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Salmonella Typhimurium poses a serious threat to human health worldwide, necessitating the development of a rapid, sensitive, and convenient method for S. Typhimurium detection. Nanozymes are considered ideal signal report elements, which are extensively used for developing colorimetric methods. However, single-component nanozymes display low catalytic activity, and colorimetric methods are susceptible to environmental interference, reducing the sensitivity and accuracy of detection results. To address these drawbacks, this study constructed a dual-mode composite nanozyme-based cascade colorimetric-fluorescence aptasensor for S. Typhimurium detection in food. In this study, the composite Fe 3 O 4 @MIL-100(Fe) nanozymes were successful synthesized and demonstrated substantial peroxide-like activity, with 4.76-fold higher specificity activity (SA) than that of Fe 3 O 4 nanozymes. Then, a glucose oxidase (GOx)-Fe 3 O 4 @MIL-100(Fe) cascade reaction was developed for colorimetric detection via an aptamer to facilitate the formation of Fe 3 O 4 @MIL-100(Fe)/ S. Typhimurium/carboxylated g-C 3 N 4 (CCN)-GOx sandwich complexes. Meanwhile, the fluorescence mode was achieved by measuring the fluorescence intensity of the sandwich complexes. In optimum conditions, the dual-mode detection limits (LOD) were 1.8 CFU/mL (colorimetric mode) and 1.2 CFU/mL (fluorescence mode), respectively, with the S. Typhimurium concentration ranging from 10 CFU/mL to 107 CFU/mL. Finally, the feasibility of the dual-mode colorimetric-fluorescence method was validated via three actual samples, yielding recovery rates of 77.32 % to91.17 % and 82.17 % to 103.7 %, respectively. This study successfully develops a composite nanozyme-based cascade colorimetric and fluorescence dual-mode aptasensor for S. Typhimurium detection. It presents several distinct benefits, such as a broader linear range (10–107 CFU/mL), a lower LOD value (1.2 CFU/mL), and more accurate results. More importantly, the proposed dual-mode method displays a low LOD in colorimetric mode, demonstrating considerable potential for S. Typhimurium on-site detection in food. [Display omitted] • A nanozyme cascade reaction was developed to improve the sensitivity of results. • The fluorescence method was introduced to improve the accuracy of results. • This dual-mode detection limits for bacteria were 1.8 and 1.2 CFU/mL, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A framework nucleic acids (FNAs) fluorescent nanoprobe was constructed. • The detection of multiple DNA repair enzymes in living cells was realized. • This method exhibits good selectivity and high sensitivity. • The FNAs enter the cell autonomously and image UDG and APE1. DNA repair enzymes play pivotal roles in DNA damage repair. Imaging multiple DNA repair enzymes in living cells is significant for DNA damage repair-related biological study and disease diagnosis. Here, we constructed a framework nucleic acids (FNAs) fluorescent nanoprobe for imaging multiple DNA repair enzymes in living cells. Uracil DNA glycosylase (UDG) and human apurinic/apyrimidinic endonuclease 1 (APE1) were used as the target analytes. Two double-stranded DNA probes (dsDNA1 and dsDNA2) were designed. dsDNA1 contained four uracil (U) bases for UDG recognition and was labeled with black hole quencher2 (BHQ2) /cyanine5 (Cy5). dsDNA2 contained one apurinic/apyrimidinic (AP) site for APE1 recognition and was labeled with black hole quencher1 (BHQ1) /fluorophore carboxyfluorescein (FAM). To obtain the FNAs fluorescent nanoprobe, dsDNA1 and dsDNA2 were attached to two vertices of a DNA tetrahedron (a type of FNAs). Under the action of UDG and APE1, dsDNA1 and dsDNA2 were both dissociated, generating fluorescence of Cy5 and FAM. Among them, Cy5 indicated the activity of UDG and FAM indicated the activity of APE1. This method had good sensitivity to UDG and APE1, and the detection limits were 0.0012 U/mL and 0.057 U/mL, respectively. This method also exhibited high selectivity for UDG and APE1. When the FNAs fluorescent nanoprobe was endocytosed, it had little toxicity to normal and cancer cells. Furthermore, this method successfully achieved multiple imaging UDG and APE1 in cancer cells. This study provides a novel strategy for imaging multiple DNA repair enzymes and holds great potential in biological applications and clinical diagnosis. [ABSTRACT FROM AUTHOR]

Luminescent materials encapsulated into zeolite imidazole framework-8 (ZIF-8) as fluorescent probes are widely applied to detect the various analytes. Notably, these analytes react with Zn2+ through the coordination, oxidation, or acidification of 2-methylimidazole (2-MIM) to cause the degradation of ZIF-8 shell, which enormously constraints the improvement of the sensor sensitivity and selectivity. Herein, we have rationally designed the new way to collapse the shell of ZIF-8 entrapped with copper nanoclusters (CuNCs@ZIF-8) triggered by p-benzoquinone. It is worth noting that p-benzoquinone reactions with 2-MIM through hydrogen bonding interaction. As a proof-of-concept, a sensitive method for the detection of hydroquinone (HQ) is developed based on the degradation of CuNCs@ZIF-8 because HQ is easily oxidized to p-benzoquinone. The limit of detection (LOD) is estimated as low as 76 nM. Importantly, this method is highly selective for HQ over other dihydroxybenzene isomers. Inspired by the generation of HQ from hydrolysis of α-arbutin as a substrate for α-glucosidase (α-Glu), we have further proposed a straightforward α-Glu activity assay. LOD is down to 0.003 U/mL, which is lower than most of other α-Glu activity assays. Moreover, the inhibition effect of acarbose and three kinds of natural flavonoids including baicalein, silibinin, and apigenin on α-Glu activity is measured with IC 50 values of 37, 155, 1940, and 2930 nM, respectively. The synergistic and antagonistic inhibition effect of α-Glu activity is also evaluated by binary combination with three types of flavonoids. This approach provides a promising strategy in clinical diagnosis and anti-diabetic drug screening. [Display omitted] • A novel strategy is designed to decompose CuNCs@ZIF-8 shell induced by p-benzoquinone. • LOD is as low as 76 nM and 0.003 U/mL for hydroquinone and α-glucosidase activity, respectively. • This system is not only applied to detect IC 50 value for many inhibitors but also inhibitory effect of binary mixtures. [ABSTRACT FROM AUTHOR]

