Green spectrophotometric and spectrofluorimetric determination of biperiden hydrochloride using erythrosine B sensing probe

Erythrosine B (EB) is a food colorant antiviral xanthene dye that has many applications as a color additive in pharmaceuticals and cosmetics. Its use as a sensor for spectrofluorimetric and spectrophotometric analysis of amine-based pharmaceuticals renders many advantages because of its availability, low cost, rapid labeling, and high sensitivity. Herein, two fast and sensitive spectrofluorimetric and spectrophotometric methods were established for the estimation of the anti-Parkinson drug, biperiden (BIP) hydrochloride (HCl), in its raw material and tablet forms. The proposed methods depended on the interaction between the phenolic group of EB and the tertiary amino group of the studied analyte to form an ion-pair complex at pH 4 using the Britton Robinson buffer. The spectrofluorimetric method is based on the measurement of the quenching power of BIP HCl on the fluorescence intensity of EB at λ_ex/em = 527.0/550.9 nm. This method was rectilinear over the concentration range of 0.1–1.0 μg/mL with a limit of detection (LOD) = 0.017 μg/mL and a limit of quantification (LOQ) = 0.05 μg/mL. Meanwhile, the colorimetric method involved monitoring the absorbance of the formed ion-pair complex at 555 nm, showing a linearity range of 0.4–5.0 μg/mL with LOD = 0.106 μg/mL and LOQ = 0.322 μg/mL. The proposed methods were assessed for the greenness, indicating the greenness of the developed methods.     

Signal-on fluorescent sensor based on N-CQDs for the detection of glutathione in human serum and pharmaceutic preparation

Nitrogen-doped carbon quantum dots (N-CQDs) with citric acid and ethylenediamine as raw materials were synthesized by an efficient one-step strategy. The N-CQDs showed a special property that the fluorescence was quenched by Fe³⁺. The quenched fluorescence of N-CQDs could be recovered by glutathione (GSH). Therefore, a “signal-on” fluorescent sensor was developed to detect GSH. The fluorescent sensor could favorably avoid the interference of ascorbic acid, dopamine, glucose, oxidized glutathione, and other amino acids in the detecting process of GSH. The proposed sensor showed a great feature that GSH can be accurately detected in the range from 0.001 to 0.1?mol/L and can be applied to detect GSH in the human serum. Therefore, the proposed method has a promising application for monitoring the blood drug concentration of GSH in clinical studies.     

Determination of omeprazole via fluorescence-quenching methodology; application to content uniformity testing

A new, proven, economical spectrofluorimetric approach has been used to determine the proton pump inhibitor omeprazole (OMP). This innovative technique is based on the ability of OMP to quench the native fluorescence of the mercurochrome dye in an acidic (pH 3.6) solution. Because it was discovered that quenching is proportional to the drug concentration, this dye was used as a sensor for OMP detection. The fluorescence intensity was measured at 518/540 nm, and its linear response ranged from 0.2–10.0 μg/mL with a linear coefficient of 0.9999. The computation yielded a limit of quantification (LOQ) of 0.20 μg/mL and a limit of detection (LOD) of 0.07 μg/mL. Every circumstance and element impacting the reaction product was examined in detail. Pharmacopeial standards carried out the validation. The approved method investigated several commercial preparations and formulations, and the results were favorably compared with those provided by a reference method. According to United States Pharmacopeia (USP) rules, content consistency for two distinct formulations was evaluated.     

