Detection of the chiral drug Ephedrine by resonance Rayleigh scattering based on Ce3+ functionalized gold nanoparticles.

Two chiral drugs, ephedrine (EH) and pseudoephedrine (PEH), were commonly used in clinical treatment. Ephedrine (EH) and pseudoephedrine (PEH) could make different changes in resonance Rayleigh scattering spectrum of the detection system which use Ce3+ functionalized gold nanoparticles as probe. Therefore, a new method of detecting EH and PEH separately was developed. The RRS spectrum and UV-Vis absorption spectrum of AuNPs-Ce3+ detection system was analyzed in order to discuss the mechanism. Under optimal experimental conditions, the linear range of EH and PEH were 20-920 ng/mL and 40-520 ng/mL, respectively. The detection limit were 1.9 ng/mL and 3.8 ng/mL, respectively. Last used for actual testing, this method had obtained good results.

Rapid detection of chiral drug ephedrine using erythrosin B for the resonance Rayleigh scattering probe.

Ephedrine (EH) and pseudoephedrine (PEH), which are chiral enantiomers commonly used clinically, have different pharmacological actions and treatment effects due to their chiral nature. In the presence of Pd2+ , the reaction system of Ery B (erythrosin B)-Pd2+ has a strong resonance Rayleigh scattering (RRS) intensity. Adding EH into this system reduced the RRS intensity, but PEH could not produce this phenomenon. The chiral recognition of these enantiomers could be achieved according to this spectral difference. At the same time, reduction in RRS strength of the reaction system is proportional to the concentration of EH. Under optimized conditions, the linear range is 40-960 ng/ml, and the detection limit is 3.9 ng/ml. A new method for the rapid detection of EH enantiomers can be established. Based on this assay, a new method for the determination of the chiral enantiomers of EH and PEH can be developed.

CdTe QDs based fluorescent sensor for the determination of gallic acid in tea.

A new fluorescent light switch method, which based on N­acetyl­l­cysteine capped CdTe QDs (NALC-CdTe QDs), was developed for the detection of gallic acid (GA). The QDs possess a fluorescence emission wavelength at 520nm and with symmetric fluorescence. When KMnO4 is added, the high fluorescence of QDs could be effectively quenched for the electron transfer process between KMnO4 and QDs. But with the addition of GA, the fluorescence of KMnO4-QDs system could recover for the reason that redox reaction of GA and KMnO4. Therefore, a fluorescent light switch method could be used for GA with a detection range of 0.6-12.6µg·mL-1 and a detection limit of 0.56ng·mL-1. Furthermore, the feasibility of the proposed fluorescence biosensor in tea was also studied and satisfactory results were obtained.

Development of a direct reverse-transcription quantitative PCR (dirRT-qPCR) assay for clinical Zika diagnosis.

OBJECTIVE: The nucleic acid-based polymerase chain reaction (PCR) assay is commonly applied to detect infection with Zika virus (ZIKV). However, the time- and labor-intensive sample pretreatment required to remove inhibitors that cause false-negative results in clinical samples is impractical for use in resource-limited areas. The aim was to develop a direct reverse-transcription quantitative PCR (dirRT-qPCR) assay for ZIKV diagnosis directly from clinical samples. METHODS: The combination of inhibitor-tolerant polymerases, polymerase enhancers, and dirRT-qPCR conditions was optimized for various clinical samples including blood and serum. Sensitivity was evaluated with standard DNA spiked in simulated samples. Specificity was evaluated using clinical specimens of other infections such as dengue virus and chikungunya virus. RESULTS: High specificity and sensitivity were achieved, and the limit of detection (LOD) of the assay was 9.5×101 ZIKV RNA copies/reaction. The on-site clinical diagnosis of ZIKV required a 5µl sample and the diagnosis could be completed within 2h. CONCLUSIONS: This robust dirRT-qPCR assay shows a high potential for point-of-care diagnosis, and the primer-probe combinations can also be extended for other viral detection. It realizes the goal of large-scale on-site screening for viral infections and could be used for early diagnosis and the prevention and control of viral outbreaks.

Chiral recognition of the carnitine enantiomers using rhodamine B as a resonance Rayleigh scattering probe.