The exposure of micro- and nanoplastics (MNPs) via medical device is still unknown to us. Herein, a visual quantitative detection of polyvinyl chloride (PVC) MPs and a fluorescent quantitative detection of PVC NPs were developed. To overcome the aggregation of PVC NPs, sodium dodecylbenzene sulfonate was used as the stabilizer of PVC NPs. The brand-new disposable PVC infusion tubes were found to carry PVC MPs with the average total number (ATN) of 931.4 particles and PVC NPs with the average mass of 0.040 μg, respectively. For four typical infusion fluids such as 0.9% sodium chloride, 5% glucose, 5% sodium bicarbonate, hydroxyethyl starch 40 sodium chloride, the released PVC MPs and NPs were ranged from 1003.6 ∼ 3494.6 particles and 0.042 ∼ 0.087 μg, respectively in stimulating normal infusion scenario (room temperature 4 h). The released PVC MPs and NPs were also increased with the infusion duration and temperature. The released PVC MPs are mainly in granular form, accounting for 38 ∼ 49% of the total PVC MPs. Our findings indicate PVC MNPs can enter the blood vessel directly with the infusion fluids during intravenous infusion and the PVC MNPs exposure risk towards patients deserves more attention. [Display omitted] • SDS was used as the stabilizer to overcome the aggregation of PVC NPs. • PVC NPs was quantitatively detected by a facile fluorescent method as common solution. • The brand-new disposable PVC infusion tubes were found to carry PVC MPs and NPs. • PVC MPs and NPs were released in stimulating infusion scenario. • The granular PVC MPs account for 38 ∼ 49% of the total released PVC MPs. [ABSTRACT FROM AUTHOR]

Herein, we report a new probe for the determination of the concentration of NF-κB p50, one kind of DNA-binding transcription factors (TFs), by using Exonuclease III (Exo III)-aided amplification and gold nanoparticle mediated fluorescence intensity. Since TFs play critical roles in various biological processes, the detection of TFs can provide a lot of useful biological information for studding gene expression regulation related disease. In our system, in the presence of transcription factor, Exo III based amplification reaction was trigged. This enzymatic digestion results in the release of intermediate DNA and ultimately liberating the fluorophore (which, separated from the quencher of AuNP and BHQ2, now fluoresces). The released intermediate DNA then hybridizes with another strand3, whence the cycle starts anew. So, the fluorescence intensity reflects the NF-κB p50 concentration with a detection limit of 1.32 pM. Importantly, this method might be further extended to selectively detect various dsDNA-binding proteins by simply changing the binding-site sequences of strand1/strand2 duplex probes. Schematic presentation of the probe for ultrasensitive detection of NF-κB p50. In this probe, AuNP was employed as the frame and fluorophore Cy3 was used as the signal output element. Image 1 • We report a new strategy here for detecting NF-κB p50 concentration. • This strategy coupled DNA duplexes on AuNP surface with Exo III-aided amplification technique. • This strategy exhibits a good sensitivity with a limit of detection (LOD) of 1.32 pM. • This strategy has the potential for screening transcription factor inhibitors for drug research and development. [ABSTRACT FROM AUTHOR]

The detection of miRNA in cells is difficult owing to its substantially low cellular content. Therefore, developing a highly sensitive sensor to detect cellular miRNA remains a significant challenge. Herein, we report an enzyme-assisted biosensor with target cycle amplification that can trigger the unlocking of locked hairpin probes for sensitive and robust let-7a gene detection. In the research, three kinds of hairpin probes were skillfully designed. The hairpin probe comprises a complementary sequence of a target, primer, and recognition site of Nt. Bbv CI restriction endonucleases. In addition, the alternating synergistic impact of polymerase and the nicking enzyme generates considerable triggers to unlock the locked hairpin probe LH1, consequently triggering a subsequent circulating strand displacement reaction to form a stable H1–H2 double strand to ensure sufficient distance between a fluorophore on H1 and a quenching group on bolt DNA (bDNA), and resulting in the recovery of fluorescence. Furthermore, this process does not require complicated operation procedures and instruments, and the target gene let-7a can be sensitively detected. Specifically, the detection limit of the biosensor is as low as 160 fM, and its linear range is 0.5 pM–250 nM. Moreover, this biosensor can be employed to detect let-7a in human serum with good selectivity. [Display omitted] • An enzyme-assisted fluorescent sensing system was proposed for the detection of the miRNA Let-7a. • The sensitivity of miRNA Let-7a fluorescence detection was further enhanced by target cyclic amplification. • Ultrasensitive enzyme-assisted fluorescent detection limit of Let-7a was estimated to be as low as 160 fM. • The biosensor has good specificity and excellent detection capabilities in a complex substrate environment. [ABSTRACT FROM AUTHOR]

A rapid, cost-effective and quencher-free fluorescence-based analytical method for sensitive detection of l -cysteine (Cys) based on 2-aminopurine (2-AP) labeled DNA probe and exonuclease I (Exo I) activity was developed. 2-AP labeled DNA probe includes two thymine (T)-T mismatches, which can bind with Hg2+ to form T-Hg2+-T pairing bases, resulting in stable hairpin with five base pairs in its stem. The target Cys can remove Hg2+ from the stem of the hairpin probe based on the high affinity of Cys with Hg2+, leading to the unfolding of the hairpin probe. At last, by adding Exo I, the resulted single-stranded DNA (ssDNA) will be digested to release free 2-AP with strong fluorescence. Under the optimal conditions, the sensing system exhibited a good and wider linear range from 0.4 to 400 nM (R2 = 0.997) and a detection limit as low as 0.16 nM for Cys. Furthermore, other amino acids without reductive sulfur group did not generate obvious change in fluorescence signals. Finally, the sensor can be used in diluted real samples with a good recovery rate, showing promising application in food, environmental and medical analysis. Image 1 • A simple, cost-effective and fluorescent method for Cys detection using 2-AP modified DNA probe was developed. • This assay owns high selectivity, low detection limit of 0.16 nM and wider linear range of 0.4–400 nM. • This method operates in manner of "mix, incubate and detect" and the analytical process is fast. [ABSTRACT FROM AUTHOR]

