Photolithographic boronate affinity molecular imprinting: a general and facile approach for glycoprotein imprinting

Rational Design of Highly Selective Sialyllactose-Imprinted Nanogels

We describe a facile method to prepare water-compatible molecularly imprinted polymer nanogels (MIP NGs) as synthetic antibodies against target glycans. Three different phenylboronic acid (PBA) derivatives were explored as monomers for the synthesis of MIP NGs targeting either α2,6- or α2,3-sialyllactose, taken as oversimplified models of cancer-related sT and sTn antigens. Starting from commercially available 3-acrylamidophenylboronic acid, also its 2-substituted isomer and the 5-acrylamido-2-hydroxymethyl cyclic PBA monoester derivative were initially evaluated by NMR studies. Then, a small library of MIP NGs imprinted with the α2,6-linked template was synthesized and tested by mobility shift Affinity Capillary Electrophoresis (msACE), to rapidly assess an affinity ranking. Finally, the best monomer 2-acrylamido PBA was selected for the synthesis of polymers targeting both sialyllactoses. The resulting MIP NGs display an affinity constant≈106 M-1 and selectivity towards imprinted glycans. This general procedure could be applied to any non-modified carbohydrate template possessing a reducing end.

Synthesis of Boronate Affinity-Based Oriented Dummy Template-Imprinted Magnetic Nanomaterials for Rapid and Efficient Solid-Phase Extraction of Ellagic Acid from Food

Ellagic acid (EA) is a natural polyphenol and possesses excellent in vivo bioactivity and antioxidant behaviors, which play an important role in the treatment of oxidative stress-related diseases, such as cancer. Additionally, EA is also known as a skin-whitening ingredient. The content of EA would determine its efficacy. Therefore, the accurate analysis of EA content can provide more information for the scientific consumption of EA-rich foods and cosmetics. Nevertheless, the analysis of EA in these samples is challenging due to the low concentration level and the presence of interfering components with high abundance. Molecularly imprinted polymers are highly efficient pretreatment materials in achieving specific recognition of target molecules. However, the traditional template molecule (EA) could not be absolutely removed. Hence, template leakage continues to occur during the sample preparation process, leading to a lack of accuracy in the quantification of EA in actual samples, particularly for trace analytes. In addition, another drawback of EA as an imprinting template is that EA possesses poor solubility and a high price. Gallic acid (GA), called dummy templates, was employed for the synthesis of MIPs as a solution to these challenges. The approach used in this study was boronate affinity-based oriented surface imprinting. The prepared dummy-imprinted nanoparticles exhibited several significant advantages, such as good specificity, high binding affinity ((4.89 ± 0.46) × 10-5 M), high binding capacity (6.56 ± 0.35 mg/g), fast kinetics (6 min), and low binding pH (pH 5.0) toward EA. The reproducibility of the dummy-imprinted nanoparticles was satisfactory. The dummy-imprinted nanoparticles could still be reused even after six adsorption-desorption cycles. In addition, the recoveries of the proposed method for EA at three spiked levels of analysis in strawberry and pineapple were 91.0-106.8% and 93.8-104.0%, respectively, which indicated the successful application to real samples.

Discrimination of cis-diol-containing molecules using fluorescent boronate affinity probes by principal component analysis

Fluorescent boronate affinity molecules have gained increasing attention in the field of fluorescence sensing and detection due to their selective recognition capability towards cis-diol-containing molecules (cis-diols). However, the conventional fluorescent boronate affinity molecules face a challenge in differentiating the type of cis-diol only by their fluorescence responses. In this study, a simple method was used to discriminate different types of cis-diols, including nucleosides, nucleotides, sugars, and glycoproteins based on the phenylboronic acid-functionalized fluorescent molecules combined with principal component analysis (PCA). Both fluorescent molecules were simply synthesized by the covalent interaction between the amino group in 3-aminophenyl boronic acid and the isothiocyanate group in fluorescein or rhodamine B. In view of their fluorescence-responsive behaviors to these cis-diols directly, it is impossible to differentiate their types even under the optimized experimental conditions. When PCA was employed to treat the fluorescence response data and the quenching constants with their molecular weight, different types of cis-diols can be distinguished successfully. As a result, by integrating the fluorescence response of the boronate affinity probes with PCA, it can greatly improve the specific recognition capability of the boronic acids, providing a simple and direct way to distinguish and identify different types of cis-diols.

