Mo5N6 nanosheets for fluorescent quenching and target recognition: Highly selectively sensing of sodium hexametaphosphate

Typical fluorescent biosensors use fluorescently labeled ssDNA for target recognition and nanomaterials for signal transduction. Herein, we propose a reverse sensing strategy that Mo5N6 nanosheets are used for target recognition while fluorescein (FAM)-labeled ssDNA only serves for signal generation. We discover that Mo5N6 nanosheets show high fluorescence quenching ability (>95%) and selective recognition for sodium hexametaphosphate (SHMP). After FAM-labeled ssDNA is adsorbed on Mo5N6 nanosheets, the fluorescence is quenched due to the photoinduced electron transfer (PET) effect between FAM and Mo5N6 nanosheets. SHMP can specifically displace the adsorbed FAM-labeled ssDNA from Mo5N6 nanosheets, resulting in more than 80% fluorescence recovery on addition of 5 μmol L-1 SHMP. This biosensor can sensitively detect SHMP down to 150 nmol L-1 and selectively recognize SHMP over glucose, lactose, common amino acids, Zn2+, Mg2+, Ca2+ and other phosphates (such as Na2HPO4, sodium pyrophosphate, sodium tripolyphosphate). This biosensor also shows great potential for the detection of SHMP in bacon sample. This work not only provides a facile sensitive and selective biosensor for SHMP but also exploits the application of transition metal nitrides in the field of sensing and biosensing.

A turn-on fluorescence probe for imaging tyrosinase at the wound site in broken tail of zebrafish

Tyrosinase (TYR) is a copper-containing oxidase that affects the synthesis of melanin in the human body, which is regulate to the pigmentation of the skin. Nevertheless, abnormal expression of TYR can lead to albinism, vitiligo and other skin diseases. Excessive accumulation of TYR is a marker of melanoma cancer and an important factor leading to pigmentation during wound healing, freckles and browning of fruits and vegetables. Efficient tracking of TYR is of significance for studying its pathophysiological mechanism. Herein, we synthesized a benzindole-based fluorescent probe Pro-OH to detect TYR in living cells and zebrafish. The probe displayed a high selectivity and sensitivity in distinguishing TYR from other analytes with the low detection limit of 1.024 U/mL. Importantly, Pro-OH was successfully used to imagine TYR at the wound site of broken tail of zebrafish.

A novel fluorescent "Off-On" probe based on phenanthro[9,10-d]imidazole conjugated polymers (PIPF) for Cr3+ detection with high selectivity and sensitivity

Trivalent chromium (Cr3+) causes serious environmental pollution, degradation of the quality of edible agricultural products and human diseases. A novel phenanthro[9,10-d]imidazole-derived conjugated polymers (PIPF) was obtained from 4-(5,10-dibromo-1H-phenanthro[9,10-d]imidazol-2-yl)phenol and diethyl 4,4'-(2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluorene-9,9-diyl)dibutyrate by Suzuki polymerization reaction, which was reasonably demonstrated by 1H NMR spectroscopy, infrared spectroscopy and quantum chemical calculations. The PIPF exhibits a "turn-on" fluorescence response to Cr3+ in DMSO/H2O (98:2, v/v) with naked-eye detection. The limit of detection for Cr3+ was calculated to be 0.073 μM with a linear range of 3-9 μM. The possible mechanism of the PIPF-based Cr3+ fluorescence "turn-on" sensor is due to the inhibition of the PET process by the coordination of Cr3+ to the hexaalkyl ester carbon chain of PIPF (RCOO-). The high sensitivity, good selectivity, and utility of this sensor indicated that PIPF-based "turn-on" fluorescence sensor is a potential fluorescence application for measuring Cr3+ in environmental samples.

A Dual-target Fluorescent Chemosensor for Detecting Indium (III) and Hypochlorite with High Selectivity

A dual-target fluorescent chemosensor BQC (((E)-N-benzhydryl-2-(quinolin-2-ylmethylene)hydrazine-1-carbothioamide) was synthesized for detecting In3+ and ClO-. BQC displayed green and blue fluorescence responses to In3+ and ClO- with low detection limits (0.83 µM for In3+ and 2.50 µM for ClO-), respectively. Importantly, BQC is the first fluorescent chemosensor capable of detecting In3+ and ClO-. The binding ratio between BQC and In3+ was determined to be a 2:1 through Job plot and ESI-MS analysis. BQC could be successfully utilized as a visible test kit to detect In3+. Meanwhile, BQC showed a selective turn-on response to ClO- even in the presence of anions or reactive oxygen species. The sensing mechanisms of BQC for In3+ and ClO- were demonstrated by 1 H NMR titration, ESI-MS and theoretical calculations.

A quinoline derived Schiff base as highly selective 'turn-on' probe for fluorogenic recognition of Al3+ ion

A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al3+ ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, 1H/13C NMR, UV-Vis and fluorescence spectral techniques. The crystal structure of the QnSb was confirmed by single crystal X-ray diffraction (SC-XRD) analysis. Notably, almost non-fluorescent QnSb served as a 'turn on' responsive probe for Al3+ by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al3+ in CH3CN/H2O (4:1, v/v) solution over several competing metal ions (e.g., Mg2+, Pb2+, Zn2+, Cd2+, Co2+, Cu2+, Ca2+, Ni2+, Fe3+/2+, Cr3+, Mn2+, Sn2+, and Hg2+). The limit of detection (LoD) was computed as low as 15.8 nM which is significantly lower than the permissible limit set by WHO for Al3+ ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al3+ was established with the help of Job's plot, ESI-MS, NMR and DFT analyses. Based on its remarkable sensing ability, the probe QnSb was utilized to establish molecular logic gates, and the fluorescence detection of Al3+ could clearly be demonstrated on the filter paper test strips.

A Novel Rhodamine-Phenolphthalein Architecture for Selective Mercury Ion Detection in Aqueous Media

In this study, the primary objective is to synthesize a novel fluorescent Rh-PP-Rh compound and explore its extensive range of photochemical behaviors. Initially, the synthesis of the novel Rh-PP-Rh was carried out for this purpose. Subsequently, UV-Vis and fluorescence spectroscopy were employed to investigate the interactions between Rh-PP-Rh and a diverse array of ions in aqueous solvent systems. Through fluorescence and UV-Vis studies, it was observed that Rh-PP-Rh demonstrated turn-on sensor properties in the presence of Hg2+ ions. Furthermore, the limits of detection (LOD) and association constant (Ka ) values for Rh-PP-Rh/Hg2+ were determined as 334 nM and 9.13×1011  M-2 , respectively. Additionally, the reversible studies demonstrated a switchable on/off response upon alternate addition of HgCl2 and [Bu4 N]F to Rh-PP-Rh. These findings suggest that the probe Rh-PP-Rh also possesses specific sensor properties for F- ions in the presence of mercury. In addition, the investigation encompassed an assessment of the visual analysis of the color alterations of Rh-PP-Rh both on filter paper and in an EtOH/H2 O solution. The findings demonstrated that Rh-PP-Rh can be successfully utilized in solutions containing mercury, as it generates significant color transformations.