Abstract It is important to establish sensitive and simple analysis methods for adenosine 5′‑triphosphate (ATP). A label-free fluorescent probe for the determination of ATP was constructed based on glutathione modified silver nanoclusters (AgNCs/GSH). AgNCs/GSH showed aggregation-induced emission enhancement (AIEE) property in the organic solvent. The effects of metal ions on the fluorescence of AgNCs/GSH were also studied. Only zinc ion enhanced the fluorescence of AgNCs/GSH obviously. This was because Zn2+ coordinated with AgNCs/GSH to cause the aggregation of AgNCs/GSH, which was sufficiently proved by TEM. With the addition of ATP, Zn2+ bound with ATP through Zn O P bond and the binding between Zn2+ and AgNCs/GSH was inhibited. Hence the fluorescence of AgNCs/GSH was decreased with increasing the ATP concentration. The fluorescence response was linear in the ATP concentration range of 1–110 μM, and the detection limit was 0.8 μM. Then this method was successfully applied for determining ATP in the samples of human urine and rat serum, the recoveries were in the range of 97.6%–103%. Graphical abstract Unlabelled Image Highlights • A label-free fluorescent probe for ATP is constructed based on AgNCs/GSH with AIEE property. • Only Zn2+ causes aggregation and fluorescence enhancement of AgNCs/GSH, which is proved by TEM and fluorescence spectra. • The detection method for ATP is simple, fast, and has the practical application in detecting biological samples. [ABSTRACT FROM AUTHOR]

Abstract Human alkyladenine DNA glycosylase (hAAG) is an important protein enzyme which can specifically recognize and initiate the repair of a variety of alkylated purines and hypoxanthine, and the dysregulation of hAAG activity is associated with various human diseases. Although there are several methods focusing on hAAG detection, they share common defects such as time-consuming protocols, laborious operation or requirement of expensive analytical instruments. Herein, taking advantage of the high amplification efficiency of hyperbranched signal amplification and the low background signals by modifying NH 2 at 3' terminus of hairpin substrate and signal probe to prevent the terminal deoxynucleotidyl transferase (TdT)-activated nonspecific amplification, a fluoresence method for sensitive detection of hAAG was established using TdT-activated Endonuclease IV (Endo IV)-assisted hyperbranched signal amplification. This method exhibits high sensitivity with a limit of detection of 0.090 U/mL for pure hAAG and shows a large dynamic range of 3 orders of magnitude from 0.1 to 50 U/mL, and it can be applied for accurate detection of hAAG in complicated HeLa nuclear extract. Moreover, the method can be used for discrimination of hAAG from other DNA glycosylases, holding great potential in hAAG-related biomedical research and clinical diagnosis. Graphical abstract fx1 Highlights • A fluoresence method is introduced to detect hAAG based on hyperbranched signal amplification. • The method shows high sensitivity with a detection limit as low as 0.090 U/mL for hAAG. • The hAAG activity detection can be finished about 100 min. • The method can be applied for the detection of hAAG in HeLa nuclear extract. [ABSTRACT FROM AUTHOR]

Highlights • A fluorescence-based method for analysis of sulfide is presented. • The method shows high selectivity and sensitivity toward sulfide. • The applicability of the method was demonstrated via analysis of real samples. Abstract With the rapid growth of agricultural and industrial sectors, a significant quantity of sulfide is released into water resources systems at an increasing rate. This has caused serious environmental problems, which calls for the development of sensitive and selective methods for determining sulfide in environmental samples. In this report, we employed carbon dots (C-dots) as fluorescence emitters and measured the decrease in their fluorescence intensity caused by Ag 2 S formation. Instead of having free Ag+ cation (which can interact with many other species besides sulfide) in the C-dot solution, we used iodide (I−) to convert Ag+ to one of the least soluble silver salts (i.e., AgI). While AgI interacts with sulfide to form Ag 2 S (because of the lower solubility of Ag 2 S), it remains stable against many other anions, thereby offering the method high selectivity. Under optimized experimental conditions, the developed method enabled quantifying sulfide in the range of 1–10 μM with the low detection limit of 0.48 μM. The applicability of the method was demonstrated by successful analysis of sulfide in a mineral water, a hot spring water, and an industrial wastewater sample. [ABSTRACT FROM AUTHOR]

Uracil-DNA glycosylase (UDG) is pivotal in maintaining genome integrity and aberrant expressed UDG is highly relevant to numerous diseases. Sensitive and accurate detecting UDG is critically significant for early clinical diagnosis. In this research, we demonstrated a sensitive UDG fluorescent assay based on rolling circle transcription (RCT)/CRISPR/Cas12a-assisted bicyclic cascade amplification strategy. Target UDG catalyzed to remove uracil base of DNA dumbbell-shape substrate probe (Sub UDG) to produce an apurinic/apyrimidinic (AP) site, at which Sub UDG was cleaved by apurinic/apyrimidinic endonuclease (APE1) subsequently. The exposed 5′-PO 4 was ligated with the free 3′-OH terminus to form an enclosed DNA dumbbell-shape substrate probe (E-Sub UDG). E-Sub UDG functioned as a template can actuate T7 RNA polymerase-mediated RCT signal amplification, generating multitudes of crRNA repeats. The resultant Cas12a/crRNA/activator ternary complex activated the activity of Cas12a, causing a significantly enhanced fluorescence output. In this bicyclic cascade strategy, target UDG was amplified via RCT and CRISPR/Cas12a, and the whole reaction was completed without complex procedures. This method enabled sensitive and specific monitor UDG down to 0.0005 U/mL, screen corresponding inhibitors, and analyze endogenous UDG in A549 cells at single-cell level. Importantly, this assay can be extended to analyze other DNA glycosylase (hAAG and Fpg) by altering the recognition site in DNA substrates probe rationally, thereby offering a potent tool for DNA glycosylase-associated clinical diagnosis and biomedical research. Schematic of the RCT/Cas12a-assisted bicyclic cascade amplification strategy for uracil-DNA glycosylase activity. [Display omitted] • A sensitive fluorescent assay based on RCT/CRISPR/Cas12a-assisted cascade amplification strategy was demonstrated for UDG. • The assay can be extended to analyze other DNA glycosylase by altering the recognition site in DNA substrates. • The strategy confers the assay with the feature of low background and high signal-to-noise ratio. • The method offers a potent tool for DNA glycosylase-associated clinical diagnosis and biomedical research. [ABSTRACT FROM AUTHOR]

