Zhong Zhang

Novel Pb2+ Ion Imprinted Polymers Based on Ionic Interaction via Synergy of Dual Functional Monomers for Selective Solid-Phase Extraction of Pb2+ in Water Samples

A novel kind of Pb(2+) ion imprinted polymers (IIPs) was prepared based on ionic interactions via the synergy of dual functional monomers of methacrylic acid and vinyl pyridine for selective solid-phase extraction (SPE) of Pb(2+) in water samples. Suspension polymerization was employed for the formation of template Pb(2+)/monomer complex by self-assembly in the presence of ethylene glycol dimethacrylate cross-linker. The resulted Pb(2+) IIPs showed fast kinetics, high binding capacity, and the adsorption processes obeyed intraparticle diffusion kinetics and Langmuir isotherm models. The IIPs displayed excellent selectivity toward Pb(2+) over other metal ions such as Cu(2+), Cd(2+), Zn(2+), and Mn(2+) with selective coefficients above 30, as well as high anti-interference ability for Pb(2+) confronting with common coexisting various ions. Through 10 adsorption-desorption cycles, the reusable IIPs exhibited a good recoverability with the standard error within 5%. These features suggested the IIPs were ideal candidates for extraction and removal of Pb(2+) ions. Consequently, the IIPs were utilized as SPE sorbents and related parameters were optimized. An excellent linearity was presented in the range of 0.2-50 μg L(-1) (R(2) = 0.9998), as well as the limits of detection and quantification were achieved of 0.06 and 0.19 μg L(-1), respectively. A good repeatability was obtained with the relative standard deviation of 2.8%. Furthermore, real water samples were successfully analyzed and satisfactory recoveries varying from 95.5 to 104.6% were attained. The IIPs-SPE demonstrated potential application perspectives for rapid and high-effective cleanup and enrichment of trace Pb(2+) ions in complicated matrices.

Label-free colorimetric detection of trace cholesterol based on molecularly imprinted photonic hydrogels

A novel colorimetric sensor for cholesterol assay was constructed by combining a molecular imprinting technique with photonic crystals. The molecularly imprinted photonic hydrogel (MIPH) film was prepared by a non-covalent, self-assembly approach using cholesterol as a template molecule, and exhibited a highly ordered three-dimensional macroporous structure characterized by scanning electron microscopy under the optimized imprinting conditions. Various factors affecting rebinding of cholesterol are discussed along with recognition specificity studies on its analogues of stigmasterol and ergosterol through estimation of UV-Vis and electrochemical impedance spectroscopy. The MIPH film generated a significantly readable optical signal directly self-reporting within less than 2 min upon binding cholesterol. The colorimetric measurement of cholesterol concentration strongly relies on the fact that the blue shift effect of the Bragg diffraction peak of the MIPH is gradually enlarged with the increase of cholesterol amounts. The detection level approached 10−13 g mL−1, which is comparable to that of fluorescence measurements. The simultaneous possession of high selectivity, high sensitivity, high stability, easy operation and being label-free enables this sensor to be potentially applicable for rapid on-site detection of trace cholesterol.

Current status and challenges of ion imprinting

Ion imprinting technology (IIT) aims to recognize ions while retaining the unique virtues of molecular imprinting technology (MIT), namely structure predictability, recognition specificity and application universality. Owing to special coordination or electrostatic interactions, ion imprinted polymers (IIPs) are generally compatible with aqueous media and have advantages over most molecularly imprinted polymers (MIPs). IIPs can achieve effective identification of water-soluble ions, especially heavy metals and radioactive elements that cause increasing concerns. The purpose of this review is to summarize recent advances of ion imprinting, focusing on the current status and challenges in fundamentals and applications that involve almost all types of ions and ion-related molecular imprinting. In addition, various smart strategies are highlighted, such as surface imprinting, stimuli-responsive imprinting, dual/multiple components imprinting, click chemistry, and microwave-assisted heating. In this review, the elemental periodic table is first utilized as a template to introduce ion classification standards for various IIPs, including main groups, transition elements, actinides, rare earths, metalloids, anion imprinting and secondary imprinting. Finally, the challenges and possible solution strategies plus future trends are also proposed (302 references).

Selective solid-phase extraction of Sudan I in chilli sauce by single-hole hollow molecularly imprinted polymers.

A new single-hole hollow molecularly imprinted polymer (SHH-MIP) was prepared by multistep seed swelling polymerization using Sudan I as template molecule and successfully applied to selective solid-phase extraction (SPE) of Sudan dyes in chilli sauce samples. The polymers possessed high specific surface area obtained by nitrogen adsorption and good thermal stability without decomposition lower than 380 °C by thermogravimetry analysis. Much higher binding capacity was exhibited than with irregular solid MIP prepared by bulk polymerization, because most of the binding sites were located in the surface of the polymers, facilitating template removal and mass transfer. Accordingly, the SHH-MIP was employed as SPE adsorbent for chilli sauce analysis and offered high recoveries for Sudan I in the range of 87.5-103.4% with the precision of 1.94-5.33% at three spiked levels. The SHH-MIP with high selectivity and high stability was demonstrated to be potentially applicable for high selective preconcentration and determination of trace Sudan dyes in complicated samples.

