Shoufang Xu

Recent advances in molecular imprinting technology: current status, challenges and highlighted applications

Molecular imprinting technology (MIT) concerns formation of selective sites in a polymer matrix with the memory of a template. Recently, molecularly imprinted polymers (MIPs) have aroused extensive attention and been widely applied in many fields, such as solid-phase extraction, chemical sensors and artificial antibodies owing to their desired selectivity, physical robustness, thermal stability, as well as low cost and easy preparation. With the rapid development of MIT as a research hotspot, it faces a number of challenges, involving biological macromolecule imprinting, heterogeneous binding sites, template leakage, incompatibility with aqueous media, low binding capacity and slow mass transfer, which restricts its applications in various aspects. This critical review briefly reviews the current status of MIT, particular emphasis on significant progresses of novel imprinting methods, some challenges and effective strategies for MIT, and highlighted applications of MIPs. Finally, some significant attempts in further developing MIT are also proposed (236 references).

Molecularly imprinted core-shell nanoparticles for determination of trace atrazine by reversible addition-fragmentation chain transfer surface imprinting

A simple and effective method was proposed to prepare uniform surface-imprinted nanoparticles. This strategy was carried out by introducing vinyl groups to the surface of silica beads by a one-step modification, followed by copolymerization of functional monomers via reversible addition–fragmentation chain transfer (RAFT) precipitation polymerization. Owing to the intrinsic advantages of controlled/living polymerization and surface imprinting technology, the resultant RAFT surface-imprinted nano-sized polymers (RAFT-SINPs) demonstrated spherical shaped particles with excellent monodispersity, and improvements in imprinting efficiency and mass transfer in comparison to molecularly imprinted polymers (MIPs) prepared by traditional precipitation polymerization. Recoveries of 93.4% and 79.8% were achieved by one-step extraction when RAFT-SINPs were used for the preconcentration and selective separation of atrazine in spiked corn and lettuce samples, respectively. These results provided the possibility for the separation and enrichment of atrazine from complicated matrices by RAFT-SINPs.

Dummy molecularly imprinted polymers-capped CdTe quantum dots for the fluorescent sensing of 2,4,6-trinitrotoluene.

Molecularly imprinted polymers (MIPs) with trinitrophenol (TNP) as a dummy template molecule capped with CdTe quantum dots (QDs) were prepared using 3-aminopropyltriethoxy silane (APTES) as the functional monomer and tetraethoxysilane (TEOS) as the cross linker through a seed-growth method via a sol-gel process (i.e., DMIP@QDs) for the sensing of 2,4,6-trinitrotoluene (TNT) on the basis of electron-transfer-induced fluorescence quenching. With the presence and increase of TNT in sample solutions, a Meisenheimer complex was formed between TNT and the primary amino groups on the surface of the QDs. The energy of the QDs was transferred to the complex, resulting in the quenching of the QDs and thus decreasing the fluorescence intensity, which allowed the TNT to be sensed optically. DMIP@QDs generated a significantly reduced fluorescent intensity within less than 10 min upon binding TNT. The fluorescence-quenching fractions of the sensor presented a satisfactory linearity with TNT concentrations in the range of 0.8-30 μM, and its limit of detection could reach 0.28 μM. The sensor exhibited distinguished selectivity and a high binding affinity to TNT over its possibly competing molecules of 2,4-dinitrophenol (DNP), 4-nitrophenol (4-NP), phenol, and dinitrotoluene (DNT) because there are more nitro groups in TNT and therefore a stronger electron-withdrawing ability and because it has a high similarity in shape and volume to TNP. The sensor was successfully applied to determine the amount of TNT in soil samples, and the average recoveries of TNT at three spiking levels ranged from 90.3 to 97.8% with relative standard deviations below 5.12%. The results provided an effective way to develop sensors for the rapid recognition and determination of hazardous materials from complex matrices.

Determination of 16 polycyclic aromatic hydrocarbons in seawater using molecularly imprinted solid-phase extraction coupled with gas chromatography-mass spectrometry

A method of solid-phase extraction (SPE) using molecularly imprinted polymers (MIPs) as adsorbent coupled with gas chromatography-mass spectrometry (GC-MS) was developed for the determination of 16 types of polycyclic aromatic hydrocarbons (PAHs) in seawater samples. The MIPs were prepared through non-covalent polymerization by using the 16 PAHs mixture as a template based on sol-gel surface imprinting. Compared with the non-imprinted polymers (NIPs), the MIPs exhibited excellent affinity towards 16 PAHs with binding capacity of 111.0-195.0 μg g(-1), and imprinting factor of 1.50-3.12. The significant binding specificity towards PAHs even in the presence of environmental parameters such as dissolved organic matter and various metal ions, suggested that this new imprinting material was capable of removing 93.2% PAHs in natural seawater. High sensitivity was attained, with the low limits of detection for 16 PAHs in natural seawater ranging from 5.2-12.6 ng L(-1). The application of MIPs with high affinity and excellent stereo-selectivity toward PAHs in SPE might offer a more attractive alternative to conventional sorbents for extraction and abatement of PAH-contaminated seawater.

