Controllably Prepared Aptamer-Molecularly Imprinted Polymer Hybrid for High-Specificity and High-Affinity Recognition of Target Proteins

Aptamer-based assembly systems for SARS-CoV-2 detection and therapeutics

Nucleic acid aptamers are oligonucleotide chains with molecular recognition properties. Compared with antibodies, aptamers show advantages given that they are readily produced via chemical synthesis and elicit minimal immunogenicity in biomedicine applications. Notably, aptamer-encoded nucleic acid assemblies further improve the binding affinity of aptamers with the targets due to their multivalent synergistic interactions. Specially, aptamers can be engineered with special topological arrangements in nucleic acid assemblies, which demonstrate spatial and valence matching towards antigens on viruses, thus showing potential in the detection and therapeutic applications of viruses. This review presents the recent progress on the aptamers explored for SARS-CoV-2 detection and infection treatment, wherein applications of aptamer-based assembly systems are introduced in detail. Screening methods and chemical modification strategies for aptamers are comprehensively summarized, and the types of aptamers employed against different target domains of SARS-CoV-2 are illustrated. The evolution of aptamer-based assembly systems for the detection and neutralization of SARS-CoV-2, as well as the construction principle and characteristics of aptamer-based DNA assemblies are demonstrated. The typically representative works are presented to demonstrate how to assemble aptamers rationally and elaborately for specific applications in SARS-CoV-2 diagnosis and neutralization. Finally, we provide deep insights into the current challenges and future perspectives towards aptamer-based nucleic acid assemblies for virus detection and neutralization in nanomedicine.

Rationally designed protein A surface molecularly imprinted magnetic nanoparticles for the capture and detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus), a commensal organism found on the human skin, is commonly associated with nosocomial infections and exhibits virulence mediated by toxins and resistance to antibiotics. The global threat of antibiotic resistance has necessitated antimicrobial stewardship to improve the safe and appropriate use of antimicrobials; hence, there is an urgent demand for the advanced, cost-effective, and rapid detection of specific bacteria. In this regard, we aimed to selectively detect S. aureus using surface molecularly imprinted magnetic nanoparticles templated with a well-known biomarker protein A, specific to S. aureus. Herein, a highly selective surface molecularly imprinted polymeric thin layer was created on ∼250 nm magnetic nanoparticles (MNPs) through the immobilization of protein A to aldehyde functionalized MNPs, followed by monomer polymerization and template washing. This study employs the rational selection of monomers based on their computationally predicted binding affinity to protein A at multiple surface residues. The resulting MIPs from rationally selected monomer combinations demonstrated an imprinting factor as high as ∼5. Selectivity studies revealed MIPs with four-fold higher binding capacity (BC) to protein A than other non-target proteins, such as lysozyme and serum albumin. In addition, it showed significant binding to S. aureus, whereas negligible binding to other non-specific Gram-negative, i.e. Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), and Gram-positive, i.e. Bacillus subtilis (B. subtilis), bacteria. This MIP was employed for the capture and specific detection of fluorescently labeled S. aureus. Quantitative detection was performed using a conventional plate counting technique in a linear detection range of 101-107 bacterial cells. Remarkably, the MIPs also exhibited approximately 100% cell recovery from milk samples spiked with S. aureus (106 CFU mL-1), underscoring its potential as a robust tool for sensitive and accurate bacterial detection in dairy products. The developed MIP exhibiting high affinity and selective binding to protein A finds its potential applications in the magnetic capture and selective detection of protein A as well as S. aureus infections and contaminations.

Fabricating Ultrathin Imprinting Layer for Fast Capture of Valsartan via a Metal Affinity-Oriented Surface Imprinting Method

Rapid separation and enrichment of targets in biological matrixes are of significant interest in multiple life sciences disciplines. Molecularly imprinted polymers (MIPs) have vital applications in extraction and sample cleanup owing to their excellent specificity and selectivity. However, the low mass transfer rate, caused by the heterogeneity of imprinted cavities in polymer networks and strong driving forces, significantly limits its application in high-throughput analysis. Herein, one novel metal affinity-oriented surface imprinting method was proposed to fabricate an MIP with an ultrathin imprinting layer. MIPs were prepared by immobilized template molecules on magnetic nanoparticles (NPs) with metal ions as bridges via coordination, and then polymerization was done. Under the optimized conditions, the thickness of the imprinting layer was merely 1 nm, and the adsorption toward VAL well matched the Langmuir model. Moreover, it took just 5 min to achieve adsorption equilibrium significantly faster than other reported MIPs toward VAL. Adsorption capacity still can reach 25.3 mg/g ascribed to the high imprinting efficiency of the method (the imprinting factor was as high as 5). All evidence proved that recognition sites were all external cavities and were evenly distributed on the surface of the NPs. The obtained MIP NPs exhibited excellent selectivity and specificity toward VAL, with good dispersibility and stability. Coupled with high-performance liquid chromatography, it was successfully used as a dispersed solid phase extraction material to determine VAL in serum. Average recoveries are over 90.0% with relative standard deviations less than 2.14% at three spiked levels (n = 3). All evidence testified that the MIPs fabricated with the proposed method showed a fast trans mass rate and a large rebinding capacity. The method can potentially use high-throughput separation and enrichment of target molecules in batch samples to meet practical applications.

Molecularly imprinted polymer-based SERS sensing of transferrin in human serum

Specific detection of glycoproteins such as transferrin (TRF) related to neurological diseases, hepatoma and other diseases always plays an important role in the field of disease diagnosis. We designed an antibody-free immunoassay sensing method based on molecularly imprinted polymers (MIPs) formed by the polymerization of multiple functional monomers for the sensitive and selective detection of TRF in human serum. In the sandwich surface-enhanced Raman spectroscopy (SERS) sensor, the TRF-oriented magnetic MIP nanoparticles (Fe3O4@SiO2-MIPs) served as capture units to specifically recognize TRF and 4-mercaptophenylboronic acid-functionalized gold nanorods (MPBA-Au NRs) served as SERS probes to label the targets. In order to achieve stronger interaction between the recognition cavities of the prepared MIPs and the different amino acid fragments that make up TRF, Fe3O4@SiO2-MIPs were obtained through polycondensation reactions between more silylating reagents, enhancing the specific recognition of the entire TRF protein and achieving high IF. This sensing method exhibited a good linear response to TRF within the TRF concentration range of 0.01 ng mL-1 to 1 mg mL-1 (R2 = 0.9974), and the LOD was 0.00407 ng mL-1 (S/N = 3). The good stability, reproducibility and specificity of the resulting MIP based SERS sensor were demonstrated. The determination of TRF in human serum confirmed the feasibility of the method in practical applications.

