Challenges for the effective molecular imprinting of proteins

Challenges in SERS-based pesticide detection and plausible solutions

Surface-enhanced Raman spectroscopy (SERS) can be used for the detection of trace amounts of pesticides in foods to ensure consumer safety. In this perspective, we highlight the trends of SERS-based assays in pesticide detection and the various challenges associated with their selectivity, reproducibility, and nonspecific binding. We also discuss and compare the target analyte capture techniques, such as the use of antibodies, aptamers, and molecularly imprinted polymers (MIPs), coupled with SERS to overcome the drawbacks as mentioned above. In addition, issues related to the nonspecific binding of analytes and its potential solution are discussed.

Evaluation of Molecularly Imprinted Polymers for Point-of-Care Testing for Cardiovascular Disease

Molecular imprinting is a rapidly growing area of interest involving the synthesis of artificial recognition elements that enable the separation of analyte from a sample matrix and its determination. Traditionally, this approach can be successfully applied to small analyte (<1.5 kDa) separation/ extraction, but, more recently it is finding utility in biomimetic sensors. These sensors consist of a recognition element and a transducer similar to their biosensor counterparts, however, the fundamental distinction is that biomimetic sensors employ an artificial recognition element. Molecularly imprinted polymers (MIPs) employed as the recognition elements in biomimetic sensors contain binding sites complementary in shape and functionality to their target analyte. Despite the growing interest in molecularly imprinting techniques, the commercial adoption of this technology is yet to be widely realised for blood sample analysis. This review aims to assess the applicability of this technology for the point-of-care testing (POCT) of cardiovascular disease-related biomarkers. More specifically, molecular imprinting is critically evaluated with respect to the detection of cardiac biomarkers indicative of acute coronary syndrome (ACS), such as the cardiac troponins (cTns). The challenges associated with the synthesis of MIPs for protein detection are outlined, in addition to enhancement techniques that ultimately improve the analytical performance of biomimetic sensors. The mechanism of detection employed to convert the analyte concentration into a measurable signal in biomimetic sensors will be discussed. Furthermore, the analytical performance of these sensors will be compared with biosensors and their potential implementation within clinical settings will be considered. In addition, the most suitable application of these sensors for cardiovascular assessment will be presented.

Adsorption and Electrochemical Detection of Bovine Serum Albumin Imprinted Calcium Alginate Hydrogel Membrane

In this paper, bovine serum albumin (BSA)-imprinted calcium alginate (CaAlg) hydrogel membrane was prepared using BSA as a template, sodium alginate (NaAlg) as a functional monomer, and CaCl₂ as a cross-linker. The thickness of the CaAlg membrane was controlled by a glass rod enlaced with brass wires (the diameter was 0.1, 0.2, 0.3, 0.4, and 0.5 mm). The swelling properties of the CaAlg membranes prepared with different contents of NaAlg were researched. Circular dichroism indicated that the conformation of BSA did not change during the preparing and eluting process. The thinner the CaAlg hydrogel membrane was, the larger the adsorption capacity and the higher the imprinting efficiency of the CaAlg. The maximum adsorption capacity of molecularly imprinted polymer (MIP) and non-imprinted CaAlg hydrogel membrane (NIP) was 38.6 mg·g⁻¹ and 9.2 mg·g⁻¹, respectively, with an imprinting efficiency of 4.2. The MIP was loaded on the electrode to monitor the selective adsorption of BSA by voltammetry curve.

Chromatographic separation of hemoglobin variants using robust molecularly imprinted polymers

Devising a robust, efficient and cost effective hemoglobin (Hb) purification strategy is one of the key challenges in the development of Hb-based blood substitutes. The aim of this study was to use molecularly imprinted polymers (MIPs) as a novel and efficient chromatographic resin to selectively recognize and purify different Hb variants. The results showed that the Hb-MIP material developed here could selectively recognize and purify various Hb directly from either crude E. coli extracts or human body fluids, such as blood plasma and cerebrospinal fluid (CSF), in one-step. The dynamic binding capacity at 10% breakthrough was around 7.4 mg mL^-1resin for adult Hb (HbA) and fetal Hb (HbF). This chromatographic material also allowed identification of changes related to amino acid substitutions on the Hb protein surface. For instance, when an additional lysine residue was introduced, the HbA αY42K mutant eluted later in an Hb-MIP column than wildtype HbA. Additional negative charges on the protein surface, such as aspartate, mitigated the interaction between the protein and imprinted polymers, and therefore an αA19D-αA12D HbF mutant eluted earlier, at -2.7 column volumes compared to wildtype HbF.

