cr3+ ions interacted differently with Pery-1 and Pery-2. These differences formed the basis of the metal ion sensor array. The sensor array was used for differentiation of eleven metal ions, and it was also capable of discrimination of metal ions at different concentrations, as well as the discrimination of metal ion mixtures. The array was further successfully used for the distinction of drinking waters, different brands of commercial mineral water, and evaluation of the quality of drinking water. We envisage that the monomer and excimer emission transition of the perylene probe could be easily adopted for efficient sensor array development for various sensing applications. [ABSTRACT FROM AUTHOR]

Monitoring and imaging the requirements of heavy metal ions in organisms are very strict, so biologists and chemists wishfully expect powerful probes to achieve. Herein, DnsP has been successfully designed and synthesized using a highly biocompatible and low biotoxic peptide backbone as an ionophore to selectively detect Zn2+ and Cu2+ in aqueous solution in different response modes. In addition, the DnsP-Cu2+ system has high selectivity for H 2 S and can restore the fluorescence of DnsP for the detection of S2−. Finally, DnsP demonstrated excellent cell permeation and low biological toxicity for biosensing in cellular and zebrafish. Therefore, DnsP represents a prominent peptide fluorescence chemosensor, capable of multifunctional analyte detection and continuous response imaging in environmental and biological systems. • Designed peptide-based fluorescence chemosensor DnsP detects heavy metal ions by different responses. • DnsP has excellent water solubility and biocompatibility, low biotoxicity. • DnsP has been successfully used for imaging in living cells and zebrafish larvae. [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]

Based on the controlled aggregation of quantum dots (QDs), a valid, reliable, and label-free fluorescence turn-on strategy is established for the detection of alkaline phosphatase activity. The aqueous solution of anionic QDs exhibits intense fluorescence. However, the addition of cationic polymer (poly-1) significantly quenched the fluorescence of the QDs via their induced aggregation. While short 3′-phosphorylated DNA (DNA-P) could not be extended by terminal deoxynucleotidyl transferase (TdT) and therefore, fluorescence of the QDs was recovered negligibly. The effective elimination of phosphate group of DNA-P in the presence of alkaline phosphatase (ALP) produced 3′-OH termini and the resulting DNA could be sufficiently extended by TdT. The presence of greater binding strength between the elongated DNA and poly-1 is very crucial to compete with the poly-1/QDs aggregates and release the QDs. Turned-on fluorescence emission is observed due to the efficient release of the QDs. A novel strategy for alkaline phosphatase detection is therefore established. Our method is quite sensitive and selective, as low as 0.1 mU/mL ALP can be easily detected. [ABSTRACT FROM AUTHOR]

A label-free fluorescence turn-on strategy for alkaline phosphatase (ALP) detection was established based on its enzymatic catalyzed hydrolysis of polyphosphoric acid (PPA, an anionic polymer) that had been utilized for aggregation with our homemade positively charged perylene derivative (Probe-1) via noncovalent interactions. The disaggregation caused turn-on fluorescence signal which was recovered by the released Proble-1 molecules whose original strong fluorescence in an aqueous buffer solution had been quenched due to their previous aggregation induced by PPA. Such method presents its great advantages of free labeling, convenience and simplicity, cost effectiveness, high selectivity, and high sensitivity, with a detection limit of 0.5 mU/mL of ALP. [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]

The development of a simple and effective method for the highly sensitive and selective discrimination of proteins is a subject of enormous interest. Herein, we report the construction of a novel fluorescence detection method based on a perylene probe for the highly efficient discrimination of multiple proteins. Single-stranded DNA (ssDNA) could induce aggregation of the perylene probe which caused quenching of probe fluorescence. After the addition of a protein, the protein could interact with the ssDNA-probe assembly complex with "turn-on" or further "turn-off" fluorescence response. A sensor array was designed based on the above phenomena which could realize the successful discrimination of proteins with 100% accuracy of cross validation. Nine representative proteins were successfully recognized. Moreover, it was observed that a protein could induce characteristic effect on the DNA-probe assembly with varying pH of assay buffer. Thus, different proteins showed unique fluorescence response towards assay buffers having different pH values. The assay buffer pH was then utilized as a sensing channel. Based on Linear Discriminant Analysis (LDA) nine proteins were successfully discriminated at the nanomolar concentration with 100% accuracy of cross validation. Furthermore, the sensor array also demonstrated differentiation of the nine proteins regardless of their concentration. The developed sensor array could also detect the proteins with great precision in human urine sample at a quite low concentration, which suggests its practical applicability for analysis of biological fluids. Fluorescence sensor array based on DNA induced PeryProbe self-assembly. Image 1 • A fluorescence sensor array is developed for the discrimination of proteins. • Negatively charged ssDNA induced self-assembly of the perylene probe. • The array was based on the different interactions between the protein and the ssDNA-PeryProbe assembly complex. • The array could discriminate proteins regardless of their concentration. • The array was applied to discriminate proteins in human urine samples. [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]

