Silver nanoparticle-based chemiluminescence enhancement for the determination of norfloxacin

A chemiluminescence (CL) method is presented for the flow injection determination of norfloxacin (NFLX). It is based on the fact that the weak CL of the Ce(IV)-Na₂SO₃ redox system is strongly enhanced in the presence of silver nanoparticles. UV-visible and fluorescence spectroscopy was carried out and showed that the energy of the intermediate SO₂*, originating from the reaction of Ce(IV) with Na₂SO₃, was transferred to Tb³⁺ via NFLX, and that the silver nanoparticles (AgNPs) accelerate the process due to the electric activity of AgNPs. Norfloxacin was detected by measuring the CL intensity which increases linearly with the concentration of NFLX in the range from 10 nM to 50 μM. The detection limit is lowered to 2.0 nM. The method was successfully applied to the determination of NFLX in eyedrops.     

Strong enhancement of the chemiluminescence of the cerium(IV)-thiosulfate reaction by carbon dots,and its application to the sensitive determination of dopamine

We show that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots). The C-dots were prepared by a solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. Possible mechanisms that lead to the effect were elucidated by recording fluorescence and CL spectra. It is found that dopamine at even nanomolar levels exerts a diminishing effect on the enhancement of CL. This was exploited to design a method for the determination of dopamine in the concentration range from 2.5 nM to 20 μM, with a limit of detection (at 3 s) of 1.0 nM. Dopamine was determined by this method in spiked human plasma samples with satisfactory results.

Coupled electrochemical-chemical procedure used in construction of molecularly imprinted polymer-based electrode: a highly sensitive impedimetric melamine sensor

A novel molecularly imprinted sensor was fabricated and used for the impedimetric detection of melamine. Considering the identity of polymeric film and the pK _a of a melamine template, an effective procedure was established to construct the MIP-based melamine sensor. The proposed method is based on the electropolymerization of pyrrole (Py) in the presence of melamine on the electrochemically reduced graphene oxide modified glassy carbon electrode (ERGO/GCE), followed by treatment with the solution of 1% H₂O₂ in alkaline water/CH₃CN-mixed solvents. The surface morphology and the electrical feature of molecularly imprinted polymer (MIP) were characterized by scanning electron microscopy (SEM), Fourier transformation infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The EIS was also utilized to transduce the change of charge transfer resistance (R _ct) at the interface of polymer film-electrolyte, after subsequent incubation of electrode in the solution containing different concentrations of analyte, and consequently, a linear response was obtained over the range of 4.0 to 240 nM with a detection limit of 0.83 nM (S/N = 3). The effect of possible interferences on the response of sensor was studied, and the results confirmed the good selectivity of the proposed device for melamine assay. The MIP sensor was successfully applied to determine melamine in a multiple concentration-spiked milk sample.     

A Flow Injection Chemiluminescence Method for the Determination of Protein Using Copper(II)-Alizarin Red S Complex as an Efficient Chemiluminescent Probe

A sensitive flow injection chemiluminescence (CL) method is proposed for the determination of bovine serum albumin (BSA) using Copper(II)-Alizarin Red S (ARS) complex as an efficient chemiluminescent probe. The detection is based on the binding of the copper(II)-ARS complex to proteins and the catalytic activity of copper(II)-ARS in the luminol-H₂O₂ CL system. Under the selected conditions, the CL intensity is linear with the concentration of BSA in the range of 5.0 × 10^?11 to 1.0 × 10^?9 mol · L^?1. The detection limit was 2.0 × 10^?11 mol · L^?1. The method is successfully applied to the determination of protein in urine.     

Efficient chemiluminescence by aptamer – reactant platform combination with activated Ag–Au alloy nanoparticles for cobalt detection

This article deals with the detection of Co(II) in real water sample using aptamer – reactant platform combination with activated Ag–Au alloy nanoparticles (NPs) by chemiluminescence (CL) method. CL is attributed to a catalytically enhanced decomposition of H₂O₂ by aptamer conjugated Ag–Au alloy NPs to produce reactive oxygen species. The Ag–Au alloy NPs were prepared by chemical method using double reducing agent (i.e. trisodium citrate and polyethylenimine) and used for detection of Co(II) from water by CL method. CL experiments were carried out with the variation of different parameters such as pH, concentration of luminol, concentration of H₂O₂ and Ag–Au alloy NPs. We found that Ag–Au alloy NPs have very good efficiency towards Co(II) detection. Analytical parameters and kinetics were studied in detail to know the nature and mechanism of CL in presence of aptamer conjugated Ag–Au alloy NPs. The linear range of the CL sensor of Co(II) is covered concentration from 0.01 to 10 µg/L with detection limit of 0.001 µg/L. The relative standard deviation for determination of Co(II) was 6.65 in 10 replicated measurements. CL method is first time applied to detect the Co(II) in real water samples at very low level using aptamer conjugated Ag–Au NPs as a catalyst.     

