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Journal: Luminescence : the journal of biological and chemical luminescence

22

This study comprises a convenient, rapid and very sensitive method for the determination of bovine serum albumin (BSA). The technique is based on fluorescence resonance energy transfer (FRET) between Rhodamine-6G (R6G) acting as donor and gold nanoparticles (AuNPs) acting as acceptors. This method takes advantage of AuNPs that have high quenching efficiency, therefore the absorption spectra range shifts from 521 to 635 nm when aggregation of the AuNPs takes place. Furthermore, when R6G was electrostatically self-adsorbed to the citrate-stabilized AuNPs surface the fluorescence intensity was quenched. After addition of BSA, the fluorescence intensity of the R6G recovered as BSA induced aggregation of the AuNPs and the adsorbed R6G was released to the solution. The recovery of intensity displays a linear relationship with BSA concentration over the range from 0.8 × 10-11  M to 5.6 × 10-11  M. The detection limit for BSA was found to be 4.58 × 10-11  M. The proposed method exhibited rapid analysis with high selectivity for BSA determination in human urine, blood and serum samples.

22

Two sensitive and accurate methods have been developed for the estimation of daclatasvir (DAC) in its raw material, dosage form and in biological fluids. Method I is based on the measurement of DAC native fluorescence in methanol at 385 nm after excitation at 315 nm. The relationship between fluorescence intensity and concentration was found to be rectilinear over the linearity range (3.0-30.0 ng/ml). There were good per cent recoveries both in the dosage form (99.87 ± 0.84) and in spiked human plasma (99.96 ± 1.54%). Method II utilized reversed-phase high performance liquid chromatography to estimate the antiviral agent daclatasvir hydrochloride against hepatitis C within 4.0 min on a C18 column (Eurosphere. 100-5 C18, 150 × 4.6 mm, Germany) using a mobile phase consisting of acetonitrile and 0.1 M sodium dihydrogen phosphate (30:70, v/v) at pH 3.0 and with a fluorescence detector adjusted to 315 nm and 385 nm for excitation and emission respectively. The calibration curve was linear over the range (20.0-200.0 ng/ml) with SD 1.38%, error 0.56%, recovery 99.99 ± 1.30% in tablets, recovery 100.28 ± 1.73% in spiked urine and recovery 99.63 ± 2.72% in spiked plasma.The new developed methods were successfully applied to the assay of the daclatasvir in tablet form and extended to its determination in real plasma, spiked human plasma and urine. The analytical performance of the proposed method was validated according to International Conference on Harmonization (ICH) guidelines. The proposed methods were compared with the results of a comparison method and it was found that there was no significant difference between the methods, as revealed by Student’s t-test and variance ratio F-test.

22

Three anthracene-based Schiff base complexes, R1-R3 (R1 = (E)-N´-((anthracen-10-yl)methylene)benzohydrazide; R2 = (E)-1-((anthracen-10-yl)methylene)-4-phenylsemicarbazide; and R3 = (E)-1-((anthracen-10-yl)methylene)-4-phenylthiosemicarbazide) were synthesized from 9-anthracenecarboxaldehyde, benzohydrazide, 4-phenylsemicarbazide and 4-phenylthiosemi-carbazide respectively, and characterized by various spectral techniques. The absorption spectral characteristics of R1-R3 were bathochromically tuned to the visible region by extending the π conjugation. These target compounds were weakly fluorescent in tetrahydrofuran (THF) solution because of rapid isomerization of the C=N double bond in the excited state. However, the aqueous dispersion of R1-R3 in the THF/water mixture by the gradual addition of water up to 90% resulted in an increase in the fluorescence intensity mainly due to aggregation-induced emission enhancement (AIEE) properties. The formation of nanoaggregates of R1-R3 were confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The compounds R1-R3 are ideal probes for the fluorescence sensing of bovine serum albumin (BSA) and breast cancer cells by optical cell imaging.

Concepts: Electron, Cancer, Breast cancer, Optics, Light, Atom, Serum albumin, Scanning electron microscope

22

The present work introduces for the first time a nanoparticulate approach for ex vivo monitoring of acetylcholinesterase-catalyzed hydrolysis of endogenous acetylcholine released from nerve varicosities in mice atria. Amino-modified 20-nm size silica nanoparticles (SNs) doped by luminescent Tb(III) complexes were applied as the nanosensors. Their sensing capacity results from the decreased intensity of Tb(III)-centred luminescence due to the quenching effect of acetic acid derived from acetylcholinesterase-catalyzed hydrolysis of acetylcholine. Sensitivity of the SNs in monitoring acetylcholine hydrolysis was confirmed by in vitro experiments. Isolated atria were exposed to the nanosensors for 10 min to stain cell membranes. Acetylcholine hydrolysis was monitored optically in the atria samples by measuring quenching of Tb(III)-centred luminescence by acetic acid derived from endogenous acetylcholine due to its acetylcholinesterase-catalyzed hydrolysis. The reliability of the sensing was demonstrated by the quenching effect of exogenous acetylcholine added to the bath solution. Additionally, no luminescence quenching occurred when the atria were pre-treated with the acetylcholinesterase inhibitor paraoxon.