Molecularly imprinted thermosensitive probe based on fluorescent advanced glycation end products to detect α-dicarbonyl compounds and inhibit pyrraline formation

A thermal-sensitive molecularly imprinted optosensing probe based on fluorescent advanced glycation end products (AGEs) was prepared by one-pot hydrothermal synthesis. Carbon dots (CDs) derived from fluorescent AGEs were used as the luminous centers, while molecularly imprinted polymers (MIPs) were wrapped outside of the CDs to form specific target recognition sites to highly selectively adsorb the intermediate product of AGEs of 3-deoxyglucosone (3-DG). Thermosensitive N-isopropylacrylamide (NIPAM) was combined with acrylamide (AM) as co-functional monomers, and ethylene glycol dimethacrylate (EGDMA) was chosen as a cross-linker for targeting identification and detection of 3-DG. Under optimal conditions, the fluorescence of MIPs could be gradually quenched with the adsorption of 3-DG on the surface of MIPs in the linear range of 1-160 μg/L, and the detection limit was 0.31 μg/L. The spiked recoveries of MIPs ranged from 82.97 to 109.94% in two milk samples, and the relative standard deviations were all less than 1.8%. In addition, the inhibition rate for non-fluorescent AGEs of pyrraline (PRL) was 23% by adsorbing 3-DG in the simulated milk system of casein and D-glucose, indicating that temperature-responsive MIPs not only could detect the dicarbonyl compound 3-DG quickly and sensitively, but also had an excellent inhibitory effect on AGEs.

Determination of ovalbumin sensing response of protein-imprinted bilayered hydrogel strips via measurement of mechanically driven bending angles based on swelling-induced deformation

Novel detection method has been developed to explore changes in mechanical bending angles on a bilayer of polyethylene terephthalate (PET) and molecularly imprinted polymer (MIP). For an ovalbumin (OVA)-imprinted hydrogel layer, functional monomers were employed to achieve sufficient binding effect in the polymer matrix. The OVA amount added in the MIP precursor solution and the dimensions of OVA-imprinted hydrogel (MIH) strips were controlled to maximize the change in bending angles as an OVA sensing response within a valid detection range. The sensing behaviors were determined by monitoring the difference in the bending angles via protein adsorption based on the swelling-induced deformation of the OVA-extracted hydrogel (E-MIH) strip. The equilibrium adsorption capacity of the E-MIH strip was calculated via the Bradford protein assay. The detection limit, quantification limit, and imprinting factor were calculated. To compare the selectivity coefficients, the adsorption behaviors of three proteins were investigated. Finally, the reusability of the E-MIH strip was explored via repeated adsorption and extraction. Based on the results, the E-MIH strips demonstrated a promising protein sensing platform monitoring mechanical bending angles affected by swelling deformation.

Microfluidic synthesis of pH-responsive molecularly imprinted silica nanospheres for fluorescence sensing target glycoprotein

Here, fluorescent artificial antibodies for sensing ovalbumin in food were synthesized by molecular imprinting technique in a microfluidic reactor. A phenylboronic acid-functionalized silane was employed as the functional monomer to enable the polymer has pH-responsive property. Fluorescent molecularly imprinted polymers (FMIPs) could be produced continuously in a short time. Both fluorescein isothiocyanate (FITC) and rhodamine B isothiocyanate (RB)-based FMIPs can specifically recognize the target ovalbumin, particularly FITC-based FMIP, giving an imprinting factor of 2.5 and cross-reactivity factors of 2.7 (ovotransferrin), 2.8 (β-lactoglobulin) and 3.4 (bovine serum albumin), and was applied for the detection of ovalbumin in milk powder with recovery rates of 93-110%; moreover, the FMIP can be reused at least four times. Such FMIPs have promising future in replacing the fluorophore-labelled antibodies to fabricate fluorescent sensing devices or establish immunoassay methods, which have extra merits of low-cost, high stability and recyclability, easy to carry and store at ambient environments.

A surface molecularly imprinted electrochemical biosensor for the detection of SARS-CoV-2 spike protein by using Cu7S4-Au as built-in probe

Sensitive detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein (S protein) is of significant clinical importance in the diagnosis of COVID-19 pandemic. In this work, a surface molecularly imprinted (SMI) electrochemical biosensor is fabricated for the detection of SARS-CoV-2 S protein. Cu₇S₄-Au is used as the built-in probe and modified on the surface of a screen-printed carbon electrode (SPCE). 4-Mercaptophenylboric acid (4-MPBA) is anchored to the surface of the Cu₇S₄-Au through Au-SH bonds, which can be used for the immobilization of the SARS-CoV-2 S protein template through boronate ester bonds. After that, 3-aminophenylboronic acid (3-APBA) is electropolymerized on the electrode surface and used as the molecularly imprinted polymers (MIPs). The SMI electrochemical biosensor is obtained after the elution of the SARS-CoV-2 S protein template with an acidic solution by the dissociation of the boronate ester bonds, which can be utilized for sensitive detection of the SARS-CoV-2 S protein. The developed SMI electrochemical biosensor displays high specificity, reproducibility and stability, which might be a potential and promising candidate for the clinical diagnosis of COVID-19.

Terminally Phosphorylated Triblock Polyethers Acting Both as Templates and Pore-Forming Agents for Surface Molecular Imprinting of Monoliths Targeting Phosphopeptides

The novel process reported here described the manufacture of monolithic molecularly imprinted polymers (MIPs) using a terminally functionalized block copolymer as the imprinting template and pore-forming agent. The MIPs were prepared through a step-growth polymerization process using a melamine-formaldehyde precondensate in a biphasic solvent system. Despite having a relatively low imprinting factor, the use of MIP monolith in liquid chromatography demonstrated the ability to selectively target desired analytes. An MIP capillary column was able to separate monophosphorylated peptides from a tryptic digest of bovine serum albumin. Multivariate data analysis and modeling of the phosphorylated and nonphosphorylated peptide retention times revealed that the number of phosphorylations was the strongest retention contributor for peptide retention on the monolithic MIP capillary column.