Novel Hg2+-imprinted polymers based on thymine-Hg2+-thymine interaction for highly selective preconcentration of Hg2+ in water samples

A novel functional monomer T-IPTS, 3-isocyanatopropyltriethoxysilane (IPTS) bearing thymine (T) bases, was synthesized for imprinting Hg(2+). Then a novel Hg(2+) ionic imprinted polymers (IIPs) based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) interactions, i.e. Hg-IIPs-T, were prepared by sol-gel process for the first time in this work. The Hg-IIPs-T exhibited excellent selectivity towards Hg(2+) over Cd(2+), Zn(2+) Pb(2+), Co(2+), Mn(2+), Mg(2+) and Ca(2+), due to the specific T-Hg(2+)-T interactions with high selectivity and high affinity. Accordingly, Hg-IIPs-T were used as solid-phase extraction (SPE) sorbents for preconcentration of trace Hg(2+) in water samples, and satisfactory recoveries ranging from 95.2 to 116.3% were obtained. Also, under optimized conditions, preconcentration factor and detection limit were achieved of 200 and 0.03 μg L(-1), respectively. The IIPs-T-SPE proved to be a rapid and high-effective cleanup and enrichment method for trace Hg(2+) in water samples. More importantly, these results indicated that devising and synthesizing new functional monomers tailor-made for template would become a general promising way to improve the selectivity and stability of IIPs.

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.

Molecularly imprinted polymers by reversible addition-fragmentation chain transfer precipitation polymerization for preconcentration of atrazine in food matrices.

Controlled/living free radical polymerization (CLRP) has been accepted as an effective technique in preparation of polymers because of its inherent advantages over traditional free radical polymerization. In this work, reversible addition-fragmentation chain transfer (RAFT) polymerization, the ideal candidate for CLRP, was applied to prepare atrazine molecularly imprinted polymers (MIPs) by precipitation polymerization. The resultant RAFT-MIPs demonstrated uniform spherical shape with rough surface containing significant amounts of micropores, leading to an improvement in imprinting efficiency compared with that of the MIPs prepared by traditional precipitation polymerization (TR-MIPs). The maximum binding capacities of the RAFT-MIPs and TR-MIPs were 2.89 mg g(-1) and 1.53 mg g(-1), respectively. The recoveries ranging from 81.5% to 100.9% were achieved by one-step extraction by using RAFT-MIPs for preconcentration and selective separation of atrazine in spiked lettuce and corn samples. These results provided the possibility for the separation and enrichment of atrazine from complicated matrices by RAFT-MIPs.

Preparation of hollow porous molecularly imprinted polymers and their applications to solid-phase extraction of triazines in soil samples

Porous polymers have aroused increasing interest due to their controllable hole(s) structure in favor of mass transfer. In this work, three types of porous molecularly imprinted polymers (MIPs) using atrazine as template, namely single-hole hollow molecularly imprinted polymers (s-HMIPs), multihole hollow molecularly imprinted polymers (m-HMIPs) and porous solid molecularly imprinted polymers (ps-MIPs), were prepared, and applied as solid-phase extraction (SPE) sorbent for selective preconcentration and specific recognition of triazines in soil samples. For porous MIPs, most of the binding cavities were located in the proximity of the surface, which remarkably facilitated template removal and mass transfer. The resultant atrazine imprinted porous polymers of s-HMIPs and m-HMIPs exhibited more than triple imprinting capacity for triazines compared to the ps-MIPs, while they were all greatly superior to that of the non-imprinted polymers (NIPs). Accordingly, the s-HMIPs employed as SPE sorbent presented much higher extraction efficiency for several triazines based on the large specific surface area and high adsorption capacity in comparison with the commercial C18 column. The validated method was also successfully applied to soil sample analysis, and satisfactory recoveries were attained, such as 73.5–102.0% with the precision of 1.17–4.24% for five triazines at 10 μg L−1. The s-HMIPs-SPE proves to be a highly-effective cleanup and enrichment method for simultaneous separation and sensitive determination of triazines in complicated samples.

Stimuli-responsive molecularly imprinted polymers: versatile functional materials

Stimuli-responsive molecularly imprinted polymers (SR-MIPs) have received widespread attention with the rapid development of stimuli responsive polymers and molecularly imprinted polymers, and significant progress has been achieved in recent years in the field of SR-MIPs. To date, magnetic responsive MIPs, temperature responsive MIPs, pH responsive MIPs, photo-responsive MIPs, and dual or multi stimuli responsive MIPs have been prepared, and display broad application perspectives in many fields such as drug delivery, biotechnology, separation sciences, and chemo/biosensors. In the present feature article, those SR-MIPs are summarized comprehensively, and particular attention is paid to the mechanism of SR-MIPs, their preparation methods, and the application aspects. Finally, some significant attempts to further develop SR-MIPs are also proposed.

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.