Functional Interface for Glycoprotein Sensing: Focusing on Biosensors

Glycosylated proteins or glycoproteins make up a large family of glycoconjugates, and they participate in a variety of fundamental biological events. Glycoproteins have become important biomarkers in the diagnosis and treatment of a number of tumors. Biosensors are quite suitable for glycoprotein detection. The design and fabrication of a functional sensing interface play a crucial role in the biosensor construction to target glycoproteins. The functional interface, particularly receptors, typically determines the key characteristics of a biosensor, such as selectivity and sensitivity. Antibody, peptide, aptamer, boronic acid derivative, lectin, and molecularly imprinted polymer are all capable receptors for glycoprotein recognition, and each of these will be discussed. Most glycoproteins exist in low abundance, thus rendering signal amplification techniques indispensable. Nucleic acid-mediated and nanomaterial-mediated signal amplification for the detection of glycoproteins will be focused on herein. This review aims to highlight these different functional interfaces for glycoprotein sensing.

Molecularly imprinted polymers-aptamer electrochemical sensor based on dual recognition strategy for high sensitivity detection of chloramphenicol

In this paper, an electrochemical sensor based on a dual recognition strategy of molecularly imprinted polymers (MIPs) and aptamer (Apt) has been designed for the high sensitivity detection of chloramphenicol (CAP). Here, MIPs and Apt have provided dual recognition sites to greatly improve the specific recognition ability of the sensor. Chitosan-multi-walled carbon nanotubes (CS-MWNTs) and AuNPs (gold nanoparticles) have been used for their excellent electrical conductivity. When CAP existed in the detection environment, the imprinted cavities with specific recognition ability bound to CAP through forces such as hydrogen bonds. It hindered the rate of electron transfer and resulted in a decrease in current value. Quantitative detection of CAP could be achieved after analyzing the relationship between the concentration of CAP and the change of current value. After optimizing the experimental parameters, the detection range of the sensor was 10-8 g/L-10-2 g/L with the limit of detection of 3.3 × 10-9 g/L, indicating that the sensor had a high practical application potential.

Glycan-specific molecularly imprinted polymers towards cancer diagnostics: merits, applications, and future perspectives

Aberrant glycans are a hallmark of cancer states. Notably, emerging evidence has demonstrated that the diagnosis of cancers with tumour-specific glycan patterns holds great potential to address unmet medical needs, especially in improving diagnostic sensitivity and selectivity. However, despite vast glycans having been identified as potent markers, glycan-based diagnostic methods remain largely limited in clinical practice. There are several reasons that prevent them from reaching the market, and the lack of anti-glycan antibodies is one of the most challenging hurdles. With the increasing need for accelerating the translational process, numerous efforts have been made to find antibody alternatives, such as lectins, boronic acids and aptamers. However, issues concerning affinity, selectivity, stability and versatility are yet to be fully addressed. Molecularly imprinted polymers (MIPs), synthetic antibody mimics with tailored cavities for target molecules, hold the potential to revolutionize this dismal progress. MIPs can bind a wide range of glycan markers, even those without specific antibodies. This capacity effectively broadens the clinical applicability of glycan-based diagnostics. Additionally, glycoform-resolved diagnosis can also be achieved through customization of MIPs, allowing for more precise diagnostic applications. In this review, we intent to introduce the current status of glycans as potential biomarkers and critically evaluate the challenges that hinder the development of in vitro diagnostic assays, with a particular focus on glycan-specific recognition entities. Moreover, we highlight the key role of MIPs in this area and provide examples of their successful use. Finally, we conclude the review with the remaining challenges, future outlook, and emerging opportunities.

Recent Advances of Biosensors for Detection of Multiple Antibiotics

The abuse of antibiotics has caused a serious threat to human life and health. It is urgent to develop sensors that can detect multiple antibiotics quickly and efficiently. Biosensors are widely used in the field of antibiotic detection because of their high specificity. Advanced artificial intelligence/machine learning algorithms have allowed for remarkable achievements in image analysis and face recognition, but have not yet been widely used in the field of biosensors. Herein, this paper reviews the biosensors that have been widely used in the simultaneous detection of multiple antibiotics based on different detection mechanisms and biorecognition elements in recent years, and compares and analyzes their characteristics and specific applications. In particular, this review summarizes some AI/ML algorithms with excellent performance in the field of antibiotic detection, and which provide a platform for the intelligence of sensors and terminal apps portability. Furthermore, this review gives a short review of biosensors for the detection of multiple antibiotics.

Linking peptide-oriented surface imprinting magnetic nanoparticle with carbon nanotube-based fluorescence signal output device for ultrasensitive detection of glycoprotein

Determination of trace glycoprotein has important guiding significance in clinical diagnosis and is usually achieved by immunoaffinity. However, immunoaffinity possesses inherent drawbacks, such as poor probability of high-quality antibodies, instability of biological reagents, and harmfulness of chemical labels to the body. Herein, we propose an innovative method of peptide-oriented surface imprinting to fabricate artificial antibody for recognition of glycoprotein. By integrating peptide-oriented surface imprinting and PEGylation, an innovative hydrophilic peptide-oriented surface imprinting magnetic nanoparticle (HPIMN) was successfully fabricated with human epidermal growth factor receptor-2 (HER2) as a model glycoprotein template. In addition, we further prepared a novel boronic acid-modified/fluorescein isothiocyanate-loaded/polyethylene glycol-covered carbon nanotube (BFPCN) as fluorescence signal output device, which was loaded with numerous fluorescent molecules could specifically label the cis-diol of glycoprotein at physiological pH via boronate-affinity interaction. To prove the practicability, we proposed a HPIMN-BFPCN strategy, in which the HPIMN first selectively captured the HER2 due to the molecular imprinted recognition and then the BFPCN specific labeled the exposed cis-diol of HER2 based on the boronate-affinity reaction. The HPIMN-BFPCN strategy exhibited ultrahigh sensitivity with limit of detection of 14 fg mL^-1 and was successfully used in the determination of HER2 in spiked sample with recovery and relative standard deviation in the range of 99.0%-103.0% and 3.1%-5.6%, respectively. Therefore, we believe that the novel peptide-oriented surface imprinting has great potential to become an universal strategy for fabrication of recognition units for other protein biomarkers, and the synergy sandwich assay could become a powerful tool in prognosis evaluation and clinical diagnosis of glycoprotein-related diseases.