A novel and simple method for simultaneous determination of chiral carnitine (CA) enantiomers was proposed. In this work, the rhodamine B (RhB) could react with D-CA and L-CA, and new resonance Rayleigh scattering (RRS) peaks were generated. According to the polarization experiments, it could be testified that scattering peak of this system was composed of resonance fluorescence and scattering light. The RRS intensity of the RhB could be enhanced with the addition of D- or L-CA. However, The RRS signal with L-CA had greater degree increased. So a useful assay program for the selective and simultaneous determination of CA enantiomers was built via the RRS signal differences of the two CA enantiomers responding to RhB. The results showing a good linear relationship and high correlation coefficient were obtained, and the detection limit was calculated as 0.086 µg·mL-1 (D-CA) and 0.042 µg·mL-1 (CA). Here, new built RRS method with RhB as chiral probe could be applied to achieve selective analysis through this work. The applicability of the chiral recognition of CA enantiomers mixtures in samples had been demonstrated by its low cost, sensitivity, enantioselectivity, simplicity, and good availability of the materials.

A highly sensitive resonance Rayleigh scattering and colorimetric assay for the recognition of propranolol in ß-adrenergic blocker.

In this work, a highly sensitive, citrate anion-capped gold nanoparticles (AuNPs)-based assay for the determination of propranolol in real samples with resonance Rayleigh scattering (RRS) and colorimetry was developed. When AuNPs were prepared by the sodium citrate reduction method, citrate anions self-assembled on the surface of AuNPs to form supramolecular complex anions. In BR 4.6 buffer solution, propranolol was positively charged and could bind with AuNPs to form larger aggregates through electrostatic force and hydrophobic effects. This results in remarkable enhancement of the RRS intensity and a color change in the AuNPs solution from red to blue via purple. Thus, a highly sensitive RRS and colorimetric assay the for detection of propranolol was developed with a linear range of 0.2-5.2 and 8-112 ng/ml, respectively. In addition, no difference was seen when comparing R-propranolol with S-propranolol, therefore, this method could not be used in the recognition of chiral propranolol. However, upon addition of other ß-adrenergic blockers, no phenomenon like that seen with propranolol was observed, meaning that this method can be used for determining the presence of propranolol in a mixture ß-adrenergic blockers. Finally, the optimum conditions, factors influencing the reaction, its mechanism and the reasons for enhancement of the RRS were discussed.

Measurement analysis of two radials with a common-origin point and its application.

In spectral analysis, a chemical component is usually identified by its characteristic spectra, especially the peaks. If two components have overlapping spectral peaks, they are generally considered to be indiscriminate in current analytical chemistry textbooks and related literature. However, if the intensities of the overlapping major spectral peaks are additive, and have different rates of change with respect to variations in the concentration of the individual components, a simple method, named the 'common-origin ray', for the simultaneous determination of two components can be established. Several case studies highlighting its applications are presented.

A convenient method for determination of quizalofop-p-ethyl based on the fluorescence quenching of eosin Y in the presence of Pd(II).

A convenient fluorescence quenching method for determination of Quizalofop-p-ethyl(Qpe) was proposed in this paper. Eosin Y(EY) is a red dye with strong green fluorescence (λex/λem=519/540nm). The interaction between EY, Pd(II) and Qpe was investigated by fluorescence spectroscopy, resonance Rayleigh scattering(RRS) and UV-Vis absorption. Based on changes in spectrum, Pd(II) associated with Qpe giving a positively charged chelate firstly, then reacted with EY through electrostatic and hydrophobic interaction formed ternary chelate could be demonstrated. Under optimum conditions, the fluorescence intensity of EY could be quenched by Qpe in the presence of Pd(II) and the RRS intensity had a remarkable enhancement, which was directly proportional to the Qpe concentration within a certain concentration range, respectively. Based on the fluorescence quenching of EY-Pd(II) system by Qpe, a novel, convenient and specific method for Qpe determination was developed. To our knowledge, this is the first fluorescence method for determination of Qpe was reported. The detection limit for Qpe was 20.3ng/mL and the quantitative determination range was 0.04-1.0µg/mL. The method was highly sensitive and had larger detection range compared to other methods. The influence of coexisting substances was investigated with good anti-interference ability. The new analytical method has been applied to determine of Qpe in real samples with satisfactory results.

Double-wavelength overlapping resonance Rayleigh scattering technique for the simultaneous quantitative analysis of three ß-adrenergic blockade.

