Dazhong Shen

Adsorption kinetics and isotherm of anionic dyes onto organo-bentonite from single and multisolute systems.

The performances of polydiallydimethylammonium modified bentonite (PDADMA-bentonite) as an adsorbent to remove anionic dyes, namely Acid Scarlet GR (AS-GR), Acid Turquoise Blue 2G (ATB-2G) and Indigo Carmine (IC), were investigated in single, binary and ternary dye systems. In adsorption from single dye solutions with initial concentration of 100 micromol/L, the dosage of PDADMA-bentonite needed to remove 95% dye was 0.42, 0.68 and 0.75 g/L for AS-GR, ATB-2G and IC, respectively. The adsorption isotherms of the three dyes obeyed the Langmuir isotherm model with the equilibrium constants of 0.372, 0.629 and 4.31 L/micromol, the saturation adsorption amount of 176.3, 149.2 and 228.7 micromol/g for ATB-2G, IC and AS-GR, respectively. In adsorption from mixed dye solutions, the isotherm of each individual dye followed an expanded Langmuir isotherm model and the relationship between the total amount of dyes adsorbed and the total equilibrium dye concentration was interpreted well by Langmuir isotherm model. In the region of insufficient dosage of PDADMA-bentonite, the dye with a larger affinity was preferentially removed by adsorption. Desorption was observed in the kinetic curve of the dye with lower affinity on PDADMA-bentonite surface by the competitive adsorption. The kinetics in single dye solution and the total adsorption of dyes in binary and ternary dye systems nicely followed pseudo-second-order kinetic model.

Behaviour of a series piezoelectric sensor in electrolyte solution: Part I. Theory

Abstract The theory, methodology and behaviour of a piezoelectric and conductivity sensor in electrolyte solution are reported. The sensor was constructed by connecting an AT-cut piezoelectric quartz crystal and a conductivity electrode in series. It has a sensitive and selective frequency response to the change in solution conductivity and permittivity. The relationship between frequency and solution conductivity was derived according to the oscillating theory and supported by the experiments. The effects of the solution conductivity, permittivity, temperature, density and viscosity, cell constant of the conductivity electrode, foreign electrolytes and the operating voltage of the integrated circuit-TTL oscillator on the behaviour of the series piezoelectric sensor were investigated. The sensor possesses high sensitivity to the solution conductivity and a low frequency-temperature coefficient, and its frequency depends very little on the operating voltage and density and viscosity of the solution. Its sensitivity and accuracy were improved in the presence of foreign electrolytes.

Quantum Dots Based Mesoporous Structured Imprinting Microspheres for the Sensitive Fluorescent Detection of Phycocyanin

Phycocyanin with important physiological/environmental significance has attracted increasing attention; versatile molecularly imprinted polymers (MIPs) have been applied to diverse species, but protein imprinting is still quite difficult. Herein, using phycocyanin as template via a sol-gel process, we developed a novel fluorescent probe for specific recognition and sensitive detection of phycocyanin by quantum dots (QDs) based mesoporous structured imprinting microspheres (SiO2@QDs@ms-MIPs), obeying electron-transfer-induced fluorescence quenching mechanism. When phycocyanin was present, a Meisenheimer complex would be produced between phycocyanin and primary amino groups of QDs surface, and then the photoluminescent energy of QDs would be transferred to the complex, leading to the fluorescence quenching of QDs. As a result, the fluorescent intensity of the SiO2@QDs@ms-MIPs was significantly decreased within 8 min, and accordingly a favorable linearity within 0.02-0.8 μM and a high detectability of 5.9 nM were presented. Excellent recognition specificity for phycocyanin over its analogues was displayed, with a high imprinting factor of 4.72. Furthermore, the validated probe strategy was successfully applied to seawater and lake water sample analysis, and high recoveries in the range of 94.0-105.0% were attained at three spiking levels of phycocyanin, with precisions below 5.3%. The study provided promising perspectives to develop fluorescent probes for convenient, rapid recognition and sensitive detection of trace proteins from complex matrices, and further pushed forward protein imprinting research.

Behaviour of series piezoelectric sensor in electrolyte solution: Part II. Applications in titrimetry

Abstract The applications of a series piezoelectric sensor for end-point determination in frequencimetric titrations, including neutralization, precipitation, complexation and redox titrations, are reported. The method is based on the fact that a series piezoelectric sensor shows a sensitive and selective frequency response to changes in conductivity of solution and can be applied to sample solutions containing large amounts of unreacted foreign electrolytes.

One-pot synthesis of magnetic molecularly imprinted microspheres by RAFT precipitation polymerization for the fast and selective removal of 17β-estradiol

A facile strategy was developed to prepare magnetic molecularly imprinted microspheres (MMIMs) for the selective recognition and effective removal of 17-beta-estradiol (17β-E2) by reversible addition-fragmentation chain transfer precipitation polymerization. One-pot synthesis was employed, which could simplify the imprinting process and shorten the experimental period. The resultant MMIMs displayed fast kinetics and high binding capacity, and the adsorption processes followed Langmuir–Freundlich isotherm and pseudo-second-order kinetic models. Excellent recognition selectivity toward 17β-E2 was attained over other phenolic estrogens such as 17-alpha-E2, estriol and estrone. The magnetic property of MMIMs provided fast and simple separation, and the recycling process for magnetic solid phase extraction (MSPE) was sustainable at least five times without obvious efficiency decrease. Furthermore, the MMIMs-MSPE presented satisfactory recoveries within 71.7–108.3% with the precisions of 1.1–6.0% for spiked 17β-E2 in water, soil and food samples. The developed MMIMs-based method proved to be a convenient and practical way in sample pretreatment and targeted pollutants removal.

