Selective turn‐on fluorescence assay of 6–thioguanine by using harmine‐modified silver nanoparticles

This article reports on a novel fluorescence resonance energy transfer (FRET) system between harmine and silver nanoparticles (AgNPs), in which harmine acts as the donor and AgNPs act as the acceptor. As a result of FRET, harmine fluorescence is quenched efficiently with a corresponding Stern–Volmer constant of 3.61 × 10¹¹ L/mol. It was found that upon addition of the anticancer drug, 6–thioguanine (6–TG), the fluorescence was recovered due to the competitive adsorption of this compound onto AgNPs. Based on this effect, a selective turn‐on fluorescence sensor was developed for the determination of 6–TG. Under optimum conditions, the enhanced fluorescence intensity displays a linear relationship with the concentration of 6–TG in the range 1.5 × 10^‐8–7.5 × 10^‐7 M with a detection limit of 9.7 nM. The developed method was applied to the determination of this drug in a pharmaceutical preparation and human plasma samples. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel chemiluminescence sensor for the determination of indomethacin based on sulfur and nitrogen co‐doped carbon quantum dot–KMnO4 reaction

We report on a simple and sensitive sulfur and nitrogen co‐doped carbon quantum dot (S,N‐CQD)‐based chemiluminescence (CL) sensor for the determination of indomethacin. S,N‐CQDs were prepared by a hydrothermal method and characterized by fluorescence spectra, Fourier transform infrared spectroscopy and transmission electron microscopy. To obtain the best CL system for determination of indomethacin, the reaction of S,N‐CQDs with some common oxidants was studied. Among the tested systems, the S,N‐CQD–KMnO₄ reaction showed the highest sensitivity for the detection of indomethacin. Under optimum conditions, the calibration plot was linear over a concentration range of 0.1–1.5 mg L^?1, with a limit of detection (3σ) of 65 μg L^?1. The method was applied to the determination of indomethacin in environmental and biological samples with satisfactory results.     

The synthesis and modification of highly fluorescent carbon quantum dots for reversible detection of water‐soluble phosphonate‐1‐hydroxyethane‐1,1‐diphosphonic acid by fluorescence spectroscopy

Photoluminescent (PL) carbon quantum dots (CQDs) were prepared successfully using a facile and green procedure. They exhibited striking blue fluorescence and excellent optical properties, with a quantum yield as high as 61.44%. Due to the fluorescence quenching effect and the stronger complexing ability of the phosphoric acid group of 1‐hydroxyethane‐1,1‐diphosphonic acid (HEDP) to Fe³⁺ , CQDs doped with Fe³⁺ were adequately constructed as an efficient and sensitive fluorescent probe for HEDP‐specific sensing. The proposed fluorescent probe had a sensitive and rapid response in the range 5–70 μ M. Furthermore, quantitative molecular surface (QMS) analysis based on the Multiwfn program was applied to explore the complexation mode of HEDP and metal ions. The distribution of electrostatic potential (ESP), average local ionization energy (ALIE), the minimum value points and the position of the lone pair electrons on the surface of molecular van der Waals were further determined. More strikingly, this experiment achieved the quantitative detection of water‐soluble phosphonate‐HEDP, for the first time using fluorescence spectrometry. It has been proved to be an effective and intuitive sensing method for the detection of HEDP in real samples.     

A N‐(2‐hydroxyethyl)piperazine dangled 2,5‐diphenyl‐1,3,4‐oxadiazole‐based fluorescent sensor for selective relay recognition of Cu2+ and sulfide in water

A new 2,5‐diphenyl‐1,3,4‐oxadiazole‐based derivative (L) was synthesized and applied as a highly selective and sensitive fluorescent sensor for relay recognition of Cu²⁺ and S^2? in water (Tris–HCl 10 mM, pH = 7.0) solution. L exhibits an excellent selectivity to Cu²⁺ over other examined metal ions with a prominent fluorescence ‘turn‐off’ at 392 nm. L interacts with Cu²⁺ through a 1:2 binding stoichiometry with a detection limit of 4.8 × 10^–7 M. The on‐site formed L–2Cu²⁺ complex exhibits excellent selectivity to S^2? with a fluorescence ‘off–on’ response via a Cu²⁺ displacement approach. Copyright © 2016 John Wiley & Sons, Ltd.     

