Xuanping Tan

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.

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.

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.

Cu2+ 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%).

A novel and sensitive turn-on fluorescent biosensor for the determination of thioctic acid based on Cu2+-modulated N-acetyl-L-cysteine capped CdTe quantum dots

A new fluorescence sensor for the determination of thioctic acid (TA) in aqueous media based on the recovered fluorescence of N-acetyl-L-cysteine capped CdTe quantum dots [NALC-CdTe QDs]–Cu2+ system was proposed. The fluorescence intensity of NALC-CdTe QDs was quenched by Cu2+ due to the binding of Cu2+ to NALC on the surface of the QDs. However, in the presence of TA, the fluorescence intensity of NALC-CdTe QDs was found to be efficiently recovered. Experimental results showed that the pH of the buffer solution and the concentration of Cu2+ affected the fluorescence intensity upon adding TA. Under the optimal conditions, the recovered fluorescence intensity was linearly proportional to the increasing TA concentration in the range 4–120 μg mL−1. In addition, among the other biologically relevant chemical species that were tested, only TA could turn on the fluorescence intensity suggesting that the [NALC-CdTe QDs]–Cu2+ system was a highly selective sensor for TA. Moreover, to further investigate the performance of the perfect analysis, the developed biosensor was applied to the determination of TA in its commercial samples and detected TA in the blood of a rabbit with the time extended.

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.

A novel fluorescence and resonance Rayleigh scattering probe based on quantum dots for the detection of albendazole

Glutathione (GSH)-capped CdTe QDs with diameters of 3 nm were synthesised. The interaction between the QDs and albendazole (ABZ) was investigated by UV-vis absorption, resonance Rayleigh scattering (RRS) and fluorescence spectroscopy. Based on changes in the UV-vis absorption spectra of QDs and ABZ, we demonstrated that the QDs associated with ABZ to form new complexes. In pH 7.1 PBS buffer solution, the fluorescence intensity of QDs was effectively quenched by ABZ. The fluorescence quenching of QDs by ABZ mainly results from the QDs–ABZ complexes, and the electrostatic attraction played a major role in stabilising these complexes. Furthermore, the interaction between QDs and ABZ led to a remarkable enhancement in RRS, which was proportional to the ABZ concentration within a certain concentration range. The suitable reaction conditions, important factors as well as the influence of coexisting substances were studied. The possible reaction mechanism was also discussed.

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

Four simple and accurate spectrophotometric methods were proposed for the simultaneous determination of three β-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 β-blockers in fresh serum with satisfactory results.

Glutathione-capped CdTe quantum dots for the determination of fleroxacin with dual-wavelength fluorescence signals

A sensitive and simple method for the determination of fleroxacin (FLO) was developed based on the changes of dual-wavelength fluorescence signals of glutathione (GSH)-capped CdTe quantum dots (QDs). Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 555 nm against the concentration of FLO was observed in the range of 0.0262–35.0 μg mL−1 with a correlation coefficient (R) of 0.9992. Meanwhile, a linear calibration plot of the enhanced fluorescence intensity at 429 nm against the concentration of FLO was observed in the range of 0.1966–35.0 μg mL−1 with a correlation coefficient (R) of 0.9986. The corresponding detection limits (3σ/K) are 17.93 ng mL−1 at 555 nm and 59.58 ng mL−1 at 429 nm. In addition, a detailed reaction mechanism has also been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-vis) absorption, fluorescence (FL) spectroscopy and the measurement of fluorescence lifetime. The method has been applied for the determination of FLO 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.