Youqiu He

Fluorescence enhancement of CdTe/CdS quantum dots by coupling of glyphosate and its application for sensitive detection of copper ion.

A novel fluorescent probe for Cu(2+) determination based on the fluorescence quenching of glyphosate (Glyp)-functionalized quantum dots (QDs) was firstly reported. Glyp had been used to modify the surface of QDs to form Glyp-functionalized QDs following the capping of thioglycolic acid on the core-shell CdTe/CdS QDs. Under the optimal conditions, the response was linearly proportional to the concentration of Cu(2+) between 2.4×10(-2)μg mL(-1) and 28μg mL(-1), with a detection limit of 1.3×10(-3)μg mL(-1) (3δ). The Glyp-functionalized QDs fluorescent probe offers good sensitivity and selectivity for detecting Cu(2+). The fluorescent probe was successfully used for the determination of Cu(2+) in environmental samples. The mechanism of reaction was also discussed.

Study on the interaction between CdSe quantum dots and chitosan by scattering spectra

Two different stabilizing agents thioglycolic acid (TGA) and L-cysteine (L-Cys) capped CdSe QDs with the diameter of 2 nm were synthesized, large amounts of stabilizing agents connected to CdSe QDs surface through Cd-S bond. The interaction between chitosan and QDs had been investigated, respectively. The interaction lead to the remarkable enhancement of RRS, RNLS and the enchantments were in proportional to the concentration of chitosan in a certain range. Under the optimal conditions, compared with TGA-CdSe QDs, the interaction between L-Cys-CdSe QDs with chitosan owned more broad linear range 0.042-3.0 microg mL(-1) and lower detect limits 1.2 ng mL(-1). The influences of factors on the interaction between chitosan with QDs and some foreign substances were all examined, which showed that the methods had a good sensitivity and selectivity. Based on this, it is hoped to build a method for the determination of chitosan using CdSe QDs as probes. Through Fourier transform infrared spectroscopy (FTIR) transmission electron microscopy (TEM), it was speculated that CdSe QDs interacted with chitosan to form a network structure aggregates through electrostatic attraction and hydrophobic forces. The reasons for the enhancement of RRS intensity were assumed as follows: resonance enhanced Rayleigh scattering effect, increase of the molecular volume, and hydrophobic effect.

Study on the interaction of CdTe quantum dots with coumaric acid and caffeic acid based on fluorescence reversible tune

This paper describes the synthesis of CdTe quantum dots (QDs) together capped by glutathione and thioglycolic acid (GSH and TGA) in aqueous solution. The narrow photoluminescence (fwhm ≤ 40 nm) CdTe QDs, whose emission spans most of the visible spectrum from green through red, has a quantum yield (QY) of 68% at room temperature. GSH/TGA-CdTe QDs are characterized by various experimental techniques such as optical absorption, photoluminescence and AFM measurements. Coumaric acid and caffeic acid is able to quench the fluorescence of GSH/TGA-CdTe QDs, and the fluorescence intensity is linearly proportional to the concentration of quenchers. The addition of bovine serum albumin (BSA) restores the fluorescence intensity of GSH/TGA-CdTe QDs-coumaric acid system and GSH/TGA-CdTe QDs-caffeic acid system. The fluorescence recovery was due to the interaction of BSA with coumaric acid and caffeic acid, leading to the freeing of the GSH/TGA-CdTe QDs. The fluorescence quenching mechanism of GSH/TGA-CdTe QDs was discussed. The binding constant and thermodynamics parameters of BSA-coumaric acid and BSA-caffeic acid during the binding process were calculated in the paper.

Resonance Rayleigh scattering and resonance non-linear scattering method for the determination of aminoglycoside antibiotics with water solubility CdS quantum dots as probe