In this work, a novel fluorescent method for the detection of dopamine (DA) was developed based on a fluorescent nanocomposite (Pdots@AMP-Cu) with polyphenol oxidase activity. Pdots@AMP-Cu was first prepared by the composite of fluorescent polymer dots and coordination nanostructures of adenosine monophosphate (AMP) and Cu2+. The Pdots@AMP-Cu exhibited obvious red fluorescence emission (668 nm), as well as polyphenol oxidase activity by catalyzing the substrate 2,4-DP and 4-AP, and resulted in obvious changes of the solution color from colorless to red. A novel detection method for DA was then developed based on Pdots@AMP-Cu. It is observed that DA can be oxidized by Pdots@AMP-Cu to form eumelanin, and at the same time, the fluorescence of Pdots@AMP-Cu is efficiently quenched by eumelanin due to electron transfer. A good linear relationship was observed between the fluorescent intensity and DA concentration from 10 to 400 μM, and the limit of detection for DA was 4 μM. Moreover, the proposed method exhibited high selectivity toward common amino acids, ascorbic acid, uric acid, etc. And it could also be utilized for DA sensing in human serum samples with satisfactory recoveries. [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]

Highlights • A novel method for the sensing of adenosine triphosphate was developed. • The detection was based on S1 nuclease, FAM-labeled ssDNA and graphene oxide. • The method was applied to the evaluation of meat freshness. Abstract A novel simple, sensitive and reliable sensor based on S1 nuclease, FAM-labeled ssDNA (DNA-F) and graphene oxide (GO) was developed for detecting adenosine triphosphate (ATP) and evaluating the freshness of meat (beef) samples. With S1 nuclease as the cleaver of DNA-F and ATP as the inhibitor of S1 nuclease, the fluorescence of DNA-F could be obviously quenched by GO, which exhibits the fluorescence of system gradually decrease as the increasing ATP concentration. Under the optimal conditions, a linear correlation between the fluorescence and the ATP concentration from 20 μM to 3500 μM is obtained with a detection limit of 3.2 μM. Furthermore, the proposed ATP detection method was applied to the ATP detection in microorganisms in meat samples, which acquired the satisfying results, respectively. [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]

A method using capillary electrophoresis-laser induced fluorescence (CE-LIF) for HSP70_hom gene polymorphism detection has been developed, which was applied to analyze the correlation between rheumatoid arthritis (RA) and HSP70_hom gene polymorphism. The conditions of CE-LIF detection were optimized using DL-1000 DNA Marker, including the concentration of sieving matrix, separation voltage and the concentration of running buffer. The whole genome DNA was extracted from 101 cases of RA and 58 control subjects, amplified by specific primers for PCR, and then digested by Nco I restriction enzyme. The enzyme-digested products were detected by the optimized CE-LIF method and the results were analyzed by logistic regression. Under the optimized conditions of CE-LIF, DL-1000 DNA Marker was detected successively in the same day and the relative standard deviations (RSDs) of migration time was 0.29%–0.41%. There were 58 cases of TT genotype, 41 cases of TC genotype and 2 cases of CC genotype in the case group; 34 cases of TT genotype, 21 cases of TC genotype and 3 cases of CC genotype in the control group. After adjusted age and gender, no significant difference was observed in the distribution of HSP70_hom gene polymorphism between the case group and the control group ( P > 0.05). The method of CE-LIF detection had the advantages of rapid analysis, high resolution and environmental friendliness, and could be applied to the detection of gene polymorphism; HSP70_hom gene polymorphism was not significantly associated with rheumatoid arthritis. [ABSTRACT FROM AUTHOR]