In this paper, a FRET (Forster resonance energy transfer) based fluorescence method was developed for the quickly detection of ochratoxin A (OTA) in agricultural products ( e.g. , flour and beer). A highly fluorescent nitrogen doped carbon dots (CD) were served as energy donor, the DNA and MCH (6-mercapto-1-hexanol) modified Ag nanoparticles were served as energy acceptor in the FRET system. OTA can be detected in a concentration range between 10 and 5000 nM, the limit of detection is 8.7 nM. This method has three advantages: (1) an enhanced fluorescent intensity can be acquired by utilizing the nitrogen doped CD synthesized by one-step approach without sophisticated modification of nanoparticles; (2) OTA detection was accomplished quickly (less than 30 min) by using MCH as assistant molecule; (3) an extended OTA detection linear range was acquired, which may facilitate the OTA detection in real agricultural samples, and is helpful for solving food safety problems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel fluorometric assay toward alkaline phosphatase activity (ALP) was proposed. • Resorcinol monophosphate ester (RME) was developed as a new substrate and synthesized simply via a two-step routine. • The mechanism is RME was converted to resorcinol, reacting with dopamine to form strong a fluorescent product. • ALP activity could be determined with high sensitivity and selectivity. • The assay was validated for verifying pasteurization of milk products. Alkaline phosphatase (ALP) is an indicator of sterilization efficacy of milk products and its activity monitoring is essential for ensuring food safety and controlling product quality. Here, a novel fluorometric method for the determination of ALP activity based on resorcinol monophosphate ester (RME) as a new substrate was proposed to verify pasteurization of milk products. RME was cheap and was simply and novelly synthesized by a two-step method using resorcinol (RC) as the raw material. The mechanism is, after dephosphorylation, RME was transformed to RC, which subsequently react with dopamine (DA) to form a strong fluorescent product, azamonardine. It has a fluorescence emission wavelength at 461 nm under the optimal excitation at 418 nm. The results show that under the optimum conditions, there is a good linear relationship between ΔF (the variation of fluorescence intensity) and ALP activity over 0–5000 mU/L. High sensitivity was achieved (detection limit of 17.34 mU/L) because of high quantum yield of the products and catalytic activity of ALP and the recovery rate is 96.8–106.1%. Compared with national and international standard methods, the detection procedures are simple, just adding RME and DA solution to milk with buffer solution. Our method was successfully applied for ALP activity detection in milk products. Moreover, the catalyst of ALP and the reaction of RME and dopamine are pH dependent, and thus the reaction time could be kept identical by terminating the reaction through adding acids. With high sensitivity, high selectivity, simple operation, and wide linear range, our assay will find more practical applications in food analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • CQD/Dex/PVA nanocomposites are prepared by low-cost green technique. • Glucose sensing by "switch-OFF" fluorescence mechanism. • Highly selective for sensing of glucose in presence of interfering sugars. • Very low detection limit of 61.1 μM. • Glucose contents in human blood serums are compared with commercial glucometer. Herein, carbon quantum dot (CQD) doped dextran/polyvinyl alcohol (PVA) (CQD/Dex/PVA) nanocomposites are synthesized for in vivo detection of glucose by non-enzymatic "switch-OFF" fluorescence mechanism in real human blood serums. Highly functional, dispersible and stable CQD is obtained from aloe vera by carbonization and a facile solution mixing technique is adopted for the preparation of CQD/Dex/PVA nanocomposites. It is noticed that hydrogen bonding between –OH group of glucose and that of the dextran and PVA quenches the fluorescence intensity of the nanocomposite. The synthesized CQD/Dex/PVA nanocomposite is highly selective for sensing of glucose in presence of other interfering sugars which proves its suitability to be implemented in complex biological environment. This biosensing technique exhibits linear range from 0.27 mM to 1.72 mM, R2 = 0.986 and a low detection limit of 61.1 μM. The measurements of glucose content in twelve real human blood serums are done and compared with commercial glucometer with satisfactory recoveries. Considering the high selectivity, sensitivity and accuracy, this "switch-OFF" fluorescence method holds promising application in diabetes management. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-sensitive and highly selective label-free fluorescent aptasensor was developed for the rapid detection of Hg(II), using water soluble cysteamine-capped CdTe/ZnS quantum dots (cysteamine@CdTe/ZnS QDs) as an luminescent probe and a single strain DNA aptamer designed to specifically bind to Hg(II) ions. Negative charge aptamers could aggregate the cationic cysteamine@CdTe/ZnS core/shell quantum dots, so the fluorescence quenching occurred. When Hg(II) ions, as a target, were added to the quantum dots solution, the aptamers with thymine (T)-rich sequences were selectively bound to the mercury ions. This is due to the powerful affinity of Hg(II) ions to the T bases of the DNA aptamer. It leads to the formation of an Hg (II)-bridged T base pair and the aptamers rearrangement into a hairpin-like structure. In the presence of Hg(II), de-aggregation of the quantum dots was occurs, so the fluorescence intensity was gradually increased with enhancing its concentration. Hg(II) could be measured in the range of 5.0 × 10 −10 to 1.0 × 10 −6 mol L −1 with a low limit of detection, 8.0 × 10 −11 mol L −1 . The fabricated fluorescent aptasensor also demonstrated excellent selectivity for Hg(II) detection, this principal was investigated by theoretical and experimental methods so it was applied lucratively for the determination of Hg(II) in real water and waste water samples. [ABSTRACT FROM AUTHOR]