Concepts: Oxygen, Nanoparticle, Ethanol, Nanotechnology, Acid dissociation constant, In vitro, Acetylcholine, Acetylcholinesterase

0

To develop conducting organic polymers (COPs) as luminescent sensors for determination of toxic heavy metals, a new benzene sulfonic acid-doped polypyrrole (PPy-BSA) thin film was electrochemically prepared by cyclic voltammetry (CV) on flexible indium tin oxide (ITO) electrode in aqueous solution. PPy-BSA film was characterized by FTIR spectrometry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The optical properties of PPy-BSA were investigated by ultraviolet (UV)-visible absorption and fluorescence spectrometry in dimethylsulfoxide (DMSO) diluted solutions. PPy-BSA fluorescence spectra were strongly quenched upon increasing copper(II) ion (Cu2+ ) and lead(II) ion (Pb2+ ) concentrations in aqueous medium, and linear Stern-Volmer relationships were obtained, which indicated the existence of a main dynamic fluorescence quenching mechanism. BSA-PPy sensor showed a high sensitivity for detection of both metallic ions, Cu2+ and Pb2+ , with very low limit of detection values of 3.1 and 18.0 nM, respectively. The proposed quenching-fluorimetric sensor might be applied to the determination of traces of toxic heavy metallic ions in water samples.

0

Acridinium salts, due to their chemiluminogenic properties, have found several applications in biomedical analysis as labels and indicators, where the assessment of emission intensity is used for the end-point detection. This work presents the use of chemiluminescent indicators in the form of selected acridinium esters in order to determine the antioxidant properties of exemplary formulations, namely quercetin, vitamin C and the dietary supplement, Apiextract. The principle of measurements is based on a change in the kinetics of emission decay derived from the acridinium cations in alkaline solutions of hydrogen peroxide in the presence of an antioxidant (the analyte). The proposed system makes a beneficial alternative to related methods, which mostly rely on the assessment of emission efficiency and use the luminometric standard luminol - due to superior parameters of acridinium chemiluminescence, among others - high temporary emission efficiency. The features of the proposed method are manifested by a shorter time period of analysis and lower background signals associated with the environmental influences, as compared to typical approaches. The chromatographic (RP-HPLC) analyses of the substrates and products generated during chemiluminogenic oxidation of acridinium cations under assay conditions are also presented.

0

The effect of halide ions (Cl- , Br- and I- ) on the fluorescence of quinine sulfate in dilute sulfuric acid solution was studied by fluorescence spectra, ultraviolet-visible (UV-visible) absorption spectra and fluorescence decay technique. The results exhibited that halide ions with heavier atomic mass could significantly reduce the fluorescence intensity of quinine sulfate, as a result, the order of fluorescence quenching caused by halide ions is Cl-  < Br-  < I- . Therefore, halide ions with high concentration could seriously quench the fluorescence of quinine sulfate. The UV-visible absorption spectra and fluorescence decay technique revealed that the fluorescence quenching of quinine sulfate caused by halide ions was attributed to dynamic quenching, static quenching process, self-quenching fluorescence effect and electronic transfer.

0

In this work, the optical and structural properties of ultrasonically prepared CaF2 :Eu3+ nanoparticles have been reported. Ultrasonically prepared CaF2 :Eu3+ phosphor shows orange, red emission bands at 591 nm and 612 nm, respectively, when it is excited by 394 light-emitting diode (LED) excitation wavelengths. Further phosphor materials are well characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) techniques to confirm the phase purity, metal oxygen (MO) bonding and crystallites size of the materials. Here synthesized materials show a tube-like structure under 100 nm resolution and 0.1 mol% is the best doping value of the europium ion (Eu3+ ) in calcium fluoride (CaF2 ) that shows highest intensity when prepared with an ultrasound assisted method.

0

An EC50 database was established to assess the acute toxicity of 16 PESTANAL pesticide standards and of seven pesticide commercial formulations using a Vibrio fischeri bioluminescence method. Half maximal effective concentration (EC50 ) is defined as the concentration of pollutant (in this case, pesticide) destroying 50% of the bacteria population and causing 50% bioluminescence inhibition, after a specified exposure time. Linear curves of bioluminescence inhibition versus pesticide concentration and EC50 values were obtained for exposure times (t) of 5 or 15 min for these pesticides. The EC50 values ranged from 6.90 × 10-4 to 0.83 mg/ml (t = 5 min), and from 9.00 × 10-4 to 0.37 mg/ml (t = 15 min) for pesticide standards, plus from 0.0077 to 0.74 mg/ml (t = 5 min), and from 0.0076 and 0.57 mg/ml (t = 15 min) for pesticide commercial formulations. The EC50 database allowed classification of the pesticides under study into three categories according to their toxicity: very toxic, toxic and moderately toxic. These results demonstrated that the establishment of an EC50 database and of linear curves of bioluminescence inhibition versus the pesticide concentration resulted in very important and irreplaceable tools to estimate the global and individual toxicity of pesticides present in environmental samples.

0

Nanoparticles of cadmium selenide (CdSe) doped with europium, were synthesized as stabilizing agents using thioglycolic acid ligand. This method is based on the enhancing effect of CdSe quantum dots (QDs) doped with europium on chemiluminescence (CL) emission. This emission was generated by mixing CdSe QDs with manganese (II), iron (II) and chrome (II) sulfates as catalysts in the presence of hydrogen peroxide (H2 O2 ). The structural characteristics and morphology of these nanoparticles were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy, X-ray pattern and dynamic light scattering methods. The CdSe QDs doped with europium were used as the sensitizer in a luminol-hydrogen peroxide CL system. The sensitized CdSe QDs were analyzed for antibacterial activity against Gram-positive or Gram-negative bacteria. The results showed that the CdSe QDs are effective against all the studied bacteria, effectiveness was especially higher for Bacillus subtilis.