Rational Development of Hypervalent Glycan Shield-Binding Nanoparticles with Broad-Spectrum Inhibition against Fatal Viruses Including SARS-CoV-2 Variants

Infectious virus diseases, particularly coronavirus disease 2019, have posed a severe threat to public health, whereas the developed therapeutic and prophylactic strategies are seriously challenged by viral evolution and mutation. Therefore, broad-spectrum inhibitors of viruses are highly demanded. Herein, an unprecedented antiviral strategy is reported, targeting the viral glycan shields with hypervalent mannose-binding nanoparticles. The nanoparticles exhibit a unique double-punch mechanism, being capable of not only blocking the virus-receptor interaction but also inducing viral aggregation, thereby allowing for inhibiting the virus entry and facilitating the phagocytosis of viruses. The nanoparticles exhibit potent and broad-spectrum antiviral efficacy to multiple pseudoviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its major variants (D614G, N501Y, N439K, Δ69-70, Delta, and Omicron; lentiviruses expressing only the spike proteins), as well as other vital viruses (human immunodeficiency virus 1 and Lassa virus), with apparent EC50 values around the 10^-9  m level. Significantly, the broad-spectrum inhibition of authentic viruses of both wild-type SARS-CoV-2 and Delta variants is confirmed. Therefore, this hypervalent glycan-shield targeting strategy opens new access to broad-spectrum viral inhibition.

A dynamic reversible phenylboronic acid sensor for real-time determination of protein-carbohydrate interactions on living cancer cells

Real-time detection of glycosylation on label-free cancer cell surfaces is of significance for the diagnosis and treatment of cancer. In this work, we have successfully developed a novel dynamic reversible sensor based on pH-sensitive phenylboronic esters to determine in real-time the binding kinetics of protein-carbohydrate interactions on suspension cancer cell surfaces using a quartz crystal microbalance (QCM) technique.

Molecularly imprinted nanoparticles with recognition properties towards diphtheria toxin for ELISA applications

Plastic antibodies can be used for in vitro neutralization of biomacromolecules with different fragments due to their potential in separation, purification, chemical sensor, catalysis and drug production studies. These polymer nanoparticles with binding affinity and selectivity comparable to natural antibodies were prepared using functional monomer synthesis and copolymerization of acrylic monomers via miniemulsion polymerization. As a result, the in vitro cytotoxic effect from diphtheria toxin was reduced by MIPs. In vitro imaging experiments of polymer nanoparticles (plastic antibodies) were performed to examine the interaction of diphtheria toxin with actin filaments, and MIPs inhibited diphtheria toxin damage on actin filaments. The enzyme-linked immunosorbent assay (ELISA) was performed with plastic antibodies labeled with biotin, and it was determined that plastic antibodies could also be used for diagnostic purposes. We report that molecularly imprinted polymers (MIPs), which are biocompatible polymer nanoparticles, can capture and reduce the effect of diphtheria toxic and its fragment A.

Electrochemical Detection of Femtomolar DNA via Boronate Affinity-Mediated Decoration of Polysaccharides with Electroactive Tags

In view of their high efficiency and cost-effectiveness, polymers are of great promise as carriers for signal tags in amplified detection. Herein, we present a polysaccharide-amplified method for the electrochemical detection of a BRCA1 breast cancer gene-derived DNA target at the femtomolar levels. Briefly, peptide nucleic acid (PNA) with a complementary sequence was tethered as the capture probe for the DNA target, to which carboxyl group-containing polysaccharides were then attached via facile phosphate-Zr(IV)-carboxylate crosslinking, followed by the decoration of polysaccharide chains with electroactive ferrocene (Fc) signal tags via affinity coupling between a cis-diol site and phenylboronic acid (PBA) group. As the polysaccharide chain contains hundreds of cis-diol sites, boronate affinity can enable the site-specific decoration of each polysaccharide chain with hundreds of Fc signal tags, efficiently transducing each target capture event into the decoration of many Fc signal tags. As polysaccharides are cheap, renewable, ubiquitous, and biodegradable natural biopolymers, the use of polysaccharides for signal amplification offers the benefits of high efficiency, cost-effectiveness, excellent biocompatibility, and environmental friendliness. The linear range of the polysaccharide-amplified method for DNA detection was demonstrated to be from 10 fM to 10 nM (R² = 0.996), with the detection limit as low as 2.9 fM. The results show that this method can also discriminate single base mismatch with satisfactory selectivity and can be applied to DNA detection in serum samples. In view of these merits, the polysaccharide-amplified PNA-based electrochemical method holds great promise in DNA detection with satisfactory sensitivity and selectivity.