• The AuNCs based on d -histidine and polylysine was first designed to detect Cr6+. • The detection mechanism was aggregation of AuNCs and FRET between AuNCs and Cr6+. • The proposed fluorescence method possessed high sensitivity and selectivity. • The proposed method possessed feasibility of usage in actual system. Hexavalent chromium (Cr6+) owns hypertoxicity, non-biodegradability, and carcinogenicity, thus the detection of Cr6+ is of paramount significance for environmental monitoring and human health maintenance. Herein, a simple, rapid, and feasible fluorescent method based on gold nanoclusters (AuNCs) was established for determination of Cr6+. The AuNCs was coated by a simple and fast one-pot method using d -histidine (d -His) and polylysine (P-Lys) as stabilizers and reductants, which could be quenched by the addition of Cr6+ owing to the aggregation of AuNCs and fluorescence resonance energy transfer (FRET) between AuNCs and Cr6+. Under the optimal conditions, the fluorescent sensor exhibited good linearity within 10–10000 μg/L with limit of detection of 7.2 μg/L. The developed sensor possessed favorable sensitivity and selectivity. Additionally, the proposed method also had favorable recovery with good precision and accuracy within the actual sample, including celery cabbage, rice, capsule shell, and river water. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu2+ and Cys/Hcy/GSH sequential sensing mechanism by Eu-DTPA-bis(AMC) is established. • Concentration of Eu-DTPA-bis(AMC)/Cu2+ has relationship with selection of biothiols. • Eu3+-DTPA-bis(AMC)/Cu2+ shows low LODs for biothiols detection. • Low concentration of Eu-DTPA-bis(AMC)/Cu2+ specifically distinguish Cys from Hcy/GSH. • Eu3+-DTPA-bis(AMC) can be applied to accurately detect Cu2+ and Cys in real samples. In this work, a novel Eu3+-DTPA-bis(AMC) complex with red luminescence was designed and synthesized for sequential detection of Cu2+ and biothiols (Cys/Hcy/GSH) based on the displacement strategy with the good selectivity, high sensitivity, and large Stokes shift (288 nm). The possible detection mechanism was verified by UV–vis, the high-resolution mass spectrometry, and the fluorescence decay curve. The experimental parameters, including the solution pH, the incubation time, the concentration ratio of Eu3+-DTPA-bis(AMC) to Cu2+ and biothiols concentration, were optimized. Under the optimal conditions, it shows a good linear relationship between the concentration (0–10 μM) of Cu2+ and the fluorescence intensity of Eu3+-DTPA-bis(AMC), with a low detection limit of 0.065 μM. The linear range and the limit of detection of the Eu3+-DTPA-bis(AMC)/Cu2+ system for Cys/Hcy/GSH were 2.5–22.5/5–45/5–50 μM and 0.11/0.07/0.05 μM, respectively. Surprisingly, the high or low concentration of Eu3+-DTPA-bis(AMC)/Cu2+ can significantly affect the selectivity of the sensing system to biothiols (Cys/GSH/Hcy). When the concentration of the Eu3+-DTPA-bis(AMC)/Cu2+ system is 10.0 μΜ, it could recognize biothiols (Cys/GSH/Hcy) from other substances, but when the concentration is as low as 3.3 μM, it could further specifically distinguished Cys from Hcy/GSH. Owing to the high anti-interference characteristics, accuracy and specificity, the sensing system was well applied to the cascade detection of Cu2+ in actual environmental samples and Cys in biological and food samples, including FBS, urine, milk, beverage, fresh juice with the satisfactory recoveries from 96.20 to 106.80 %. [ABSTRACT FROM AUTHOR]

Understanding the binding mechanisms of drug–protein interactions is a crucial factor in determining the pharmacokinetics and pharmacodynamics of a drug. In this study, the binding affinity of inosine toward the HSA, as well as the dynamic properties of HSA-inosine complexes was obtained from applying NMR methodology. The changes in proton selective and non-selective relaxation rates suggested that inosine interacts with HSA. The values of normalized affinity indexes and equilibrium constant K provided information about the binding strength, which were in accordance with fluorescence result. The detailed binding mechanisms were obtained through fluorescence method, and the binding mode was displayed using Discovery Studio. Circular dichroism data further confirmed the secondary structure changes in HSA upon inosine addition. This study provided insights on the interactions between inosine and HSA. [ABSTRACT FROM AUTHOR]

Chemosensors are the molecule of abiotic origin that binds with different analyte by covalent or non-covalent interactions to create a change in colour or optical properties. In this context, colorimetric anion sensors are unique, because they detect target anions through visual detection with no sophisticated instrumentation technique. A chromophore or a fluorophore plays a significant role as a signalling unit in chemosensors. A variety of chemosensors designed with organic and inorganic chromophores or fluorophores used for the detection of various analytes. Among them anthraquinone has found significant application in anion recognition and sensing for their important role in various photochemical and colorimetric sensor systems. In this review we summarise the development of chromogenic anion sensors using colorimetric and fluorometric reagent anthraquinone as a signalling unit. We have attempted to cover almost all the reports of modified anthraquinone moiety as anion sensor reported until now. [ABSTRACT FROM AUTHOR]

• An exhaustive study of various optical methods for heavy metal detection, i.e. , fiber grating method, modal interference method, fluorescence method, optical absorbance method, and surface plasmon method. • Practical demonstration of the various fiber optics sensor and sensing setup for heavy metal detection. • Detail information about several antigens and antibodies, chelators, chemicals to detect heavy metal ions along with their chemical and structural formula. Several pollutants are getting added to the water content in today's world, sometimes intentionally and sometimes unintentionally. These pollutants, chemicals, and heavy metals can severely affect people's health, causing cancer, tuberculosis, and even death. An optical sensor has tremendous potential to detect heavy metals ion. These sensors possess several properties like minute size, remote sensing monitoring, real-time investigation, chemical inertness, non-reactiveness, etc. , which are considered ideal for heavy metal detection. This work has presented an exhaustive study of different optical methods like fiber grating method, modal interference method, fluorescence method, optical absorbance method, surface plasmon method, and surface-enhanced Raman scattering method to detect heavy metals ions. Various advantages and shortcomings of these methods are analyzed, along with details of the chemicals, structural formulas, and multiple setups developed to detect heavy metal ions. Finally, the advancement in fiber optics sensors from future perspectives is also discussed. [ABSTRACT FROM AUTHOR]

Specific and accurate detection of transcription factors is critical for disease diagnosis and drug development. Here, we developed a novel and versatile fluorescent sensing strategy for specific and accurate detection of transcription factors based on the inhibition of endonuclease Fok I-catalyzed DNA cleavage reaction. A FAM-labeled double-stranded DNA probe (dsDNA probe) with transcription factor binding site and Fok I recognition site was designed for target recognition and signal transduction. With the binding of transcription factors, the dsDNA probes are protected from cleavage by Fok I. These protected dsDNA probes then cannot hybridize with the added BHQ-DNA, keeping the fluorescence of FAM in an on state. However, in the absence of targets, the dsDNA probes were cleaved to release the FAM-DNA, which subsequently hybridized with BHQ-DNA, resulting in the fluorescence of the FAM being quenched. With the Fok I–DNA interaction that can specifically recognize the transcription factor-DNA binding and accurately convert the detection of transcription factors to the detection of DNA, the proposed strategy realized the reliable detection of model target NF-κB p50 with a nanomolar detection limit. This strategy was also employed to detect the inhibition effect of oridonin, a known inhibitor of NF-κB. Furthermore, perfect recoveries were obtained when detecting the targets in HeLa cells lysate, demonstrating the feasibility of this strategy for transcription factor detection in biological samples. [ABSTRACT FROM AUTHOR]