An optical sensor with specific binding sites for the detection of thioridazine hydrochloride based on ZnO-QDs coated with molecularly imprinted polymer

Here, an optical sensor with specific binding sites for sensitive and selective detection of thioridazine hydrochloride (THZ) was prepared. The optosensor was developed based on ZnO quantum dots (QDs) coated with molecularly imprinted polymers (MIPs). Initially, ZnO quantum dots (QDs) were synthesized by precipitation from Zn(CH₃COO)₂ and NaOH then, reverse microemulsion method was applied for fixing the MIPs layer on the surface of QDs. It was perceived that the fluorescence intensity of the QDs-MIPs quenched with increasing THZ concentration. Several parameters affect the optical sensor response were studied and optimized. Under the optimal conditions, THZ could be determined with a linear dynamic range of 4-120 nmol L^-1 and with a low detection limit of 0.43 nmol L^-1. The relative standard deviations for 25 and 60 nmol L^-1 of THZ were obtained as 4.9% and 3.1%, respectively (three times measurement). High selectivity, simplicity, and cost-efficient for THZ measurement are the most important advantages of the fluorimetric sensor.

New protocol for optimisation of polymer composition for imprinting of peptides and proteins

A novel screening tool for high-throughput optimisation of monomer composition for imprinting of peptides and proteins.

Sensitive electrochemical detection of gp120 based on the combination of NBD-556 and gp120

As is known, the employment of molecular imprinting polymer (MIP) as specific sensing materials in sensors, namely MIP-based sensors. In this contribution, we devised a MIP electrochemical sensor for the detection of variable-format conformations protein gp120. The sensor was constructed by using a grapheme-like carbon nanfragment (CNF) and bismuth oxides composites (CNF-Bi) as decoration material, small-molecule entry inhibitor NBD-556 and gp120 conjugates NBD-556@gp120 instead of gp120 as the template, and pyrrole as an electropolymerization monomer. Cyclic voltammetry, differential pulse voltammetry, scanning electron microscopy and transmission electron microscope were used to characterize the preparation process of the sensor. Results showing that, under optimized conditions, the introduction of NBD-556 make the specific recognition and analytical properties of the MIP sensor towards gp120 more efficient. The response currents were proportional to the NBD-556@gp120 concentrations in the range of 0.0002 ng mL^-1 to 200 ng mL^-1 with the detection limit of 0.0003 ng mL^-1 based on S/N = 3. Meanwhile, the NBD-556@gp120 based MIP sensor also shows acceptable stability and reproducibility. When used for the detection of gp120 in human plasma, it also showed good accuracy. This research idea is in great promising for the early diagnosis of HIV-1 virus and can also be extended to the detection of other conformationally unstable proteins.

Guide to Selecting a Biorecognition Element for Biosensors

Biosensors are powerful diagnostic tools defined as having a biorecognition element for analyte specificity and a transducer for a quantifiable signal. There are a variety of different biorecognition elements, each with unique characteristics. Understanding the advantages and disadvantages of each biorecognition element and their influence on overall biosensor performance is crucial in the planning stages to promote the success of novel biosensor development. Therefore, this review will focus on selecting the optimal biorecognition element in the preliminary design phase for novel biosensors. Included is a review of the typical characteristics and binding mechanisms of various biorecognition elements, and how they relate to biosensor performance characteristics, specifically sensitivity, selectivity, reproducibility, and reusability. The goal is to point toward language needed to improve the design and development of biosensors toward clinical success.

Preparation of Magnetic Polymers for the Elimination of 3-Isobutyl-2-Methoxypyrazine from Wine

3-Isobutyl-2-methoxypyrazine (IBMP), the most prevalent grape-derived methoxypyrazine, can contribute green bell pepper, vegetative and herbaceous aromas and flavours to wines. At elevated concentrations, this potent odorant may mask desirable fruity and floral aromas in wine and may be considered as a fault. A new remediation method for wines with elevated IBMP levels has been trialled using magnetic polymers, prepared in the same way as ordinary polymers but with the incorporation of iron oxide nanoparticles as magnetic substrates. Characterisation by Fourier transform-infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed no difference between thermally synthesised and microwave synthesised polymers. Magnetic polymers were found to have removed over 40% of the IBMP present in spiked model wine and white wine within ten minutes. The addition of magnetic nanoparticles and microwave-induced polymerisation did not affect the adsorption properties of the polymer in model wine and the polymer could be regenerated at least five times. Both Langmuir and Freundlich isotherms were found to fit the data for both types of polymer. However, attempts to produce imprinted polymers were not achieved, as they were found not to be differentiated from non-imprinted counterparts via adsorption tests.