Molecular imprinted electrochemical sensor for ovalbumin detection based on boronate affinity and signal amplification approach

Ovalbumin (OVA), a class of glycoproteins, is the main allergen in hen egg white that often causes allergies in humans, especially in babies. Therefore, it is pivotal to be able to detect and separate OVA. This work presents an ingenious sandwich-structured magnetic molecular imprinted electrochemical sensor for OVA detection by utilizing boronate affinity and signal amplification strategy. With anti-OVA antibody-modified gold nanoparticles (AuNPs) as amplifiers, the imprinted cavities in the probe could capture protein to form a sandwich structure. Due to its specific recognition of antibody and molecular imprinted polymers and the signal amplification of AuNPs, the sensor had good selectivity and sensitivity toward OVA and a low detection limit of 3.0 fg/mL. The sensor also had excellent stability and could satisfactorily detect OVA in real red wine samples.

Targeted degradation of ABCG2 for reversing multidrug resistance by hypervalent bispecific gold nanoparticle-anchored aptamer chimeras

Hypervalent bispecific gold nanoparticle-anchored aptamer chimeras (AuNP-APTACs) were designed as a new tool of lysosome-targeting chimeras (LYTACs) for efficient degradation of the ATP-binding cassette, subfamily G, isoform 2 protein (ABCG2) to reverse multidrug resistance (MDR) of cancer cells. The AuNP-APTACs could effectively increase the accumulation of drugs in drug-resistant cancer cells and provide comparable efficacy to small-molecule inhibitors. Thus, this new strategy provides a new way to reverse MDR, holding great promise in cancer therapy.

Analytical Perspectives in the Study of Polyvalent Interactions of Free and Surface-Bound Oligonucleotides and Their Implications in Affinity Biosensing

The high affinity and/or selectivity of oligonucleotide-mediated binding offers a myriad of therapeutical and analytical applications, whose rational design implies an accurate knowledge of the involved molecular mechanisms, concurring equilibrium processes and key affinity parameters. Oligonucleotide-functionalized gold surfaces or nanostructures are regularly employed analytical platforms for the development of label-free optical or electrochemical biosensors, and recently, novel detection platform designs have been increasingly considering the synergistic effect of polyvalent binding, involving the simultaneous interaction of two or several oligonucleotide strands. Considering the general lack of studies involving ternary single-stranded DNA (ssDNA) interactions, a complementary analytical workflow involving capillary gel electrophoretic (CGE) mobility shift assay, microcalorimetry and computational modeling has been deployed for the characterization of a series of free and surface-bound binary and ternary oligonucleotide interactions. As a proof of concept, the DNA analogue of MicroRNA 21 (miR21), a well-known oncogenic short MicroRNA (miRNA) sequence, has been chosen as a target molecule, simulating limiting-case scenarios involved in dual molecular recognition models exploited in affinity (bio)sensing. Novel data for the characterization of oligonucleotide interacting modules is revealed, offering a fast and complete mapping of the specific or non-specific, often competing, binary and ternary order interactions in dynamic equilibria, occurring between various free and metal surface-bound oligonucleotides.

A sensitive MnO2 nanosheet sensing platform based on a fluorescence aptamer sensor for the detection of zearalenone

An aptamer sensor based on manganese dioxide (MnO₂) nanosheets was developed for the detection of zearalenone (ZEN). The ZEN aptamer was modified at the 5'-end by a 6-carboxyfluorescein (6-FAM) fluorophore with self-assembly on MnO₂ nanosheets. Interaction of the 6-FAM fluorophore at the 5'-end of the ZEN aptamer with the MnO₂ nanosheet lowered fluorescence (FL) intensity due to fluorescence resonance energy transfer (FRET). The introduction of ZEN into the sensing system resulted in hybridization with the ZEN aptamer, forming a stable G-quadruplex/ZEN, which exhibited a low affinity for the MnO₂ nanosheet surface. The distance between the 6-FAM fluorophore and MnO₂ nanosheet hampered FRET, with a consequent strong FL signal. Under the optimal experimental conditions, the FL intensity of the sensing system showed a good linear correlation with ZEN concentration in the range of 1.5-10.0 ng mL^-1, and a detection limit (S/N = 3) of 0.68 ng mL^-1. The sensing system delivered enhanced specificity for the detection of ZEN, and can find wide application in the detection of other toxins by replacing the sequence of the recognition aptamer.

Spatially-directed magnetic molecularly imprinted polymers with good anti-interference for simultaneous enrichment and detection of dual disease-related bio-indicators

As the changes of biomarkers directly reflect the occurrence of degenerative diseases, accurate detection of biomarkers is of great significance for disease diagnosis and control. However, single index detection has high uncertainties to accurately reflect the pathological characteristics because of the complexity of the human internal environment and the extremely trace concentration of indicators. To this end, a method for simultaneous detection of dual-biomarkers based on anti-interference magnetic molecularly imprinted polymers (D-mag-MIPs) is thereby proposed, and successfully applied in human urine analysis for the detection of Parkinson's disease bio-indicators 4-dihydroxyphenylacetic acid (DOPAC) and dopamine (DA). In this work, carboxyl functionalized ferric oxide served as a magnetic core, laying a solid foundation for batch detection. Hyperbranched polyethylenimine, whose abundant amino groups can provide multiple interaction forces to templates with high affinity, is employed as a functional monomer. Relative to single-template MIPs, D-mag-MIPs achieve the detection of dual bio-indicators in a one-time test, reducing the false positive result probability and enhancing the detection accuracy. The proposed methodology has been evaluated to exhibit good anti-interference, satisfactory precision, low detection limits, wide linear ranges and fast batch detection for DA and DOPAC. This work thus offers an alternative and efficient pathway for convenient batch detection of dual bio-indicators from biofluids at once.

