A fluorescent magnetic nanosensor for imidacloprid based on the incorporation of polymer dots and Fe3 O4 nanoparticles into the covalent organic framework.

A magnetic nanoprobe was designed for imidacloprid by encapsulating nonconjugated polymer dots (NCPDs) and Fe3 O4 nanoparticles in the covalent organic framework (COF). The fluorescence intensity of the COF-based nanocomposite is markedly suppressed by imidacloprid. As the absorption spectrum of imidacloprid was close to the band-gap of the NCPDs, and due to the presence of a nitro group (as an electron acceptor), the electrons can be easily transferred from the conduction band of NCPDs to the LUMO of imidacloprid, so fluorescence quenching was more likely to have been caused by the electron transfer process. The COF-based nanosensor was used for the determination of imidacloprid in the linear range 1.3-130 nM with a detection limit of 1.2 nM. The high sensitivity of the nanoprobe for imidacloprid is due to the combination of COF benefits (accumulation of the imidacloprid into the COF cavities) and the high adsorption ability of the Fe3 O4 nanoparticles, which leads to further enrichment of imidacloprid. The magnetic nature of the nanocomposite enables the preconcentration and easy separation of the analyte, and so reduces matrix interference and lowers the detection limits. The practicality of this nanoprobe was confirmed by quantification of imidacloprid in the wastewater and fruit juice samples.

A Simple and Novel Sensor for the Determination of Acetamiprid Based on Its Reducing Effect on the Chemiluminescence of S, N-CQDs in CH3CN-H2O2 System.

A simple and novel method for the determination of acetamiprid in water samples is suggested. The method is based on the reducing effect of acetamiprid on the chemiluminescence intensity of new sulfur and nitrogen co-doped carbon dots (S, N-CQDs) in an acetonitrile-hydrogen peroxide (CH3CN-H2O2) system. The possible mechanism was investigated, and it was found that S, N-CQDs react with (1O2)2*, produced from the CH3CN-H2O2 reaction, leading to excited state S, N-CQDs, which deactivate to the ground state by photon emission. Acetamiprid diminishes the chemiluminescence (CL) intensity by competing with S, N-CQDs. The CL intensity reduction is proportional to the concentration of acetamiprid. S, N-CQDs were easily prepared by a hydrothermal method. Under the optimal conditions, a linear range of 2.5 - 25.0 µg L-1 with a detection limit (3σ) of 0.4 µg L-1 was obtained. This method was successfully applied to the determination of trace amounts of residual pesticides in water samples.

Exploring the behavior of gold nanostar@reduced graphene oxide composite in chemiluminescence: Application to highly sensitive detection of glutathione.

Gold nanostar@reduced graphene oxide (GNS@rGO) nanocomposite was used as a catalyst in a chemiluminescence (CL) reaction. Composites with different sizes of gold nanostars were prepared without any surfactant, and characterized by transmission electron microscopy, UV-visible, FT-IR and Raman spectroscopy. We showed that GNS@rGO can strongly enhance the intensity of luminol­sodium periodate CL system and the larger the GNS size, the greater the enhancing effect. This effect results from the unique catalytic action of GNS@rGO, which leads to the acceleration of reactive oxygen species generation. We also found that a remarkable increase in the CL intensity of GNS@rGO-luminol-NaIO4 system occurs in the presence of glutathione (GSH). Based on this observation, a simple and highly sensitive CL probe was developed for detection of GSH. Under the optimum conditions, the calibration curve exhibits a linear range from 1.0 nM to 1.0 µM for GSH with a detection limit of 0.2 nM. The developed method was applied to the detection of GSH in human plasma samples.

An amplified chemiluminescence system based on Si-doped carbon dots for detection of catecholamines.

We report on a chemiluminescence (CL) system based on simultaneous enhancing effect of Si-doped carbon dots (Si-CDs) and cetyltrimethylammonium bromide (CTAB) on HCO3--H2O2 reaction. The possible CL mechanism is investigated and discussed. Excited-state Si-CDs was found to be the final emitting species, which are probably produced via electron and hole injection by oxy-radicals. The effect of several other heteroatom-doped CDs and undoped CDs was also investigated and compared with Si-CDs. Furthermore, it was found that catecholamines such as dopamine, adrenaline and noradrenaline remarkably diminish the CL intensity of Si-CD-HCO3--H2O2-CTAB system. By taking advantage of this fact, a sensitive probe was designed for determination of dopamine, adrenaline and noradrenaline with a limit of detection of 0.07, 0.60 and 0.01 µM, respectively. The method was applied to the determination of catecholamines in human plasma samples.