Techniques for Preparation of Cross-Linked Enzyme Aggregates and Their Applications in Bioconversions

Enzymes are biocatalysts. They are useful in environmentally friendly production processes and have high potential for industrial applications. However, because of problems with operational stability, cost, and catalytic efficiency, many enzymatic processes have limited applications. The use of cross-linked enzyme aggregates (CLEAs) has been introduced as an effective carrier-free immobilization method. This immobilization method is attractive because it is simple and robust, and unpurified enzymes can be used. Coimmobilization of different enzymes can be achieved. CLEAs generally show high catalytic activities, good storage and operational stabilities, and good reusability. In this review, we summarize techniques for the preparation of CLEAs for use as biocatalysts. Some important applications of these techniques in chemical synthesis and environmental applications are also included. CLEAs provide feasible and efficient techniques for improving the properties of immobilized enzymes for use in industrial applications.

Molecularly imprinted polymers fabricated via Pickering emulsions stabilized solely by food-grade casein colloidal nanoparticles for selective protein recognition

Novel molecularly imprinted polymers (MIPs) based on denatured casein nanoparticle (DCP)-stabilized Pickering emulsions were developed for the first time. Casein, a phosphoprotein, is the main protein in milk. In this work, DCPs were solely used as Pickering-type interfacial emulsifiers for fabrication of MIPs for the selective recognition of proteins for the first time. DCPs were prepared by acidification and heat denaturation (at 80 °C) of casein. Their dispersions have satisfactory colloidal stability over a wide pH range. The DCPs acted as natural, food-grade, and edible interfacial emulsifiers, and adsorbed at the oil-water interface to form Pickering emulsions. After the polymerization of monomers, the template protein was removed by elution. During the elution, the interfacial DCPs were also removed, allowing more imprinted cavities to become exposed. The interfacial imprinting technology causes nearly all the imprinted sites to locate on the surface of the polymeric material. Therefore, the MIPs obtained exhibit fast rebinding and excellent specific recognition ability toward the analytes. Overall, this work provides a promising method for designing and fabricating natural-protein-based structured emulsions to prepare MIPs and thus offers new insight into protein separation and purification. Graphical Abstract Pickering emulsions stabilized by denatured casein particles.

Surface-initiated synthesis of bulk-imprinted magnetic polymers for protein recognition

Bulk imprinting of proteins was used combined with a grafting approach onto maghemite nanoparticles to develop a faster and simpler polymerization method for the synthesis of magnetic protein imprinted polymers with very high adsorption capacities and very strong affinity constants.

Magnetic protein imprinted polymers: a review

Protein imprinted polymers have received a lot of interest in the past few years because of their applications as tailor-made receptors for biomacromolecules. Generally, the preparation of these polymers requires numerous and time-consuming steps. But their coupling with magnetic nanoparticles simplifies and speeds up the synthesis of these materials. Some recent papers describe the use of protein imprinted polymer (PIP) coupled to magnetic iron oxide nanoparticles (MION) for the design of MION@PIP biosensors. With such systems, a target protein can be specifically and selectively captured from complex media due to exceptional chemical properties of the polymer. Despite such performances, only a limited number of studies address these hybrid nanosystems. This review focuses on the chemistry and preparation of MION@PIP nanocomposites as well as on the metrics used to characterize their performances.

A novel thermal detection method based on molecularly imprinted nanoparticles as recognition elements