Probing Queuosine Modifications of Transfer RNA in Single Living Cells via Plasmonic Affinity Sandwich Assay

Queuosine (Q) modification on tRNA plays an essential role in protein synthesis, participating in many tRNA functions such as folding, stability, and decoding. Appropriate analytical tools for the measurement of tRNA Q modifications are essential for the exploration of new roles of Q-modified tRNAs and the rationalization of their exact mechanisms. However, conventional methods for Q modification analysis suffer from apparent disadvantages, such as destructive cells, tedious procedure, and low sensitivity, which much hamper in-depth studies of Q modification-related biological questions. In this study, we developed a new approach called plasmonic affinity sandwich assay that allows for facile and sensitive determination of Q-modified tRNAs in single living cells. This method relies on the combination of plasmon-enhanced Raman scattering detection, base-paring affinity in-cell microextraction, and a set of boronate affinity and molecularly imprinted labeling nanotags for selective recognition of individual Q modifications, including queuosine, galactosyl queuosine (Gal-Q), and mannosyl queuosine (Man-Q). The developed method exhibited high affinity extraction and high specificity recognition. It allowed for the measurement of tRNA Q modifications in not only Q-rich cultured tumor cells but also Q-deficient primary tumor cells. Usefulness of this approach for investigation of the change of the Q modification level in single cells under oxidative stress was demonstrated. Because of its significant advantages over conventional methods, this approach provides a promising analytical tool for the exploration of more roles of Q-modified tRNAs and elucidation of their mechanisms.

Molecularly imprinted polymers for selective extraction/microextraction of cancer biomarkers: A review

Over recent years, great efforts have been extensively documented in top scientific journals on the development of methods for early diagnosis, treatment, and monitoring of cancers which are prevalent critical diseases with a high mortality rate among men and women. The determination of cancer biomarkers using different optimum methodologies is one of the finest options for achieving these goals with more precision, speed, and at a lower cost than traditional clinical procedures. In this regard, while focusing on specific biomarkers, molecularly imprinted technology has enabled novel diagnostic techniques for a variety of diseases. Due to the well-known advantages of molecularly imprinted polymers (MIPs), this review focuses on the current trends of MIPs-based extraction/microextraction methods, specifically targeting cancer biomarkers from various matrices. These optimized methods have demonstrated high selectivity, accuracy, sorbent reusability, extraction recovery, and low limits of detection and quantification for a variety of cancer biomarkers, which are a powerful tool to provide early diagnosis, prognosis, and treatment monitoring, with potential clinical application expected soon. This review highlights the key progress, specific modifications, and strategies used for MIP synthesis. The future perspectives for cancer biomarkers purification and determination by fabricating MIP-based techniques are also discussed.

Antibiotic-Like Activity of Atomic Layer Boron Nitride for Combating Resistant Bacteria

The global rise of antimicrobial resistance (AMR) that increasingly invalidates conventional antibiotics has become a huge threat to human health. Although nanosized antibacterial agents have been extensively explored, they cannot sufficiently discriminate between microbes and mammals, which necessitates the exploration of other antibiotic-like candidates for clinical uses. Herein, two-dimensional boron nitride (BN) nanosheets are reported to exhibit antibiotic-like activity to AMR bacteria. Interestingly, BN nanosheets had AMR-independent antibacterial activity without triggering secondary resistance in long-term use and displayed excellent biocompatibility in mammals. They could target key surface proteins (e.g., FtsP, EnvC, TolB) in cell division, resulting in impairment of Z-ring constriction for inhibition of bacteria growth. Notably, BN nanosheets had potent antibacterial effects in a lung infection model by P. aeruginosa (AMR), displaying a 2-fold increment of survival rate. Overall, these results suggested that BN nanosheets could be a promising nano-antibiotic to combat resistant bacteria and prevent AMR evolution.

Recent advances in protein-imprinted polymers: synthesis, applications and challenges

The molecular imprinting technique (MIT), also described as the "lock to key" method, has been demonstrated as an effective tool for the creation of synthetic polymers with antibody-like sites to specifically recognize target molecules. To date, most successful molecular imprinting researches were limited to small molecules (<1500 Da); biomacromolecule (especially protein) imprinting remains a serious challenge due to their large size, chemical and structural complexity, and environmental instability. Nevertheless, protein imprinting has achieved some significant breakthroughs in imprinting methods and applications over the past decade. Some special protein-imprinted materials with outstanding properties have been developed and exhibited excellent potential in several advanced fields such as separation and purification, proteomics, biomarker detection, bioimaging and therapy. In this review, we critically and comprehensively surveyed the recent advances in protein imprinting, particularly emphasizing the significant progress in imprinting methods and highlighted applications. Finally, we summarize the major challenges remaining in protein imprinting and propose its development direction in the near future.