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.

A sensitive fluorescent nanosensor for chloramphenicol based on molecularly imprinted polymer-capped CdTe quantum dots.

A novel fluorescent nanosensor using molecularly imprinted silica nanospheres embedded CdTe quantum dots (CdTe@SiO2 @MIP) was developed for detection and quantification of chloramphenicol (CAP). The imprinted sensor was prepared by synthesis of molecularly imprinting polymer (MIP) on the hydrophilic CdTe quantum dots via reverse microemulsion method using small amounts of solvents. The resulting CdTe@SiO2 @MIP nanoparticles were characterized by fluorescence, UV-vis absorption and FT-IR spectroscopy and transmission electron microscopy. They preserved 48% of fluorescence quantum yield of the parent quantum dots. CAP remarkably quenched the fluorescence of prepared CdTe@SiO2 @MIP, probably via electron transfer mechanism. Under the optimal conditions, the relative fluorescence intensity of CdTe@SiO2 @MIP decreased with increasing CAP by a Stern-Volmer type equation in the concentration range of 40-500 µg L(-1). The corresponding detection limit was 5.0 µg L(-1). The intra-day and inter-day values for the precision of the proposed method were all <4%. The developed sensor had a good selectivity and was applied to determine CAP in spiked human and bovine serum and milk samples with satisfactory results.

Determination of fluoxetine in pharmaceutical and biological samples based on the silver nanoparticle enhanced fluorescence of fluoxetine-terbium complex.

In this study, a simple and sensitive spectrofluorimetric method is presented for the determination of fluoxetine based on the enhancing effect of silver nanoparticles (AgNPs) on the terbium-fluoxetine fluorescence emission. The AgNPs were prepared by a simple reduction method and characterized by UV-Vis spectroscopy and transmission electron microscopy. It was indicated that these AgNPs have a remarkable amplifying effect on the terbium-sensitized fluorescence of fluoxetine. The effects of various parameters such as AgNP and Tb3+ concentration and the pH of the media were investigated. Under obtained optimal conditions, the fluorescence intensity of the terbium-fluoxetine-AgNP system was enhanced linearly by increasing the concentration of fluoxetine in the range of 0.008 to 19 mg/L. The limit of detection (b + 3s) was 8.3 × 10-4 mg/L. The interference effects of common species found in real samples were also studied. The method had good linearity, recovery, reproducibility and sensitivity, and was satisfactorily applied for the determination of fluoxetine in tablet formulations, human urine and plasma samples. Copyright © 2016 John Wiley & Sons, Ltd.

Spectrofluorimetric determination of cefixime using terbium-danofloxacin probe.

OBJECTIVES: Cefixime (Cfx), is a semi-synthetic third-generation oral cephalosporin antibiotic that is prescribed for the treatment of susceptible infections. There are some procedures for the determination of Cfx in pharmaceutical formulations and biological samples. Herein a spectrofluorimetric method was proposed for Cfx determination based on the fluorescence quenching of terbium-danofloxacin (Tb(3+)-Dano) in the presence of Cfx. MATERIALS AND METHODS: Cfx was detected based on fluorescence quenching of terbium-danofloxacin (Tb(3+)-Dano) in the presence of Cfx with maximum excitation and emission wavelengths at 347 nm and 545 nm, respectively. The quenched fluorescence intensity of Tb(3+)- Dano system is proportional to the concentration of Cfx. The optimum conditions for the determination of Cfx were studied. RESULTS: The maximum response was achieved under optimum conditions of [Tris buffer]= 0.008 mol/l (pH 6.5), [Tb(3+)]=1×10(-4) mol/l and [Dano]=1×10(-4) mol/l. The developed method was evaluated in terms of accuracy, precision and limit of detection. The linear concentration ranges for quantification of Cfx were 8.8×10(-8)-8.8×10(-7) mol/l and 1.1×10(-7)-8.8×10(-7) mol/l in standard and human serum samples with the detection limits (S/N=3) of 2.8×10(-8) mol/l and 3.9×10(-8) mol/l, respectively. The Cfx was determined in pharmaceutical tablets and spiked serum samples and the results were satisfactory. CONCLUSION: This method is simple, practical and relatively interference-free for determination of Cfx in pharmaceutical tablets and serum samples.