Flow Injection Chemiluminescence Sensor with Novel Rhodanine Ramification for Determination of Fenfluramine Based on Molecularly Imprinted Polymer

Abstract

Flow injection chemiluminescence (FI-CL) with molecularly imprinted polymer (MIP) was applied to determine fenfluramine. The fenfluramine-imprinted polymer was prepared with acrylamide (AM) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker. Methyl and sulfonic group were introduced to rhodanine matrix, and a novel rhodanine ramification 3MORASP was synthesized by the author, and it was used as chemiluminescence reagent. 3-(3′-Methoxyphenyl)-5(2′-sulfonylphenylazo)-rhodanine (3MORASP), first synthesized by the authors, was used as chemiluminescence (CL) reagent. The novel flow path of FI-CL was designed, which made three merged streams of reactants injected into MIP column move through different pathways simultaneously. Fenfluramine was detected based on the reaction of fenfluramine, 3MORASP, and potassium permanganate in an acidic medium. The CL intensity was correlated linearly with the concentration of fenfluramine over the range of 1.0 × 10^?7 to 5.0 × 10^?6 g · mL^?1, and the detection limit was 9.48 × 10^?9 g · mL^?1. The relative standard deviation (RSD) was 2.4% for determination of 1.0 × 10^?6 g · mL^?1 fenfluramine (n = 11). This method was successfully applied to the determination of fenfluramine in weight-reducing tonic.     

Capillary Electrophoresis Chemiluminescence for the Analysis of Flavonoids in Pharmaceuticals and Human Plasma

A capillary electrophoresis (CE)-chemiluminescence (CL) method has been developed for the determination of the pharmacologically active flavonoids, including rutin and quercetin in pharmaceuticals and human plasma containing Ginkgo biloba leaves extract (EGb). The separation was conducted in borate buffer and luminol. The post-column CL reagent was K₃Fe(CN)₆ in NaOH medium. Rutin and quercetin were baseline separated within 10 min with detection limits of 1.0 and 5.0 nM, respectively. The maximum intra- and inter-day relative standard deviations (RSD) of migration time of analytes were <3.5 %. Moreover, the high selectivity of the CL detection and the high-separation efficiency of CE render the method the potential of quick analyzing the pharmacologically active substances in complex matrix with satisfactory results.

     

Size dependent active effect of CdTe quantum dots on pyrogallol-H2O2 chemiluminescence system for chromium(III) detection

Water-soluble CdTe quantum-dots (QDs) of different sizes and capped with mercaptosuccinic acid were prepared by the microwave irradiation method. The QDs can significantly enhance the chemiluminescence (CL) of the pyrogallol-H₂O₂ system. Those with a diameter of 3.8 nm produce the most intense CL. UV-vis, photoluminescence, and CL spectra were acquired in order to explore the effect. The results showed that the chromium(III) ion in the concentration range from 20 pM to 30 µM enhances CL, and this is exploited for its trace determination.The limit of detection (3σ) is 6 pM, with a relative standard deviation (n?=?11) of 1.7%. A continuous flow injection CL method was developed and applied to the determination of chromium(III) in tap water and lake water samples with satisfactory results.     

A Novel Enhanced Chemiluminescence System with Ag(III) Complex for the Determination of Ofloxacin and Levofloxacin in Pharmaceutical Preparation and Biological Fluid

A novel chemiluminescence (CL) method is developed for determination of ofloxacin and levofloxacin with Ag(III) complex in H₂SO₄ solution medium. The CL intensity is proportional to drug concentration in a wider range with a correlation coefficient of 0.999. The limit of detection (s/n = 3) for ofloxacin and levofloxacin was 5.3 × 10^?9 g ml^?1 and 8.3 × 10^?9 g ml^?1, respectively, and their recoveries from urine and serum samples were in the range of 90.1–112% with the RSDs of 1.0–2.8%. The proposed method was applied for analysis of real samples with satisfactory result. The possible CL mechanism was discussed.     

