Recent Advances in Molecular Imprinting for Proteins on Magnetic Microspheres

The separation of proteins in biological samples plays an essential role in the development of disease detection, drug discovery, and biological analysis. Protein imprinted polymers (PIPs) serve as a tool to capture target proteins specifically and selectively from complex media for separation purposes. Whereas conventional molecularly imprinted polymer is time-consuming in terms of incubation studies and solvent removal, magnetic particles are introduced using their magnetic properties for sedimentation and separation, resulting in saving extraction and centrifugation steps. Magnetic protein imprinted polymers (MPIPs), which combine molecularly imprinting materials with magnetic properties, have emerged as a new area of research hotspot. This review provides an overview of MPIPs for proteins, including synthesis, preparation strategies, and applications. Moreover, it also looks forward to the future directions for research in this emerging field.

Improving the Identification of Lysine-Acetylated Peptides Using a Molecularly Imprinted Monolith Prepared by a Deep Eutectic Solvent Monomer

To overcome the identification challenge of low-abundance lysine acetylation (Kac), a novel approach based on a molecularly imprinted polymer (MIP) was developed to improve the extraction capacity of Kac peptides in real samples. Green deep eutectic solvents (DESs) were introduced and used as one of the synergistic functional monomers with zinc acrylate (ZnA). Glycine-glycine-alanine-lysine(ac)-arginine (GGAKacR) was chosen as a template and N,N'-methylenbisacrylamide (MBAA) was used as a cross-linker. The obtained GGAKacR-MIP had excellent selectivity for the template with an imprinting factor (IF) of up to 21.4. The histone digest addition experiment demonstrated that GGAKacR-MIP could successfully extract GGAKacR from a complex sample. Finally, the application to the extraction of Kac peptides from mouse liver protein digestion was studied in detail. The number of Kac peptides and Kac proteins identified was 130 and 110, which were 3.71-fold and 3.93-fold higher than those of the untreated sample. In addition, the number of peptides and proteins identified after treatment increased from 5535 and 1092 to 17 149 and 4037 (3.10-fold and 3.70-fold, respectively). The results showed that the obtained MIP may provide an effective technical tool for the identification of Kac-modification and peptide fractionation, as well as a potential approach for simultaneously identifying post-translational-modified proteomic and proteomic information.

Protein-imprinted polymer films prepared via cavity-selective multi-step post-imprinting modifications for highly selective protein recognition

The use of molecularly imprinted polymers (MIPs) for achieving synthetic receptors capable of selective molecular recognition is promising; however, these polymers exhibit low selectivity derived from the heterogeneity of their created, imprinted cavities. To achieve highly selective protein recognition, we herein report the cavity-selective, multi-step, post-imprinting modification of MIPs. An MIP film for lysozyme was prepared by the copolymerization of {[2-(2-methacrylamido)ethyldithio]ethylcarbamoyl}methoxy acetic acid, a functional monomer possessing a modifiable disulfide bond, with acrylamide and N,N'-methylenebisacrylamide in the presence of lysozyme. After the removal of lysozyme, the disulfide bonds were cleaved by treatment with a reductant. A low concentration of lysozyme was then added to occupy the high-affinity cavities of the polymer and sterically protect the thiol groups within them. A poly(ethylene glycol)-based capping agent was reacted with the thiol groups residing in low-affinity cavities to hinder them. After the regeneration of the high-affinity cavities by washing out the bound lysozyme, the remaining thiol groups were reacted with 3-(2-pyridyldithio)propionic acid to introduce interacting groups, which produced capped MIPs. Comparing the capped and uncapped MIPs revealed that off-target protein binding was effectively suppressed by the capping treatment without any reduction in binding affinity (1.1 × 10⁹ M^-1). Further investigation revealed that the lysozyme concentration during the capping process is critical for the selectivity of the capped MIP. In this case, highly selective MIPs were achieved when the lowest lysozyme concentration (100 nM) was used. This facile process for creating highly selective, synthetic polymer receptors is a powerful approach for achieving plastic antibodies.