Molecularly Imprinting–Aptamer Techniques and Their Applications in Molecular Recognition

Molecular imprinting–aptamer techniques exhibit the advantages of molecular imprinting and aptamer technology. Hybrids of molecularly imprinted polymer–aptamer (MIP–aptamer) prepared by this technique have higher stability, binding affinity and superior selectivity than conventional molecularly imprinted polymers or aptamers. In recent years, molecular imprinting–aptamer technologies have attracted considerable interest for the selective recognition of target molecules in complex sample matrices and have been used in molecular recognition such as antibiotics, proteins, viruses and pesticides. This review introduced the development of molecular imprinting–aptamer-combining technologies and summarized the mechanism of MIP–aptamer formation. Meanwhile, we discussed the challenges in preparing MIP–aptamer. Finally, we summarized the application of MIP–aptamer to the molecular recognition in disease diagnosis, environmental analysis, food safety and other fields.

Construction of PEGylated boronate-affinity-oriented imprinting magnetic nanoparticles for ultrasensitive detection of ellagic acid from beverages

Molecularly imprinted polymers (MIPs) can exhibit antibody-level affinity for target molecules. However, the nonspecific adsorption of non-imprinted regions for non-target molecules limits the application range of MIPs. Herein, we fabricated PEGylated boronate-affinity-oriented ellagic acid-imprinting magnetic nanoparticles (PBEMN), which first integrated boronate-affinity-oriented surface imprinting and sequential PEGylation for small molecule-imprinted MIPs. The resultant PBEMN possess higher adsorption capacity and faster adsorption rate for template ellagic acid (EA) molecules than the non-PEGylated control. To prove the excellent performance, the PBEMN were linked with hydrophilic boronic acid-modified/fluorescein isothiocyanate-loaded graphene oxide (BFGO), because BFGO could selectively label cis-diol-containing substances by boronate-affinity and output ultrasensitive fluorescent signals. Based on a dual boronate-affinity synergy, the PBEMN first selectively captured EA molecules by boronate-affinity-oriented molecular imprinted recognition, and then the EA molecules were further labeled with BFGO through boronate-affinity. The PBEMN linked BFGO (PBPF) strategy provided ultrahigh sensitivity for EA molecules with a limit of detection of 39.1 fg mL^-1, resulting from the low nonspecific adsorption of PBEMN and the ultrasensitive fluorescence signal of BFGO. Lastly, the PBPF strategy was successfully employed in the determination of EA concentration in a spiked beverage sample with recovery and relative standard deviation in the range of 96.5 to 104.2% and 3.8 to 5.1%, respectively. This work demonstrates that the integration of boronate-affinity-oriented surface imprinting and sequential PEGylation may be a universal tool for improving the performance of MIPs.

The Protein‐Templated Synthesis of Enzyme‐Generated Aptamers

Inspired by the chemical synthesis of molecularly imprinted polymers, we demonstrated for the first time, the protein‐target mediated synthesis of enzyme‐generated aptamers (EGAs). We prepared pre‐polymerisation mixtures containing different ratios of nucleotides, an initiator sequence and protein template and incubated each mixture with terminal deoxynucleotidyl transferase (TdT). Upon purification and rebinding of the EGAs against the target, we observed an enhancement in binding of templated‐EGAs towards the target compared to a non‐templated control. These results demonstrate the presence of two primary mechanisms for the formation of EGAs, namely, the binding of random sequences to the target as observed in systematic evolution of ligands by exponential enrichment (SELEX) and the dynamic competition between TdT enzyme and the target protein for binding of EGAs during synthesis. The latter mechanism serves to increase the stringency of EGA‐based screening and represents a new way to develop aptamers that relies on rational design.

PEGylation of boronate-affinity-oriented surface imprinting magnetic nanoparticles with improved performance

High specific selectivity is the continuous goal of exploit glycoprotein-imprinted materials. Boronate-affinity-oriented surface imprinting can limit the heterogeneity of imprinted cavities, and PEGylation can reduce the nonspecific adsorption of imprinted materials towards non-target molecules. However, there are no reports on the integration of the above two advantages. Herein, we first integrated the boronate-affinity-oriented surface imprinting and PEGylation, and fabricated PEGylated boronate-affinity-oriented surface imprinting magnetic nanoparticles (PBSIMN) with horseradish peroxidase (HRP) as a model glycoprotein template. The successful synthesis of PBSIMN was demonstrated in detail by various characterization. Compared with non-PEGylated control, the PBSIMN showed greater adsorption capacity for HRP, and faster adsorption rate. To evaluate the improved performance, the PBSIMN was linked with hydrophilic boronic acid-modified/fluorescein isothiocyanate-loaded graphene oxide (BFGO), and used for the detection of HRP in real samples. Because PEGylation led to decrease of non-specific binding on PBSIMN, the proposed strategy provided ultrahigh sensitivity with limit of detection of 6.0 fg mL^-1 for HRP, which were an order of magnitude lower than the non-PEGylated counterparts. When spiked with 0.05, 0.5 and 5.0 mg mL^-1, recoveries of HRP were in the range of 97.4%-101.8% with relative standard deviation (RSD) no more than 5.4% for mouse serum, and between 98.2% and 103.2% with RSD no more than 5.0% human serum. This work indicates that the boronate-affinity-oriented surface imprinting and PEGylation can improve the performance of imprinted materials.

Molecular imprinted polymer combined with aptamer (MIP-aptamer) as a hybrid dual recognition element for bio(chemical) sensing applications. Review

The development of diagnostic devices based on memetic molecular recognitions are becoming highly promising due to high specificity, sensitivity, stability, and low-cost comparing to natural molecular recognition. During the last decade, molecular imprinted polymers (MIPs) and aptamer have shown dramatic enhancement in the molecular recognition characteristics for bio(chemical) sensing applications. Recently, MIP-aptamer, as an emerging hybrid recognition element, merged the advantages of the both recognition components. This dual recognition-based sensor has shown improved properties and desirable features, such as high sensitivity, low limit of detection, high stability under harsh environmental conditions, high binding affinity, and superior selectivity. Hybrid MIP-aptamer as dual recognition element, was used in the real sample analysis, such as detection of proteins, neurotransmitters, environmental pollutants, biogenic compounds, small ions, explosives, virus detections and pharmaceuticals. This review focuses on a comprehensive overview of the preparation strategies of various MIP-aptamer recognition elements, mechanism of formation of MIP-aptamer, and detection of various target molecules in different matrices.