Direct chemiluminescence of carbon dots induced by potassium ferricyanide and its analytical application.

The chemiluminescence (CL) of water-soluble fluorescent carbon dots (C-dots) induced by direct chemical oxidation was investigated. C-dots were prepared by solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. It was found that K3Fe(CN)6 could directly oxidize C-dots to produce a relatively intense CL emission. The mechanism of CL generation was investigated based on the fluorescence and CL emission spectra and the effect of radical scavengers on the CL intensity. The inhibitive effect of some metal ions and biologically important molecules on the CL intensity of the system was examined and the potential of the system for the determination of these species at trace levels was studied. In order to evaluate the capability of method to real sample analysis, it was applied to the determination of Cr(VI) and adrenaline in water and injection samples, respectively.

Permanganate-bromide-silver nanoparticles as a new chemiluminescence system and its application to captopril determination.

A novel chemiluminescence (CL) system based on the oxidation of bromide by permanganate in sulfuric acid medium is introduced. The enhancing effect of silver nanoparticles (NPs), synthesized by chemical reduction method, on this reaction was studied. It was demonstrated that spherical silver nanoparticles with average size of 18 nm had a most remarkable catalytic effect on this reaction. CL emission wavelengths and UV-vis spectra were used to characterize the system and propose a possible mechanism. Furthermore, it was found that captopril inhibits the action of NPs and decreases the intensity of CL. Based on this phenomenon, a new CL method was developed for the determination of captopril in the 3.0 × 10(-10) to 1.0 × 10(-7) mol L(-1) concentration range with a detection limit (3s) of 0.12 nmol L(-1). The method was successfully applied to the determination of captopril in pharmaceutical formulations, human urine and serum samples.

Gold nanorods-enhanced rhodamine B-permanganate chemiluminescence and its analytical application.

A novel enhanced chemiluminescence system was developed by applying gold nanorods (Au NRs) as catalysts in rhodamine B-permanganate reaction. Au NRs with three different aspect ratios were synthesized by seed mediated growth method and characterized by UV-Vis spectra and transmission electron microscopy. It was demonstrated that Au NRs have much higher catalytic effect than spherical nanoparticles on rhodamine B-permanganate chemiluminescence reaction. Among various sizes of Au NRs, those with average aspect ratio of 3.0 were found to have the most remarkable catalytic activity. As an analytical application of the new chemiluminescence system, albumin as a model protein was quantified based on its interaction with NRs. Albumin binds to Au NRs active surfaces and inhibits their catalytic action and therefore decreases the intensity of chemiluminescence. This diminution effect is linearly related to the concentration of the human and bovine serum albumin over the ranges of 0.45-90 and 0.75-123 nmol L(-1), respectively with the corresponding limits of detection of 0.18 and 0.30 nmol L(-1). The method was successfully applied to the determination of albumin in human and bovine serum samples.

Spectrofluorimetric determination of human serum albumin using terbium-danofloxacin probe.

A spectrofluorimetric method is proposed for the determination of human serum albumin (HSA) and bovine serum albumin (BSA) using terbium-danofloxacin (Tb(3+)-Dano) as a fluorescent probe. These proteins remarkably enhance the fluorescence intensity of the Tb(3+)-Dano complex at 545 nm, and the enhanced fluorescence intensity of Tb(3+)-Dano is proportional to the concentration of proteins (HSA and BSA). Optimum conditions for the determination of HSA were investigated and found that the maximum response was observed at: pH = 7.8, [Tb(3+)] = 8.5 × 10(-5) mol L(-1), [Dano] = 1.5 × 10(-4) mol L(-1). The calibration graphs for standard solutions of BSA, HSA, and plasma samples of HSA were linear in the range of 0.2 × 10(-6) - 1.3 × 10(-6) mol L(-1), 0.2 × 10(-6) - 1.4 × 10(-6) mol L(-1), and 0.2 × 10(-6) - 1 × 10(-6) mol L(-1), respectively. The detection limits (S/N = 3) for BSA, HSA, and plasma sample of HSA were 8.7 × 10(-8) mol L(-1), 6.2 × 10(-8) mol L(-1), and 8.1 × 10(-8) mol L(-1), respectively. The applicability of the method was checked using a number of real biological plasma samples and was compared with the UV spectrometric reference method. The results was showed that the method could be regarded as a simple, practical, and sensitive alternative method for determination of albumin in biological samples.