Study on the interaction between erythrosine B and the cardiac drug amiodarone using fluorescence,scattering, and absorbance spectra and their analytical application

In an acidic buffered solution, erythrosine B can react with amiodarone to form an association complex, which not only generates great enhancement in resonance Rayleigh scattering (RRS) spectrum of erythrosine B at 346.5 nm but also results in quenching of fluorescence spectra of erythrosine B at λ_emission = 550.4 nm/λ_excitation = 528.5 nm. In addition, the formed erythrosine B–amiodarone complex produces a new absorbance peak at 555 nm. The spectral characteristics of the RRS, absorbance, and fluorescence spectra, as well as the optimum analytical conditions, were studied and investigated. As a result, new spectroscopic methods were developed to determine amiodarone by utilizing erythrosine B as a probe. Moreover, the ICH guidelines were used to validate the developed RRS, photometric, and fluorimetric methods. The enhancements in the absorbance and the RRS intensity and the decrease in the fluorescence intensity of the used probe were proportional to the concentration of amiodarone in ranges of 2.5–20.0, 0.2–2.5, and 0.25–1.75 μg/mL, respectively. Furthermore, limit of detection values were 0.52 ng/mL for the spectrophotometric method, 0.051 μg/mL for the RRS method, and 0.075 μg/mL for the fluorimetric method. Moreover, with good recoveries, the developed spectroscopic procedures were applied to analyze amiodarone in its commercial tablets.     

Utilization of N,S-doped carbon dots as a fluorescent nanosensor for determination of cromolyn based on inner filter effect: application to aqueous humour

A simple and eco-friendly hydrothermal technique is used to prepare water soluble N- and S-co-doped carbon quantum dots probes (N,S-CQDs) from thiosemicarbazide and citric acid. Several characterization techniques were performed to ensure the successful synthesis of highly luminescent N,S-CQDs. The prepared probe exhibited analytical potential as an optical nanosensor for the spectrofluorimetric determination of cromolyn sodium (CRO) in its pharmaceutical dosage forms and aqueous humour. The emission intensity of the synthesized N,S-CQDs was measured at 411 nm after excitation at 345 nm. Addition of increasing concentrations of CRO to N,S-CQDs led to quenching of its fluorescence intensity. CRO was investigated within a wide concentration range 10.0–150.0 μM with a limit of detection of 2.0 μM and a limit of quantification of 6.0 μM. The quenching of fluorescent N,S-CQDs occurred through the inner filter effect (IFE). The developed spectrofluorimetric method was successfully optimized and validated according to the International Council of Harmonisation guidelines (ICH). The method greenness is proved through using both Eco-Scale and AGREE approaches.     

Turning waste into wealth: nitrogen-doped carbon quantum dots derived from fruits wastes for sensing

Hydrothermal treatment of m-phenylenediamine and grape seed powder has been adopted to synthesize nitrogen-doped carbon quantum dots (N-CQDs). The prepared N-CQDs possessed outstanding optical properties and high quantum yield. Based on the combined effect of static quenching effect and inner filter effect of permanganate (MnO₄⁻) to N-CQDs and the redox reaction that occurred between MnO₄⁻ and l -ascorbic acid (l -AA), an ‘off–on’ fluorescence strategy with N-CQDs has been proposed for the detection of MnO₄⁻ and l -AA. The proposed fluorescent probe was fast, sensitive and selective to MnO₄⁻ and l -AA under mild conditions. In addition, the satisfactory results of the proposed strategy for the detection of MnO₄⁻ and l -AA in real samples indicated its practicability.     

Detection of Indigo Carmine dye in juices via application of photoluminescent europium-doped carbon dots from tannic acid

Indigo Carmine is a hazardous dye and produces an allergic action for humans despite the excessive use of the dye in several industrial fields. A sensitive and simple fluorescent assay for determining Indigo Carmine relying on quenching of the fluorescent europium-doped carbon dots by the action of inner filter effect was developed. This sensing platform involved the preparation of europium-doped carbon dots from the hydrothermal carbonization of tannic acid and europium chloride, which was used as fluorescent reagent with a distinctive excitation/emission wavelength at 307/340 nm. Both excitation and emission fluorescence of prepared carbon dots can be successfully quenched by adding Indigo Carmine dye. The developed spectrofluorimetric method exhibits good linearity with the concentration of Indigo Carmine dye in the range of 1.5 to 10.0 μg/ml and provided a limit of detection (LOD) value of 0.40 μg/ml. Furthermore, the prepared carbon nanoparticles were identified and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR), and ultraviolet (UV)-spectrophotometer techniques. In addition, the developed detecting approach was applied to determine Indigo Carmine in juice samples with acceptable recovery.     