Capillary Electrophoresis Chemiluminescence for the Analysis of Flavonoids in Pharmaceuticals and Human Plasma

A capillary electrophoresis (CE)-chemiluminescence (CL) method has been developed for the determination of the pharmacologically active flavonoids, including rutin and quercetin in pharmaceuticals and human plasma containing Ginkgo biloba leaves extract (EGb). The separation was conducted in borate buffer and luminol. The post-column CL reagent was K₃Fe(CN)₆ in NaOH medium. Rutin and quercetin were baseline separated within 10 min with detection limits of 1.0 and 5.0 nM, respectively. The maximum intra- and inter-day relative standard deviations (RSD) of migration time of analytes were <3.5 %. Moreover, the high selectivity of the CL detection and the high-separation efficiency of CE render the method the potential of quick analyzing the pharmacologically active substances in complex matrix with satisfactory results.     

Strong enhancement of the chemiluminescence of the Cu(II)-H<Subscript>2</Subscript>O<Subscript>2</Subscript> system on addition of carbon nitride quantum dots,and its application to the detection of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

The authors report that carbon nitride quantum dots (CN QDs) exert a strong enhancing effect on the Cu(II)/H₂O₂ chemiluminescent system. Chemiluminescence (CL) intensity is enhanced by CN QDs by a factor of ~75, while other carbon nanomaterials have a much weaker effect. The possible mechanism of the effect was evaluated by recording fluorescence and CL spectra and by examining the effect of various radical scavengers. Emitting species was found to be excited-state CN QDs that produce green CL peaking at 515 nm. The new CL system was applied to the sensitive detection of H₂O₂ and glucose (via glucose oxidase-catalyzed formation of H₂O₂) with detection limits (3σ) of 10 nM for H₂O₂ and 100 nM for glucose. The probe was employed for glucose determination in human plasma samples with satisfactory results.

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Graphical abstract The effect of carbon nitride quantum dots (CN QDs) on Cu(II)-H₂O₂ chemiluminescence reaction was studied and the new CL system was applied for sensitive detection of glucose based on the glucose oxidase (GOx)-catalyzed formation of H₂O₂.

     

Chemiluminometric Determination of the Pesticide Pirimicarb by a Flow Injection Analysis Assembly

Abstract

A flow injection (FI) method is described for the determination of pirimicarb. It was found that an enhanced chemiluminescence (CL) signal is obtained when employing the luminol–H₂O₂–horseradish peroxidase (HRP) system. Under the optimum experimental conditions, the enhanced CL intensity was linear with the concentration 4.25–30.75 ng mL^?1 (r = 0.997, n = 8) with a relative standard deviation of 0.99%, containing 12.75 ng mL^?1 (n = 8). The limit of detection of the investigated compound was 0.12 ng mL^?1. The method shows a moderate selectivity against other pesticides (Amitrole, Atrazine, 2,4,5-T, Dichlorprop, and Metamidophos).The proposed method was sensitive, simple, rapid, and successfully applied to the determination of pirimicarb when it is applied in freshwater; the mean recoveries were 98.3–118.5%.     

Determination of Trenbolone Acetate in Cattle Feeds by a Flow Injection Chemiluminescence Method

A flow injection chemiluminescence (CL) method is described for the determination of trenbolone acetate based on the CL generated during its reaction with KMnO₄ in acidic medium. The CL intensity is greatly enhanced by alizarin yellow R. The CL intensity is linear with trenbolone acetate concentration in the range 0.1–100.0 mg L^?1 with a detection limit of 0.05 mg L^?1. The sample throughout is about 90 h^?1 and the relative standard deviation for 2.0 mg L^?1 trenbolone acetate solution is 1.5% (n = 11). The proposed method was applied to the determination of trenbolone acetate in cattle feeds.     

Determination of formaldehyde based on the enhancement of the chemiluminescence produced by CdTe quantum dots and hydrogen peroxide

Water-soluble cadmium telluride quantum dots (CdTe QDs) capped with glutathione (GSH) display chemiluminescence (CL) emission on reaction with hydrogen peroxide (H₂O₂) in strongly alkaline medium. It is found that the CL is strongly enhanced on addition of formaldehyde in aqueous solution. A flow injection system was developed, and it is shown that there is good linearity between CL intensity and the concentration of formaldehyde in the 0.06–3.0 μg L^?1 range. The limit of detection is as low as 10 ng L^?1. The method was successfully applied to the determination of formaldehyde in indoor air after adsorption into an aqueous phase. The recoveries for the real samples range from 97 % to 102.5 %, and the relative standard deviation is <3.8 % for intra- and inter-assay precision.