Alkaline phosphatase triggered gold nanoclusters turn-on fluorescence immunoassay for detection of Ochratoxin A

Ochratoxin A (OTA) is a highly toxic mycotoxin which can cause a variety of diseases. Sensitive detection of OTA is significant for food safety. Herein, a feasible and sensitive immunoassay was established for OTA detection by alkaline phosphatase (ALP) triggered gold nanoclusters (AuNCs) turn-on fluorescence. The fluorescence of the AuNCs can be quenched by Cr6+ induced aggregation of AuNCs and the fluorescence resonance energy transfer (FRET) between AuNCs and Cr6+. Under the catalytic action of ALP-labelled IgG (IgG-ALP), the ascorbic acid 2-phosphate (AA2P) was hydrolyzed to ascorbic acid (AA) for the reducing of Cr6+ to Cr3+. As a result, the degrees of AuNCs aggregation and FRET were weakened and the fluorescence of AuNCs was turned on. The amount of OTA in the sample was negatively correlated with the amount of IgG-ALP captured by anti-OTA monoclonal antibody (McAb) in the microplate. In optimal conditions, the turn-on fluorescence immunoassay had a good linear range of 6.25-100 ng/mL, and the detection limit was 0.693 ng/mL. The recoveries of OTA from corn were 95.89%-101.08% for the fluorescence immunoassay. This work provided a feasible, sensitive and good selectivity fluorescence method for OTA detection.

A novel 2-(2-aminophenyl) imidazo [1,5-a] pyridine-based fluorescent probe for rapid detection of phosgene

Phosgene is a highly concealed and highly toxic gas that seriously threatens human health and public security. Therefore, the detection of phosgene is of great significance to world security. Herein, a new type of fluorescent probe based on 2-(2-aminophenyl) imidazo [1,5-a] pyridine is reported for the rapid detection of phosgene. The probe itself only emits a faint green fluorescence, while phosgene allows it to produce a strong blue fluorescence. During the recognition process, phosgene interacts simultaneously with both amino site and imidazole moiety in the probe molecule, resulting in a four-ring-fused rigid structure with high fluorescence quantum yield. The probe not only has the characteristics of high efficiency, high sensitivity (detection limit 2.68 nM), and high selectivity, but also has remarkable spectral changes. Finally, a portable test strip is used to detect phosgene in the gas phase, and the fluorescent color change of the test strip can be easily observed. The most exciting thing is that the portable test strip with the probe PMPY-NH2 can produce a strong fluorescence response to 1 ppm of phosgene, which is far lower than the level of phosgene that seriously threatens to human health.

A novel turn-on fluorescent probe for detection of pH in extremely acidic environment and its application

A water-soluble turn-on fluorescent probe PNAP for pH has been designed and synthesized. PNAP was consist of pyrene as fluorophore and morpholine as receptor. Owing to the photoinduced electron transfer (PET) effect, the fluorescence of PNAP was quenched, while PNAP exhibited a remarkable "turn-on" fluorescence with the increase of acidity. Notably for its pKa of 2.15, PNAP was one of the pH fluorescent probes used in extremely acidic environments. Furthermore, PNAP also displayed good repeatability, strong anti-ion interference ability, high sensitivity and selectivity toward pH. In addition, PNAP has been successfully applied to the test strips and monitor the pH of environment water samples and realistic samples, showing its good promising prospect.

Carbon dots-based fluorescence enhanced probe for the determination of glucose

In this work, a novel "turn-on" fluorescence sensor for the detection of H2O2 and glucose was developed based on green fluorescent carbon dots (CDs). The CDs was newly prepared by a facile one-pot hydrothermal method with Eosin Y and branched polyethylenimine as precursors. Interestingly, in the presence of H2O2 and HRP, the fluorescence of the CDs enhanced significantly with a red-shift emission due to their "aggregation". Meanwhile, the oxidation of glucose catalyzed by glucose oxidase could generate H2O2. Thus, a simple sensing system based on the CDs as fluorescent probes was constructed for H2O2 and glucose determination, avoiding the fluorescence quenching and subsequent recovery process in conventional turn-on strategy. The method showed good selectivity and sensitivity for glucose sensing with the detection limit of 0.12 μM. The method was further applied to glucose detection in real samples. The obtained results demonstrated the simplicity, selectivity and practicality of the method. This work expands the carbon nanomaterials with fluorescence emission enhancement properties. It provides a new and direct "turn-on" strategy for H2O2 and glucose detection, which could be a simple and effective tool for screening biological substances involved in H2O2-generation reaction.

Fluorescence turn-on mode of Eu3+ complex nanocomposite to detect histamine for seafood freshness

Biogenic amines (BAs), which naturally occur as chemicals in seafood, are indicators of food freshness and quality. High concentrations of BAs can cause an undesirable inflammatory response. However, traditional detection methods cannot meet the needs of rapid analysis nowadays. It is essential to explore a simple and valid method to monitor the food quality. Herein, we design and prepare a nanoclay-based turn on fluorescent material with BAs response, which could be used for the real-time and visual detection of raw fish freshness. As the concentration of BAs increase, the sensor of the fluorescence signal is significantly enhanced. The sensor demonstrated wonderful response and sensitivity which showed a detection limit of 0.935 mg/L for typical BAs histamine within a linear range of 2-14 mg/L in an aqueous solution. More importantly, we developed a responsive BAs device by doping the sensor into polyvinyl alcohol (PVA), which is well applied as a rapid-responsive fluorescent marker for visual monitoring the freshness of raw fish.

Chromium hydroxide nanoparticles-based fluorescent aptameric sensing for sensitive patulin detection: The significance of nanocrystal and morphology modulation

The widespread of patulin (PAT) and its potential hazards to human health call for alternative rapid assays to monitor it in food and the environment. Herein, we prepared chromium hydroxide [Cr(OH)₃] nanoparticles via a one-pot chemical precipitation strategy and used them to fabricate a turn-on fluorescent aptasensor employing a morphological effect for sensitive PAT detection. Three Cr(OH)₃ nanoparticle structures were synthesized by changing the solvent, and their structures and physicochemical properties were investigated. Then, we evaluated the effects of morphological structures on the fluorescence quenching-recovery capability of Cr(OH)₃ nanoparticles before and after incubation with PAT. We found that the Cr(OH)₃-3 nanoparticles efficiently absorbed the fluorescence dye 6-carboxyfluorescein labeled aptamer (FAM-Apt) and quenched the fluorophore through photoinduced electron transfer. Under optimal experimental conditions, the turn-on fluorescent aptasensor for PAT determination displayed two linear ranges (0.01-10 ng/mL and 1-200 ng/mL) with a low detection limit of 7.3 pg/mL. Moreover, the proposed aptasensor had no cross-reactivity with interferents that usually coexist with PAT and can be used to detect PAT in apple juices accurately. The results of the as-fabricated method were not significantly different from the high-performance liquid chromatography. Hence, we demonstrated that different Cr(OH)₃ nanoparticles can be prepared by changing reaction conditions, and provided a novel strategy to improve the detection performance of fluorescent aptasensor by changing the morphological structure and crystalline properties of nano-quenchers.