Cupric oxide nanoparticles‐enhanced chemiluminescence method for measurement of β‐lactam antibiotics

A simple, sensitive cupric oxide nanoparticles (CuO NPs) enhanced chemiluminescence (CL) method was developed for the measurement of β‐lactam antibiotics, including amoxicillin and cefazolin sodium. The method was based on suppression of the CuO NPs–luminol–H₂O₂ CL reaction by β‐lactam antibiotics. Experimental parameters that influenced the inhibitory effect of the antibiotic drugs on the CL system, such as NaOH (mol/L), luminol (µmol/L), H₂O₂ (mol/L) and CuO NPs (mg/L) concentrations, were optimized. Calibration graphs were linear and had dynamic ranges of 1.0 × 10^–6 to 8.0 × 10^–6 mol/L and 3.0 × 10^–5 to 5.0 × 10^–3 mol/L for amoxicillin and cefazolin sodium, respectively, with corresponding detection limits of 7.9 × 10^–7 mol/L and 1.8 × 10^–5 mol/L. The relative standard deviations of five replicate measurements of 5.0 × 10^–6 amoxicillin and 5 × 10^–4 cefazolin sodium were 5.43 and 5.01%, respectively. The synthesized CuO NPs were characterized by X‐ray diffraction (XRD) and transmission electronmicroscopy (TEM). The developed approach was exploited successfully to measure antibiotics in pharmaceutical preparations. Copyright © 2014 John Wiley & Sons, Ltd.     

Fluorescent probe for detection of Cu2+ using core‐shell CdTe/ZnS quantum dots

Core‐shell CdTe/ZnS quantum dots capped with 3‐mercaptopropionic acid (MPA) were successfully synthesized in aqueous medium by hydrothermal synthesis. These quantum dots have advantages compared to traditional quantum dots with limited biological applications, high toxicity and tendency to aggregate. The concentration of Cu²⁺ has a significant impact on the fluorescence intensity of quantum dots (QDs), therefore, a rapid sensitive and selective fluorescence probe has been proposed for the detection of Cu²⁺ in aqueous solution. Under optimal conditions, the fluorescence intensity of CdTe/ZnS QDs was linearly proportional to the concentration of Cu²⁺ in the range from 2.5 × 10^–9 M to 17.5 × 10^–7 M with the limit of 1.5 × 10^–9 M and relative standard deviation of 0.23%. The quenching mechanism is static quenching with recoveries of 97.30–102.75%. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and application of solvent‐modulated self‐doped N–S multicolour fluorescence carbon quantum dots

In this paper, two types of carbon quantum dot (CQDs) were prepared using biocompatible l ‐methionine as the carbon source and urea as the nitrogen source and a one‐step hydrothermal treatment. By changing the reaction solvents (deionized (DI) water and dimethylformamide (DMF)), the maximum emission of the resulting CQDs shifted from blue to red light. Specifically, the emission wavelength of the CQDs moved from 433 nm to 625 nm following embedding of a new functional group (–CONH–) on the surface of the CQDs. Photoluminescence quantum yields of the CQDs with blue and red emission reached 64% and 61%, respectively. The R‐CQDs were used to detect metal ions and a linear relationship was demonstrated between ln(F/F₀) and Fe³⁺ concentration in the range 0–0.5 mmol/L with a detection limit of 0.067 μM. Therefore these R‐CQDs have great potential as fluorescent probes for Fe³⁺ detection. We expect that the excellent water‐soluble, biocompatible and optical properties of the CQDs developed in this work mean that they will be widely used to detect biological cells.     

Sensitive and selective detection of Cu(II) ion: A new effective 1,8‐naphthalimide‐based fluorescence ‘turn off’ sensor

The present study reports the development of a new 1,8‐naphthalimide‐based fluorescent sensor V for monitoring Cu(II) ions. The sensor exhibited pH independence over a wide pH range 2.52–9.58, and indicated its possible use for monitoring Cu(II) ions in a competitive pH medium. The sensor also showed high selectivity and sensitivity towards the Cu(II) ions over other competitive metal ions in DMSO–HEPES buffer (v/v, 1:1; pH 7.4) with a fluorescence ‘turn off’ mode of 79.79% observed. A Job plot indicated the formation of a 1:1 binding mode of the sensor with Cu(II) ions. The association constant and detection limit were 1.14 × 10⁶ M^–1 and 4.67 × 10^–8 M, respectively. The fluorescence spectrum of the sensor was quenched due to the powerful paramagnetic nature of the Cu(II) ions. Potential application of this sensor was also demonstrated when determining Cu(II) ion levels in two different water samples.     