Sensitive and selective "signal-off" electrochemiluminescence sensing of prostate-specific antigen based on an aptamer and molecularly imprinted polymer

Specific and sensitive determination of prostate-specific antigen (PSA) in complex real samples holds significant importance as it is an effective molecular biomarker for the clinical diagnosis of prostate cancer. Herein, we constructed a dual-recognition electrochemiluminescence (ECL) sensor based on both the recognition elements of an aptamer and molecularly imprinted polymers (MIP) for the selective and ultrasensitive determination of PSA. The aptamer was self-assembled on gold nanoparticle (AuNP) modified electrodes through Au-S bonds. Subsequently, a layer of MIP membrane was synthesized by electropolymerization of dopamine (DA) to fabricate an aptamer-MIP sensor. After the rebinding of PSA onto imprinted cavities, the ECL response of luminol in the solution decreased. This "signal-off" strategy was employed for PSA detection with a wide linear range and a low limit of detection of 5 pg mL^-1-50 ng mL^-1 and 3.0 pg mL^-1, respectively. Compared with individual aptamer sensors, the dual-recognition sensor showed higher specific recognition ability for the determination of PSA. Meanwhile, the good stability, reproducibility, and regenerability endowed the dual recognition sensor with favorable application value in early clinical diagnosis.

Evaluation the effect of nanoparticles on the structure of aptamers by analyzing the recognition dynamics of aptamer functionalized nanoparticles

Aptamer-functionalized nanoparticles have been widely studied as targeted probes in biomedical applications for targeted therapy and imaging. The rigidity of the nanoparticle could stabilized the spatial structure of the aptamer, ensuring the selectivity and affinity for target recognition in the complex environment. The main aim of this article study was to explore the effect of the spatial structure of aptamer in the interaction between aptamer nanoprobes and receptors. We designed and synthesized aptamer functionalized nanoparticle systems with different derivation lengths, and developed a unique kinetic analysis to quantify affinity interactions. The system used silver decahedral nanoparticles (Ag₁₀NPs), which was then chemically functionalized with thrombin (or IgE) aptamers of different tail lengths to produced different nanoprobes, and employed thrombin (or IgE) as target on a surface plasmon resonance (SPR) biosensor to evaluate the binding of these nanoprobes. Kinetic analysis of the SPR binding curve was performed to evaluated the affinity between nanoprobes and targets. Under the premise of eliminating multivalent interactions, we found that the distance between aptamer and nanoparticle could affect the affinity between nanoprobe and target. Furthermore, we found that keeping a certain distance between aptamer and nanoparticle could effectively improved the recognition efficiency of the aptamer nanoprobe and target. It shows that the rigidity of nanomaterials could maintain the spatial structure of the aptamer.

Dual-recognition colorimetric sensing of thrombin based on surface-imprinted aptamer-Fe3O4

Thrombin plays an essential role in blood coagulation and some physiological and pathological processes. The convenient, rapid, sensitive, and specific detection of thrombin is of great significance in clinical research and diagnosis. Herein, surface molecularly imprinted polymer (MIP) was modified on aptamer-functionalized Fe3O4 nanoparticles (MIP-aptamer-Fe3O4 NP) for thrombin colorimetric assay by taking advantage of the peroxidase-like activity of Fe3O4 NP. With the adsorption of thrombin into imprinted cavities, the exposed surface area of Fe3O4 NP decreased, causing a decrease in its peroxidase-like activity toward 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. On the other hand, the reductive amino acids on the thrombin surface also impeded the oxidation of TMB. Both phenomena caused the light blue color of the sensing solution. Thus, a specifically sensitive colorimetric approach for the visual detection of thrombin was proposed with a linear range and limit of detection of 108.1 pmol L-1-2.7 × 10-5 mol L-1 and 27.8 pmol L-1, respectively. Moreover, due to the double recognition elements of MIP and aptamer, the prepared MIP-aptamer-Fe3O4 NP showed higher selectivity to thrombin than that based on only one recognition element. It is worth noting that no special property (e.g. electrochemical or fluorescence activity) of the template was required in this work. Thus, more template molecules can be easily, selectively, and sensitively detected based on the proposed MIP-aptamer-mimic enzyme colorimetric sensing strategy.

Molecular Imprinting: Green Perspectives and Strategies

Advances in revolutionary technologies pose new challenges for human life; in response to them, global responsibility is pushing modern technologies toward greener pathways. Molecular imprinting technology (MIT) is a multidisciplinary mimic technology simulating the specific binding principle of enzymes to substrates or antigens to antibodies; along with its rapid progress and wide applications, MIT faces the challenge of complying with green sustainable development requirements. With the identification of environmental risks associated with unsustainable MIT, a new aspect of MIT, termed green MIT, has emerged and developed. However, so far, no clear definition has been provided to appraise green MIT. Herein, the implementation process of green chemistry in MIT is demonstrated and a mnemonic device in the form of an acronym, GREENIFICATION, is proposed to present the green MIT principles. The entire greenificated imprinting process is surveyed, including element choice, polymerization implementation, energy input, imprinting strategies, waste treatment, and recovery, as well as the impacts of these processes on operator health and the environment. Moreover, assistance of upgraded instrumentation in deploying greener goals is considered. Finally, future perspectives are presented to provide a more complete picture of the greenificated MIT road map and to pave the way for further development.

Probing low-copy-number proteins in single living cells using single-cell plasmonic immunosandwich assays

Cellular heterogeneity is pervasive and of paramount importance in biology. Single-cell analysis techniques are indispensable for understanding the heterogeneity and functions of cells. Low-copy-number proteins (fewer than 1,000 molecules per cell) perform multiple crucial functions such as gene expression, cellular metabolism and cell signaling. The expression level of low-copy-number proteins of individual cells provides key information for the in-depth understanding of biological processes and diseases. However, the quantitative analysis of low-copy-number proteins in a single cell still remains challenging. To overcome this, we developed an approach called single-cell plasmonic immunosandwich assay (scPISA) for the quantitative measurement of low-copy-number proteins in single living cells. scPISA combines in vivo microextraction for specific enrichment of target proteins from cells and a state-of-the-art technique called plasmon-enhanced Raman scattering for ultrasensitive detection of low-copy-number proteins. Plasmon-enhanced Raman scattering detection relies on the plasmonic coupling effect (hot-spot) between silver-based plasmonic nanotags and a gold-based extraction microprobe, which dramatically enhances the signal intensity of the surface-enhanced Raman scattering of the nanotags and thereby enables sensitivity at the single-molecule level. scPISA is a straightforward and minimally invasive technique, taking only ~6-15 min (from in vivo extraction to Raman spectrum readout). It is generally applicable to all freely floating intracellular proteins provided that appropriate antibodies or alternatives (for example, molecularly imprinted polymers or aptamers) are available. The entire protocol takes ~4-7 d to complete, including material fabrication, single-cell manipulation, protein labeling, signal acquisition and data analysis.