In pH 6.6 Britton-Robinson buffer medium, the CdS quantum dots capped by thioglycolic acid could react with aminoglycoside (AGs) antibiotics such as neomycin sulfate (NEO) and streptomycin sulfate (STP) to form the large aggregates by virtue of electrostatic attraction and the hydrophobic force, which resulted in a great enhancement of resonance Rayleigh scattering (RRS) and resonance non-linear scattering such as second-order scattering (SOS) and frequency doubling scattering (FDS). The maximum scattering peak was located at 310 nm for RRS, 568 nm for SOS and 390 nm for FDS, respectively. The enhancements of scattering intensity (DeltaI) were directly proportional to the concentration of AGs in a certain ranges. A new method for the determination of trace NEO and STP using CdS quantum dots probe was developed. The detection limits (3 sigma) were 1.7 ng mL(-1) (NEO) and 4.4 ng mL(-1) (STP) by RRS method, were 5.2 ng mL(-1) (NEO) and 20.9 ng mL(-1) (STP) by SOS method and were 4.4 ng mL(-1) (NEO) and 25.7 ng mL(-1) (STP) by FDS method, respectively. The sensitivity of RRS method was the highest. The optimum conditions and influence factors were investigated. In addition, the reaction mechanism was discussed.

Studying the interaction between CdTe quantum dots and Nile blue by absorption, fluorescence and resonance Rayleigh scattering spectra.

Thioglycolic acid (TGA) capped CdTe quantum dots (QDs) with the diameter of 2-3nm were synthesized. The interaction between CdTe QDs and Nile blue (NB) was investigated by ultraviolet-visible (UV-vis) absorption, resonance Rayleigh scattering (RRS) and fluorescence spectroscopy. UV-vis absorption spectrum of CdTe QDs and NB obviously changed, showing that CdTe QDs could associate with NB to form a new complex. At pH 6.8, NB effectively quenched the fluorescence of CdTe QDs. It was proved that the fluorescence quenching of CdTe QDs by NB was mainly result of the formation of CdTe QDs-NB complex, electrostatic attraction and hydrophobic forces played a major role in stabilizing the complex. The binding molar ratio of CdTe QDs and NB was 5:1 by a mole-ratio method. The interaction between CdTe QDs and NB lead to the remarkable enhancement of RRS and the enchantments were in proportional to the concentration of NB in a certain range. The mechanism of the interaction between CdTe QDs and NB, reasons for the enhancement of RRS intensity were also discussed. The obtained results suggested the more satisfactory mechanism for the interaction between CdTe QDs and NB.

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.

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.

Resonance Rayleigh-scattering spectral method for the determination of some aminoglycoside antibiotics using CdTe quantum dots as a probe.

A novel method is used for the determination of some aminoglycoside antibiotics (AGs) such as etimicin (ETM), isepamicin (ISP) and amikacin (AMK). It is based on the resonance Rayleigh scattering (RRS) intensities enhanced by AGs-induced CdTe quantum dots aggregation. Under the optimum conditions, the increments in RRS intensity were directly proportional to the concentration of AGs in certain ranges. At the same time, the second-order scattering, the frequency-doubling scattering and the frequency-trebling scattering intensities were also enhanced and their increments were proportional to the concentration of AGs. Among them, the RRS method had the highest sensitivity; the linear ranges and detection limits for ETM, ISP and AMK were 0.085-7.2, 0.0067-1.2, 0.017-6.0 and 0.025, 0.0051, 0.0020 μg mL(-1) . This method was applied to the measurement of AGs in human serum and urine with satisfactory results. In addition, the reaction mechanism and the reasons for the enhancement of RRS are discussed using fluorescence, RRS, transmission electron microscope technology and quantum chemistry method.

Electron transfer and fluorescence “turn-off” based CdTe quantum dots for vancomycin detection at nanogram level in aqueous serum media

A simple and sensitive fluorescence “turn-off” biosensor for detection of vancomycin at nanogram level was proposed based on the electron transfer mechanism and the fluorescence quenching of CdTe quantum dots (QDs). The electron transfer process during the interaction between vancomycin and GSH (glutathione)-CdTe QDs was investigated not only by ultraviolet/visible (UV/vis) absorption and fluorescence (FL) spectroscopy but also by fluorescence lifetime measurements. The degree of the electron transfer and as resulted fluorescence quenching was proportional to the increasing of vancomycin concentration in the range of 1.534 ng mL−1–20 μg mL−1, with a corresponding detection limit of 0.4605 ng mL−1. This proposed a biosensor that could be used to determine vancomycin in environmental water samples, pharmaceutical formulation and spiked human serum with all of the recoveries over 95.8%. The mechanism of the detection was dynamic quenching with an electron transfer (ET) process. The experimental conditions, key affecting factors and the influence of the coexisting substances have also been optimized and studied.

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.