Volume 1, Issue 2013 -

The facile and controlled synthesis of narrowly dispersed molecularly imprinted polymer (MIP) microspheres with both photo- and thermo-responsive template binding properties in pure aqueous media is described. Narrowly dispersed "living" core polymer microspheres with surface-immobilized dithioester groups were firstly prepared via reversible addition-fragmentation chain transfer (RAFT) precipitation polymerization (RAFTPP). The polymer microspheres were then successively grafted with an azobenzene (azo)-containing MIP layer and thermo-responsive poly(N-isopropylacrylamide) (PNIPAAm) brushes via surface-initiated RAFT polymerization to provide the desired product. The successful grafting of the azo-containing MIP layer and PNIPAAm brushes was confirmed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and static contact angle experiments. The attachment of an azo-containing MIP layer onto the "living" core polymer beads with a narrow size distribution allows the direct generation of narrowly dispersed photoresponsive core-shell MIP microspheres. Moreover, the introduction of PNIPAAm brushes onto the core-shell MIP microspheres has been shown to significantly improve their surface hydrophilicity leading to pure water-compatibility. Additionally, this modification confers thermo-responsive template binding properties upon the microspheres.

The polymers based on ethylene glycol dimethacrylate (EGDMA) and dimethylaminoethyl methacrylate (DMAEMA) and molecularly imprinted with uric acid (UA), UA-MIPs, were successfully synthesized. The binding activity of UA-MIPs towards UA was studied in depth using batch methods. The optimized sorbent UA-MIP-7-16 was synthesized; this is an EGDMAcrosslinked system containing 16 mol% of UA as the template. The character of binding between UA and UA-MIP-7-16 was studied using xanthine as a reference substance, since its chemical structure is similar to that of UA. The studies of equilibrium sorption of UA and xanthine from model aqueous solutions by the imprinted sorbent demonstrate the predominance of specific UA sorption. The sorption kinetic data were analyzed using the Boyd model and shell and core. Selectivity of UAMIP- 7-16 was further demonstrated by biochemical analysis of serum containing UA and other components conducted before and after sorption. UA-MIP-7-16 showed high recognition selectivity and affinity towards the template molecule (UA).

Molecular imprinting of nicotine and related carcinogenic chemicals in itaconic acid – ethylene glycol dimethacrylate copolymer is described. Molecularly imprinted polymers (MIPs) are made to contain binding sites capable of recognizing nicotine; thus the fingerprint of the nicotine created in the polymer allows it to serve as an ideal molecular recognition element. We demonstrate that the imprinted polymers show high selective binding affinity in biological buffers. This is a previously un-described initiative for molecular imprinting, since the binding occurs under conditions relevant to biological systems. Due to effect of molecular imprinting nanocavities with size 24±5 nm were formed and these nicotine receptor sites were distributed homogeneously in the nicotine imprinted polymer. The nicotine receptors showed highly selective to nicotine with Kd values as low as 10 -5 M, and the levels of selectivity similar to those of natural molecules - acetylcholine esterase (AChE). The recognition properties of the polymer receptor were analyzed using ultra-violet spectroscopy, computer simulations and adsorption assay. Importantly, the receptors were effective in wide pH range (6.8-8.2) while the natural nicotine receptors showed high binding only at pH 7.6. The high specificity and stability of artificial receptors rendered them promising alternatives to enzymes, antibodies, and other natural receptors useful in biomedical assays, sensors and drug development.

In February 1993, the group of Klaus Mosbach published their milestone study in Nature where, for the first time, non-covalent molecular imprints were employed in a competitive binding assay. In this seminal piece of work, and also for the first time, they refer to molecularly imprinted polymers as being ‘antibody mimics’ and hypothesised that these synthetic materials could one day provide ‘a useful, general alternative to antibodies’. This perspective article examines how far we have come in the 20 years since this publication in terms of realising this hypothesis and poses the question of whether we actually need molecularly imprinted polymers to be a general alternative to antibodies.

Immunoassay is one of the most popular analytical methods with widespread applications. However, it presents several drawbacks because of the proteic nature of the antibodies. Molecular imprinting technology has shown a growing ability to prepare artificial molecular recognition systems, with binding properties very similar to those of natural antibodies. This review deals with the application of molecular imprinting technology to immunoassay, with an attention for the state of the art, the current limitations and the possible solutions to these issues.

In this study, an in-cell extraction and clean-up approach, employing pressurized hot water extraction (PHWE) coupled to a molecularly imprinted polymer (MIP) is proposed. The selectivity of PHWE was improved through the use of a chlorophyll MIP (PHWE-MIP) for the determination of organochlorine pesticides residue levels in various edible and medicinal plants of the Okavango Delta, Botswana. The PHWE-MIP method achieved simultaneous extraction and clean-up. PHWE employed an optimal temperature of 260 °C, pressure of 90 bar and flow rate of 1 mL min -1 in 10 min for the extraction of the pesticides from plants while the MIP selectively overcame the interfering chlorophyll prior to analysis with gas chromatograph coupled to electron capture detector or mass spectrometer (GC-ECD/MS). The results obtained were compared to the QuEChERS Official Method 2007:01 for pesticides residue analysis. The proposed method seems to be nearly fully automated, environmental friendly, selective, simple and quick. Moreover, the recoveries of planar pesticides were improved (93-95%) with relative standard deviations (%RSD) of less than 10%.