Four simple and accurate spectrophotometric methods were proposed for the simultaneous determination of three ß-adrenergic blockade, e.g. atenolol, metoprolol and propranolol. The methods were based on the reaction of the three drugs with erythrosine B (EB) in a Britton-Robinson buffer solution at pH4.6. EB could combine with the drugs to form three ion-association complexes, which resulted in the resonance Rayleigh scattering (RRS) intensity that is enhanced significantly with new RRS peaks that appeared at 337 nm and 370 nm, respectively. In addition, the fluorescence intensity of EB was also quenched. The enhanced scattering intensities of the two peaks and the fluorescence quenched intensity of EB were proportional to the concentrations of the drugs, respectively. What is more, the RRS intensity overlapped with the double-wavelength of 337 nm and 370 nm (so short for DW-RRS) was also proportional to the drugs concentrations. So, a new method with highly sensitive for simultaneous determination of three bisoprolol drugs was established. Finally, the optimum reaction conditions, influencing factors and spectral enhanced mechanism were investigated. The new DW-RRS method has been applied to simultaneously detect the three ß-blockers in fresh serum with satisfactory results.

A simple and rapid resonance Rayleigh scattering method for detection of indigo carmine in soft drink.

A novel method that uses acridine orange (AO) to detect indigo carmine (IC) in soft drinks was developed. The method is highly sensitive and is based on a resonance Rayleigh scattering (RRS) technique. In Britton-Robinson (BR) buffer solution, pH 4.3, the weak RRS intensity of AO was greatly enhanced by the addition of IC, with the maximum peak located at 332 nm. Under optimum conditions, it was found that the enhanced RRS intensity was proportional to the concentration of IC over a range of 2-32 × 10(-6)  mol/L. A low detection limit of 2.4 × 10(-8)  mol/L was achieved. The sensitivity and selectivity of the method are high enough to permit the determination of trace amounts of IC without any significant interference from high levels of other components such as common anions and other amino acids. Finally, the concentration of IC in three different soft drinks was determined with satisfactory results. Copyright © 2016 John Wiley & Sons, Ltd.

Sensitive determination of enoxacin in pharmaceutical formulations by its quench effect on the fluorescence of glutathione-capped CdTe quantum dots.

A sensitive and simple method for the determination of enoxacin (ENX) was developed based on the fluorescence quenching effect of ENX for glutathione (GSH)-capped CdTe quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 4.333 × 10(-9) mol⋅L(-1) to 1.4 × 10(-5) mol⋅L(-1) with a correlation coefficient (R) of 0.9987, and the detection limit (3σ/K) was 1.313 × 10(-9) mol⋅L(-1). The corresponding mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV) light absorption, fluorescence spectroscopy, and the measurement of fluorescence lifetime. The method has been applied to the determination of ENX in pharmaceutical formulations (enoxacin gluconate injections and commercial tablets) with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

Detection of glutathione with an "off-on" fluorescent biosensor based on N-acetyl-L-cysteine capped CdTe quantum dots.

This paper reports a quantum dot (QD)-based "off-on" fluorescent biosensor specifically for the determination of glutathione (GSH) with high sensitivity. The biosensor was based on the following two properties. Firstly, the high fluorescence of N-acetyl-L-cysteine (NALC) capped CdTe QDs could be effectively quenched by Hg(2+) due to the binding of Hg(2+) to the NALC on the surface of the QDs and the electron transfer from the photoexcited NALC-capped CdTe QDs to Hg(2+). Secondly, in the presence of GSH, the fluorescence intensity of NALC-capped CdTe QDs was found to be efficiently recovered. Under some optimized conditions, the relatively restored fluorescence intensity was proportional to the concentration of GSH in the range of 4-64 µg mL(-1), with a correlation coefficient of 0.9980 and a limit of detection of 2.49 ng mL(-1). In addition, the established method shows a high selectivity for some amino acids except cysteine. Moreover, to further investigate its performance, the biosensor was applied to the determination of GSH in human serum samples through a standard addition method and determination of normal GSH concentration in original human serum samples with satisfactory results.

Cu²âº functionalized N-acetyl-L-cysteine capped CdTe quantum dots as a novel resonance Rayleigh scattering probe for the recognition of phenylalanine enantiomers.

A simple protocol that can be used to simultaneously determinate enantiomers is extremely intriguing and useful. In this study, we proposed a low-cost, facile, sensitive method for simultaneous determination. The molecular recognition of Cu(2+) functionalized N-acetyl-l-cysteine capped CdTe quantum dots (Cu(2+)-NALC/CdTe QDs) with phenylalanine (PA) enantiomers was investigated based on the resonance Rayleigh scattering (RRS) spectral technique. The RRS intensity of NALC/CdTe QDs is very weak, but Cu(2+) functionalized NALC/CdTe QDs have extremely high RRS intensity, the most important observations are that PA could quench the RRS intensity of Cu(2+)-NALC/CdTe QDs, and that l-PA and d-PA have different degree of influence. In addition, those experimental factors such as acidity, concentration of Cu(2+) and reaction time were investigated in regards to their effects on enantioselective interaction. Finally, the applicability of the chiral recognized sensor for the analysis of chiral mixtures on enantiomers has been demonstrated, and the results that were obtained high precision (<4.63%) and low error (<3.06%).