Specific determination of HBV using a viral aptamer molecular imprinting polymer sensor based on ratiometric metal organic framework

An approach is reported based on the combination of aptamer and metal organic frameworks (MOF) to prepare a molecularly imprinted sensor that recognizes viruses with high specificity and sensitivity. Using MIL-101-NH₂ as a polymer carrier, viral aptamers were introduced into the carrier surface through an amide reaction to specifically identify the target, and surface imprinting is carried out through tetraethyl silicate (TEOS) self-polymerization. The MIL-101-NH₂ is also used as the reference fluorescence signal (λex/λem = 290/460 nm) and rhodamine B as the change signal (λex/λem = 550/570 nm). The ratiometric fluorescence detection and dual recognition strategy not only reduce environmental interference but also greatly improve the sensor's anti-interference ability, the obtained imprinting factor was 5.72, and the detection limit as low as 1.8 pmol L^-1. Therefore, the molecular imprinting sensor designed realizes the specific and highly sensitive identification of viruses, which provides theoretical support for the application of molecular imprinting technology in clinical diagnosis of viruses. Graphical abstract Aptamer-molecular imprinting polymer based on metal-organic framework ratiometric fluorescent detect virus.

Enhancing anti-PD-1 Immunotherapy by Nanomicelles Self-Assembled from Multivalent Aptamer Drug Conjugates

A tumor-targeting enhanced chemotherapy, enabled by aptamer-drug conjugate nanomicelles, is reported that boosts antitumor immune responses. Multivalent aptamer drug conjugate (ApMDC), an amphiphilic telodendrimer consisting of a hydrophilic aptamer and a hydrophobic monodendron anchored with four anticancer drugs by acid-labile linkers, was designed and synthesized. By co-self-assembly with an ApMDC analogue, in which aptamer is replaced with polyethylene glycol, the surface aptamer density of these nanomicelles can be screened to reach an optimal complementation between blood circulation and tumor-targeting ability. Optimized nanomicelles can enhance immunogenic cell death of tumor cells, which strikingly augments the tumor-specific immune responses of the checkpoint blockade in immunocompetent tumor-bearing mice. ApMDC nanomicelles represent a robust platform for structure-function optimization of drug conjugates and nanomedicines.

Sensitive 'two-steps' competitive assay for gonadotropin-releasing hormone detection via SPR biosensing and polynorepinephrine-based molecularly imprinted polymer

The work reports an innovative bioassay for the detection of gonadorelin in urine, a gonadotropin-releasing hormone agonist widely used in fertility medicine and to treat hormonal dysfunctions. Gonadorelin is also a synthetic hormone listed by the World Anti-Doping Agency (WADA) and of interest in anti-doping controls. The main novelty relies on the development of a biocompatible, stable, and low-cost biomimetic receptor alternative to classic antibodies. Starting from norepinephrine monomer, a highly selective and sensitive molecularly imprinted polymer (MIP) was developed and optimized for optical real-time and label-free SPR biosensing. The selectivity has been addressed by testing a series of peptides, from high to low similarity, both in terms of molecular weight and primary sequence. Due to the very low molecular weight of gonadorelin (1182 Da), a 'two-steps' competitive assay was developed. Particular attention has been paid to the design of the competitor and its binding affinity constant towards the MIP, being a key step for the success of the competitive strategy. The SPR assay was first optimized in standard conditions and finally applied to untreated urine samples, achieving the sensitivity required by WADA guidelines. The MIP, tested in parallel with a monoclonal antibody, gave comparable results in terms of affinity constants and selectivity towards possible interfering analytes. However, the biomimetic receptor appears clearly superior in terms of sensitivity and reproducibility. This, together with its preparation simplicity, the extremely low-cost of the monomer and its reusability for hundreds of measurements, make polynorepinephrine-based MIPs powerful rivals to immune-based approaches in the near future for similar applications.

Hybrid peptide-molecularly imprinted polymer interface for electrochemical detection of vancomycin in complex matrices

A hybrid recognition interface combining peptide and molecularly imprinted polymer (MIP) was achieved by introducing a vancomycin binding tripeptide in the preparation of MIP to implement high affinity and specificity recognition of vancomycin in complex matrices. The tripeptide that can specifically bind vancomycin was immobilized onto gold nanoparticles (GNPs) deposited on a glassy carbon electrode (GCE) by Au-S bond, and then a controlled electropolymerization of dopamine was carried out to imprint the vancomycin-peptide complex. After removing vancomycin from the polydopamine (PDA), hybrid peptide-MIP cavities containing multiple binding sites for vancomycin in the MIPDA/peptide/GNPs/GCE were obtained. The electrode had better selectivity and higher sensitivity toward vancomycin than either peptide or MIP modified GNPs/GCE, and the limit of quantification was as low as 10 pM by electrochemical impedance spectroscopy. The real samples, including fetal calf serum, probiotic drink and honey spiked with 0.17-2.0 μM vancomycin were analyzed on the MIPDA/peptide/GNPs/GCE, with the recoveries of 92.16-104.67%. The present study provides a sensitive, reliable method for the detection of vancomycin in complex matrices.