Paper mill sludge-based carbon quantum dots as a specifically ratiometric fluorescent probe for the sensitive and selective detection of coptisine

Coptisine (COP), one of the bioactive components in Rhizoma Coptidis, has many pharmacological effects. Meanwhile, the determination of COP is essential in pharmacological and clinical applications. Herein, we prepared carbon quantum dots (CQDs) by one-step oil-thermal method using paper mill sludge (PMS) as precursor, and developed a ratiometric fluorescence method for the determination of COP. The structural and optical properties of PMS-CQDs were evaluated through high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), ultraviolet-visible (UV-vis), fluorescence, zeta potential and fluorescence lifetime experiments. Fluorescence intensity ratio at 550 nm and 425 nm (I₅₅₀/I₄₂₅) was recorded as an index for quantitative detection of COP. The detection concentration of COP ranges from 0.1 to 50 μM in good linear correlation (R² = 0.9974) with a limit of detection of 0.028 μM (3σ/k). The quenching mechanism was deduced to be inner filter effect and static quenching. The ratiometric fluorescent probe showed impressive selectivity and sensitivity towards COP, and was successfully applied to the detection of COP in human urine with expected recoveries (95.22–111.00%) and relative standard deviations (0.46–2.95%), indicating that our developed method has a great application prospect in actual sample detection.     

The Interactions of Glutathione-Capped CdTe Quantum Dots with Trypsin

Due to their unique fluorescent properties, quantum dots present a great potential for biolabelling applications; however, the toxic interactions of quantum dots with biopolymers are little known. The toxic interactions of glutathione-capped CdTe quantum dots with trypsin were studied in this paper using synchronous fluorescence spectroscopy, fluorescence emission spectra, and UV–vis absorption spectra. The interaction between CdTe quantum dots and trypsin resulted in structure changes of trypsin and inhibited trypsin's activity. Fluorescence emission spectra revealed that the quenching mechanism of trypsin by CdTe quantum dots was a static quenching process. The binding constant and the number of binding sites at 288 and 298 K were calculated to be 1.98 × 10⁶ L mol⁻¹ and 1.37, and 6.43 × 10⁴ L mol⁻¹ and 1.09, respectively. Hydrogen bonds and van der Waals' forces played major roles in this process.     

Utility of a xanthene-based dye for determination of nilotinib using two spectroscopic approaches. Applications to bulk powder,capsules, and spiked human plasma

Novel, selective, facile, and precise spectroscopic approaches were validated to determine nilotinib hydrochloride, a tyrosine kinase inhibitor used to treat patients with chronic myeloid leukemia. These approaches depend on the reaction of the tertiary amine group of nilotinib with erythrosine B in the Britton–Robinson buffer at pH 4. Method I, depends on measuring the absorbance of the formed complex at 551 nm. The absorbance concentration plot showed linearity over the concentration range of 1.0 to 9.0 μg/ml. Method II, involved the measurement of the quenching of the native fluorescence of erythrosine B by adding nilotinib in an acidic medium. The fluorescence quenching of erythrosine B was measured at 549 nm after excitation at 528 nm. This approach showed excellent linearity in the concentration range of 0.04 to 0.7 μg/ml. The limit of detection values for Method I and Method II were 0.225 and 0.008 μg/ml, respectively, while the limit of quantitation values for Method I and Method II were 0.68 and 0.026 μg/ml, respectively. To get the optimal conditions, factors that may affect the formation of the ion-pairing complex were thoroughly examined. The two approaches were carefully validated following the International Conference of Harmonization (ICH Q2R1) guidelines. Statistical assessment of the results achieved using the suggested and previously published comparison approaches showed no significant difference. The approaches were successful in determining nilotinib in a pharmaceutical dosage form as well as spiked human plasma samples. The eco-friendly properties of the methods were evaluated by three different tools.     