In this paper, a novel biosensor based on Carbon dots (C-dots) for sensitive detection of hydroquinone (H 2 Q) is reported. It is interesting to find that the fluorescence of the C-dots could be quenched by H 2 Q directly. The possible quenching mechanism is proposed, which shows that the quenching effect may be caused by the electron transfer from C-dots to oxidized H 2 Q-quinone. Based on the above principle, a novel C-dots based fluorescent probe has been successfully applied to detect H 2 Q. Under the optimal condition, detection limit down to 0.1 μM is obtained, which is far below U.S. Environmental Protection Agency estimated wastewater discharge limit of 0.5 mg/L. Moreover, the proposed method shows high selectivity for H 2 Q over a number of potential interfering species. Finally, several water samples spiked with H 2 Q are analyzed utilizing the sensing method with satisfactory recovery. The proposed method is simple with high sensitivity and excellent selectivity, which provides a new approach for the detection of various analytes that can be transformed into quinone. [ABSTRACT FROM AUTHOR]

Abstract: We report on an ultrasensitive and selective fluorescence assay for Sudan I and III against the influence of Sudan II and IV based on ligand exchange mechanism. Calcein as a fluorescence indicator and Sudan I–IV as model analytes were employed to investigate the analytical feature of this assay platform. Results show that the fluorescence of calcein can be efficiently quenched by Cu(II). When the ligand exchange reaction proceeds, calcein is deprived of Cu(II) by Sudan I and III, resulting in the fluorescence recovery of calcein. However, the ligand exchange reaction does not happen in the presence of Sudan II or IV due to the 2-methyl steric effects, which is favorable for selective determination of Sudan I and III against the influence of Sudan II and IV. It was found that the fluorescence enhancement efficiency (FEE) against the concentration of Sudan (c Sudan, nmol L−1) shows a linear relationship. The calibration equations are FEESudan I=0.0032 c Sudan I−0.02613, and FEESudan III=0.0033 c Sudan III−0.02467 over the corresponding linear range of 11.25–2078.29 and 9.44–1035.78nmolL−1 with the correlation coefficients (R 2) of 0.9984 and 0.9955, respectively. And the detection limits (3σ/slope) are calculated to be 211.3 and 208.5pmolL−1 for Sudan I and III, respectively, showing ultralow detection limit. The Sudan dye in a commercial chilli powder sample was assayed with satisfactory results. [Copyright &y& Elsevier]

Abstract: In this paper, aiming at the trans-membrane transport properties of the different DLCs related with the cytotoxicities, we have studied photophysics of DLCs in RMs. MTT assays indicated that DLC 1 were more cytotoxic than DLC 2 and 3. Steady-state absorption and fluorescence method have been used to characterize the binding model of three DLCs (1, 2, and 3) in RMs and bovine serum albumin (BSA). The progressive red-shift of compound 1 indicated that it can experience the hydrophilic and hydrophobic environment owing to the rigid structure, thus it can more easily cross the double membrane of cell than compounds 2 and 3. In conclusion, we simulated a model of compound 1 in RMs. The present study of F16 derivatives in microenvironment would provide some useful information to the cell membrane simulation and design of DLCs. [Copyright &y& Elsevier]

Abstract: The fluorescence of ciprofloxacin (CIP) in HAc–NaAc buffer solution and the presence of cetyltrimethylammonium bromide (CTMAB) enhanced visibly with adding Al(III) and La(III). This enhanced fluorescence spectra were studied, and a new co-luminescence system of CIP+Al(III)+La(III)+CTMAB was discovered. There was a linear relationship between the enhanced fluorescence intensity and the concentration of CIP in the range of 0.50–80.2μgl−1 under the optimized condition. A novel enhanced fluorescence method for the determination of trace CIP was established by using this co-luminescence system. The detection limit of the proposed method was 0.17μgl−1 for CIP. This method is simple, rapid and sensitive. The CIP in milk samples were analyzed by the proposed method with satisfactory results. The relative standard deviation and the recovery were in ranges of 3.21–4.34% and 97.1–100.1%, respectively. The mechanism of the co-luminescence reaction and the reasons for fluorescence enhancement has been discussed. [Copyright &y& Elsevier]

Abstract: The interactions between fluoroquinolones and human serum albumin (HSA) were investigated by affinity capillary electrophoresis (ACE) and fluorescence quenching technique. Based on the efficient separation of several fluoroquinolones using a simple phosphate buffer, the binding constants of fluoroquinolones with HSA were determined simultaneously during one set of electrophoresis by ACE method. The thermodynamic parameters were obtained from data at different temperatures, and the negative ΔH and ΔS values showed that both hydrogen bonds and van der Waals interaction played major roles in the binding of fluoroquinolones to HSA. The interactions were also studied by fluorescence quenching technique. The results of fluorescence titration revealed that fluoroquinolones had the strong ability to quenching the intrinsic fluorescence of HSA through the static quenching procedure. The binding site number n, apparent binding constant K b and the Stern–Volmer quenching constant K sv were determined. The thermodynamic parameters were also studied by fluorescence method, and the results were consonant with that of ACE. [Copyright &y& Elsevier]

Abstract: There is a constant need for simple, economical and time-efficient methods which allow evaluating a compound''s ability to penetrate the biological membrane, one of the key parameters needed to characterize biologically active compounds. In the paper we propose a new method of permeability determination. Instead of detecting the compound''s concentration directly, we employ an approach in which the membrane interface is labeled with a fluorescein lipid probe; the probe is sensitive to the presence of charged compounds. The fluorescence intensity changes of the dye permanently attached to both sides of a model lipid bilayer are measured. Specifically, the time course of the fluorescence intensity changes following a rapid induction of a non-equilibrium state of the sample allows the evaluation of the membrane permeability for the compound. The method was validated by the determination of the phenyltin compound''s transport through the model phosphatidylcholine unilamellar liposome bilayer. [Copyright &y& Elsevier]