Synchronized separation,concentration and determination of trace chloramphenicol,thiamphenicol and florfenicol in food by using polyoxyethylene cetyl ether-salt aqueous two-phase system coupled with high-performance liquid chromatography

As a novel and green pretreatment technique to trace samples, polyoxyethylene cetyl ether (POELE20)–(NH₄)₂SO₄ aqueous two-phase extraction system was coupled with high-performance liquid chromatography to analyse synchronously chloramphenicol (CAP), thiamphenicol (TAP) and florfenicol (FF) in chicken and pork samples. It was found that the extraction efficiency (E%) and enrichment factor (F) of the three antibiotics were influenced by the types of salts, the concentration of salt, the concentration of POELE20, system temperature and pH. The final optimal condition was as following: the phase-forming salt is (NH₄)₂SO₄, the concentration of (NH₄)₂SO₄ is 0.141 g mL^?1, the concentration of POELE20 is 0.03 g mL^?1, the temperature is 298.15 K, and the system pH is 4.5. This POELE20–(NH₄)₂SO₄ ATPS was applied to separate and enrich three antibiotics in real sample under the optimal conditions, and it was found that the recovery was 97.20–102.00 % with a RSD of 0.61–4.85 %. The limit of detection for CAP, TAP and FF were 0.10, 0.50 and 0.50 μg kg^?1, and the limit of quantitation for CAP, TAP and FF was 0.15, 1.50 and 1.50 μg kg^?1. Seven times the experiments were used to verify the repeatability and veracity of this method, and the RSD for the intra-day and inter-day were 1.13–3.22 and 1.74–4.72 %.     

Determination of Vitamin A in Infant Milk-Based Formulas and Pharmaceutical Formulations Using Flow Injection with Ce(IV)–Na2SO3 Chemiluminescence Detection

A rapid and simple flow injection (FI) method is reported for the determination of vitamin A (retinol) based on its strong enhancing effect on the Ce(IV)–Na₂SO₃ chemiluminescence (CL) reaction in an acidic solution. The effect of key chemical and physical parameters (i.e., reagent concentrations, flow rate, and sample volume) was optimized and potential interferences examined. Under the selected experimental conditions, a linear calibration was obtained between the CL intensity and vitamin A concentration in the range 0.1–8.0 µg mL^?1 (r ²  = 0.9986, n = 8). The limit of detection (3 s x blank) was 0.01 µg mL^?1 retinol (n = 6) and the relative standard deviation (RSD) for 0.25 µg mL^?1 retinol was 2.3% (n = 10) with a sampling rate of 180 h^?1. The method was successfully applied to infant milk-based formulas and pharmaceutical formulations and the results were not significantly different at 95% confidence interval with those obtained by using a spectrophotometric reference method. The possible CL mechanism is also discussed briefly supporting with UV-visible, fluorescence, and CL spectra.     

Improved peroxidase mimetic activity of a mixture of WS<Subscript>2</Subscript> nanosheets and silver nanoclusters for chemiluminescent quantification of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

It is reported that a mixture of WS₂ nanosheets (WS₂ NS) and silver nanoclusters (AgNCs) displays strongly enhanced peroxidase-mimicking activity. The catalytic effect of the mixture was studied by colorimetry, fluorometry, chemiluminescence (CL) and electrochemistry. The effect is interpreted in terms of a difference between the Fermi energy level of the two nanomaterials. This leads to the formation of charge separation regions which act as active sites for enzyme mimetic interaction with the substrates. The mixture of WS₂ NS and AgNCs was exploited for the non-enzymatic determination of H₂O₂ and glucose. A stopped-flow method was applied as a sensitive CL detection system using the bicarbonate-H₂O₂ reaction. The mixture has a powerful peroxidase mimicking activity on the bicarbonate-H₂O₂ CL reaction, and this effect is much larger than that of any single constituent. In addition, the CL emission is improved several times by using the stopped-flow technique. Under optimum condition, H₂O₂ can be determined in the 2.5–1500 nM concentration range. Moreover, glucose levels in human serum can be quantified via glucose oxidase based oxidation which leads to the generation of H₂O₂. Using this CL assay, a linear relationship was obtained between the intensity of the CL emission and glucose concentration in the range of 0.03–20 μM, with a limit of detection (3S) of 13 nM.