Fluorescent sensing of mercury(II) based on formation of catalytic gold nanoparticles

A fluorescence assay for the highly sensitive and selective detection of Hg(2+) using a gold nanoparticle (AuNP)-based probe was proposed. The assay was based on the formation of Hg-Au alloys, which accelerated the oxidization of o-phenylenediamine by dissolved oxygen to produce 2,3-diaminophenazine, a fluorescent product.

A molecular imprinting-based turn-on Ratiometric fluorescence sensor for highly selective and sensitive detection of 2,4-dichlorophenoxyacetic acid (2,4-D)

A novel molecular imprinting-based turn-on ratiometric fluorescence sensor was constructed via a facile sol-gel polymerization for detection of 2,4-dichlorophenoxyacetic acid (2,4-D) on the basis of photoinduced electron transfer (PET) by using nitrobenzoxadiazole (NBD) as detection signal source and quantum dots (QDs) as reference signal source. With the presence and increase of 2,4-D, the amine groups on the surface of QDs@SiO2 could bind with 2,4-D and thereby the NBD fluorescence intensities could be significantly enhanced since the PET process was inhibited, while the QDs maintained constant intensities. Accordingly, the ratio of the dual-emission intensities of green NBD and red QDs could be utilized for turn-on fluorescent detection of 2,4-D, along with continuous color changes from orange-red to green readily observed by the naked eye. The as-prepared fluorescence sensor obtained high sensitivity with a low detection limit of 0.14μM within 5min, and distinguished recognition selectivity for 2,4-D over its analogs. Moreover, the sensor was successfully applied to determine 2,4-D in real water samples, and high recoveries at three spiking levels of 2,4-D ranged from 95.0% to 110.1% with precisions below 4.5%. The simple, rapid and reliable visual sensing strategy would not only provide potential applications for high selective ultratrace analysis of complicated matrices, but also greatly enrich the research connotations of molecularly imprinted sensors.

Novel monodisperse molecularly imprinted shell for estradiol based on surface imprinted hollow vinyl-SiO2 particles

A novel monodisperse molecularly imprinted shell was prepared based on surface imprinted hollow vinyl-SiO2 particles and applied to selective recognition and adsorption of estradiol (E2). This method was carried out by introducing vinyltriethoxysilane to the surface of polystyrene (PS) spheres by a simple one-step modification, followed by dissolution to remove the PS cores, and then by copolymerization of functional monomers via surface imprinted on the hollow vinyl-SiO2 particles to prepare uniform E2-imprinted shells. Two interesting characteristics were found: first, the obtained hollow molecularly imprinted polymer shells (H-MIPs) had highly monodispersity, uniform spherical shape with a shell thickness of about 40 nm; and then, the method was simple, easy to operate by directing coating of a uniform shell on hollow particles via surface imprinting. The resultant H-MIPs demonstrated improvements in imprinting factor and binding kinetics, owing to the high selectivity to template molecules, surface imprinting technique and hollow porous structure. Furthermore, satisfactory recoveries of 97.0 and 94.8% with respective precisions of 2.5 and 2.7% were achieved by one-step extraction when H-MIPs were used for the preconcentration and selective separation of estradiol in milk samples at two spiked levels. The simple, effective H-MIPs based strategy provided new insights into the formation of various functionalized coating layers on different kinds of support materials with versatile potential applications.

Molecular imprinting ratiometric fluorescence sensor for highly selective and sensitive detection of phycocyanin

A facile strategy was developed to prepare molecular imprinting ratiometric fluorescence sensor for highly selective and sensitive detection of phycocyanin (PC) based on fluorescence resonance energy transfer (FRET), via a sol-gel polymerization process using nitrobenzoxadiazole (NBD) as fluorescent signal source. The ratio of two fluorescence peak emission intensities of NBD and PC was utilized to determine the concentration of PC, which could effectively reduce the background interference and fluctuation of diverse conditions. As a result, this sensor obtained high sensitivity with a low detection limit of 0.14 nM within 6 min, and excellent recognition specificity for PC over its analogues with a high imprinting factor of 9.1. Furthermore, the sensor attained high recoveries in the range of 93.8-110.2% at three spiking levels of PC, with precisions below 4.7% in seawater and lake water samples. The developed sensor strategy demonstrated simplicity, reliability, rapidity, high selectivity and high sensitivity, proving to be a feasible way to develop high efficient fluorescence sensors and thus potentially applicable for ultratrace analysis of complicated matrices.

Surface acoustic wave sensor system for the determination of total salt content in serum

Abstract A surface acoustic wave (SAW) sensor system was constructed by combining a SAW resonator with conductive electrodes. The responses of the SAW system operating at 61 MHz were investigated for different electrolyte solutions and different capacitances in series. Comparisons of SAW devices and bulk acoustic wave (BAW) devices were also made. A frequency shift (ΔF)-electrolytic conductivity ( k ) equation is presented as ΔF = a k + b, where a can be positive or negative depending on a series capacitor. The sensor was applied to the rapid determination of the total salt content in serum.