Energy transfer between CdSe/ZnS core/shell quantum dots and fluorescent proteins

Fluorescent proteins from the green fluorescent protein (GFP) family interact strongly with CdSe/ZnS quantum dots. Photoluminescence of GFP5 is suppressed by red-emitting CdSe/ZnS quantum dots with high efficiency in a pH-dependent manner. The elevated degree of quenching, around 90%, makes it difficult to analyze the remaining signal, and it is not clear yet whether FRET is the reason behind the quenching. When the donor is a green-emitting CdSe/ZnS quantum dot and the acceptor is the HcRed1 protein, it is possible to detect quenching of the donor and sensitized emission from the acceptor. It was verified that the sensitized emission has the low anisotropy characteristic of FRET. The present characterization identifies donor-acceptor pairs formed by fluorescent proteins and CdSe/ZnS quantum dots that are suitable for the exploration of cellular events. These donor-acceptor pairs take advantage of the exceptional photochemical properties of quantum dots allied with the unique ability of fluorescent proteins to act as gene-based fluorescent probes.     

Fluorescence quenching investigation on the interaction of glutathione‐CdTe/CdS quantum dots with sanguinarine and its analytical application

Water‐soluble glutathione (GSH)‐capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. In pH 5.4 sodium phosphate buffer medium, the interaction between GSH‐CdTe/CdS QDs and sanguinarine (SA) was investigated by spectroscopic methods, including fluorescence spectroscopy and ultraviolet‐visible absorption spectroscopy. Addition of SA to GSH‐CdTe/CdS QDs results in fluorescence quenching of GSH‐CdTe/CdS QDs. Quenching intensity was in proportion to the concentration of SA in a certain range. Investigation of the quenching mechanism, proved that the fluorescence quenching of GSH‐CdTe/CdS QDs by SA is a result of electron transfer. Based on the quenching of the fluorescence of GSH‐CdTe/CdS QDs by SA, a novel, simple, rapid and specific method for SA determination was proposed. The detection limit for SA was 3.4 ng/mL and the quantitative determination range was 0.2–40.0 µg/mL with a correlation coefficient of 0.9988. The method has been applied to the determination of SA in synthetic samples and fresh urine samples of healthy human with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.     

Validated spectrofluorimetric method for the determination of carbamazepine in pharmaceutical dosage forms after reaction with 4‐chloro‐7‐‐nitrobenzo‐2‐oxa‐1,3‐diazole (NBD‐Cl)

A sensitive and simple spectrofluorimetric method has been developed and validated for the determination of the anti‐epileptic drug carbamazepine (CBZ) in its dosage forms. The method was based on a nucleophilic substitution reaction of CBZ with 4‐chloro‐7‐nitrobenzo‐2‐ oxa‐1,3‐diazole (NBD‐Cl) in borate buffer (pH 9) to form a highly fluorescent derivative that was measured at 530 nm after excitation at 460 nm. Factors affecting the formation of the reaction product were studied and optimized, and the reaction mechanism was postulated. The fluorescence–concentration plot is rectilinear over the range of 0.6–8 µg/mL with limit of detection of 0.06 µg/mL and limit of quantitation of 0.19 µg/mL. The method was applied to the analysis of commercial tablets and the results were in good agreement with those obtained using the reference method. Validation of the analytical procedures was evaluated according to ICH guidelines. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of a Threshold Dose to Reduce or Eliminate CdTe-Induced Toxicity in L929 Cells by Controlling the Exposure Dose