Determination of deferiprone in urine and serum using a terbium-sensitized luminescence method.

Optimized conditions, validation and practical applications of a new, rapid and specific fluorometric method for the determination of deferiprone (DFP) in urine and serum samples are reported. The proposed method, which is based on the formation of a luminescent complex with Tb(3+) ion, is evaluated in terms of linearity, accuracy, precision, stability, recovery and limits of detection (LOD) and quantification (LOQ). Under optimum conditions (pH 7.5, [Tb(3+)] = 3 × 10(-4) mol/L, temperature 0 °C and excitation wavelength 295 nm), the relative intensities at 545 nm are linear, with the concentration of DFP in the range 0.072-13 mmol/L for urine and serum samples. The LOD and LOQ, respectively, are calculated to be 0.014 and 0.045 mmol/L for urine and 0.022 and 0.072 mmol/L for serum samples. The intra-day and inter-day values for the precision and accuracy of the proposed method are all < 5%, and the recovery of the method is in the range 97.1-103.8%. The method was applied to human urine and serum samples collected from patients receiving DFP. The results indicated that the method can be successfully applied to the determination of DFP in human urine and serum samples collected for clinical or biopharmaceutical investigations in which simple, rapid, cheap and specific determination methods facilitate and speed up the analytical procedure.

Terbium-sensitized fluorescence method for the determination of deferasirox in biological fluids and tablet formulation.

A novel, rapid and sensitive spectroflurimetric method was developed and validated for the determination of deferasirox in urine, serum and tablet samples based on sensitization of terbium fluorescence. The excitation and emission wavelengths were 328 and 545 nm, respectively. The optimum conditions for the determination of deferasirox were investigated considering the effects of various parameters. The method was quantitatively evaluated in terms of linearity, recovery, reproducibility and limit of detection. Under the optimal conditions, the fluorescence intensities were linear with the concentration of deferasirox in the range of 5 × 10(-9) to 5×10(-6) mol L(-1) , with a detection limit of 1.5 × 10(-9) mol L(-1) and a relative standard deviation of 1.1-2.3%. Linearity, reproducibility, recovery and limit of detection made the method suitable for determination of deferasirox in urine, serum and tablets samples.

Spectrofluorimetric determination of folic acid in tablets and urine samples using 1,10-phenanthroline-terbium probe.

A new spectrofluorimetric method was reported for the determination of folic acid (FA), based on its quenching effect on the fluorescence intensity of Tb(3+) -1,10-phenanthroline complex as a fluorescent probe. The quenched fluorescence intensity at an emission wavelength of 545 nm was proportional to the concentration of FA in Tris-HCl buffer solution of pH 6.2. The effects of pH, time, order of addition of reagents, temperature and concentrations of Tb(3+) , buffer and 1,10-phenanthroline were investigated and optimized. The linear range for the determination of FA was 0.01-1.1 mg/L. The detection limit was 0.003 mg/L and the relative standard deviation for replicated determination of 1 mg/L of folic acid was 1.2%. This method was simple, practical and relatively free from interference effects. It was successfully applied to assess FA in pharmaceutical tablets and urine samples.

Spectrofluorimetric determination of buparvaquone in biological fluids, food samples and a pharmaceutical formulation by using terbium-deferasirox probe.

A simple spectrofluorimetric method is described for the determination of buparvaquone (BPQ), based on its quenching effect on the fluorescence intensity of Tb(3+)-deferasirox (DFX) complex as a fluorescent probe. The excitation and emission wavelengths were 328 and 545nm, respectively. The optimum conditions for determination of BPQ were investigated considering the effects of various affecting parameters. The variations in fluorescence intensity of the system showed a good linear relationship with the concentration of BPQ in the range of 10-1500µgL(-1), its correlation coefficient was 0.999 with the detection and quantification limits of 1.1 and 3.4µgL(-1), respectively. Linearity, reproducibility, recovery, limits of detection and quantification made the method suitable for BPQ assay in biological fluids, meat, dairy products and BPQ parenteral solutions (vials). The method was applied to real samples of serum and milk of three cows receiving BPQ.