Molecularly Imprinted Polymers (MIPs) are synthetic receptors that are able to selectively bind their target molecule and, for this reason, they are currently employed as recognition elements in sensors. In this work, MIP nanoparticles (nanoMIPs) are produced by solid-phase synthesis for a range of templates with different sizes, including a small molecule (biotin), two peptides (one derived from the epithelial growth factor receptor and vancomycin) and a protein (trypsin). NanoMIPs are then dipcoated on the surface of thermocouples that measure the temperature inside a liquid flow cell. Binding of the template to the MIP layer on the sensitive area of the thermocouple tip blocks the heat-flow from the sensor to the liquid, thereby lowering the overall temperature measured by the thermocouple. This is subsequently correlated to the concentration of the template, enabling measurement of target molecules in the low nanomolar regime. The significant improvement in the limit of detection (a magnitude of three orders compared to previously used MIP microparticles) can be attributed to their high affinity, enhanced conductivity and increased surface-to-volume ratio. It is the first time that these nanosized recognition elements are used in combination with thermal detection, and it is the first report on MIP-based thermal sensors for determining protein levels. The developed thermal sensors have a high selectivity, fast measurement time (<5 min), and data analysis is straightforward, which makes it possible to monitor biomolecules in real-time. The set of biomolecules discussed in this manuscript show that it is possible to cover a range of template molecules regardless of their size, demonstrating the general applicability of the biosensor platform. In addition, with its high commercial potential and biocompatibility of the MIP receptor layer, this is an important step towards sensing assays for diagnostic applications that can be used in vivo.

Novel surface imprinted magnetic mesoporous silica as artificial antibodies for efficient discovery and capture of candidate nNOS–PSD-95 uncouplers for stroke treatment

Magnetic mesoporous silica imprinted materials as artificial antibodies for the discovery and capture of candidate nNOS–PSD-95 uncouplers for stroke treatment.

Dispersive solid-phase imprinting of proteins for the production of plastic antibodies

A new imprinting technique, so called dispersive solid-phase imprinting, has been developed for the production of nano-sized molecularly imprinted polymers (nanoMIPs) as plastic antibodies.

Core-Shell Molecularly Imprinted Polymer Nanoparticles as Synthetic Antibodies in a Sandwich Fluoroimmunoassay for Trypsin Determination in Human Serum

We describe the application of a fluorescently labeled water-soluble core-shell molecularly imprinted polymer (MIP) for fluorescence immunoassay (FIA) to detect trypsin. p-Aminobenzamidine (PAB), a competitive inhibitor of trypsin, was immobilized in the wells of a microtiter plate enabling the capture of trypsin in an oriented position, thus maintaining its native conformation. Fluorescent MIP nanoparticles, which bound selectively to trypsin, were used for quantification. The MIP was prepared by a multistep solid-phase synthesis approach on glass beads functionalized with PAB, orientating all trypsin molecules in the same way. The core-MIP was first synthesized, using a thermoresponsive polymer based on N-isopropylacrylamide, so as to enable its facile liberation from the immobilized template by a simple temperature change. The shell, mainly composed of allylamine to introduce primary amino groups for postconjugation of fluorescein isothiocyanate (FITC), was grafted in situ on the core-MIP, whose binding cavities were still bound and protected by the immobilized trypsin. The resulting core-shell MIP was endowed with a homogeneous population of high-affinity binding sites, all having the same orientation. The MIP has no or little cross-reactivity with other serine proteases and unrelated proteins. Our MIP-based FIA system was successfully applied to detect low trypsin concentrations spiked into nondiluted human serum with a low limit of quantification of 50 pM, which indicates the significant potential of this assay for analytical and biomedical diagnosis applications.

Guide to the Preparation of Molecularly Imprinted Polymer Nanoparticles for Protein Recognition by Solid-Phase Synthesis

Molecularly imprinted polymers (MIPs) are synthetic antibody mimics possessing specific cavities designed for a target molecule. Nowadays, molecular imprinting of proteins still remains a challenge as the generation of selective imprinted cavities is extremely difficult, due to their flexible structure and the presence of a multitude of functional sites. To overcome this difficulty, we propose a solid-phase synthesis strategy to prepare MIPs specific for any protein that can be immobilized in an oriented way on a solid support. Trypsin and kallikrein were used as model proteins. The solid-phase support consists of glass beads functionalized with two affinity ligands of the enzymes, the competitive inhibitor p-aminobenzamidine to orient the enzymes via their active site, or a Cu²⁺chelate to orient via the surface histidine residues of the enzyme. Thermoresponsive molecularly imprinted polymer nanoparticles (MIP-NPs) are then synthesized around the immobilized enzyme. The MIP-NPs are released by a simple temperature change, resulting in protein-free polymers endowed with improved binding site homogeneity since all binding sites have the same orientation. The MIP-NPs exhibit apparent dissociation constants between 0.02 and 2nM toward their target proteins, which is comparable to those of natural antibodies. Moreover, these water-compatible polymers, targeting different domains of the enzyme, can also function as protective agents (armor), hence preventing the target proteins from denaturation by heat or pH.