Eco‐friendly synthesis of gelatin‐capped bimetallic Au–Ag nanoparticles for chemiluminescence detection of anticancer raloxifene hydrochloride

This study described the utility of green analytical chemistry in the synthesis of gelatin‐capped silver, gold and bimetallic gold–silver nanoparticles (NPs). The preparation of nanoparticles was based on the reaction of silver nitrate or chlorauric acid with a 1.0 wt% aqueous gelatin solution at 50°C. The gelatin‐capped silver, gold and bimetallic NPs were characterized using transmission electron microscopy, UV–vis, X‐ray diffraction and Fourier transform infrared spectroscopy, and were used to enhance a sensitive sequential injection chemiluminescence luminol–potassium ferricyanide system for determination of the anticancer drug raloxifene hydrochloride. The developed method is eco‐friendly and sensitive for chemiluminescence detection of the selected drug in its bulk powder, pharmaceutical injections and biosamples. After optimizing the conditions, a linear relationship in the range of 1.0 × 10^–9 to 1.0 × 10^–1 mol/L was obtained with a limit of detection of 5.0 × 10^–10 mol/L and a limit of quantification of 1.0 × 10^‐9 mol/L. Statistical treatment and method validation were performed based on ICH guidelines. Copyright © 2016 John Wiley & Sons, Ltd.     

BSA‐conjugated zinc oxide nanoparticles as luminescent probes for the determination of histidine

Zinc oxide nanoparticles doped with bovine serum albumin were used to determine histidine in aqueous solutions using a fluorescence spectroscopic technique. The results showed that histidine effectively quenched the fluorescence of the modified ZnO nanoparticles, whereas other amino acids did not significantly affect the light emission, thereby allowing selective and sensitive histidine detection in amino acid mixtures. Under optimal conditions (pH 7.0, 25 °C, 10 min preincubation), the detection limit for histidine was ~ 9.87 × 10^–7 mol/L. The high value of the determined quenching rate constant K_q (3.30 × 10¹³ L/mol/s) was consistent with a static quenching mechanism. Copyright © 2015 John Wiley & Sons, Ltd.     

A fluorescent terbium-metal–organic framework material for high-sensitivity detection of vomitoxin and oxytetracycline hydrochloride in water

A unique luminescent lanthanide metal–organic framework (LnMOF)–based fluorescence detection platform was utilized to achieve sensitive detection of vomitoxin (VT) and oxytetracycline hydrochloride (OTC-HCL) without the use of antibodies or biomolecular modifications. The sensor had a fluorescence quenching constant of 9.74 × 10⁶ M⁻¹ and a low detection limit of 0.68 nM for vomitoxin. Notably, this is the first example of a Tb-MOF sensor for fluorescence detection of vomitoxin. We further investigated its response to two mycotoxins, aflatoxin B1 and ochratoxin A, and found that their Stern–Volmer fluorescence quenching constants were lower than those of VT. In addition, the fluorescence sensor realized sensitive detection of OTC-HCL with a detection limit of 0.039 μM. In conclusion, the method has great potential as a sensitive and simple technique to detect VT and OTC-HCL in water.     

Highly luminescent S,N co‐doped carbon quantum dots‐sensitized chemiluminescence on luminol–H2O2 system for the determination of ranitidine

S,N co‐doped carbon quantum dots (N,S‐CQDs) with super high quantum yield (79%) were prepared by the hydrothermal method and characterized by transmission electron microscopy, photoluminescence, UV–Vis spectroscopy and Fourier transformed infrared spectroscopy. N,S‐CQDs can enhance the chemiluminescence intensity of a luminol–H₂O₂ system. The possible mechanism of the luminol–H₂O₂–(N,S‐CQDs) was illustrated by using chemiluminescence, photoluminescence and ultraviolet analysis. Ranitidine can quench the chemiluminescence intensity of a luminol–H₂O₂–N,S‐CQDs system. So, a novel flow‐injection chemiluminescence method was designed to determine ranitidine within a linear range of 0.5–50 μg ml^?1 and a detection limit of 0.12 μg ml^?1. The method shows promising application prospects.     

Low‐Temperature‐Processed Colloidal Quantum Dots as Building Blocks for Thermoelectrics

Colloidal quantum dots (CQDs) are demonstrated to be promising materials to realize high‐performance thermoelectrics owing to their low thermal conductivity. The most studied CQD films, however, are using long ligands that require high processing and operation temperature (>400 °C) to achieve optimum thermoelectric performance. Here the thermoelectric properties of CQD films cross‐linked using short ligands that allow strong inter‐QD coupling are reported. Using the ligands, p‐type thermoelectric solids are demonstrated with a high Seebeck coefficient and power factor of 400 μV K^?1 and 30 µW m^?1 K^?2, respectively, leading to maximum ZT of 0.02 at a lower measurement temperature (<400 K) and lower processing temperature (<300 °C). These ligands further reduce the annealing temperature to 175 °C, significantly increasing the Seebeck coefficient of the CQD films to 580 μV K^?1. This high Seebeck coefficient with a superior ZT near room temperature compared to previously reported high temperature‐annealed CQD films is ascribed to the smaller grain size, which enables the retainment of quantum confinement and significantly increases the hole effective mass in the films. This study provides a pathway to approach quantum confinement for achieving a high Seebeck coefficient yet strong inter‐QD coupling, which offers a step toward low‐temperature‐processed high‐performance thermoelectric generators.     

