Yizhong Shen

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.

Synergistic fluorescence quenching of quinolone antibiotics by palladium(II) and sodium dodecyl benzene sulfonate and the analytical application

In weakly acidic and neutral media, palladium(II) or sodium dodecyl benzene sulfonate (SDBS) can separately quench the fluorescence of quinolone antibiotics (FLQs) in varying degrees. When Pd(II) reacts with SDBS and FLQs to form ternary complexes, enhanced fluorescence quenching of FLQs can be observed. This synergistic fluorescence quenching effect has high sensitivity for Pd(II) detection, and the detection limit could reach 0.13 ng mL−1. Based on this, a rapid, simple and reliable method for the determination of Pd(II) in aqueous samples was established. The optimum reaction conditions of the method were tested. The reaction information of the FLQs–SDBS–Pd(II) system was investigated by absorption spectra and fluorescence spectra, and quantum chemical calculations using density functional theory B3LYP under a polarizable continuum model (PCM). The results showed that the pefloxacin (PEF) molecule exists as a zwitter-ion of HL±, reacting with Pd(II) to form plane bis(PEF)Pd chelates, which further bind with two SDBS molecules to form ternary complexes. The composition of Pd(II)–PEF–SDBS complex was found to be 1 : 2 : 2. The ternary complexes resulted in a higher fluorescence quenching efficiency and enhanced the sensitivity for the determination of Pd(II).

Determination of ellagic acid by fluorescence quenching method with glutathione capped CdTe quantum dots as the probe

A sensitive and simple method for the determination of ellagic acid (EA) was developed based on the fluorescence quenching effect of EA for glutathione (GSH)-capped CdTe quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.3118 to 55.0 μg mL−1 with a correlation coefficient of 0.9983, and the detection limit (3σ/K) was 0.0936 μg mL−1. The fluorescence quenching mechanism has 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 to the determination of EA in synthetic samples and fresh urine samples of healthy humans with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

A sensitive assay of chelerythrine using a fluorescence quenching approach with glutathione capped CdTe/CdS quantum dots as a probe

A sensitive and simple method for the determination of chelerythrine (CHE) was developed based on the fluorescence quenching effect of CHE for glutathione (GSH)-capped CdTe/CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.073 to 24.0 μg mL−1 with a correlation coefficient of 0.9988, and the detection limit (3σ/κ) was 21.9 ng mL−1. The fluorescence quenching mechanism that has been proposed is based on electron transfer supported by ultraviolet-visible (UV-vis) absorption, fluorescence (FL) spectroscopy and electrochemical techniques. The method has been applied to the determination of CHE in synthetic samples and fresh serum samples from healthy humans with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation.

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 pH5.4 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.

Sensitive Detection of Luteolin Using Thioglycolic Acid–Capped Cadmium Telluride/Cadmium Sulphide Quantum Dots as the Fluorescent Probe

ABSTRACT A sensitive and simple method for the determination of luteolin (LTL) was developed based on the fluorescence quenching effect of LTL for thioglycolic acid–capped (TGA-capped) CdTe/CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.3 to 20.0 µg · mL−1 with a correlation coefficient of 0.9972, and the detection limit was 7.2 ng · mL−1. The fluorescence quenching mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-Vis) absorption, fluorescence (FL) spectroscopy. The proposed method was successfully applied to the determination of LTL in commercial capsules and human urine samples. It manifested several advantages such as high sensitivity, short analysis time, low cost, and ease of operation.

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.

Molecular spectroscopic studies on the interactions of rhein and emodin with thioglycolic acid-capped core/shell CdTe/CdS quantum dots and their analytical applications

Water-soluble thioglycolic acid (TGA)-capped core/shell CdTe/CdS quantum dots (QDs) were synthesized. The interactions of rhein and emodin with TGA-CdTe/CdS QDs were evaluated by fluorescence and ultraviolet-visible absorption spectroscopy. Experimental results showed that the high fluorescence intensity of TGA-CdTe/CdS QDs could be effectively quenched in the presence of rhein (or emodin) at 570 nm, which may have resulted from an electron transfer process from excited TGA-CdTe/CdS QDs to rhein (or emodin). The quenching intensity was in proportion to the concentration of both rhein and emodin in a certain range. Under optimized conditions, the linear ranges of TGA-CdTe/CdS QDs fluorescence intensity versus the concentration of rhein and emodin were 0.09650-60 µg/mL and 0.1175-70 µg/mL with a correlation coefficient of 0.9984 and 0.9965, respectively. The corresponding detection limits (3σ/S) of rhein and emodin were 28.9 and 35.2 ng/mL, respectively. This proposed method was applied to determine rhein and emodin in human urine samples successfully with remarkable advantages such as high sensitivity, short analysis time, low cost and easy operation. Based on this, a simple, rapid and highly sensitive method to determine rhein (or emodin) was proposed.