With the widespread use of quantum dots (QDs), the likelihood of exposure to quantum dots has increased substantially. The application of quantum dots in numerous biomedical areas requires detailed studies on their toxicity. In this study, we aimed to determine the threshold dose which reduced or eliminated CdTe-induced toxicity in L929 cells by controlling the exposure dose. We established a cellular model of acute exposure to CdTe QDs. Cells were exposed to different concentrations of CdTe QDs (2.2 nm and 3.5 nm) followed by illustrative cytotoxicity analysis. The results showed that low concentrations of CdTe QDs (under 10 µg/mL) promoted cell viability, caused no obvious effect on the rate of cell apoptosis, intracellular calcium levels and changes in mitochondrial membrane potential, while high concentrations significantly inhibited cell viability. In addition, reactive oxygen species in the 10 µg/mL-treated group was significantly reduced compared with the control group. In summary, the cytotoxicity of CdTe QDs on L929 cell is dose-dependent, time-dependent and size-dependent. Low concentrations of CdTe QDs (below 10 µg/mL) may be nontoxic and safe in L929 cells, whereas high concentrations (above 10 µg/mL) may be toxic resulting in inhibition of proliferation and induction of apoptosis in L929 cells.     

Phytochemical profiling of Azima tetracantha Lam. leaf methanol extract and elucidation of its potential as a chain-breaking antioxidant,anti-inflammatory and anti-proliferative agent

Azima tetracantha, a traditional medicinal plant included in the order Brassicales and family Salvadoraceae, is widely used as a dietary supplement in folklore medicines. The plant is also used for the treatment of rheumatism, diarrhea and other inflammatory disorders. The present investigation focused on the phytochemical composition, radical scavenging, reducing potential and anti-proliferative activities of the A. tetracantha leaves. Quantitative estimation of the polyphenols and flavonoids revealed significantly elevated levels in the methanol extract. Corroborating with this, methanol extract exhibited higher in vitro anti-radical scavenging effect against 2,2-diphenyl-1- picrylhydrazyl (34.14 ± 2.19 μg/mL), and hydrogen peroxide (44.96 ± 1.77 μg/mL), as well as ferric reducing properties (58.24 ± 6.98 μg/mL). The methanolic extract also showed strong lipoxygenase (71.42 ± 6.36 μg/mL) and nitric oxide inhibitory activities (94.23 ± 8.11 μg/mL). Cytotoxic activity against MCF7 cells was found to be higher (IC50= 37.62 ± 2.94 μg/mL), than that of MDAMB231 cells (IC50= 69.11 ± 5.02 μg/mL). The qPCR-based analysis indicated dose-dependent increase in the expression of the pro-apoptotic genes such as executioner caspases and apoptotic protease activating factor-1. Overall, the results indicated the possible use of methanol extract of A. tetracantha leaves as a chain-breaking antioxidant molecule and are capable of inhibiting inflammatory enzymes and the proliferative potential of breast cancer cells.     

High quantum yield and well‐dispersed quantum dots luminescent composite through sodium carboxymethyl starch

It is a challenging task to prepare well‐dispersed and highly luminescent quantum dots (QDs) powder and a new strategy is reported in this article. Sodium carboxymethyl starch (CMS‐Na) was employed in this work to prepare the QDs–starch composite. Ultraviolet (UV) light shows that the blank starches had no fluorescence, while the QDs‐starches were highly luminescent. Scanning electron microscopy (SEM) observation shows that the QDs–starch composite has the typical particle morphology with the diameter around 200 nm. Energy dispersive X‐ray spectroscopy (EDX) results show that there are intensive tellurium (Te) and cadmium (Cd) element signals. Combined fluorescent lifetime and steady‐state spectrometer show that the QDs–starch quantum yields (QYs) increase when the QDs loading increases from 1 × 10^?6 mol/g to 2 × 10^?6 mol/g, but when the loadings further increase, the QYs decrease slightly. For the red colour (λ_em = 660 nm) QDs, the QYs can reach to as high as 28.2%, and for the other colour QDs they can also have the QYs above 22%. Time‐resolved photobleaching experiments show that the fluorescent QDs–starch composite has a half‐decay time of 40.23 s. These results indicate that the CMS‐Na is a promising QDs dispersant to obtain high QY QD composites.     

