Yeqing Xu

Highly-controllable imprinted polymer nanoshell at the surface of silica nanoparticles based room-temperature phosphorescence probe for detection of 2,4-dichlorophenol

This paper reports a facile and general method for preparing an imprinted polymer thin shell with Mn-doped ZnS quantum dots (QDs) at the surface of silica nanoparticles by stepwise precipitation polymerization to form the highly-controllable core-shell nanoparticles (MIPs@SiO2-ZnS:Mn QDs) and sensitively recognize the target 2,4-dichlorophenol (2,4-DCP). Acrylamide (AM) and ethyl glycol dimethacrylate (EGDMA) were used as the functional monomer and the cross-linker, respectively. The MIPs@SiO2-ZnS:Mn QDs had a controllable shell thickness and a high density of effective recognition sites, and the thickness of uniform core-shell 2,4-DCP-imprinted nanoparticles was controlled by the total amounts of monomers. The MIPs@SiO2-ZnS:Mn QDs with a shell thickness of 45 nm exhibited the largest quenching efficiency to 2,4-DCP by using the spectrofluorometer. After the experimental conditions were optimized, a linear relationship was obtained covering the linear range of 1.0-84 μmol L(-1) with a correlation coefficient of 0.9981 and the detection limit (3σ/k) was 0.15 μmol L(-1). The feasibility of the developed method was successfully evaluated through the determination of 2,4-DCP in real samples. This study provides a general strategy to fabricate highly-controllable core-shell imprinted polymer-contained QDs with highly selective recognition ability.

Determination of Aspirin Using Functionalized Cadmium-Tellurium Quantum Dots as a Fluorescence Probe

A simple and sensitive method is reported for the synthesis of photoluminescent semiconductor CdTe quantum dots. The CdTe quantum dots were synthesized by using mercaptosuccinic acid for protection in the aqueous phase and used for the determination of aspirin by a quenching reaction. By comparison with thioglycolic acid stabilized CdTe quantum dots, the mercaptosuccinic acid shortened the reaction time. Transmission electron microscopy was used to characterize the CdTe quantum dots; their size was approximately 5.0 nm. The interaction between the CdTe quantum dots and aspirin was characterized by fluorescence and absorption spectroscopy. The optimum pH for measurements was 8.0. Under the optimized conditions, the fluorescence intensity of the CdTe quantum dots had a linear relationship with the concentration of aspirin between 1.7 and 56 µmol/L and the quenching reaction was shown to have a static mechanism. As the concentration of aspirin increased, the fluorescence quenching of mercaptosuccinic acid stabilized CdTe quantum dots increased. This method was successfully used for the determination of aspirin in tablets.

Sol-Gel Method for the Preparation of Solid-Phase Microextraction Fibers

A novel sol-gel method is applied for the preparation of solid-phase microextraction (SPME) fibers. Scanning electron microscopy experiments suggested a porous structure for the poly(dimethylsiloxane) (PDMS) coating. SPME-GC analysis provided evidence that the sol-gel fibers have some advantages, such as high thermal stability, efficient extraction rates, high velocities of mass transfer, and spacious range of application.

Boric acid functionalized ratiometric fluorescence probe for sensitive and on-site naked eye determination of dopamine based on two different kinds of quantum dots

In this work, 3-aminophenylboronic acid (APBA) modified CdTe quantum dots (QDs) and carbon quantum dots (CQDs) were combined and used as a ratiometric fluorescence probe for the on-site naked eye detection of dopamine (DA). The probe combined the ratiometric fluorescence technique with boric acid functional materials together, and had the features of sensitivity and selectivity. Two kinds of QDs with different emission wavelengths were mixed into one system. To simplify the experimental operation processes, the blue-emission CQDs were introduced to serve as the reference signal, while the red-emission CdTe QDs acted as the response signal. With the addition of DA, the cis-diol compounds of DA covalently linked with APBA on the surface of the CdTe QDs, then the red-emission of the CdTe QDs decreased gradually and the blue-emission of the CQDs kept constant due to the surface quenching state induced mechanism, resulting in the color change of the mixture (from deep pink to blue). Under optimum measurement conditions, the proposed ratiometric probe had the advantage of sensitive detection of DA in a concentration range of 10–220 μM with a detection limit of 0.36 μM. The developed ratiometric fluorescence probe was proved to detect other cis-diol substances, like gallate and catechol. In addition, the developed probe was also applied for the detection of DA in human serum samples successfully. The present study provides a new and facile approach for the detection of DA and other similar substances without the requirement of complex equipment.