Selective recognition of a cyclic peptide hormone in human plasma by hydrazone bond-oriented surface imprinted nanoparticles

As a kind of artificial recognition material, molecularly imprinted polymers (MIPs) offer a promising perspective to be developed as synthetic chemical binders capable of selectively recognize biomacromolecules. However, owing to the large size and conformational flexibility of proteins and peptides, imprinting of these biomacromolecules remains a challenge. Novel imprinting strategies still need exploration for the improvement of recognition performance of MIPs. Herein, we developed a hydrazone bond-oriented surface imprinting strategy for an endogenous peptide hormone, human atrial natriuretic peptide (ANP). Surface-oriented imprinting of peptide via reversible covalent bond anchoring approach increased the orientation homogeneity of imprinted cavities as well as the utility of templates. The prepared nanoparticles exhibited high selectivity and fast recognition kinetics for ANP epitope. The dissociation constant between ANP epitope and MIP was measured as 5.3 μM. The applicability of the material in real samples was verified by the selective magnetic extraction of ANP from human plasma samples. This hydrazone bond-oriented surface imprinting strategy provides an alternative approach for the separation of peptides or proteins in complex bio-samples.

Ultra-durable, multi-template molecularly imprinted polymers for ultrasensitive monitoring and multicomponent quantification of trace sulfa antibiotics

Traditional analysis methods are susceptible to interference caused by the complexity of sample matrices, and detector surface fouling arising from nonspecific adsorption of microorganisms (in biological samples) which leads in particular to a gradual loss of sensitivity. Imprinted materials can be used to effectively reduce interference originating in the matrices. However, the poor reproducibility and multicomponent quantification of trace antibiotics represent significant challenges to the detection process. Meanwhile, the high biological risk presented by bacterial antibiotic immunity and the persistence of antibiotics in foodstuffs, especially meat, both caused by the overuse of sulfonamide antibiotics, remain urgent issues. Here, we present the first example of a method for the accurate quantification of trace sulfa antibiotics (SAs) based on multi-template imprinted polymers (MMIPs). Levels of multiple SAs have been simultaneously successfully quantified by applying MMIP extraction coupled with UPLC-MS/MS analysis. This method shows excellent linearity of detection in the range of 0.1-500 μg L^-1, and ultrasensitivity with low limits of detection of 0.03 μg L^-1. The maximum SA residue recovered from sample tissues by using MMIPs was 5.48 μg g^-1. MMIP-coupled UPLC-MS/MS quantification of SAs is an accurate and repeatable method for the monitoring of SA accumulation in mouse tissue samples. It also provides an effective strategy for the tracking and quantification of drugs in other biological samples.

Boronoisophthalic acid as a novel affinity ligand for the selective capture and release of glycoproteins near physiological pH

Boronic acid-based affinity materials have gained tremendous attention for the selective separation and recognition of cis-diol containing biomolecules. But often, these boronate affinity materials are stuck to some serious issues like high binding pH and weak affinity, especially in the case of glycoproteins. Here in this study, we used 5-boronoisophthlic acid as a novel affinity ligand for the selective capture and release of glycoproteins. The pKa value of 5-boronoisophthalic acid is investigated to be 7.8 which is just closed to physiological pH and is ideally suitable for the fast binding and elution kinetics of glycoproteins to avoid their degradation and deactivation. The affinity ligand is attached to the surface of polymer support using branched polyethyleneimine (PEI) which enhances the binding strength as it has multiple amine groups available for the attachment of 5-boronoisophthalic for synergistic interactions. The resulting affinity material is characterized and packed in a micropipette-tip using hydrophilic melamine foam as a frit to make the separation process smooth, simple, reliable, and robust. This boronic acid-based affinity tip exhibits binding constants for model glycoproteins in the range of 10^-6-10^-7 M, binding capacities in the range of 0.662 μM/g, and selectivity up to 1:1000 (HRP to BSA) under optimized extraction conditions. Finally, the boronic-based affinity tip is successfully applied to selectively capture the glycoproteins from the human milk sample, especially lactoferrin which is highly important in dairy manufacture.

Metal-organic frameworks as advanced materials for sample preparation of bioactive peptides

Development of novel affinity materials and separation techniques is crucial for the progress of modern proteomics and peptidomics. Detection of peptides and proteins from complex matrices still remains a challenging task due to the highly complicated biological composition, low abundance of target molecules, and large dynamic range of proteins. As an emerging area of analytical science, metal-organic framework (MOF)-based separation of proteins and peptides is attracting growing interest. This minireview summarizes the recent advances in MOF-based affinity materials for the sample preparation of proteins and peptides. Some newly emerging MOF nanoreactors for the degradation of peptides and proteins are introduced. An update of MOF-based affinity materials for the isolation of glycopeptides, phosphopeptides and low-abundance endogenous peptides in the last two years is focused on. The separation mechanism is discussed along with the chemical structures of MOFs. Finally, the remaining challenges and future development of MOFs in analyzing peptides and proteins in complicated biological samples are discussed.

Microwave-assisted preparation of a molecularly imprinted monolith combining an imidazolium ionic liquid and POSS for enhanced extraction of baicalin-like compounds in Scutellaria baicalensis by means of in-capillary SPME followed by on-line LC and off-line LC-MS/MS

An imidazolium-type ionic liquid and polyhedral oligomeric silsesquioxane were combined to produce an imprinted monolith in capillary endowed with wide selectivity to enrich baicalin and its analogues for analysis by multidimensional LC systems.

Oriented Immobilization of Protein Templates: A New Trend in Surface Imprinting

In this Review, we have summarized recent trends in protein template imprinting. We emphasized a new trend in surface imprinting, namely, oriented protein immobilization. Site-directed proteins were assembled through specially selected functionalities. These efforts resulted in a preferably oriented homogeneous protein construct with decreased protein conformation changes during imprinting. Moreover, the maximum functionality for protein recognition was utilized. Various strategies were exploited for oriented protein immobilization, including covalent immobilization through a boronic acid group, metal coordinating center, and aptamer-based immobilization. Moreover, we have discussed the involvement of semicovalent as well as covalent imprinting. Interestingly, these approaches provided additional recognition sites in the molecular cavities imprinted. Therefore, these molecular cavities were highly selective, and the binding kinetics was improved.