Hydrophilic magnetic covalent triazine frameworks for differential N-glycopeptides enrichment in breast cancer plasma membranes

Alterations in plasma membrane glycoproteins (PMGs) have been identified as a hallmark of cancer. The comparison and identification of differential PMGs is significant for finding new markers and understanding pathological processes. However, the research on PMGs is often constrained by the low abundance and the disturbance of abundant endogenous biomolecules during direct analysis. Here, we report a bottom-up strategy to enrich the PMGs of breast cancer cells using hydrophilic magnetic covalent triazine frameworks (CTFs). A total of 972 N-glycopeptides and 1006 N-glycosites belonging to 526 N-glycoproteins were enriched in MCF-10A plasma membrane tryptic digest by magnetic CTFs. And 680 N-glycopeptides and 806 N-glycosites belonging to 443 N-glycoproteins were enriched in SK-BR-3 plasma membrane tryptic digest. Furthermore, comparative analysis was performed based on gene ontology to verify breast cancer biomarkers (SUSD2 and ALCAM) and differential PMGs' function. This strategy which systematically integrates efficient enrichment of differential PMGs and in-depth comparative analysis has great potential for helping illuminate the atlas of breast cancer PMGs and the causes of tumor metastasis.

Construction of DNA ligase-mimicking nanozymes via molecular imprinting

Enzyme mimics are of significant importance due to their facile preparation, low cost and stability to rigorous environment. Molecularly imprinted polymers (MIPs) have been important synthetic mimics of enzymes. However,...

Molecularly Imprinted Polymers Outperform Lectin Counterparts and Enable More Precise Cancer Diagnosis

Accurately analysing the particular glycosylation status of protein biomarkers is of significant importance in the precise, early diagnosis of cancer. Existing methods mainly rely on the use of antibodies and lectins. However, due to the macroscopic and microscopic heterogeneity of glycans, precise analysis of glycosylation status still remains a challenge. Molecularly imprinted polymers (MIPs), as a synthetic alternative to antibodies or lectins, may provide new solutions but have not yet been explored. Herein, we report an appealing strategy called triple MIP-based plasmonic immunosandwich assay (triMIP-PISA) for precise cancer diagnosis in terms of the relative glycosylation expression of glycoprotein biomarkers. As proof of the principle, alpha fetoprotein (AFP), which has been used as a clinical biomarker for early detection of hepatocellular carcinoma (HCC), as well as its Lens culinaris agglutinin (LCA)-reactive fraction (AFP-L3), which is mainly composed of core-fucosylated glycans, were used as two target proteoforms to test in this study. Using two MIPs that can specifically recognize the peptide sequence of AFP as well as a fucose-imprinted MIP that can specifically recognize the AFP-L3 fraction, facile simultaneous plasmon-enhanced Raman detection of AFP and AFP-L3 in serum was achieved, which allowed HCC patients to be distinguished from healthy individuals. Due to the excellent recognition properties of the MIPs that are comparable to those of antibodies and superior to those of lectins, our triMIP-PISA method exhibited improved precision as compared with an antibody plus lectin-based immunofluorescence assay. Thus, this strategy opened a new avenue towards the precise diagnosis of cancer.

A triple molecularly imprinted polymer (MIP)-based plasmonic assay was developed for precise cancer diagnosis in terms of the relative glycosylation expression of glycoprotein biomarkers.

A microfluidic approach for rapid and continuous synthesis of glycoprotein-imprinted nanospheres

Many strategies have been reported for the preparation of glycoproteins imprinted polymers, but they take a long time and cannot produce imprinted polymers continuously. Herein, a microfluidic synthesis approach was developed to make glycoproteins imprinted nanospheres rapidly and continuously. By using ovalbumin as a model template and a synthesized phenylboronic acid-tagged silane reagent as the functional monomer, the synthetic conditions including the polymerization contents, the flow rate and the microfluidic reactor size were comprehensively studied. Under the optimized conditions, the glycoprotein imprinted nanospheres could be synthesized rapidly (<2 h), and exhibited high specificity with cross-reactivity factors of 1.3 (ovotransferrin), +∞ (horse-radish peroxidase), 5.1 (β-lactoglobulin) and 101 (bovine serum albumin). The kinetic and equilibrium binding behaviors, reusability and potential applications of the glycoprotein imprinted nanosphere were investigated. Such microfluidic synthesis strategy can be easily extended to produce other target glycoproteins imprinted nanospheres, as well as non-glycoproteins by using suitable functional monomers.

A review on recent advances in the enrichment of glycopeptides and glycoproteins by liquid chromatographic methods: 2016-Present

Among various protein post-translational modifications (PTMs), glycosylation has received special attention due to its immense role in molecular interactions, cellular signal transduction, immune response, etc. Aberration in glycan moieties of a glycoprotein is associated with cancer, diabetes, and bacterial and viral infections. In biofluids (plasma, saliva, urine, milk, etc.), glycoproteins are low in abundance and are masked by the presence of high abundant proteins. Hence, prior to their identification using mass spectrometry methods, liquid chromatography (LC)-based approaches were widely used. A general enrichment strategy involves a protein digestion step, followed by LC-based enrichment and desorption of glycopeptides, and enzymatic excision of the glycans. The focus of this review article is to highlight the articles published since 2016 that dealt with different LC-based approaches for glycopeptide and glycoprotein enrichment. The preparation of stationary phases, their surface activation, and ligand immobilization strategies have been discussed in detail. Finally, the major developments and future trends in the field have been summarized.

