Recent progress and application of boronate affinity materials in bioanalysis

Automated and ultrasensitive point-of-care glycoprotein detection using boronate-affinity enhanced organic electrochemical transistor patch

Quantifying trace glycoproteins in biofluids requires ultrasensitive components, but feedback is not available in the current portable platforms of point-of-care (POC) diagnosis technologies. A compact and ultrasensitive bioelectrochemical patch was based on boronate-affinity amplified organic electrochemical transistors (BAAOECTs) for POC use was developed to overcome this dilemma. Benefit from the cascading signal enhancement deriving from boronate-affinity targeting multiple regions of glycoprotein and OECTs' inherent signal amplification capability, the BAAOECTs achieved a detection limit of 300 aM within 25 min, displaying about 3 orders of magnitude improvement in sensitivity compared with the commercial electrochemical luminescence (ECL) kit. By using a microfluidic chip, a microcontroller module, and a wireless sensing system, the testing workflows of the above patch was automated, allowing for running the sample-to-answer pipeline even in a resource-limited environment. The reliability of such portable biosensing platform is well recognized in clinical diagnostic applications of heart failure. Overall, the remarkable enhanced sensitivity and automated workflow of BAAOECTs biosensing platform provide a prospective and generalized design policy for expanding the POC diagnosis capabilities of glycoproteins.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Chemoselectivity Strategy Based on B-Label Integrated with Tailored COF for Targeted Metabolomic Analysis of Short-Chain Fatty Acids by UHPLC-MS/MS

Chemoselective extraction strategy is an emerging and powerful means for targeted metabolomics analysis, which allows for the selective identification of biomarkers. Short-chain fatty acids (SCFAs) as functional metabolites for many diseases pose challenges in qualitative and quantitative analyses due to their high polarity and uneven abundance. In our study, we proposed the B-labeled method for the derivatization of SCFAs using easily available 3-aminobenzeneboronic acid as the derivatization reagent, which enables the introduction of recognition unit (boric acid groups). To analyze the B-labeled targeted metabolites accurately, cis-diol-based covalent organic framework (COF) was designed to specifically capture and release target compounds by pH-response borate affinity principle. The COF synthesized by the one-step Schiff base reaction possessed a large surface area (215.77 m2/g), excellent adsorption capacity (774.9 μmol/g), good selectivity, and strong regeneration ability (20 times). Combined with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis, our results indicated that the detection sensitivities of SCFAs increased by 1.2-2500 folds compared with unlabeled method, and the retention time and isomer separation were improved. Using this strategy, we determined twenty-six SCFAs in the serum and urine of rats in four groups about osteoporosis and identified important biomarkers related to the tricarboxylic acid cycle and fatty acid metabolism pathways. In summary, UHPLC-MS/MS based on B-labeled derivatization with tailored COF strategy shows its high selectivity, excellent sensitivity, and good chromatographic behavior and has remarkable application prospect in targeted metabolomics study of biospecimens.

Enrichment of sialic acid-containing casein glycomacropeptide in protein hydrolysates using phenylboronic acid-functionalized mesoporous silica nanoparticles

Glycomacropeptide (GMP) is a bioactive peptide of high value, rich in glycosylation sites and with physiological and dietary therapeutic value. The enrichment and detection of GMP facilitates the accurate quantification and the identification of adulteration of GMP in food products. In GMP, sialic acid is an abundant glycosyl group and is mainly located at the end of the sugar chain. Here, we propose a novel GMP enrichment strategy based on the affinity of sialic acid for phenylboronic acid groups that shift with environmental pH. As an enrichment material, mesoporous silica nanoparticles were progressively modified with aminopropyl and phenylboronic acid groups. The developed material showed excellent selectivity for sialic acid in the presence of galactose and fucose as interferents. The adsorption behavior of sialic acid-containing GMP fits the Langmuir adsorption model, offering a recovery of 71.72% (in terms of sialic acid content) and a GMP relative purity of 0.957. Results from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography confirm that the enriched GMP contains almost no other unexpected proteins and peptides, indicating that the developed strategy holds promise for purifying GMP in various dairy systems.

Preparation of restricted-access boronate affinity adsorbent with excellent anti-protein adsorption property for directly extracting small cis-diol molecules from biological matrices

Boronate affinity adsorbents are of great promise in the enrichment of small cis-diol-containing molecules (cis-diols) from biological matrices. This work develops a restricted-access boronate affinity mesoporous adsorbent, in which boronate sites are only distributed on the internal surface of mesopores and the external surface is a strongly hydrophilic layer. The adsorbent has high binding capacities (30.3 mg g-1, 22.9 mg g-1 and 14.9 mg g-1 for dopamine, catechol and adenosine, respectively) in spite of removal of the boronate sites on the external surface of adsorbent. The adsorption specific of adsorbent towards cis-diols was assessed by dispersive solid-phase extraction (d-SPE) method, and the results show that the adsorbent can selectively extract small cis-diols in the biosamples while exclude proteins completely. Under the optimal d-SPE, the nucleosides and cis-diol drugs in human serum were successfully analyzed by coupling d-SPE with high-performance liquid chromatography. Where, the detection limits are between 6.1 and 13.4 ng mL-1 for four nucleosides, and 24.9 and 34.3 ng mL-1 for two cis-diol drugs; the relative recoveries of all the analytes vary from 84.1% to 110.1% (RSDs <13.4%, n = 6). The results indicate that the adsorbent can directly treat the real biosamples without the necessary protein precipitation steps in advance, thus simplifying the analysis process.