Sol-gel process: the inorganic approach in protein imprinting

Proteins play a central role in the signal transmission in living systems since they are able to recognize specific biomolecules acting as cellular receptors, antibodies or enzymes, being themselves recognized by other proteins in protein/protein interactions, or displaying epitopes suitable for antibody binding. In this context, the specific recognition of a given protein unlocks a range of interesting applications in diagnosis and in targeted therapies. Obviously, this role is already fulfilled by antibodies with unquestionable success. However, the design of synthetic artificial systems able to endorse this role is still challenging with a special interest to overcome limitations of antibodies, in particular their production and their stability. Molecular Imprinted Polymers (MIPs) are attractive recognition systems which could be an alternative for the specific capture of proteins in complex biological fluids. MIPs can be considered as biomimetic receptors or antibody mimics displaying artificial paratopes. However, MIPs of proteins remains a challenge due to their large size and conformational flexibility, their complex chemical nature with multiple recognition sites and their low solubility in most organic solvents. Classical MIP synthesis conditions result in large polymeric cavities and unspecific binding sites on the surface. In this review, the potential of the sol-gel process as inorganic polymerization strategy to overcome the drawbacks of protein imprinting is highlighted. Thanks to the mild and biocompatible experimental conditions required and the use of water as a solvent, the inorganic polymerization approach better suited to proteins than organic polymerization. Through numerous examples and applications of MIPs, we proposed a critical evaluation of the parameters that must be carefully controlled to achieve sol-gel protein imprinting (SGPI), including the choice of the monomers taking part in the polymerization.

Sensitive and selective detection of glycoprotein based on dual-signal and dual-recognition electrochemical sensing platform

Glycoproteins play extraordinary roles in biology and clinic. The specifically sensitive detection of glycoproteins by electrochemical methods is still a challenging task due to their poor electro-activity and sensitive nature to environment. In this work, ovalbumin (OVA), a model glycoprotein, was sensitively detected by a molecularly imprinted polymer (MIP) based electrochemical sensor, which was prepared by electropolymerizing 3-thiophene boric acid in the presence of OVA. Due to boronate affinity, the rebound OVA interacted with ferrocene boric acid (Fc-BA) to construct a sandwich structural sensing platform. Dual-recognition elements, imprinted effect and the boronate affinity, enabled the sensor to recognize OVA from other proteins. The rebinding of OVA caused the current changes of thionine and Fc-BA, which were combined as a dual-signal for OVA sensitive detection with a low limit of detection of 0.82 pg/mL (S/N = 3). The good performances of sensor indicated its potential applications in clinical diagnosis and other related fields.

Facile Fabrication of Surface-Imprinted Macroporous Films for Chemosensing of Human Chorionic Gonadotropin Hormone

We present an improved approach for the preparation of highly selective and homogeneous molecular cavities in molecularly imprinted polymers (MIPs) via the combination of surface imprinting and semi-covalent imprinting. Toward that, first, a colloidal crystal mold was prepared via the Langmuir-Blodgett (LB) technique. Then, human chorionic gonadotropin (hCG) template protein was immobilized on the colloidal crystal mold. Later, hCG derivatization with electroactive functional monomers via amide chemistry was performed. In a final step, optimized potentiostatic polymerization of 2,3'-bithiophene enabled depositing an MIP film as the macroporous structure. This synergistic strategy resulted in the formation of molecularly imprinted cavities exclusively on the internal surface of the macropores, which were accessible after dissolution of silica molds. The recognition of hCG by the macroporous MIP film was transduced with the help of electric transducers, namely, extended-gate field-effect transistors (EG-FET) and capacitive impedimetry (CI). These readout strategies offered the ability to create chemosensors for the label-free determination of the hCG hormone. Other than the simple confirmation of pregnancy, hCG assay is a common tool for the diagnosis and follow-up of ectopic pregnancy or trophoblast tumors. Concentration measurements with these EG-FET and CI-based devices allowed real-time measurements of hCG in the range of 0.8-50  and 0.17-2.0 fM, respectively, in 10 mM carbonate buffer (pH = 10). Moreover, the selectivity of chemosensors with respect to protein interferences was very high.

Hydrogels with novel hydrolytically labile trehalose-based crosslinks: small changes – big differences in degradation behavior

Novel crosslinkers based on trehalose diacetals were synthesized and applied to the fabrication of degradable polyacrylamide-type hydrogels with pH-dependent degradation characteristics at around physiological pH.

Covalent Incorporation of Trehalose within Hydrogels for Enhanced Long-Term Functional Stability and Controlled Release of Biomacromolecules

Hydrogels with covalently incorporated trehalose are synthesized using thiol-ene Michael addition. Trehalose hydrogels afford prolonged stabilization and -controlled release of model enzymes in vitro and in vivo as well as preservation of protein stability under heat and -lyophilization stressors. Strong and -ordered hydrogen bonding interactions within covalently incorporated trehalose hydrogels represent a possible mechanism for protein stabilization.

Improving molecularly imprinted nanogels by pH modulation

Non-specific binding between template molecule and the imprinted gel is significantly reduced by pH modulation.