Determination of ampicillin sodium using the cupric oxide nanoparticles–luminol–H2O2 chemiluminescence reaction

A simple and sensitive chemiluminescence (CL) method has been developed for the determination of ampicillin sodium at submicromolar levels. The method is based on the inhibitory effect of ampicillin sodium on the cupric oxide nanoparticles (CuO NPs)–luminol–H₂O₂ CL reaction. Experimental parameters affecting CL inhibition including concentrations of CuO NPs, luminol, H₂O₂ and NaOH were optimized. Under optimum conditions, the calibration plot was linear in the analyte concentration range 4.0 × 10^‐7–4.0 × 10^‐6 mol/L. The limit of detection was 2.6 × 10^‐7 mol/L and the relative standard deviation (RSD) for six replicate determinations of 1 × 10^‐6 mol/L ampicillin sodium was 4.71%. Also, X–ray diffraction (XRD) and transmission electron microscopy (TEM) analysis were employed to characterize the CuO NPs. The utility of the proposed method was demonstrated by determining ampicillin sodium in pharmaceutical preparation. Copyright © 2013 John Wiley & Sons, Ltd.     

A selective and sensitive fluorescent sensor for cysteine detection based on bi‐8‐carboxamidoquinoline derivative and Cu2+ complex

In this paper, a novel fluorescent sensor 1 for selective and sensitive detection of cysteine was developed based on a complex between bi‐8‐carboxamidoquinoline derivative ligand ( L ) and Cu²⁺. The interaction of Cu²⁺ with the ligand causes a dramatic fluorescence quenching most likely due to its high affinity towards Cu²⁺ and a ligand–metal charge transfer (LMCT) process. The in situ generated L–Cu ² complex was utilized as a chemosensing ensemble for cysteine. In the presence of cysteine, the fluorophore, L , was released from L–Cu ² complex because of the strong affinity of cysteine to Cu²⁺ via the Cu–S bond, leading to the fluorescence recovery of the ligand. The proposed displacement mechanism was confirmed by the results of mass spectrometry (MS) study. Under optimized conditions, the recovered fluorescence intensity is linear with cysteine concentrations in the range 1 × 10^?6 mol/l to 8 × 10^?6 mol/l. The detection limit for cysteine is 1.92 × 10^?7 mol/l. Furthermore, the established method showed a highly sensitive and selective response to cysteine among the 20 fundamental α‐amino acids used as the building blocks of proteins, after Ni²⁺ was used as a masking agent to eliminate the interference of His. The proposed sensor is applicable in monitoring cysteine in practical samples with good recovery rate.     

A new benzimidazole‐based selective and sensitive ‘on–off’ fluorescence chemosensor for Cu2+ ions and application in cellular bioimaging

Two new twinborn benzimidazole derivates ( L and A ), which bonded pyridine via the ester space on the opposite and adjacent positions of the benzene ring of benzimidazole respectively, were designed and synthesized. Compound L displayed fluorescence quenching response only towards copper(II) ions (Cu²⁺) in acetonitrile solution with high selectivity and sensitivity. However, compound A presented ‘on–off’ fluorescence response towards a wide range of metal ions to different degrees and did not have selectivity. Furthermore, compound L formed a 1:1 complex with Cu²⁺ and the binding constant between sensor L and Cu²⁺ was high at 6.02 × 10⁴ M^?1. Job's plot, mass spectra, IR spectra, ¹H‐NMR titration and density functional theory (DFT) calculations demonstrated the formation of a 1:1 complex between L and Cu²⁺. Chemosensor L displayed a low limit of detection (3.05 × 10^?6 M) and fast response time (15 s) to Cu²⁺. The Stern–Volmer analysis illustrated that the fluorescence quenching agreed with the static quenching mode. In addition, the obvious difference of L within HepG2 cells in the presence and absence of Cu²⁺ indicated L had the recognition capability for Cu²⁺ in living cells.     