Iminobenzophenone-thiophen hydrazide schiff base: a selective turn on sensor for paramagnetic Fe3+ ion and application in real sample analysis

A highly selective turn-on sensor for paramagnetic Fe³⁺ ions based on (E)-N'-((2-aminophenyl)(phenyl)methylene)thiophene-2-carbohydrazide is successfully synthesized. The sensor BPTH is significantly selective and sensitive towards Fe³⁺ ions over other interfering metal ions especially Cu²⁺ and Co²⁺ ions with a lowest limit of recognition 1.48 × 10^-7 M. The turn-on sensing mechanism involves enhanced charge transfer. Fe³⁺ ion forms strong binding with the ligand with a K_a value about 8.23 × 10⁴ M^-1 and a 1:1 stoichiometric ratio is confirmed by Job's plot experiment. With Fe³⁺ ion, the yellow ligand BPTH change to a green fluorescent and reversible with 1 equivalent of EDTA. Practical application of sensor is demonstrated in real sample analysis.

Selective turn-on fluorescence sensing of Fe2+ in real water samples by chalcones

The design of fluorescence sensor for selective detection of Fe²⁺ is very important as it is part of different biochemical redox system related to a number of diseases. In many occasion sensors are unable to distinguish Fe²⁺ from Fe³⁺ ions. In the present work, we report simple chalcone type sensors for sensing Fe²⁺ ions in semi aqueous system. The receptors R1 and R2 have showed excellent sensing properties at pH 7 in CH₃OH-H₂O (1:1, v/v) solvent system. The fluorescence emission intensity of the complexes between hosts and Fe²⁺ is least affected by the other competitive metal ions leading to the formation of very tight host-guest complex. The LOD for the R1 and R2 for Fe²⁺ are 1.91 μM and 3.54 μM respectively, which is quite low in compared to the many other reported sensors. The practical applicability of these sensors is determined by the detection of Fe²⁺ in real water samples. So chalcones would be cost effective PET inhibited fluorescence sensor for Fe²⁺.

Tetraphenylethylene sulfonate derivative as turn-on fluorescent sensor for berberine chloride detection in aqueous solution

A negatively-charged tetraphenylethylene derivative (TPE-SE) was designed and synthesized as turn-on fluorescent sensor for berberine chloride (BBC) detection in aqueous solution. The fluorescent property and detection mechanism were elucidated by UV-vis absorption spectra, photoluminescence spectra, dynamic light scattering experiments. The results reveal that the BBC can lead to aggregation-induced emission of TPE-SE due to the electrostatic interactions, endowing TPE-SE with excellent turn-on detecting ability, high selectivity and sensitivity to BBC. The detection limit is as low as 6.58 × 10^-6M. These results should be applicable to fabricate special turn-on fluorescent sensors towards various antibiotics, and it is crucially important for achieving reasonable control and intake of small biomolecules.

Fluorescence Variation in Selective Sensing of Hg2+and Cu2+ Ions By Coumarin-xanthene Fused Optical Probe

The fluorescent moieties coumarin and xanthene (R6GCP) combined in a single molecule was designed and synthesized. The colorimetric and fluorescent variation of the probe towards the copper and mercury ions sensing is examined. With the added copper/mercury ions to the solution of R6GCP in DMF:H2O (2:8, v/v), the probe showed deep red color from yellow color. The probe showed turn-off and turn-on fluorescence for copper and mercury ion respectively. In the presence of other competing metal ions, the probe showed better sensitivity towards copper and mercury ions. The probe's detection limit found to be 5.29 × 10^-6 M and 1.24 × 10^-5 M for Cu²⁺ and Hg²⁺ ion respectively by the UV-visible spectral measurement. Fluorescence measurement, the detection limit for the Cu²⁺ and Hg²⁺ ions detection by this probe is 1.91 × 10^-7 M, and 1.32 × 10^-8 M respectively. 1:1 binding stoichiometry was confirmed between the probe and Cu²⁺/Hg²⁺ ions from jobs plot by UV-visible spectral technique. Moreover, R6GCP combined filter paper were prepared. These test paper containing probe could detect Cu²⁺/Hg²⁺ ions in real-time with a spontaneous color change.

Novel nitrogen-doped carbon dots for "turn-on" sensing of ATP based on aggregation induced emission enhancement effect

In this work, a nitrogen-doped carbon dots (CDs) was successfully synthesized by hydrothermal synthesis of polyethylenimine (PEI) and citric acid. The as-prepared CDs suffered from aggregation-caused quenching (ACQ) with a high concentration, but after adding adenosine triphosphate (ATP), the CDs aggregated. The generation of aggregates caused the rotation of the surface groups on CDs and reduced the non-radiation decay. The QY of CDs in water was 9.25 %, and increased to 16.60 % and 63.38% in the addition of 100 and 1000 μM ATP. And then, the enhancement of the radiation rate led to the aggregation induced enhancement effect (AIEE). Moreover, we also found that the proportion of precursors for CDs synthesis was a key factor in the occurrence of AIEE. Therefore, such CDs would be excellent candidates as fluorescent probes for the label-free detection of ATP. Our proposed method exhibited simple and easy preparation of nanoprobe, quick response (3 min), wide range of linear rage (1-2000 μM) and eco-friendly. In addition, the method performed successfully as a "turn-on" sensor for detection of ATP in the tablet with a recovery of 100.1~106.9% and RSD below 3.5%.

Methyl viologen induced fluorescence quenching of CdTe quantum dots for highly sensitive and selective "off-on" sensing of ascorbic acid through redox reaction

A turn-on fluorescent sensor based on CdTe quantum dots (QDs) is designed for highly sensitive and selective ascorbic acid (AA) detection. CdTe shows a strong emission centered at 578 nm. When assembled with poly(sodium 4-styrenesulfonate) (PSS) and methyl viologen (Mv²⁺) through electrostatic interaction, the emission is found to be effectively quenched. In the presence of AA, Mv²⁺ is reduced to Mv⁺, making the fluorescence of CdTe QDs restored. Under the optimal conditions, the proposed AA sensing method shows a linear proportional response from 0.8 µM to 20 µM, with the detecting limit as low as 50 nM. The developed method was successfully applied in the analysis of AA in human serum samples and cell lysates with satisfactory results.