Emerging Antibacterial Strategies with Application of Targeting Drug Delivery System and Combined Treatment

At present, some bacteria have developed significant resistance to almost all available antibiotics. One of the reasons that cannot be ignored is long-term exposure of bacteria to the sub-minimum inhibitory concentration (MIC) of antibiotics. Therefore, it is necessary to develop a targeted antibiotic delivery system to improve drug delivery behavior, in order to delay the generation of bacterial drug resistance. In recent years, with the continuous development of nanotechnology, various types of nanocarriers that respond to the infection microenvironment, targeting specific bacterial targets, and targeting infected cells, and so on, are gradually being used in the delivery of antibacterial agents to increase the concentration of drugs at the site of infection and reduce the side effects of drugs in normal tissues. Here, this article describes in detail the latest research progress on nanocarriers for antimicrobial, and commonly used targeted antimicrobial strategies. The advantages of the combination of nanotechnology and targeting strategies in combating bacterial infections are highlighted in this review, and the upcoming opportunities and remaining challenges in this field are rationally prospected.

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.

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.

Molecular Boronic Acid-Based Saccharide Sensors

Boronic acids can reversibly bind diols, a molecular feature that is ubiquitous within saccharides, leading to their use in the design and implementation of sensors for numerous saccharide species. There is a growing understanding of the importance of saccharides in many biological processes and systems; while saccharide or carbohydrate sensing in medicine is most often associated with detection of glucose in diabetes patients, saccharides have proven to be relevant in a range of disease states. Herein the relevance of carbohydrate sensing for biomedical applications is explored, and this review seeks to outline how the complexity of saccharides presents a challenge for the development of selective sensors and describes efforts that have been made to understand the underpinning fluorescence and binding mechanisms of these systems, before outlining examples of how researchers have used this knowledge to develop ever more selective receptors.

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.

Advances in epitope molecularly imprinted polymers for protein detection: a review

Epitope molecularly imprinted polymers (EMIPs) are novel imprinted materials using short characteristic peptides as templates rather than entire proteins. To be specific, the amino acid sequence of the template peptide is the same as an exposed N- or C-terminus of a target protein, or its amino acid composition and sequence replicate a similar conformational arrangement as the same amino acid residues on the surface of the target protein. EMIPs have a good application prospect in protein research. Herein, we focus on classification of epitope imprinting techniques, methods of epitope immobilization on matrix materials including boronate affinity immobilization, covalent bonding immobilization, physical adsorption immobilization and metal ion chelation immobilization, and application of EMIPs in peptides, proteins, target imaging and target therapy fields. Finally, the main problems and future development are summarized.

A molecularly imprinted polymer-based potentiometric sensor based on covalent recognition for the determination of dopamine

Polymeric membrane potentiometric sensors based on molecularly imprinted polymers (MIPs) have been successfully designed for the detection of organic compounds both in ionic and neutral forms. However, most of these sensors are based on the non-covalent recognition interactions between the functional groups of the MIP in the polymeric sensing membrane and the target. These weak non-covalent interactions are unfavorable for the detection of hydrophilic organic compounds (e.g., dopamine). Herein novel MIP potentiometric sensor based covalent recognition for the determination of protonated dopamine is described. Uniform-sized boronate-based MIP beads are utilized as the recognition receptors. These receptors can covalently bind with dopamine with a cis-diol group to form a five-membered cyclic ester and thus provide a higher affinity because of the stronger nature of the covalent bonds. It has been found that the proposed electrode shows an excellent sensitivity towards dopamine with a detection limit of 2.1 μM, which could satisfy the needs for in vivo analysis of dopamine in the brain of living animals. We believe that the covalent recognition MIP-based sensing strategy provides an appealing way to design MIP-based electrochemical and optical sensors with excellent sensing properties.

Magnetic imprinted nanoparticles with synergistic tailoring of covalent and non-covalent interactions for purification and detection of procyanidin B2

A synergistic imprinting strategy of covalent and non-covalent interactions is proposed to prepare magnetic molecularly imprinted polymers (DI-MMIPs) for highly selective separation of procyanidin B2 (PC) from grape seed samples. Dopamine and 3-amino-phenylboronic acid as cooperative functional monomers endow the imprinted sites with synergistic tailoring. Benefiting from the synergistic effect, the DI-MMIPs exhibit enhanced imprinting performance with high adsorption capacity (27.71 mg g^-1), fast kinetic equilibrium time (within 30 min), outstanding selectivity (IF = 5.8, SC > 3.2), and satisfactory regeneration ability. In addition, the DI-MMIPs possess good magnetism, uniform morphology with typical core-shell structure, and stable crystallization. Furthermore, the established DI-MMIPs coupled with HPLC-UV (~ 280 nm) method has a wide linearity range of 0.05-200 μg mL^-1 with correlation coefficient of 0.9997, high recoveries (> 93.1%) with RSDs from 2.9 to 5.5%, and low LOD (0.0008 μg mL^-1). Consequently, this work provides an effective and easily tailored way to fabricate magnetic imprinted nanomaterials with both rapid recognition rate and high selectivity and thus holds great promise to realize the extraction and detection of PC from real samples.