Water‐soluble polymeric chemosensor for selective detection of Hg2+ in aqueous solution using rhodamine‐based modified poly(acrylamide–acrylic acid)

We report the fabrication of a novel easily available turn‐on fluorescent water‐soluble polymeric chemosensor for Hg²⁺ ions that was simply prepared by micellar free radical polymerization of a water‐insoluble organic rhodamine‐based Hg²⁺‐recognizing monomer (GR6GH), with hydrophilic monomers acrylamide (AM) and acrylic acid (AA). The chemical structure of the polymeric sensor was characterized by FT‐IR and ¹H NMR spectroscopy. The apparent viscosity average molecular weight M_η of poly(acrylamide–acrylic acid) [poly(AM–NaAA)] and the water‐soluble polymeric chemosensor poly(AM–NaAA–GR6GH) were 1.76 × 10⁶ and 6.84 × 10⁴ g/mol, respectively. Because of its amphiphilic property, the water‐soluble polymeric chemosensor can be used as a chemosensor in aqueous media. Upon addition of Hg²⁺ ions to an aqueous solution of poly(AM–NaAA–GR6GH), fluorescence enhancements were observed instantly. Moreover, other metal ions did not induce obvious changes to the fluorescence spectra. This approach may provide an easily measurable and inherently sensitive method for Hg²⁺ ion detection in environmental and biological applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Bovine serum albumin‐confined silver nanoclusters as fluorometric probe for detection of biothiols

Fluorescent bovine serum albumin‐confined silver nanoclusters (BSA–AgNCs) were demonstrated to be a novel and environmentally friendly probe for the rapid detection of biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH). The sensing was ascribed to the strong affinity between the mercapto group of the biothiols and the silver nanoclusters. The fluorescence intensity of BSA–AgNCs was quenched efficiently on increasing the concentration of biothiol, corresponding with a red‐shift in emission wavelength. However, the fluorescence of the silver nanoclusters was almost unchanged in the presence of other α‐amino acids at 10‐fold higher concentrations. By virtue of this specific response, a new, simple and rapid fluorescent method for detecting biothiols has been developed. The linear ranges for Cys, Hcy and GSH were 2.0 × 10^‐6 to 9.0 × 10^‐5 M (R² = 0.994), 2.0 × 10^‐6 to 1.2 × 10^‐4 M (R² = 0.996) and 1.0 × 10^‐5 to 8.0 × 10^‐5 M (R² = 0.980), respectively. The detection limits were 8.1 × 10^‐7 M for Cys, 1.0 × 10^‐6 M for Hcy and 1.1 × 10^‐6 M for GSH. Our proposed method was successfully applied to the determination of thiols in human plasma and the recovery was 94.83–105.24%. It is potentially applicable to protein‐stabilized silver nanoclusters in a chemical or biochemical sensing system. Copyright © 2014 John Wiley & Sons, Ltd.     

Glutathione‐stabilized Cu nanocluster‐based fluorescent probe for sensitive and selective detection of Hg2+ in water

In this paper, an innovative and facile one‐pot method for synthesizing water‐soluble and stable fluorescent Cu nanoclusters (CuNCs), in which glutathione (GSH) served as protecting ligand and ascorbic acid (AA) as reducing agent was reported. The resultant CuNCs emitted blue‐green fluorescence at 440 nm, with a quantum yield (QD) of about 3.08%. In addition, the prepared CuNCs exhibited excellent properties such as good water solubility, photostability and high stability toward high ionic strength. On the basis of the selective quenching of Hg²⁺ on CuNCs fluorescence, which may be the result of Hg²⁺ ion‐induced aggregation of the CuNCs, the CuNCs was used for the selective and sensitive determination of Hg²⁺ in aqueous solution. The proposed analytical strategy permitted detection of Hg²⁺ in a linear range of 4 × 10^?8 to 6 × 10^?5 M, with a detection limit of 2.2 × 10^?8 M. Eventually, the practicability of this sensing approach was confirmed by its successful application to assay Hg²⁺ in tap water, Lotus lake water and river water samples with the quantitative spike recoveries ranging from 96.9% to 105.4%.     

A new Schiff base as a turn‐off fluorescent sensor for Cu2+ and its photophysical properties

A new Schiff base receptor 1 was synthesized and its photophysical properties were investigated by absorption, emission and excitation techniques. Furthermore, its chromogenic and fluorogenic sensing abilities towards various metal ions were examined. Receptor 1 selectively detects Cu²⁺ ion through fluorescence quenching and detection was not inhibited in the presence of other metal ions. From fluorescence titration, the limit of detection of receptor 1 as a fluorescent ‘turn‐off’ sensor for the analysis of Cu²⁺ was estimated to be 0.35 μM.