Glutathione-capped CdTe nanocrystals as probe for the determination of fenbendazole.

Water-soluble glutathione (GSH)-capped CdTe quantum dots (QDs) were synthesized. In pH 7.1 PBS buffer solution, the interaction between GSH-capped CdTe QDs and fenbendazole (FBZ) was investigated by spectroscopic methods, including fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, and resonance Rayleigh scattering (RRS) spectroscopy. In GSH-capped CdTe QDs solution, the addition of FBZ results in the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs. And the quenching intensity (enhanced RRS intensity) was proportional to the concentration of FBZ in a certain range. Investigation of the interaction mechanism, proved that the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs by FBZ is the result of electrostatic attraction. Based on the quenching of fluorescence (enhancement of RRS) of GSH-capped CdTe QDs by FBZ, a novel, simple, rapid and specific method for FBZ determination was proposed. The detection limit for FBZ was 42 ng mL(-1) (3.4 ng mL(-1)) and the quantitative determination range was 0-2.8 µg mL(-1) with a correlation of 0.9985 (0.9979). The method has been applied to detect FBZ in real simples and with satisfactory results.

Chiral recognition of tyrosine enantiomers based on decreased resonance scattering signals with silver nanoparticles as optical sensor.

A novel chiral sensing platform, employing silver nanoparticles capped with N-acetyl-L-cysteine (NALC-Ag NPs), was utilized for the discrimination of L-tyrosine and D-tyrosine. This nanosensor, which could be used as an optical sensing unit and chiral probe, was characterized by transmission electron microscopy (TEM) and resonance Rayleigh scattering (RRS) spectroscopy. After the proposed sensing platform interacted with L-tyrosine and D-tyrosine, a decreased resonance scattering signal was only obtained from L-tyrosine. This phenomenon offered a useful assay for the selectivity and determination of L-tyrosine with the RRS method. The linear range and detection limit of L-tyrosine were 0.2838-20.0 µg⋅mL(-1) and 0.0860 µg⋅mL(-1) , respectively. In addition, experimental factors such as acidity, interaction time, and the concentration of enantiomers were investigated with regard to the effect on enantioselective interaction.

Detection of DNA using an "off-on" switch of a regenerating biosensor based on an electron transfer mechanism from glutathione-capped CdTe quantum dots to nile blue.

Although various strategies have been reported for double-stranded DNA (DNA) detection, development of a time-saving, specific, and regeneratable fluorescence sensing platform still remains a desired goal. In this study, we proposed a new DNA detection method that relies on an "off-on" switch of a regenerated fluorescence biosensor based on an electron transfer mechanism from glutathione (GSH)-capped CdTe quantum dots (QDs) to nile blue (NB). Initially, the high fluorescence of GSH-capped CdTe QDs could be effectively quenched by NB due to the binding of NB to the GSH on the surface of the QDs and the electron transfer from the photoexcited GSH-capped CdTe QDs to NB. Then, the high affinity of DNA to NB enabled the NB to be dissociated from the surface of GSH-capped CdTe QDs to form a more stable complex with DNA and suppress the electron transfer process between GSH-capped CdTe QDs and NB, thereby restoring the fluorescence of NB surface modified GSH-capped CdTe QDs (QDs-NB). In addition, we have testified the regenerability of the proposed DNA senor. The corresponding result shows that this DNA sensor is stable for two reuses. This fluorescence "off-on" signal was sensitive to the concentration of DNA in the range from 0.0092 to 25.0 µg mL(-1) with a good correlation coefficient of 0.9989, and the detection limit (3σ/S) was 2.78 ng mL(-1). To further investigate for perfect analysis performance, the developed biosensor was applied for the determination of DNA in human fresh serum samples with satisfactory results.

Quantum dots (QDs) based fluorescence probe for the sensitive determination of kaempferol.

In this work, using the quenching of fluorescence of thioglycollic acid (TGA)-capped CdTe quantum dots (QDs), a novel method for the determination of kaempferol (KAE) has been developed. Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 552nm against the concentration of KAE was observed in the range of 4-44µgmL(-1) with a detection limit (3σ/K) of 0.79µgmL(-1). In addition, the detailed reaction mechanism has also been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-vis) absorption and fluorescence (FL) spectroscopy. The method has been applied for the determination of KAE in pharmaceutical preparations with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.