Label-free SERS detection of Raman-Inactive protein biomarkers by Raman reporter indicator: Toward ultrasensitivity and universality

It is still challenging to sensitively detect protein biomarkers via surface-enhanced Raman scattering (SERS) technique owing to their low Raman activity. SERS tag-based immunoassay is usually applied; however, it is laborious and needs specific antibodies. Herein, an ultrasensitive and universal "Raman indicator" sensing strategy is proposed for protein biomarkers, with the aid of a glass capillary-based molecularly imprinted SERS sensor. The sensor consists of an inner SERS substrate layer for signal enhancement and an outer mussel-inspired polydopamine imprinted layer as a recognition element. Imprinted cavities have two missions: first, selectively capturing the target protein, and second, the only passageway of Raman indicator to access SERS substrate. Specific protein recognition means filling imprinted cavities and blocking Raman indicator flow. Thus, the quantity of captured protein can be reflected by the signal decrease of ultra-Raman active indicator molecule. The capillary sensor exhibited specific and reproducible detection at the level down to 4.1 × 10^-3 μg L^-1, for trypsin enzyme in as-received biological samples without sample preparation. The generality of the mechanism is confirmed by using three different protein models. This platform provides a facile, fast and general route for sensitive SERS detection of Raman inactive biomacromolecules, which offers great promising utility for in situ and fast point-of-care practical bioassay.

A rational route to hybrid aptamer-molecularly imprinted magnetic nanoprobe for recognition of protein biomarkers in human serum

Although antibody has played a great role in highly specific recognition of protein biomarkers, it faces poor stability, reproducibility, high-cost and time-consuming preparation, etc. Here, aptamer and molecularly imprinted polymers (MIPs), both as promising substitutes of antibody, were integrated onto magnetic nanoparticles by Au-S bonds and SiO₂ as imprinted layer for preparing a new nanoprobe. Highly specific and sensitive recognition of different protein biomarkers, such as insulin for diabetes and alpha-fetoprotein (AFP) for hepatic carcinoma, were achieved respectively by the system of combining hybrid aptamer-molecularly imprinted magnetic nanoprobe and mass spectrometry. With the double affinities offered by aptamer-MIPs, insulin can be detected at 0.5 ng mL^-1 in human serum dilution, the equlibrium dissociation constant between nanoprobe and insulin is measured as 23.61 ± 2.27 μM. Likewise, AFP can be sufficiently detected in human saliva dilution from 1000 ng mL^-1 to 20 ng mL^-1, and two patients with hepatic carcinoma are discriminated from healthy person due to the abnormally high expression of AFP in serum.

Epitope-Imprinted Magnetic Nanoparticles as a General Platform for Efficient In Vitro Evolution of Protein-Binding Aptamers

Aptamers are usually created by in vitro selection using a strategy termed systematic evolution of ligands by exponential enrichment (SELEX). Although numerous SELEX alternatives with improved selection efficiency have been developed, the overall success rate of SELEX at present is still not very ideal, which remains a great obstacle to aptamer-based research and application. In this study, an efficient and facile SELEX method was developed for in vitro screening of protein-binding aptamers, applying epitope-imprinted magnetic nanoparticles (MNPs) that exhibit highly favorable binding properties as a general affinity platform. As a proof of the principle, myoglobin (Mb) and β₂-microglobulin were employed as two target proteins. Two satisfied aptamers toward each target protein, with the dissociation constant at the 10^-8 M level and cross-reactivity less than 16.5%, were selected within three rounds, taking only 1 day. A dual aptamer-based fluorescence sandwich assay was constructed using a pair of the selected aptamers. The resulting assay allowed for quantitatively detecting Mb in human serum and distinguishing acute myocardial infarction patients from healthy individuals. The epitope-imprinted MNP-based SELEX is straightforward and generally applicable for a wide range of target proteins, providing a promising aptamer selection tool for aptamer-based research and real-world applications.

Convenient Construction of Orthogonal Dual Aptamer-Based Plasmonic Immunosandwich Assay for Probing Protein Disease Markers in Complex Samples and Living Animals

Aptamers, because of their outstanding merits including simple synthesis and easy modification, have been widely used as antibody alternatives to construct novel immunosandwich assays. Dual aptamer-based sandwich assays exhibit multiple advantages over conventional immunosandwich assays and single aptamer-based sandwich assays. However, their construction is hampered by the limited knowledge of binding orthogonality of aptamers reported in the literature. Herein, we present a new strategy for conveniently constructing an orthogonal dual aptamer-based plasmonic immunosandwich assay (odA-PISA) for probing proteins in complex samples and living animals. An orthogonal aptamer pair was first efficiently selected from the aptamers reported in the literature by affinity capillary electrophoresis. Then, a target protein-capturing gold thin-layer-coated probe and silver nanoparticle-based Raman labeling nanotags were conveniently prepared with the selected aptamers and used to construct the assay. The double aptamers used ensured the specificity, whereas the plasmonic coupling effect between the target-capturing probe and the generated Raman nanotags significantly enhanced the Raman signal intensity, providing high sensitivity. As a proof of principle, alkaline phosphatase (ALP) was used as the target. The constructed odA-PISA exhibited high specificity and high sensitivity toward ALP, giving cross-reactivity ≤ 4.2% and the limit of detection of 3.8 pM (S/N = 4). The quantitative determination of ALP in human serum and probing ALP in tumor-bearing mice were achieved, showing the great application potential of the method. This strategy is widely applicable to other protein disease markers. Therefore, it opened a new access to the construction of sensitive dual aptamer-based sandwich assays for real-world applications, particularly disease diagnosis.

Covalently bonded aptamer-functionalised magnetic mesoporous carbon for high-efficiency chloramphenicol detection

A novel aptamer-modified magnetic mesoporous carbon was prepared to develop a specific and sensitive magnetic solid-phase extraction method through combination with ultra-high performance liquid chromatography-tandem mass spectrometry for the analysis chloramphenicol in complex samples. More specifically, the chloramphenicol aptamer-modified Mg/Al layered double hydroxide magnetic mesoporous carbon was employed as a novel magnetic solid-phase extraction sorbent for analyte enrichment and sample clean-up. The extraction solvent, extraction time, desorption solvent, and desorption time were investigated. It was found that the mesoporous structure and aptamer-based affinity interactions resulted in acceptable selective recognition and a good chemical stability toward trace amounts of chloramphenicol. Upon combination with the ultra-high performance liquid chromatography-tandem mass spectrometry technique, a specific and sensitive recognition method was developed with a low limit of detection (0.94 pmol/L, S/N = 3) for chloramphenicol analysis. The developed method was successfully employed for the determination of chloramphenicol in complex serum, milk powders, fish and chicken samples, giving recoveries of 87.0-107% with relative standard deviations of 3.1-9.7%.