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.

Regioselective SN2-Type Reaction for the Oriented and Irreversible Immobilization of Antibodies to a Glass Surface Assisted by Boronate Formation

Antibodies have exquisite specificities for molecular recognition, which have led to their incorporation into array sensors that are crucial for research, diagnostic, and therapeutic applications. Many of these platforms rely heavily on surface-bound reactive groups to covalently tether antibodies to solid substrates; however, this strategy is hindered by a lack of orientation control over antibody immobilization. Here, we report a mild electrophilic phenylsulfonate (tosylate) ester-containing boronic acid affinity ligand for attaching antibodies to glass slides. A high level of antibody coupling located near the Fc region of the boronated antibody complex could be achieved by the proximal nucleophilic amino acid driven substitution reaction at the phenylsulfonate center. This enabled the full-length antibodies to be permanently tethered onto surfaces in an oriented manner. The advantages of this strategy were demonstrated through the individual and multiplex detection of protein and serum biomarkers. This strategy not only confers stability to the immobilized antibodies but also presents a different direction for the irreversible attachment of antibodies to solid supports in an orientation-controlled way.

Fluorescent molecularly imprinted nanoparticles with boronate affinity for selective glycoprotein detection

Specific recognition and sensing of glycoproteins are of great importance in clinical diagnostics considering their frequent utilization as biomarkers and therapeutic targets. In this work, a biomimetic fluorescent sensor for the selective and sensitive detection of glycoprotein was developed, which was based on late-model boronate fluorescent molecularly imprinted nanoparticles (B-FMIP NPs). The B-FMIP NPs were fabricated via the macromolecular assembly of a fluorescent photo-crosslinkable amphiphilic copolymer containing boronic acid with glycoprotein in aqueous solution and in situ photo-crosslinking. Due to the synergism of boronate affinity and the molecular imprinting effect, the resultant B-FMIP NPs demonstrated specific recognition and remarkable selectivity toward the template glycoprotein (ovalbumin, OVA) with a high imprinted factor (α) of 6.0 and gave rise to obvious fluorescence quenching after binding with OVA in water. Under optimized experimental conditions, the as-prepared B-FMIP NPs exhibited linearity over the OVA concentration range of 10^-13 to 10^-3 mg mL^-1 with a detection limit of 3.3 × 10^-14 mg mL^-1, as well as a rapid response time (about 10 min), which was superior to that of other previously reported OVA sensors. Finally, these B-FMIP NPs have been applied for the determination of OVA in real samples.

Targeting Oligosaccharides and Glycoconjugates Using Superselective Binding Scaffolds

Recognition of oligosaccharides is associated with very limited specificity due to their strong solvation in water and the high degree of subtle structural variations between them. Here, oligosaccharide recognition sites are created on material surfaces with unmatched, binary on-off binding behavior, sharply discriminating a target oligosaccharide over closely related carbohydrate structures. The basis for the superselective binding behavior relies on the highly efficient generation of a pure, high order complex of the oligosaccharide target with synthetic carbohydrate receptor sites, in which the spatial arrangement of the multiple receptors in the complex is preserved upon material surface incorporation. The synthetic binding scaffolds can easily be tailored to recognize different oligosaccharides and glycoconjugates, opening up a realm of possibilities for their use in a wide field of applications, ranging from life sciences to diagnostics.

One-step synthesis of hydrophilic microspheres for highly selective enrichment of N-linked glycopeptides

A polyacrylamide-based hydrophilic microsphere with a lot of hydroxyl groups on surface (PAM-OH HMS) was prepared in one step. The synthetic process was simple reverse suspension polymerization without any chemical derivation or grafting steps. The properties of obtained HMS were characterized by scanning electron microscopy (SEM), static water contact angle measurement, and FT-IR. The abundant hydroxyl groups on the surface make the material highly good hydrophilic and thus it was utilized for N-glycopeptides enrichment. The enrichment efficiency of PAM-OH HMSs was demonstrated by capturing N-linked glycopeptides from tryptic digest of human immunoglobulin G (IgG). The detection sensitivity for N-glycopeptides identification by MALDI-TOF MS was as low as 10 fmol for tryptic digest of standard human IgG. The selectivity of the HMS towards N-glycopeptides had almost no decrease when the molar ratio of BSA tryptic digest to IgG tryptic digest was increased from 10:1 to 100:1. Moreover, in the LC-MS/MS analysis of real biological sample, a total of 344 unique N-glycosites in 598 unique N-glycopeptides from 172 N-glycoproteins were identified from 2 μL human serum after deglycosylated by PNGase F, and 825 intact N-glycopeptides with different types of glycoform were detected when directly analyzed the N-glycopeptides enriched by PAM-OH HMS. To show the potential of our material in solving real biological issues, N-glycopeptides in the serum from hepatocelluar carcinoma (HCC) patient and health control were enriched and quantified. All the experiments demonstrated that this polyacrylamide-based hydrophilic microsphere shows a great potential to enrich the low-abundance N-glycopeptides for glycoproteome analysis of real complicated biological samples.