Development and validation of a reverse phase HPLC method for the determination of caprylic acid in formulations of therapeutic immunoglobulins and its application to antivenom production

A novel method of high performance liquid chromatography with UV detection for the quantification of caprylic acid in formulations of therapeutic immunoglobulins was developed and validated. Samples have interfering proteins that were removed by ultrafiltration in a centrifugal filter unit of 10 kDa nominal molecular weight limit. Then, compounds present in ultrafiltrates were separated on an Eclipse XDB-C8 5 μm column (150 mm × 4.6 mm i.d.), using a mixture of acetonitrile–water (60:40, v/v) as the mobile phase at a flow rate of 1 mL/min. The UV detection was performed at 210 nm. The method was found to be precise and accurate, with a linearity range from 400 μg/mL to 600 μg/mL (r = 0.9948). The limit of detection (LOD) and the limit of quantification (LOQ) were found to be 13.46 μg/mL and 44.85 μg/mL, respectively. To illustrate the usefulness of the method in the in-process and final quality control for production of therapeutic immunoglobulin formulations, permeates obtained from the industrial diafiltration step in the manufacture of equine-derived snake antivenoms and ten batches of finished product were analyzed.     

A selective determination of copper ions in water samples based on the fluorescence quenching of thiol‐capped CdTe quantum dots

CdTe quantum dots (QDs) capped with different stabilizers, i.e. thioglycolic acid (TGA), 3‐mercaptopropionic acid (MPA) and glutathione (GSH) were investigated as fluorescent probes for the determination of Cu²⁺. The stabilizer was shown to play an important role in both the sensitivity and selectivity for the determination of Cu²⁺. TGA‐capped CdTe QDs showed the highest sensitivity, followed by the MPA and GSH‐capped CdTe QDs, respectively. The TGA‐ and MPA‐capped CdTe QDs were not selective for Cu²⁺ that was affected by Ag⁺. The GSH‐capped CdTe QDs were insensitive to Ag⁺ and were used to determine Cu²⁺ in water samples. Under optimal conditions, quenching of the fluorescence intensity (F₀/F) increased linearly with the concentration of Cu²⁺ over a range of 0.10–4.0 µg/mL and the detection limit was 0.06 µg/mL. The developed method was successfully applied to the determination of Cu²⁺ in water samples. Good recoveries of 93–104%, with a relative standard deviation of < 6% demonstrated that the developed simple method was accurate and reliable. The quenching mechanisms were also described. Copyright © 2015 John Wiley & Sons, Ltd.     

Luminescent and hydrophilic LaF3–polymer nanocomposite for DNA detection

Luminescent LaF₃–Ce³⁺/Tb³⁺ nanocrystals have been successfully prepared via a simple wet chemical technique. For the next bioapplication, these nanoparticles dispersed in cyclohexane have also been functionalized with poly(St‐co‐MAA), based on a designed oil‐in‐water microemulsion system. These polymer‐coated nanospheres are water‐soluble and bioconjugable. Unlike semiconductor quantum dots, the as‐prepared lanthanum fluoride nanocrystals possess non‐size‐dependent emissions and completely stable photocycles. With functionalized LaF₃ nanospheres as fluorescence probes, a fluorescence method was developed for the rapid quantitative analysis of DNA, due to the quenching effect of fluorescence by the DNA. Under optimum conditions, the fluorescence intensity was proportional to the concentration of the introduced DNA over the range 2.5–35 µg/mL for calf thymus DNA (ctDNA) and 2.5–30 µg/mL for fish sperm DNA (fsDNA), respectively. Copyright © 2008 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.