Ionic liquid-based, single-drop microextraction for preconcentration of cobalt before its determination by electrothermal atomic absorption spectrometry.

An effective and environmentally friendly single-drop microextraction method was developed for the preconcentration of ultratraces of cobalt before its determination by electrothermal atomic absorption spectrometry (ETAAS). A microdrop of 1-hexyl-3-methylimidazolium hexafluorophosphate, [C6MIM][PF6], was used to extract Co(II) ions as an ammonium pyrroldinedithiocarbamate (APDC) complex. The sensitivity was improved by increasing the volume of the suspended drop. Several variables affecting microextraction efficiency and the ETAAS signal-such as pyrolysis and atomization temperature, pH, APDC concentration, extraction time, drop volume, and stirring rate-were investigated and optimized. Under the optimum experimental conditions, the detection limit (3 SD) was 0.04 microg/L, and the enrichment factor was 120. The RSD for five replicate determinations of Co(II) at 0.5 microg/L was 4.5%. The developed method was validated by analysis of a Standard Reference Material and applied to the determination of cobalt in water samples.

Hollow fiber based-liquid phase microextraction using ionic liquid solvent for preconcentration of lead and nickel from environmental and biological samples prior to determination by electrothermal atomic absorption spectrometry.

A simple and effective hollow fiber based-liquid phase microextraction (HF-LPME) technique by using ionic liquid, 1-hexyl-3-methylimidazolium hexafluorophosphate, [C(6)MIM][PF(6)], coupled with electrothermal atomic absorption spectrometry (ETAAS) was developed for the determination of lead and nickel in environmental and biological samples. Ammonium pyrroldinedithiocarbamate (APDC) was used as chelating agent. Several factors that influence the microextraction efficiency and ETAAS signal, such as pH, APDC concentration extraction time, amounts of ionic liquid, stirring rate, pyrolysis and atomization temperature were investigated and the microextraction conditions were established. In the optimum experimental conditions, the detection limits (3 s) of the method were 0.03 and 0.02 microg L(-1), for Ni and Pb, respectively and corresponding relative standard deviations (0.5 microg L(-1), n=6) were 4.2% and 5%. The developed method was validated by the analysis of certified reference materials and applied to the determination of lead and nickel in real samples.

Ultra-trace determination of lead in water and food samples by using ionic liquid-based single drop microextraction-electrothermal atomic absorption spectrometry.

An improved single drop microextraction procedure was developed for the preconcentration of lead prior to its determination by electrothermal atomic absorption spectrometry. Ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6], was used as an alternative to volatile organic solvents for extraction. Lead was complexed with ammonium pyrroldinedithiocarbamate (APDC) and extracted into a 7-microL ionic liquid drop. The extracted complex was directly injected into the graphite furnace. Several variables affecting microextraction efficiency and ETAAS signal, such as pyrolysis and atomization temperature, pH, APDC concentration, extraction time, drop volume and stirring rate were investigated and optimized. In the optimum experimental conditions, the limit of detection (3s) and the enhancement factor were 0.015 microg L(-1) and 76, respectively. The relative standard deviation (RSD) for five replicate determinations of 0.2 microg L(-1) Pb was 5.2%. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of lead in several real samples.

Ionic liquid-based single drop microextraction combined with electrothermal atomic absorption spectrometry for the determination of manganese in water samples.

Room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C(4)MIM][PF(6)], was used as an alternative to volatile organic solvents in single drop microextraction-electrothermal atomic absorption spectrometry (SDME-ETAAS). Manganese was extracted from aqueous solution into a drop of the ionic liquid after complextaion with 1-(2-thiazolylazo)-2-naphthol (TAN) and the drop was directly injected into the graphite furnace. Several variables affecting microextraction efficiency and ETAAS signal, such as pyrolysis and atomization temperature, pH, TAN concentration, extraction time, drop volume and stirring rate were investigated and optimized. In the optimum experimental conditions, the limit of detection (3s) and the enhancement factor were 0.024 microg L(-1) and 30.3, respectively. The relative standard deviation (RSD) for five replicate determinations of 0.5 microg L(-1) Mn(II) was 5.5%. The developed method was validated by the analysis of a certified reference material (NIST SRM 1643e) and applied successfully to the determination of manganese in several natural water samples.