Selective extraction of myoglobin from human serum with antibody-biomimetic magnetic nanoparticles

Myoglobin (Mb) is an ideal biochemical marker for the diagnosis of certain diseases caused by damage to heart muscle or skeletal muscle. Nevertheless, serum myoglobin levels are usually very low while the interference components in real sample are extremely abundent. Hence, it is of great clinical significance to establish an effective method for Mb targeting. To obtain desired selectivity, targeting biomolecules like antibody and aptamer are essential to 'the state of the art'. However, such biomolecules suffer from many disadvantages, such as hard to prepare, susceptible to protease degradation, and high cost. Thus, novel alternatives that can overcome these issues are highly desirable. Herein, we pioneered a template-anchored controllable surface imprinting strategy for selective extraction of Mb from human serum via combining with facile magnetic separation of magnetic nanoparticles (MNPs). Mb-imprinted MNPs, as antibody-biomimetic materials, were prepared using amino group-modified MNPs as substrates and water-soluble self-polymerizable dopamine as imprinting monomer. The optimized imprinting time was 70 min, giving an optimal performance with high practical imprinting efficiency (up to 41%), high imprinting factor (4.2), high binding affinity (K_d=(2.05 ± 0.09) × 10^-5 M), as well as excellent recognition selectivity. Moreover, compared to bare MNPs, Mb-imprinted MNPs possessed markedly better pH tolerance. Finally, the selective extraction of Mb from human serum sample by Mb-imprinted MNPs was experimentally confirmed and the recoveries of Mb in spiked serum ranged from (91.12 ± 6.81)% to (107.99 ± 7.76)%, indicating that the Mb-imprinted MNPs could be competent for the selective analysis of Mb in real bio-samples like human serum with high precision and reliability.

Solid-Contact Potentiometric Sensors Based on Stimulus-Responsive Imprinted Polymers for Reversible Detection of Neutral Dopamine

Herein, we present for the first time a novel potentiometric sensor based on the stimulus-responsive molecularly imprinted polymer (MIP) as a selective receptor for neutral dopamine determination. This smart receptor can change its capabilities to recognize according to external environmental stimuli. Therefore, MIP-binding sites can be regenerated in the polymeric membrane by stimulating with stimulus after each measurement. Based on this effect, reversible detection of the analyte via potentiometric transduction can be achieved. MIPs based on 4-vinylphenylboronic acid as the functional monomer were prepared as the selective receptor. This monomer can successfully bind to dopamine via covalent binding and forming a five- or six-membered cyclic ester in a weakly alkaline aqueous solution. In acidic medium, the produced ester dissociates and regenerates new binding sites in the polymeric membrane. The proposed smart sensor exhibited fast response and good sensitivity towards dopamine with a limit of detection 0.15 µM over the linear range 0.2–10 µM. The selectivity pattern of the proposed ISEs was also evaluated and revealed an enhanced selectivity towards dopamine over several phenolic compounds. Constant-current chronopotentiometry is used for evaluating the short-term potential stability of the proposed ISEs. The obtained results confirm that the stimulus-responsive MIPs provide an attractive way towards reversible MIP-based electrochemical sensors designation.

Oriented boronate affinity-imprinted inverse opal hydrogel for glycoprotein assay via colorimetry

A biomimetic antibody is described for colorimetric determination of glycoprotein, and horseradish peroxidase (HRP) is used as model analyte. Use is made of oriented surface imprinted inverse opal hydrogel particles functionalized with phenylboronic acid. The inverse opal hydrogel particles were negatively replicated from silica colloidal crystal beads (SCCBs), so that they were endowed with larger specific surface area than the bulk structure. Benefit from that, there were abundant surface molecularly imprinting sites in the hydrogel particles. Because the imprinting sites match the structure of the template molecules, they can recognize HRP with high selectivity and sensitivity. The recognized glycoprotein was bonded with the phenylboronic acid within the sites. The bonded HRP was determined by colorimetry of 3, 3', 5, 5'-tetramethylbenzidine (TMB) single-component solution at 450 nm, and it shows a 16.03 imprinting factor under optimized conditions. Alpha-fetoprotein (AFP) was also investigated and demostrated the value of this strategy in practical applications. The results show that the absorbance increases linearly in the 1-50 ng mL^-1 AFP concentration range and has a 1.32 ng mL^-1 detection limit. The assay of human serum was realized by the standard addition method. This strategy is promising to open new horizons for glycoprotein assay. Graphical abstract Schematic representation of the preparation of oriented boronate affinity-imprinted inverse opal hydrogel particles for glycoprotein assay.