A mesoporous fluorescent sensor based on ZnO nanorods for the fluorescent detection and selective recognition of tetracycline

Due to tetracycline (TC) being harmful to the environment and animals, versatile fluorescent sensors have been developed and applied for the specific recognition and determination of TC. In the present paper, a mesoporous fluorescent sensor was successfully prepared by using TC as the template, cetyl trimethyl ammonium bromide (CTAB) as the porogen, and ZnO nanorods (NRs) as the core substrate material and optical material. The synthesized composite materials were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fluorescent measurements of the target TC were then measured by a spectrofluorometer. Under optimal conditions, the linear range and correlation coefficient of the mesoporous MIPs-ZnO NRs were 2.0–120 μmol L−1 and 0.9993, respectively, and the imprinting factor (IF) was up to 3.50. Moreover, in order to further investigate the effect of the mesoporous structure, a fluorescent sensor without a mesoporous structure was synthesized as a comparison and measured by the same processes. Through analysis of the data, it was found that the mesoporous fluorescent sensor showed a lower response time, higher utilization, and higher selective recognition and sensitive determination than the non-mesoporous fluorescent sensor. This study provides a novel strategy to fabricate mesoporous-imprinted polymer layer-coated ZnO NRs with excellent fluorescent performance for TC.

A Novel Fluorescent Nanoswitch Based on Carbon Dots for Sensitive Detection of Hg2+ and I−

In this paper, a novel fluorescent nanoswitch based on carbon dots (CDs) was developed for the sensitive and selective determination of Hg2+ and I−. The CDs were obtained by simple hydrothermal process and had a strong fluorescence emission at 440nm. The fluorescence of the CDs can be selectively quenched by Hg2+ ion, and then the I− was added into the system, which can interact with Hg2+ and recover fluorescence of the CDs. Under optimal conditions, the quenching fluorescence intensity on addition of Hg2+ has obtained a satisfactory linear relationship covering the linear range of 0–50μM with the linear relationship (R12=0.9991), and the limit of detection is 0.047μM. The additions of I− could lead to the fluorescence intensity of the solution of CDs and Hg2+ (50μM) recover rapidly, which is linearly related (R22=0.9957) to the concentration of I− in the range from 0 to 70μM, the detection limit for I− was calculated to be 0.084μM. Moreover, the developed method to detect Hg2+ and I− was evaluated in real examples, and the fluorescence switching can sensitively and selectively detect Hg2+ and I− over some potentially interfering ions, the recoveries were up to 97.8–107.0% and 96.7–106.6%, respectively.

Swelling technique inspired synthesis of a fluorescent composite sensor for highly selective detection of bifenthrin

Pesticide pollution has become a serious problem that threatens public health, so it is necessary to develop a method that can detect pesticides rapidly and sensitively. In this study, we report a novel fluorescent imprinted sensor based on quantum dots (QDs) synthesized via a facile and versatile swelling technique for highly selective detection of bifenthrin (BI). Compared with other fluorescent molecularly imprinted polymers (MIPs), it has three significant differences: firstly, polystyrene (PS) microspheres make up the polymer matrix and were prepared in advance; secondly, the interactions are not hydrogen bonding and covalent interactions, but van der Waals and hydrophobic forces; thirdly, aqueous QDs were successful applied to the swelling process using a polymerizable surfactant. The unique fluorescent sensor (MIPs (PS)-OVDAC/CdTe QDs) possesses the strong fluorescence and sensitivity of QDs and the high selectivity of molecularly imprinted polymers as well as a uniform morphology via this novel swelling strategy. As a result, the fluorescence intensity of the MIPs (PS)-OVDAC/CdTe QDs was strongly decreased within less than 25 min upon binding BI, and the quenching fractions of the MIPs (PS)-OVDAC/CdTe QDs presented a good linearity with BI concentrations in the range of 0.5–40 μM with a correlation coefficient of 0.9918. In addition, the limit of detection (LOD) was as low as 0.08 μmol L−1 and a high imprinting factor of 4.11 was obtained. The developed method was successfully applied to the determination of BI in honey samples. The present study provides a facile and efficient strategy to develop fluorescent sensors for rapid recognition and selective detection of organic pollutants from complex matrices.

Convenient Determination of Sulfamethazine in Milk by Novel Ratiometric Fluorescence with Carbon and Quantum Dots with On-site Naked-eye Detection and Low Interferences

ABSTRACT Sulfamethazine, one of the most widely applied feed additives, has been shown to cause negative health effects to humans. In the present work, a novel and facile fluorescence visual detection probe was established to determine sulfamethazine in milk samples with naked-eye detection. Considering the good stability, excellent optical properties, and easy synthesis, blue-emission carbon dots were used as the standard signal and red-emission CdTe quantum dots as the responsive signal for the determination of sulfamethazine. The fluorescence intensity of red-emission CdTe quantum dots was gradually quenched with increasing concentration of sulfamethazine, while the blue-emission carbon dots response remained constant. Apparent color variations were observed by naked-eye detection in the concentration range from 9.0 to 54 µmol · L−1. In addition, the presented strategy was shown to be promising to provide a rapid, facile, and sensitive method for the determination of sulfamethazine in milk samples with few interferences.