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Graphical abstract An enhanced peroxidase-like catalytic activity for WS₂ nanosheets (WS₂ NS) was revealed in the presence of silver nanoclusters (AgNCs), and was exploited for the non-enzymatic determination of H₂O₂, and of glucose (via glucose oxidase; GOx) using a stopped-flow CL method.

     

Simultaneous Determination of Hydrochlorothiazide, Cilazapril and Its Active Metabolite Cilazaprilat in Urine by Gradient RP-LC

A rapid and simple liquid chromatographic method with UV detection has been developed for the determination of hydrochlorothiazide (HCTZ), cilazapril (CL) and its active metabolite cilazaprilat (CLT) in urine. Sample preparation for urine consisted of solid-phase extraction using styrene-divinylbenzene (SDB-2) cartridges. The chromatographic system was a Zorbax Eclipse XDB-C₁₈ column with a mixture of methanol and 10 mM phosphate buffer, pH 2.3 with gradient (20 to 60% of methanol) as mobile phase at a flow rate of 1.0 mL min^?1. The detection was performed at the wavelength of 206 nm. Enalapril maleat was used as an internal standard. The detector response was linear in the range of 2.4–30.0, 1.6–15.0 and 1.8–20.0 μg mL^?1 for HCTZ, CL and CLT, respectively. LOQ was determined to be 2.4, 1.6 and 1.8 μg mL^?1 for HCTZ, CL and CLT, respectively. Both intra- and inter-day precision were within acceptable limits. The method has been applied to urine samples obtained from three hypertensive patients after intake of HCTZ and CL therapeutic dose.     

Voltammetric determination of paracetamol using a glassy carbon electrode modified with Prussian Blue and a molecularly imprinted polymer,and ratiometric read-out of two signals

The authors report on a ratiometric electrochemical sensor for paracetamol (PR) which was fabricated by successively electropolymerizing a layer of Prussian blue (PB) and a layer of molecularly imprinted polypyrrole (MIP) on the surface of a glassy carbon electrode (GCE). The binding of PR molecules to the MIP has two effects: The first is an increase of the oxidation current for PR at 0.42 V (vs. SCE), and the second is a decrease in the current for PB (at 0.18 V) due to partial blocking of the channels which results in reduced electron transmissivity. Both currents, and in particular their ratio, can serve as analytical information. Under optimized conditions, the sensor displays enhanced sensitivity for PR in the 1.0 nM to 0.1 mM concentration range and a 0.53 nM lower limit of detection. The sensor was applied to the determination of PR in tablets and urines where it gave recoveries in the range between 94.6 and 104.9 %. This dual-signal (ratiometric) detection scheme (using electropolymerized Prussian Blue and analyte-specific MIP) in our perception has a wide scope in that it may be applied to numerous other electroactive species for which specific MIP can be made available.

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Graphical Abstract Prussian blue (PB) and molecularly imprinted polymer (MIP) were combined to fabricate an electrochemical sensor for paracetamol (PR) detection. The ratio of both currents, increase of PR current and decrease of PB current, was employed for PR selective detection with enhanced sensitivity.

     

Detection of trace nitrite in waters using a QDs-based chemiluminescence analysis system

In the present work, a novel flow-injection chemiluminescence method based on CdTe quantum dots (QDs) was developed for the determination of nitrite. Weak chemiluminescence (CL) signals were observed from a CdTe QDs–H₂O₂ system under basic conditions. The addition of a trace amount of hemoglobin (Hb) caused the CL from the CdTe QDs–H₂O₂ system to increase substantially. In the presence of nitrite, the ferrous Hb reacted with the nitrate to form ferric Hb and NO. The NO then bound to ferrous Hb to generate iron nitrosyl Hb. As a result, the CL signal from the CdTe QDs–H₂O₂–Hb system was quenched. Thus, a flow-injection CL analytical system for the determination of trace nitrite was established. Under optimum conditions, there was a good linear relationship between CL intensity and the concentration of nitrite in the range 1.0?×?10^?9 to 8.0?×?10^?7 mol L^?1 (R ²?=?0.9957). The limit of detection for nitrite using this system was 3.0?×?10^?10 mol L^?1 (S/N?=?3). This method was successfully applied to detect nitrite in water samples.