A novel hydrazone-based fluorescent "off-on-off" probe for relay sensing of Ga3+ and PPi ions

A novel hydrazone-based fluorescent probe (E)-3-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-4H-chromen-4-one (BTC) has been rationally designed and synthesized. BTC can subsequently detect Ga³⁺ and PPi ions through the absorption and emission off-on-off response with high specificity. Importantly, fluorescent probe BTC can well discriminate Ga³⁺ from Al³⁺ and In³⁺. The association constant (K) was calculated as 2.06 × 10⁴M^-1, and the limit of detection (LOD) was calculated as 4.88 × 10^-2μM. Competitive binding studies also illustrated good results of the probe BTC towards Ga³⁺. Job's plot and HRMS results substantiated the 1:1 stoichiometry between BTC and Ga³⁺ ion. The interaction binding mode of BTC with Ga³⁺ was proposed by HRMS, ¹H NMR spectral titration, UV-vis absorption and fluorescence spectral measurements. The combination of the restraint of the photo-induced electron transfer (PET) process and the chelation enhanced fluorescence (CHEF) process is responsible for the fluorescence enhancement of this probe. The in situ chelated BTC-Ga³⁺ could further monitor pyrophosphate ion (PPi) by demetallization process with quenching fluorescence emission. Additionally, the BTC and BTC-Ga³⁺ showed good cell permeability and could detect Ga³⁺ and PPi ions in onioninner epidermal cells, respectively.

A two-photon fluorescence probe with endoplasmic reticulum targeting ability for turn-on sensing photosensitized singlet oxygen in living cells and brain tissues

Endoplasmic reticulum (ER) is an indispensable organelle responsible for protein synthesis, transportation, and maintenance of Ca²⁺ homeostasis in eukaryotic cells. Recent studies highlighted that ER-targeted photosensitizers with high yield of singlet oxygen (¹O₂) are effective in selectively disrupting ER function and are promising candidates for anticancer therapy. Unfortunately, no ER targetable fluorescent probes for determining ¹O₂ photosensitized in this photodynamic therapy process is available. In this work, we synthesized an ER-targetable, two-photon fluorescence probe, ER-¹O₂, for fluorescence turn-on sensing of ¹O₂. ER-¹O₂ demonstrated high sensitivity to ¹O₂ sensing with a wide detection range (0-2.75 μM) and a low detection limit (0.11 μM). ER-¹O₂ also displayed excellent selectivity toward ¹O₂ out of other ROS and metal ions. Notably, ER-¹O₂ exhibited low cytotoxicity but with specific ER targetable capability. On account of these advantageous features, fluctuations of ¹O₂ in living cells and brain tissues were effectively visualized by ER-¹O₂.

Graphene oxide-regulated low-background aptasensor for the "turn on" detection of tetracycline

Tetracyclines (TC) are a common antibiotic for using in livestock breeding and healthcare; however, due to the inappropriate application of TCs, more than 75% of TCs are excreted and released into the environment in an active form through human and animal urine and feces, which results in high levels of TCs in the ecological system, causing adverse effects on the food safety and human health. Thus, the high-performance monitoring of TC pollution is necessary. In this work, a highly sensitive fluorescent aptasensor was developed that was based on graphene oxide (GO) regulation of low background signal and target-induced fluorescence restoration. In the absence of analyte, the DNA probe (TC aptamer) was adsorbed completely by GO and failed to enhance the fluorescence of SYBR gold (SG), thereby resulting in a low background signal. When the TC-included samples were added, the DNA probe formed an aptamer-TC complex, thereby separating from the surface of the GO and inducing the fluorescence of SG. Under optimal conditions, the proposed strategy could detect TC concentrations of less than 6.2 × 10^-3 ng mL^-1, which is four orders of magnitude better than the detection limit of the "turn off" mode (53.9511 ng mL^-1). Moreover, this aptasensor has been used to detect TC from milk samples and wastewater samples, and its satisfactory performances demonstrate that the proposed strategy can be applied in practice for TC monitor in food safety and environmental protection. Therefore, we believe that this work is meaningful in pollution monitoring, environment restoration and emergency treatment.

A hydrazone-based spectroscopic off-on probe for sensing of basic arginine and lysine

A simple probe BHN based on naphthol and benzothiazole is reported for detecting of arginine (Arg) and lysine (Lys) with high selectivity and sensitivity. The BHN in aqueous solution upon reacting with Arg or Lys induced a visible color change from colorless to yellow. The probe BHN can also be employed for fluorescence turn-on sensing of Arg and Lys with the limits of detection (LOD) of 5.20 × 10^-2 μM and 3.69 × 10^-2 μM, respectively. The naked eye colorimetric and fluorimetric detecting is lack of sensitive to other common amino acids including Gly, Ala, Ser, Pro, Val, Thr, Cys, Leu, Ile, Asn, Asp, Glu, Gln, Met, His, and Phe. The sensing mechanism has been proposed by pH investigation and ¹H NMR spectra.

A switchable and signal-amplified aptasensor based on metal organic frameworks as the quencher for turn-on detection of T-2 mycotoxin

A simple and low-cost fluorescence aptasensor was developed for rapid and sensitive signal amplification detection of T-2 mycotoxin (T-2). Dual-terminal-fluorescein amidite (FAM)-labeled aptamer (D-aptamer) acted as a recognition element and signal indicator. The metal organic frameworks (MOFs) of N, N'-bis(2-hydroxyethyl)dithiooxamidato copper (II) (H₂dtoaCu) were as the quencher. The D-aptamer was initially adsorbed to the surface of H₂dtoaCu, leading to efficient quenching of the aptasensor. Upon addition of T-2, the D-aptamer underwent a conformation change to form the T-2/T-2 aptamer complex, which induced the signaling probe to be released from the H₂dtoaCu surface. Thus, the fluorescence intensity (FL) of the D-aptamer was recovered. Versus the single-terminal-FAM-labeled aptamer (S-aptamer), the D-aptamer showed a lower detection limit of 0.39 ng/mL. The aptasensor was also successfully applied to detect T-2 in corn and wheat samples with good recoveries.

A near-infrared-emission aza-BODIPY-based fluorescent probe for fast, selective, and "turn-on" detection of HClO/ClO. Talanta 2021;233:122581. [PMID: 34215073 DOI: 10.1016/j.talanta.2021.122581]

A novel near-infrared-emitting aza-BODIPY-based fluorescent probe with two tellurium atoms at two upper benzyl rings has been prepared and explored for its fluorescent sensing properties towards hypochlorous acid/hypochorite (HClO/ClO^-), which showed high selectivity and absolutely fluorescent "turn-on" phenomenon at 738 nm. The fluorescence of this probe was sufficiently quenched due to photoindued electron transfer by two tellurium atoms. Upon exposure to HClO/ClO^-, a strong near-infrared emission at 738 nm appeared with fluorescence quantum yields changing from 0 to 0.11. This remarkable fluorescence change was ascribed to the oxidation of both electron-rich tellurium atoms. The detection limit of this probe towards HClO/ClO^- was calculated to 0.09 μM in acetonitrile aqueous solution by the linear fluorescence change at 738 nm in the HClO/ClO^--concentration range of 0-30 μM. Interestingly, this probe was found to be applicable in a broad pH range (2-10). Meanwhile, the oxidized probe could be further responsive to biothiols with substantial fluorescence disappearance. The bioimaging experiments in RAW264.7 cells showed the appearance of intracellular near-infrared fluorescence after addition of HClO/ClO^- and PMA, and the fluorescence could also be reversed to be silenced by further introduction of GSH, confirming its potential application for exogenous and endogenous detection of HClO/ClO^- in living cells.