A facile fluorescence turn-on approach for the detection of l -ascorbic acid (AA) and alkaline phosphatase (ALP) activity was designed based on graphene quantum dots (GQDs). It is found that the fluorescence intensity of GQDs can be efficiently quenched by para-benzoquinone (BQ). And a turn-on fluorescence signal can be observed if BQ is reduced by AA. In addition, ALP can hydrolyze l -ascorbic acid-2-phosphate (AAP) to produce AA, which also results in the recovery of the GQDs fluorescence. The recovered fluorescence intensity of GQDs was proportional to the concentration of AA or ALP in the concentration ranges of 5.0 × 10 −7 to 2.0 × 10 −5 mol/L and 1.0–90 U/L, respectively. The detection limit for AA and ALP were 2.0 × 10 −7 mol/L and 0.45 U/L. The established method showed a high selectivity for ALP activity compared with other interference components. Furthermore, the detection system as a fluorescence probe has great potential in the development of sensors for widely detecting various analytes with AA producing process. [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]

A novel fluorescence turn-on microRNA (miRNA) detection method based on duplex-specific nuclease (DSN) and a perylene probe is presented in this study. A positively charged perylene derivative (compound 1 ) was used as the fluorescent probe. Compound 1 exhibits strong monomer fluorescence in an aqueous buffer solution. It is well known that single-stranded DNA is a polyanion in nature. Thus, it can induce the aggregation of compound 1 through strong electrostatic, hydrophobic and π−π stacking interactions. As a result, the fluorescence of compound 1 was efficiently quenched. When the target miRNA was added, the formation of DNA-RNA hybridized duplex initiated the cleavage of the DNA strand by DSN cycle reaction, which resulted in disaggregation of compound 1 . A fluorescence turn-on signal was detected, and a novel miRNA sensing method was therefore established. The presented method is label-free, simple, cost effective, sensitive and selective. [ABSTRACT FROM AUTHOR]

• A novel sensor array is developed for the identification of milk adulteration. • The sensor array is based on perylene probe monomer-excimer emission transition. • Cationic polymer induced aggregation of a perylene probe. • The sensor array can be applied for the quantification of milk adulteration. A novel fluorescence sensor array based on cationic polymer induced self-assembly of a perylene probe is developed. Cationic polymer induced aggregation of the carboxyl modified negatively charged perylene probe, and resulted in large quenching of monomer emission and generation of excimer emission. Upon the addition of negatively charged protein, monomer fluorescence restored with a decrease in excimer fluorescence. Based on these observations, we developed a six-channel sensor array to discriminate five main proteins in milk. In addition, we successfully identified pure milk out of different drinks using the developed sensor array since different drinks contained distinct species and contents of proteins. Furthermore, the sensor array exhibited excellent performance to discriminate milk adulterated by different concentrations of adulterants with 100% accuracy of cross validation. The analysis results also presented excellent linear correlation of adulterants contents and thus the developed sensor array shows great potential for quantitative detection of milk adulteration. [ABSTRACT FROM AUTHOR]

A new approach for the sensitive and selective sensing of a protein has been developed. Cytochrome c could quench the fluorescence of a fluorophore labeled aptamer efficiently. The specific binding between the aptamer and the target protein resulted in a turn-on emission signal, which could be used for protein quantification. [ABSTRACT FROM AUTHOR]

• A new peptide-based chemosensors L used for the detection of Cu2+, Ag+ and S2− ions. • L can detect Cu2+ and S2− at pH under physiological conditions. • L is almost non-cytotoxic. Cu2+ and S2− play important roles in our environment, so it is beneficial to develop sensors capable of detecting Cu2+ and S2− in biological samples. To accomplish this goal, a new peptide-based fluorescent chemical sensor L (FITC-Ahx-His-Glu-Phe-Cys-NH 2) has been designed and synthesized. It can specifically recognize Cu2+ by forming a L -Cu complex which can quench the fluorescence of L. The subsequent addition of S2− can remove Cu2+ from the L -Cu complex, thereby restoring the fluorescence in a process described as an "On-Off-On" cycle. Cu2+ and S2− can be detected by L with extremely high sensitivity and the detection limits is 32 nM and 53 nM respectively. Additionally, the sensor L can detect Cu2+ and S2− at physiological pH conditions. The result of this research is the development of a peptide-based fluorescent chemical sensor L, which can specifically detect Cu2+ and S2− in the environment. [ABSTRACT FROM AUTHOR]