Abstract: A new simple, selective and sensitive method for the determination of trace chlorine dioxide in water has been developed, based on the oxidation by chlorine dioxide to reduction the fluorescence of rhodamine dyes in ammonia–ammonium chloride buffer solution. Four rhodamine dyes systems such as rhodamine S, rhodamine G, rhodamine B and butyl-rhodamine B were tested. The rhodamine S system is the best, with a linear range of 0.0060–0.450μgmL−1 and a detection limit of 0.0030μgmL−1 ClO2. It was applied to the determination of chlorine dioxide in synthetic samples and real samples, with satisfactory results. This method has good selectivity, especially, other chlorine species such as chlorine, hypochlorite, chlorite and chlorate do not interfere the determination. The mechanism of fluorescence reduction was also considered. [Copyright &y& Elsevier]

The electrochemical characteristics of kanamycin onto self-assembled monolayer (SAM) modified gold electrode (SAM/Au) is investigated by cyclic voltammetry. In the potential range 0–0.6 V, Cu(II) yields a pair of stable redox waves at the bare gold electrode. Epa is located at 0.189 V and Epc at 0.254 V. In contrast, Cu(II) is reduced at a more positive potential and a decreasing current at the kanamycin SAM/Au electrode. Cu(II) and kanamycin can form a stoichiometry complex with chemical ratio of 2:1. The interaction of Cu(II)–kanamycin complex with calf thymus DNA is also studied in the solution. And the interactive mode between Cu(II)–kanamycin complex and DNA is verified by the fluorescence method. Binding constants (K) of the Cu(II)–kanamycin complex to DNA and binding site size (s) are calculated from voltammetric data and equal to 1.5 × 107 l/mol and 4 bp, respectively. [Copyright &y& Elsevier]

The location of isoniazid and rifampicin, two tuberculostatics commonly used for the treatment of Mycobacterium tuberculosis and Mycobacterium avium complex infectious diseases, in bilayers of dimyristoyl-l-α-phosphatidylcholine (DMPC) and dimyristoyl-l-a-phosphatidylglycerol (DMPG) have been studied by 1H NMR and fluorimetric methods. Steady-state fluorescence intensity and fluorescence energy transfer studies between rifampicin and a set of functionalized probes {n-(9-anthroyloxy)stearic acids, n=2, 12} reveal that, in both systems, isoniazid is located at the membrane surface whereas rifampicin is deeply buried inside the lipid bilayers. Steady-state fluorescence anisotropy studies performed with the probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and trimethylammonium-diphenylhexa-triene (TMA-DPH), not only corroborate the above results, but also show that no changes in membrane fluidity were detected in either liposome. The 1H NMR results, in DMPC liposomes, confirm the location of rifampicin near the methylene group of the acyl chains of the lipid bilayers. [Copyright &y& Elsevier]

[Display omitted] • A novel sensor for multiple metal ions is developed with fluorescent lanthanide coordination polymers. • Depending on principal component analysis (PCA), a series of metal ions can be clearly differentiated. • The fluorescence-PCA sensor is capable of quantitatively analyzing Cu2+ and Ag+ with desirable performance. • Composition of Eu3+/Tb3+ and Fe3+/Fe2+ pairs is also quantified with the proposed method, manifesting great potential of the sensor in multi-target analysis. Approaches oriented toward multi-target analysis are of practical value in obtaining comprehensive information. Herein, discrimination and quantification of multiple metal ions are achieved with fluorescent lanthanide coordination polymer networks (Ln-CPNs) and principal component analysis (PCA). By self-assembly of poly-phosphates (pyrophosphate, PPi or tripolyphosphate, STPP) and cerium ion (Ce3+), two Ln-CPNs are synthesized and emit intense fluorescence due to the ligand field effects of PPi and STPP on Ce3+. Relying on the coordination between poly-phosphates and various metal ions, additional metal ions may compete with Ce3+ for PPi or STPP, forming metal ion-doped Ln-CPNs and adjusting ligand field effect, which subsequently results in the variation of fluorescence intensity. The changes in fluorescence are further processed with PCA and presented with two principal component factors (PC1 and PC2). Accordingly, 14 lanthanide and 12 transition/post-transition metal ions can be evidently identified. Meanwhile, Cu2+ and Ag+ can be accurately quantified depending on relations between dominant PC1 and concentrations of metal ions. Moreover, the fluorescence-PCA sensor is employed to evaluate the composition of Eu3+/Tb3+ and Fe3+/Fe2+ pairs in their mixtures, manifesting its superiority over inductively coupled plasma-atomic emission spectroscopy. Therefore, this work provides an alternative perspective of developing nanomaterials-based fluorescence sensor for multi-target analysis. [ABSTRACT FROM AUTHOR]

In this work, the Pt nanoclusters with an average size of 1.7 ± 0.3 nm were prepared by a facile and green method using polyvinylpyrrolidone (PVP) as both stabilizer and reductant. The oxidase-like activity of PVP-stabilized Pt nanoclusters (PVP-Pt NCs) was investigated by the catalytic oxidation of o-phenylenediamine (OPD). The mechanism studies indicated that PVP-Pt NCs performed as oxidase enzyme mimics by catalyzing the dissolved oxygen to generate the reactive oxygen species (singlet oxygen and superoxide anion) intermediates. Ascorbic acid (AA) could also be oxidized to dehydroascorbic acid (DHA) which could react with OPD to generate a fluorescent compound. On the basis of the robust oxidase-like activity of PVP-Pt NCs, both colorimetric assay and fluorescence method for AA determination were established. Compared with colorimetric assay, the fluorescence method showed higher sensitivity and selectivity for AA detection. The proposed fluorescence method with the LOD of 1.17 μM could overcome the interference of most reducing substances and showed promising applications in biosensor. The as-prepared PVP-Pt NCs possessed intrinsic oxidase-like property by catalyzing dissolved oxygen to ROS (superoxide anions (·O 2 -) and singlet oxygen (1O 2)) which could oxide the OPD to OPD ox. The inhibition of AA to the catalytic oxidation of OPD was employed to establish the colorimetric assay for AA determination. AA could also be oxidized to DHA by·O 2 - and 1O 2 intermediates, and the DHA could react with OPD to form QD with a fluorescence emission peak at 434 nm. The fluorescence method for AA detection was carried out when the solution changed to yellow color which was the signal of the reaction terminal. Comparing with colorimetric assay, the fluorescence method exhibited enhanced sensitivity and selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