Highly Emissive Metal-Organic Frameworks for Sensitive and Selective Detection of Nitrofuran and Quinolone Antibiotics

The overuse of antibiotics makes its detection very significant for human health. New facile methods and high-performance sensory materials will be urgently needed for detection of antibiotics. Unfortunately, there are few reports on fluorescence enhancement of antibiotics detection. Herein, based on the modulability of the coordination mode, we proposed two MOFs with different coordination modes based on different metal ions: Zn-MOF (1) and Cd-MOF (2). The fluorescence of 1 and 2 can be efficiently and selectively quenched by nitrofuran antibiotics (nitrofurazone, NFZ and furazolidone, FZD) and chloramphenicol (CAP), respectively. Particularly, the matched energy levels between 2 and enrofloxacin (ENR) enables 2 with turn-on sensing for ENR. Moreover, apart from the sensitivity and selectivity, 1 and 2 also have strong recyclable ability, fast response time and anti-interference ability, which make them great potential sensory materials to detect antibiotics.

Individual and successive detection of H2S and HClO in living cells and zebrafish by a dual-channel fluorescent probe with longer emission wavelength

Reactive oxygen species (ROS) and reactive sulfur species (RSS) participate in many physiological activities and help maintaining the redox homeostasis in biological system. The complicated intrinsic connection between specific ROS/RSS needs to be further explored. Herein, a novel fluorescent probe (MB-NAP-N₃) with longer emission wavelength has been rationally designed and synthesized based on the conjugation of the methylene blue moiety and the naphthalimide moiety for the detection of hypochlorous acid (HClO) and hydrogen sulfide (H₂S). The dual-signal probe exhibits rapid turn-on fluorescence responses for individual and successive detection of H₂S and HClO in green and red channels, respectively. Owning to its advantages such as fast response, good selectivity and high sensitivity, the probe was successfully applied to detect endogenous and exogenous HClO/H₂S in living cells. Furthermore, the outstanding luminescence performance makes it suitable for the visualization of the in vivo interaction between the two analytes in zebrafish.

"Turn-on" fluorescent sensor for Th4+ in aqueous media based on a combination of PET-AIE effect

Previously reported fluorescent sensors for Th⁴⁺ experienced emission quenching or generated false positive signal upon aggregate formation in aqueous media. Herein, a simple and novel thorium sensor (CDB-BA) based on cyanodistyrene structure was designed and synthesized, which integrated the highly emitting characteristic of AIE effect and off-on response of PET modulation for the first time to construct the "turn-on" fluorescent probe for Th⁴⁺. Besides excellent selectivity, CDB-BA exhibited remarkable fluorescent enhancement which was linearly related to the concentration of Th⁴⁺ in the range of 0.25-8 μM. The detection limit was attained 0.074 μM, which was lower than that of most previously reported sensors. The mechanism of tris-chelate complex of CDB-BA with Th⁴⁺ was confirmed by mass spectra, IR spectra and DFT calculation. The excellent Th⁴⁺ sensing ability of CDB-BA was successfully applied to detecting Th⁴⁺ on TLC plates, in real water samples and living-cell imaging. This work suggested that the combination of AIE and PET photophysical mechanism could offer the merits of minimized background and enhanced signal fidelity to develop novel "turn-on" fluorescent probe in complicated aqueous environment and biological research.

Fluorimetric detection of methylated DNA of Sept9 promoter by silver nanoclusters at intrastrand 6C-loop

Methylation of DNA at carbon 5 of cytosines is the most common epigenetic modification of human genome. Due to its critical role in many normal cell processes such as growth and development, any aberrant methylation pattern in a particular locus may lead to abnormal functions and diseases such as cancer. Development of methods to detect methylation state of DNA which may eliminate labor-intensive chemical or enzymatic treatments has received considerable attention in recent years. Herein, we report a DNA methylation detection procedure based on fluorescence turn-on strategy. Target sequence was selected from Sept9 promoter region that has been reported as one of the most frequently methylated sites in colorectal cancer. Probe DNA was designed to be complementary to this sequence with an additional six cytosines in the middle to form an internal loop to host silver nanoclusters. The fluorescence intensity of the synthesized silver nanoclusters with the duplexes of probe-non-methylated target was significantly different from that of probe-methylated target. The fluorescence enhanced with increasing the methylated DNA concentration with a linear relation in the range of 1.0 × 10^-8 M to 5.0 × 10^-7 M with the detection limit of 8.2 × 10^-9 M, and quenched with non-methylated ones. The method was very specific in the presence of non-complementary sequences with maximum similarity of 40%. Circular dichroism spectra indicated that silver ions significantly affected the structure of methylated and non-methylated DNA into different extents which could further influence the nanocluster fluorescence. Finally, a method was introduced to meet the concerns in the applicability of the proposed method in real situation.

An endoplasmic reticulum targetable turn-on fluorescence probe for imaging application of carbon monoxide in living cells

Carbon monoxide (CO) is a significant mediator in regulating endoplasmic reticulum (ER) stress, and its level may play a potential role in the treatment of vascular diseases combined with ER stress. In-situ visualization of CO in the ER helps to elucidate its physiological and pathological mechanistic behavior. Herein, a novel CO fluorescent probe (Na-CM-ER) with ER-targeting characteristics was structured. Na-CM-ER with naphthalimide as a fluorescent group, under the trigger of CO, an ICT (Intramolecular Charge Transfer) mechanism was constructed by converting a nitro group to an amino group and showed dazzling green fluorescence. Na-CM-ER exhibited satisfactory response speed, selectivity, photo-stability and sensitivity to CO in vitro. Furthermore, biological imaging experiments demonstrated that Na-CM-ER could monitor the changes of exogenous/endogenous CO in living cells and possess an ER-targeting property. To sum up, we hope that Na-CM-ER can be as a serviceable molecular tool for imaging CO in cellular ER.

A simple "turn-on" fluorescence sensor for salicylaldehyde skeleton based on switch of PET-AIE effect

The selective detection of salicylaldehyde skeleton is of great significance in phytochemistry and biological research but rarely reported. In this research, a simple and highly selective "turn-on" fluorescence sensor (CDB-Am) for salicylaldehyde skeleton was developed based on switch of photoinduced electron transfer (PET) and aggregation-induced emission (AIE). CDB-Am bearing amino-cyanodistyrene structure responded to salicylaldehyde in the range of 3.1 to 40 μM with a detection limit of 0.94 μM. The sensing process of formation of Schiff-base adduct CDB-SA was confirmed by ¹H NMR, MS, and FT-IR spectra, revealing that a recovered AIE property accounted for the turn-on fluorescence response of CDB-Am and the intramolecular hydrogen bonding played a crucial role in the disruption of PET process. This sensing ability was successfully applied for both fluorescence qualitative test of salicylaldehyde skeleton on TLC analysis and quantitative detection of salicylaldehyde skeleton with good accuracy in the root bark of Periploca sepium, suggesting the extensive applications in phytochemistry and traditional Chinese herbal medicine. Furthermore, CDB-Am exhibited the first excellent fluorescence imaging ability in detecting salicylaldehyde skeleton in a living system. This work supplied a new strategy of preparing a novel "turn-on" fluorescence probe for detecting salicylaldehyde skeleton in complex environments and living bodies.