A pH-responsive nano-carrier with mesoporous silica nanoparticles cores and poly(acrylic acid) shell-layers: Fabrication, characterization and properties for controlled release of salidroside

A novel pH-responsive nano-carrier MSNs-PAA, possessing mesoporous silica nanoparticles (MSNs) cores and poly(acrylic acid) (PAA) shell-layers, was developed for controlled release of salidroside. The vinyl double bonds modified MSNs were synthesized by using cetyltrimethylammonium bromide (CTAB) as templates, tetraethyl orthosilicate (TEOS) as silicon source, and 3-(trimethoxylsilyl) propyl methacrylate (MPS) as surface modification functionalities. The pH-responsive layers of PAA were grafted onto the vinyl double bonds of the MSNs via precipitation polymerization, producing the MSNs-PAA with a hollow cubic core and mesoporous shell with penetrating pore channels. The characteristic results also showed that PAA was successfully grafted onto the surface of the MSNs. The MSNs-PAA was investigated as carriers for loading and regulating the release of salidroside in different pH solutions for the first time. The results demonstrated that the PAA layers on the surface of MSNs-PAA exhibited opened and closed states at different pH values, and thus could regulate the uptake and release of salidroside. The application of such pH-responsive nano-carrier might offer a potential platform for controlled delivery and increasing the bioavailability of drugs.

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.

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.

Molecularly Imprinted Photonic Hydrogels as Colorimetric Sensors for Rapid and Label-free Detection of Vanillin

A novel colorimetric sensor for the rapid and label-free detection of vanillin, based on the combination of photonic crystal and molecular imprinting technique, was developed. The sensing platform of molecularly imprinted photonic hydrogel (MIPH) was prepared by a noncovalent and self-assembly approach using vanillin as a template molecule. Morphology characterization by scanning electron microscope (SEM) showed that the MIPH possessed a highly ordered three-dimensional (3D) macroporous structure with nanocavities. The vanillin recognition events of the created nonocavities could be directly transferred into readable optical signals through a change in Bragg diffraction of the ordered macropores array of MIPH. The Bragg diffraction peak shifted from 451 to 486 nm when the concentration of the vanillin was increased from 10⁻¹² to 10⁻³ mol L⁻¹ within 60 s, whereas there were no obvious peak shifts for methyl and ethyl vanillin, indicating that the MIPH had high selectivity and rapid response for vanillin. The adsorption results showed that the hierarchical porous structure and homogeneous layers were formed in the MIPH with higher adsorption capacity. The application of such a label-free sensor with high selectivity, high sensitivity, high stability, and easy operation might offer a potential method for rapid real-time detection of trace vanillin.

Magnetic molecularly imprinted microsensor for selective recognition and transport of fluorescent phycocyanin in seawater

Phycocyanin with excellent fluorescence characteristics and important physiological significance is an effective indicator for cyanobacterial bloom assessment due to its close relationship with cyanobacterial biomass. Molecularly imprinted polymers (MIPs) have attracted great interest owing to their recognition specificity; micromotor-driven targeted transport capability holds considerable promise. Herein, we propose an attractive magnetic microsensor for selective recognition, enrichment and transport of label-free fluorescent phycocyanin by combining MIPs and catalytic micromotors. The MIP-based catalytic microsensor was fabricated using phycocyanin as the imprinting molecule, Ni (0.55%) as the magnetic navigation material, and Pt (24.55%) as the solid support/catalyst to facilitate free movement in solutions, as well as an additional magnetic field was employed for trajectory control. The autonomous self-propulsion microsensor vividly displayed their motion states, presenting two different trajectories. The movement velocity was calculated based on the body-deformation model, suggesting a linear positive correlation between the velocity and hydrogen peroxide concentration, with a high average speed of 163 μm s−1. In addition, highly efficient targeted identification and enrichment abilities were demonstrated based on the magnetically imprinted layer. More excitingly, no obvious interference was found from complicated matrices such as seawater samples, along with real-time visualization of phycocyanin loading and transport. The sensing strategy would not only provide potential applications for rapid microscale monitoring of algae blooms, but also enrich the research connotations of protein imprinting.

Hg2+ ion-imprinted polymers sorbents based on dithizone–Hg2+ chelation for mercury speciation analysis in environmental and biological samples

For mercury speciation analysis in environmental and biological samples, novel Hg2+ ion-imprinted polymers (IIPs) were synthesized by a sol-gel process using the chelating agent dithizone, and then dithizone-Hg2+ chelate as a template and 3-aminopropyltriethoxysilane as a functional monomer, followed by solid-phase extraction (SPE) and atomic fluorescence spectroscopy (AFS) detection. The resultant Hg-IIPs offered high binding capacity, fast kinetics, and their adsorption processes followed a Langmuir isotherm and pseudo-second-order kinetic models. The IIPs displayed excellent selectivity toward Hg2+ over its organic forms and other metal ions with selectivity factors of 19-34, as well as high anti-interference ability for Hg2+ confronting with common coexistent ions. Through 10 adsorption-desorption cycles, the IIPs showed a good reusability with a relative standard deviation within 5%. Moreover, because of the chelation of dithizone, the IIPs could readily discriminate Hg2+ from organic mercury. Thus, mercury speciation analysis could be attained by using IIPs-SPE-AFS, presenting high detectability of up to 0.015 mu g L-1 for Hg2+ and 0.02 mu g L-1 for organic mercury. This method was validated by using two certified reference materials with very consistent results. Satisfactory recoveries ranging from 93.0-105.2% were attained for spiked seawater and lake water samples with three concentration levels of Hg2+. Furthermore, the analytical results for the spiked mercury species in real biological samples, such as human hair and fish meat, confirmed that the methods are practically applicable to speciation analysis. The IIPs-SPE-AFS demonstrated significant application perspectives for rapid and high-effective cleanup, enrichment and determination of trace mercury species in complicated matrices.