DNA glycosylase is an indispensable DNA damage repair enzyme which can recognize and excise the damaged bases in the DNA base excision-repair pathway. The dysregulation of DNA glycosylase activity will give rise to the dysfunction of base excision-repair and lead to abnormalities and diseases. The simultaneous detection of multiple DNA glycosylases can help to fully understand the normal physiological functions of cells, and determine whether the cells are abnormal in pre-disease. Regrettably, the synchronous detection of functionally similar DNA glycosylases is a great challenge. Herein, we developed a multifunctional dsDNA probe mediated exponential rolling circle amplification (E-RCA) method for the simultaneously sensitive detection of human alkyladenine DNA glycosylase (hAAG) and uracil-DNA glycosylase (UDG). The multifunctional dsDNA probe contains the hypoxanthine sites and the uracil sites which can be recognized by hAAG and UDG respectively to generate apyrimidinic (AP) sites in the dsDNA probe. Then the AP sites will be recognized and cut by endonuclease Ⅳ (Endo IV) to release corresponding single-stranded primer probes. Subsequently, two padlock DNA templates are added to initiate E-RCA to generate multitudinous G-quadruplexes and/or double-stranded dumbbell lock structures, which can combine N-methyl mesoporphyrin IX (NMM) and SYBR Green Ⅰ (SGI) for the generation of respective fluorescent signals. The detection limits are obtained as low as 0.0002 U mL−1 and 0.00001 U mL−1 for hAAG and UDG, respectively. Notably, this method can realize the simultaneous detection of two DNA glycosylases without the use of specially labeled probes. Finally, this method is successfully applied to detect hAAG and UDG activities in the lysates of HeLa cells and Endo1617 cells at single-cell level, and to detect the inhibitors of DNA glycosylases. hAAG and UDG in cell lysates could induce E-RCAs, respectively. SGⅠ and NMM could combine to the double-stranded dumbbell lock structures and G-quadruplexes respectively to generate "turn-on" fluorescent signals, which represented the activities of hAAG and UDG, respectively. [Display omitted] • A highly sensitive and selective method for simultaneous detection of hAAG and UDG activities was proposed. • This method was achieved in homogeneous solution without additional enrichment or separation operation. • The detection limits were obtained as low as 0.0002 U mL−1 and 0.00001U mL−1 for hAAG and UDG, respectively. • The method was applied to detect hAAG and UDG activities in lysates of HeLa and Ende1617 cells at single-cell level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluorescence-method for specific determination of tedizolid phosphate was designed. • Determination of the studied drug in real human plasma. • Facile application of the designed fluorescence-method. • The method presented a novel alternative for pharmacokinetics and bioavailability studies of tedizolid phosphate. A distinctive fluorescence method for specific and sensitive determination of tedizolid (a novel oxazolidinone antibacterial) was designed. The presented method relies on fluorescence quencher-removal strategy, which turns the weak fluorescence signal of tedizolid into a stronger one, in acidic ethanolic system (pH 3.5), due to suppression of the intramolecular twisted internal charge transfer (TICT) process. Allowing its determination in bio-fluids and commercial dosage form without any interference at 395 nm after excitation at 300 nm, for the first attempt, the detection and quantification limits were 5.27 and 15.97 (n g m L - 1) , respectively over a concentration range of 25.0–800.0 n g m L - 1 . Moreover, the high sensitivity of the developed method permits its clinical application for efficient and direct determination of the studied drug in biological fluids with good recovery (90.63 ± 1.84%). Additionally, facile application of our intended method paves the way for application in quality control laboratories without sample pretreatment or exhausting extraction steps. [ABSTRACT FROM AUTHOR]

Abnormal DNA glycosylases are concerned with the aging process as well as numerous pathologies in humans. Herein, a sensitive fluorescence method utilizing target-induced ligation-dependent tricyclic cascade amplification reaction was developed for the detecting DNA glycosylase activity. The presence of DNA glycosylase triggered the cleavage of damaged base in hairpin substrate, successively activating ligation-dependent strand displacement amplification (SDA) and exponential amplification reaction (EXPAR) for the generation of large amount of reporter probes. The resultant reporter probes bound with the signal probes to form stable dsDNA duplexes. And then the signal probes could be digested circularly in the dsDNA duplexes by T7 exonuclease, leading to the generation of an enhanced fluorescence signal. Due to the high efficiency of tricyclic cascade amplification and the low background signal deriving from the inhibition of nonspecific amplification, this method exhibited a detection limit of 0.14 U/mL and a dynamic range from 0.16 to 8.0 U/mL. Moreover, it could be applied for detecting DNA glycosylase activity in human serum with good selectivity and high sensitivity, and even quantifying other types of enzyme with 5′-PO 4 residue cleavage product by rationally designing the corresponding substrate. Importantly, this method could be performed in homogenous solution without any complicated separation steps, providing a new strategy for DNA glycosylase-related biomedical research. We develop a fluorescence method for sensitive detection of formamidopyrimidine-DNA glycosylase (FPG) by target-triggering ligation-dependent tricyclic cascade amplification. Image 1 • A ligation-dependent tricyclic cascade amplification reaction is introduced to detect DNA glycosylase. • The method shows high sensitivity with a detection limit as low as 0.14 U/mL for FPG DNA glycosylase. • The method could be performed in homogenous solution. [ABSTRACT FROM AUTHOR]

Two beams superposition is one common knotty problem in many scientific research fields like stimulated emission depletion (STED) microscopy related technology. The mainstream method of two laser beams are mutually aligned by using scattering image. This process is pretty complicated, time-consuming and non-real-time. Here we demonstrate a novel method that can improve the two beams superposition course by using spectrum method and this advance has been facilitated by a confocal facility. Any fluorescent materials can be used so long as they can be induced fluorescence by the corresponding laser beams wavelengths in the experiment. This approach is very simple and more practical relative to other ways and we believe it will be extensively used by lots of researchers in the future. [ABSTRACT FROM AUTHOR]