A simple, quantitative method for spectroscopic detection of metformin using gold nanoclusters

We synthesized bovine serum albumin (BSA)-stabilized gold nanoclusters (BSA-GNCs) and confirmed their ultra-small size using HRTEM (High-resolution Transmission Electron Microscope) and DLS (Dynamic Light Scattering). The fluorescence intensity of BSA-GNCs is "turned off" in the presence of Cu(II) metal ions. The resulting Cu(II)-mediated BSA-GNCs were utilized to detect metformin, a drug used to control diabetes. Metformin binds to and displaces Cu(II) ions from the BSA on the surface of the nanoclusters, which turns on the fluorescence of the nanoclusters. The interactions between the protein-stabilized nanoclusters were investigated in the absence and presence of Cu(II) using circular dichroism (CD) and Fourier-transform infrared spectroscopy (FTIR). Cu(II)-quenched BSA-GNCs had an extremely high sensitivity to detect metformin, with a low limit of detection (LOD) of 0.068 μM and a dynamic range of limit of quantification (LOQ = 10/3 LOD) of 0.22 to 11 μM. The ability of this novel "turn-on" nanosensor to detect metformin in human serum and urine samples was confirmed: the percentage recovery in fluorescence for spiked analyte ranged from 96.00-98.50% and 92.60-96.62% in human serum and urine samples, respectively. Thus, BSA-GNCs provide a valid, sensitive, specific fluorometric methodology for the detection of metformin in biomedical applications.

A selective N,N-dithenoyl-rhodamine based fluorescent probe for Fe3+ detection in aqueous and living cells

A novel N,N-dithenoyl-rhodamine based fluorescent and colorimetric Fe³⁺ probe 1 was designed and synthesized by only one step from Rhodamine B hydrazide and 2-thiophenecarbonyl chloride. The structure of probe 1 was characterized by ¹H NMR/¹³C NMR spectroscopy, IR spectroscopy, and HRMS spectrometry. Accompanying with significant changes in visual color and fluorescent spectrum, probe 1 displayed good sensitivity for Fe³⁺ with an abroad pH span. The detection limit (3.76 μmol/L, 0.2 mg/L) for Fe³⁺ was lower than WHO recommended value (0.3 mg/L) for drinking water. Using two thiophene carbonyl groups as coordinating functional recognition group, probe 1 showed excellent selectivity towards Fe³⁺ over diverse coexistent metal ions and anions. The sensing mechanism between dithenoyl-substituted probe 1 and Fe³⁺ was further confirmed by ¹H NMR and IR titration experiments, binding constants study, and Job's plot analysis. Furthermore, probe 1 also exhibited good cell membrane permeability and could be used as an efficient Fe³⁺ probe in living human cells.

A lysosome-targetable fluorescent probe for imaging trivalent cations Fe3+, Al3+ and Cr3+ in living cells

An effective morpholine-type naphthalimide chemsensor, N-p-chlorophenyl-4-(2-aminoethyl)morpholine-1,8-naphthalimide (CMN) has been developed as a lysosome-targeted fluorometric sensor for trivalent metal ions (Fe³⁺, Al³⁺ and Cr³⁺). Upon the addition of Fe³⁺, Al³⁺ or Cr³⁺ ions, the probe CMN showed an evident naked-eye color changes which pale yellow solution of CMN turned deepened and it displayed turn-on fluorescence response in methanol. CMN showed a significant selective and sensitive toward Fe³⁺, Al³⁺ or Cr³⁺ ions, while there was no obvious behavior to other monovalent or divalent metal ions from the UV-vis and fluorescence spectrum. Based on the Job's plot analyses the 1:1 coordination mode of CMN with Fe³⁺, Al³⁺ or Cr³⁺ was proposed. The limit of detection (LOD) observed were 0.65, 0.69 and 0.68 μM for Fe³⁺, Al³⁺ and Cr³⁺ ions, respectively. The N-atom of morpholine directly involved in complex formation, CMN emitted fluorescence through inhibition of photoinduced electron transfer (PET). This probe exhibited excellent imaging ability for Fe³⁺, Al³⁺and Cr³⁺ ions in living cells with low cytotoxicity. Significantly, the cellular confocal microscopic research indicated that the lysosome-targeted group of morpholine moiety was introduced which realized the capability of imaging lysosomal trivalent metal ions in living cells for the first time.

Gold nanoparticle-based detection of dopamine based on fluorescence resonance energy transfer between a 4-(4-dialkylaminostyryl)pyridinium derived fluorophore and citrate-capped gold nanoparticles

A colorimetric/fluorometric dual-signal assay is described for the determination of dopamine (DA). A nanoprobe was obtained by linking a 4-(4-dialkylaminostyryl)pyridinium derived fluorophore to citrate-capped gold nanoparticles (AuNPs). The fluorescence of the fluorophore is quenched by the AuNPs via fluorescence resonance energy transfe. In the presence of DA, the catechol group of DA can absorb on the surface of AuNPs to induce aggregation, which is accompanied by a color change from red to blue. The yellow fluorescence of the fluorophore with excitation/emission maximum at 365/570 nm is recovered. The dual-signal detection allows the quantitative analysis of DA within 300 μM by the colorimetric method and 80 μM by the fluorometric method. The detection limits for the colorimetric/fluorometric methods are 1.85 μM and 0.29 μM, respectively. Quantitative determination of DA in spiked urine samples was successfully demonstrated, with recoveries ranging from 98.2 to 106.0%. Graphical abstract A colorimetric/fluorometric dual-signal assay is described for the determination of dopamine by linking a fluorophore to gold nanoparticles. The dopamine causes aggregation of the nanoparticles to induce color change, which is followed by the recovery of the fluorescence.

Recyclable fluorescent chemodosimeters based on 8-hydroxyquinoline derivatives for highly sensitive and selective detection of mercury(II) in aqueous media and test strips

Four novel highly selective 8-hydroxyquinoline-based fluorescent chemodosimeters (1-4) were synthesized for the rapid analysis of Hg²⁺ in aqueous solution and on paper strips, which probably attributed to the excited state intramolecular proton transfer (ESIPT) process. Chemodosimeter 1 was evaluated as a Hg²⁺-ratiometric fluorescent sensor while others (2, 3 and 4) displayed fluorescence turn-on response for Hg²⁺ among the various survey metal ions. We demonstrated that chemodosimeters (1-4) could recognized Hg²⁺ ions based on a 1:1 stoichiometric binding event with fast detection time. More importantly, the detection limits for Hg²⁺ could reach at 10^-9 M level except chemodosimeter 1 (4.05 × 10^-8 M). In addition, it was found that chemodosimeters (1-4) were recycled efficiently because the Hg²⁺ induced emission spectra were reversed after adding NaBH₄. Finally, these four sensors were successfully applied for fabrication of simple device test strips for rapid and on-site detection of Hg²⁺ ions.

A highly turn-on fluorescent CHEF-type chemosensor for selective detection of Cu2+ in aqueous media

An efficient "turn on" fluorescence chemosensor Schiff base LH based on the combination of 2-Hydroxy-5-(p-tolyldiazenyl)benzaldehyde and N-(3-Aminopropyl)imidazole was prepared and characterized then evaluated for its selective fluorescent sensing of Cu²⁺ amongst other metal ions. The CN isomerization inhibition process induced by the Cu²⁺ binding warrants the chelation-induced enhanced fluorescence (CHEF) effect. In addition, the detection limit sensing of LH for Cu²⁺ was found to be 1.8 × 10^-6 M that is below the WHO recommendation level (20 μM) for drinking water.

Fluorometric dopamine assay based on an energy transfer system composed of aptamer-functionalized MoS2 quantum dots and MoS2 nanosheets

The authors describe a fluorometric strategy for the determination of dopamine (DA). It is based on the use of aptamer-functionalized MoS₂ quantum dots (QDs) and MoS₂ nanosheets (NSs). The QDs and NSs were extensively characterized with regard to their physical and chemical properties using methods such as TEM, XRD, FT-IR, EDX and molecular spectroscopies. The aptamer against dopamine was labeled with QDs acting as the energy donor in an energy transfer system, while the NSs serve as the energy acceptor. Under the optimal conditions, the fluorescence (FL) intensity (best measured at excitation/emission peaks of 315/412 nm) increases with increasing DA concentration in the range from 0.1 nM to 1000 nM, with a lower detection limit of 45 pM. The method was successfully applied to the determination of DA in complex matrices. In our perception, the method has a wide scope in that it may be extended to other biomolecules for which respective aptamer are available. The QDs show excellent optical properties, good stability, low cytotoxicity, and may also be applied to fluorometric imaging of live cells. Graphical abstract A "turn-on" fluorometric aptasensor for the determination of dopamine (DA) was established based on aptamer-functionalized molybdenum disulfide quantum dots (MoS₂ QDs) and MoS₂ nanosheets. This assay exhibits high selectivity and sensitivity with a detection limit as low as 45 pM.

An erythrosin B-based "turn on" fluorescent sensor for detecting perfluorooctane sulfonate and perfluorooctanoic acid in environmental water samples

Because of the serious harm to animals and the environment associated with perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), a rapid, sensitive and low-cost method for detecting PFOS and PFOA is of great importance. In this paper, a novel sensing method has been proposed for the highly sensitive detection of PFOS and PFOA in environmental water samples based on the "turn-on" switch of erythrosine B (EB)-hexadecyltrimethylammonium bromide (CTAB) system. In pH 8.55 Britton-Robinson (BR) buffer, EB can react with CTAB by electrostatic attraction, resulting in a strong fluorescence quenching of EB. With a subsequent addition of the CTAB, a red-shift occurred (11 nm), followed by a significant increase in fluorescence at high surfactant concentrations. It was found that PFOS and PFOA can obviously enhance fluorescence intensity of EB-CTAB system. The enhanced fluorescence intensity is proportional to the concentration of PFOS and PFOA in the range of 0.05-10 μM with detection limit of 12.8 nM and 11.8 nM (3σ), respectively. The presented assay has been successfully applied to sensing PFOS and PFOA in real water samples with RSD ≤ 4.3% and 2.9%, respectively.

Rapid aptasensor capable of simply detect tumor markers based on conjugated polyelectrolytes

In this paper, a very simple, easily-operated and universal platform is proposed for tumor marker detection. In this strategy, tumor marker-specific aptamer, which can quench the fluorescence of polyfluorene-based cationic conjugated polyelectrolytes (PFN⁺), are used as recognizing probes. Upon addition of tumor marker, the aptamer can be assembled into the tumor marker-aptamer complex, resulting in fluorescence recovery of PFN⁺ and the detection of the targets. The most widely-used tumor markers, carcinoembryonic antigen (CEA) and fetoprotein (AFP) have been chosen as the model analytes for this work. The sensing method is capable of rapidly detect target protein within 5 min without complex handling procedure and expensive instruments. Compared with previous studies, the assay presented here is really simple and avoids either conjugated polyelectrolytes (CPEs) modification or oligonucleotide labeling. This method also shows a wide detection range of 3 orders of magnitude and the detection limit is 0.316 ng/mL for CEA and 1.76 ng/mL for AFP. Furthermore, the approach requires only a convenient"mix-and-detect" procedure and offers a universal platform for the sensitive detection of any target molecule of choice according to the selected aptamer.

A simple pyrene-based fluorescent probe for highly selective detection of formaldehyde and its application in live-cell imaging

A novel and simple pyrene-based fluorescent probe (B1) was synthesized and used for the detection of formaldehyde (FA). When B1 was added to FA in CH₃CH₂OH/HEPES (10 mM, pH = 7.4, 1:99, v/v) solution, the solution system strongly enhanced the fluorescence. Over various small molecular species, probe B1 showed high sensitivity and selectivity for detecting FA, with a low limit of detection (0.107 μM). Furthermore, probe B1 was successfully applied for visualizing FA in human embryonic kidney (HEK293T) cells, demonstrating its value of application in living biomedical samples.

A fluorescence probe acted on Site I binding for Human Serum Albumin

A sensitive turn-on probe XYQ, has been developed for the monitoring of HSA species with highly selective and instantaneous response to real- urine sample and living cells imaging. Furthermore, the fluorescence probe acted on Site I and discrimination of HSA from BSA.

A novel fluorescein-based "turn-on" probe for the detection of hydrazine and its application in living cells

We constructed a novel probe for hydrazine detection based on ICT and PET mechanism. Phthalimide and acetyl ester groups were used as the recognition units. Addition of hydrazine produced a turn-on fluorescence at 525nm along with the fluorescent color change from dark to yellow. The probe could selectively detect hydrazine over other related interfering species. The detection limit of the probe for hydrazine was calculated to be 0.057μM which was lower than the EPA standard (0.320μM). Furthermore, the probe could also be applied for the imaging of hydrazine in living cells.

UV and fluorescent spectra study the reaction between 1, 8-Naphthalimide derivative and hypochlorite their applications

Two simple, efficient turn-on fluorescent probes for hypochlorite have been rationally designed and developed by utilizing the oxidation of hypochlorite. Notably, probe 1 and 2 displayed rapid and remarkable turn-on responses to ClO^- in PBS buffer solution (pH7.4). Further, the optical properties of two probes and their ClO^--addition products were confirmed by density functional theory calculations. And detection limits of two probes for ClO^- based on the definition by IUPAC were calculated for 2.882nM and 0.354μM. More importantly, cell imaging experiments demonstrated that probe 1 was more suitable for detecting the ClO^- in living A549 cells. And both two probes had the possibility of potentially applied in practical applications such as detecting the hypochlorite concentration of tap water and river water.

A new fluorescent probe with a large turn-on signal for imaging nitroreductase in tumor cells and tissues by two-photon microscopy

Hypoxia is the important characteristic of solid tumors, and it may cause the bioactivity of nitroreductase (NTR) to display an elevated level. Hence, the development of effective monitoring methods of NTR in living systems is of great importance for detecting the occurrence and progress of tumors. Toward this goal, a novel two-photon fluorescence turn-on NTR probe GCTPOC-HY, based on the two-photon platform GCTPOC and the NTR recognition site p-nitrobenzyl ether, is designed and synthesized. The probe GCTPOC-HY exhibits eminent properties such as high sensitivity and selectivity, highly stable photo-stability, and low cytotoxicity. Besides, the probe responds to 1.5μg/mL NTR with a 130-fold fluorescence enhancement, which is larger than the reported two-photon fluorescent NTR probes. Moreover, the probe GCTPOC-HY is suitable for fluorescence imaging of NTR in living cells by one- and two-photon modes. Importantly, the probe GCTPOC-HY is successfully applied to monitor NTR in the tumor tissues with a significant fluorescence signal and a penetration depth of 70µm by using two-photon microscopy.

A nuclease-assisted label-free aptasensor for fluorescence turn-on detection of ATP based on the in situ formation of copper nanoparticles

Owing to their promising advantages in biochemical analysis, aptamer-based sensing systems for the fluorescence detection of important biomolecules are being extensively investigated. Herein, we propose a turn-on fluorescent aptasensor for label-free detection of adenosine triphosphate (ATP) by utilizing the in situ formation of copper nanoparticles (CuNPs) and the specific digestion capability of exonuclease I (Exo I). In this assay, the addition of ATP can effectively hinder the digestion of aptamer-derived oligonucleotides due to the G-quadruplex structure. Accordingly, the remaining poly thymine at 5'-terminus of substrate DNA can serve as an efficient template for red-emitting fluorescent CuNPs with a Mega-Stokes shifting in buffered solution, which can be used to evaluate the concentration of ATP. This method is cost-effective and facile, because it avoids the use of traditional dye-labeled DNA strands and complex operation steps. Under optimized conditions, this method achieves a selective response for ATP with a detection limit of 93nM, and exhibits a good detection performance in biological samples.

Highly sensitive and selective detection of Al(III) ions in aqueous buffered solution with fluorescent peptide-based sensor

A fluorescent sensor based on a tripeptide (SerGluGlu) with a dansyl fluorophore detected selectively Al(III) among 16 metal ions in aqueous buffered solutions without any organic cosolvent. The peptide-based sensor showed a highly sensitive turn on response to aluminium ion with high binding affinity (1.84×10(4)M(-1)) in aqueous buffered solutions. The detection limit (230nM, 5.98ppb) of the peptide-based sensor was much lower than the maximum allowable level (7.41μM) of aluminium ions in drinking water demanded by EPA. The binding mode of the peptide sensor with aluminium ions was characterized using ESI mass spectrometry, NMR titration, and pH titration experiments.

An eosin Y-based "turn-on" fluorescent sensor for detection of perfluorooctane sulfonate

In this paper, a novel sensing method with a higher sensitivity of perfluorooctane sulfonate (PFOS) than perfluorooctanoic acid (PFOA) has been proposed detection of PFOS in aqueous solution replying on the "off-on" switch of eosin Y/polyethyleneimine (PEI)/PFOS fluorescence system due to the higher affinity of PEI to PFOS than eosin Y. In pH 7.0 Britton-Robinson buffer solution, eosin Y reacts with protonated PEI to form complex by electrostatic attraction, which leads to a strong fluorescence quenching of the eosin Y. When PFOS presents, the fluorescence of eosin Y is recover due to the electrostatic and hydrophobic interactions between PFOS and PEI. The recovered fluorescence intensity is proportional to the concentration of PFOS in the ranging from 0 to 2.0×10(-6) mol/L with the limit of detection (LOD, 3σ) being 1.5×10(-8) mol/L without preconcentration. In this study, the optimum reaction conditions and the interferences of foreign substances were investigated. In addition, the effects of PFOA, the analog of PFOS, on the fluorescence recovery of the system were also studied. The presented approach has been successfully used to detect PFOS in real samples with RSD ⩽2.9%.

Solvent-dependent "turn-on" fluorescence chemosensor for Mg(2+) based on combination of C=N isomerization and inhibition of ESIPT mechanisms

A fluorescent chemosensor (L) for Mg(2+) has been synthesized and characterized, which exhibits turn-on fluorescence response for Mg(2+) only in alcohol solvent (methanol or ethanol) with high sensitivity and selectivity. But in both nonpolar and polar solvents (cyclohexane, DCM, DMSO or MeCN), L showed negligible fluorescent response for Mg(2+). In order to discover the unique phenomenon, optical measurements, liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and a high performance liquid chromatography with a fluorescence detector (HPLC-FLD) of L and L with Mg(2+) ions in solvents were studied. In alcohol solvent, [L+alcohol molecule] was formed and the mechanism aspect of L concerning the remarkable fluorescence response for Mg(2+) has been discussed.

Quantum dots-based label-free fluorescence sensor for sensitive and non-enzymatic detection of caffeic acid

We have developed a label-free fluorescence sensor for caffeic acid (CA) by the use of CdTe:Zn(2+) quantum dots (CdTe:Zn(2+) QDs) as an output signal. The principle of sensor is based on the fluorescence quenching and binding properties of Fe(2+) toward QDs and CA, respectively. To provide a fluorescence turn-on mode for CA detection, Fe(2+) is first mixed with QDs solution, leading to a low fluorescence emission. With the addition of CA, the fluorescence of QDs is recovered due to the strong binding interaction between CA and Fe(2+). Thus, a QDs-based label-free fluorescence sensor, designed in a simple mix-and-detect format, is established for CA detection. This study demonstrated here not only offers simple, sensitive and non-enzymatic detection method for CA, but also brings to light a new application of QDs in the food analysis.

Turn-on electrochemiluminescence sensing of Cd(2+) based on CdTe quantum dots

A simple and sensitive method for the detection of cadmium ion was proposed based on the electrochemiluminescence (ECL) of thioglycolic acid capped-CdTe quantum dots (CdTe QDs). The ECL of CdTe QDs was firstly quenched by introduction of S(2)(-) and was restored due to following addition of Cd(2+), on the basis of which, a "turn-on" ECL method for the detection of Cd(2+) was demonstrated. The ECL of CdTe QDs exhibited linear response toward Cd(2+) concentration in the range from 6.3nM to 3.4μM (R=0.999) with a detection limit of 2.1nM. The proposed assay was simple, sensitive, selective, and practicable in real water samples.