A reactive matrix for in situ chemical derivatisation and specific detection of cis-diol compounds by matrix-assisted laser desorption/ionisation mass spectrometry

Analysis of cis-diol compounds is essential, because they play important roles in cosmetics, food, pharmaceuticals, and living organisms. Herein, we describe the development of a matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) method to analyse cis-diol compounds. In this method, a 6-borono-1-methylquinoline-1-ium (BMQI) reactive matrix was designed for in situ derivatisation of cis-diol compounds based on the boronate affinity interaction between boronic acid and cis-diol groups. Compared to traditional commercial matrices and other boronic acid reagents, BMQI can significantly accelerate the desorption/ionisation process, improve reproducibility, exhibit free background interference, and enhance signal intensity in the analysis of various cis-diol compounds even for amounts as low as 1 nmol. The BMQI-assisted laser desorption/ionisation mass spectrometry (LDI-MS) was successfully applied to the rapid screening and identification of sugar alcohols in different sugar-free foods. This work provides an alternative method to the LDI-MS analysis of cis-diol-containing molecules, and the method can be extended to other food samples and biofluids.

Zwitterion-neutral form equilibria and binding selectivity of pyridineboronic acids

A 11B NMR study of 3-pyridineboronic acid at variable pH in water and 50 vol% aqueous dioxane confirms that the tautomeric equilibrium of the acid is shifted to the zwitterionic form in water, but to the molecular form in the mixed organic solvent. Interactions of 3- and 4-pyridineboronic acids with sialic acid, fructose and several other diols were studied by potentiometric titrations in a wide range of pH in water and water-organic mixtures. In all reaction media the stability of boronate complexes increases upon an increase in pH for neutral low acidic diols such as fructose and glucose but has the opposite trend for highly acidic sialic and lactic acids occurring as anionic species. The selectivity of pyridineboronic acids to sialate anions in an acidic medium is interpreted quantitatively by combining the pH-profiles with Brønsted type correlations for binding constants. In addition, mathematical expressions allowing one to predict the optimum pKa value of a boronic acid for the strongest binding of a given diol (sialic acid or fructose) at a given pH are suggested. The shifts in the tautomeric equilibrium induced by changing the solvent polarity in aqueous-organic mixtures are manifested in the magnitude of relative shifts of pKa of pyridineboronic acids induced by diol complexation.

Benzoxaborole-grafted high molecular weight chitosan from prawn: Synthesis, characterization, target recognition and antibacterial properties

Boronated polymers are in the focus of dynamic functional materials due to the versatility of the B-O interactions and accessibility of precursors. Polysaccharides are highly biocompatible, and therefore, an attractive platform for anchoring boronic acid groups for further bioconjugation of cis-diol containing molecules. We report for the first time the introduction of benzoxaborole by amidation of the amino groups of chitosan improving solubility and introducing cis-diol recognition at physiological pH. The chemical structures and physical properties of the novel chitosan-benzoxaborole (CS-Bx) as well as two phenylboronic derivatives synthesized for comparison, were characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), rheology and optical spectroscopic methods. The novel benzoxaborole grafted chitosan was perfectly solubilized in an aqueous buffer at physiological pH, extending the possibilities of boronated materials derived from polysaccharides. The dynamic covalent interaction between boronated chitosan and model affinity ligands, was studied by means of spectroscopy methods. A glycopolymer derived from poly(isobutylene-alt-anhydride) was also synthesized to study the formation of dynamic assemblies with benzoxaborole-grafted chitosan. A first approximation to apply fluorescence microscale thermophoresis for the interactions of the modified polysaccharide is also discussed. Additionally, the activity of CSBx against bacterial adhesion was studied.

Electrochemical detection of glycoproteins using boronic acid-modified metal-organic frameworks as dual-functional signal reporters

The sensitive analysis of glycoproteins is of great importance for early diagnosis and prognosis of diseases. In this work, a sandwich-type electrochemical aptasensor was developed for the detection of glycoproteins using 4-formylphenylboric acid (FPBA)-modified Cu-based metal-organic frameworks (FPBA-Cu-MOFs) as dual-functional signal probes. The target captured by the aptamer-modified electrode allowed the attachment of FPBA-Cu-MOFs based on the interaction between boronic acid and glycan on glycoproteins. Large numbers of Cu2+ ions in FPBA-Cu-MOFs produced an amplified signal for the direct voltammetric detection of glycoproteins. The electrochemical aptasensor showed a detection limit as low as 6.5 pg mL-1 for prostate specific antigen detection. The method obviates the use of antibody and enzymes for molecular recognition and signal output. The dual-functional MOFs can be extended to the design of other biosensors for the determination of diol-containing biomolecules in clinical diagnosis.

pH-responsive magnetic graphene oxide composite as an adsorbent with high affinity for rapid capture of nucleosides

A novel pH-responsive magnetic graphene oxide composite (MGO@PEI-BA) is proposed for the first time as an adsorbent for the rapid capture and detection of nucleosides (cytidine, uridine, guanosine, and adenosine). The morphology, structure, and magnetic properties of the composite were evaluated using various characterization techniques. The results indicated that the composite was successfully fabricated. A series of parameters that affect extraction and elution were optimized through one-factor-at-a-time and Box-Behnken design of response surface methodology (BBD-RSM). The unique layered structures and easily accessible active sites of the composite facilitated molecular transport, resulting in instantaneous equilibrium of nucleosides adsorption within 5 min. Based on this study, a magnetic dispersive micro-solid-phase extraction (MD-μ-SPE) method assisted by the MGO@PEI-BA was developed in combination with UHPLC-UV analysis for the determination of nucleosides in rat urine. Under the optimum conditions, a wide linear range (10-2000 ng mL-1), good linearity (r > 0.99), low detection limits (1-3 ng mL-1), low relative standard deviations (RSDs ≤ 3.9%), and satisfactory recoveries (82.7-96.3%) were achieved. These results demonstrate that the MGO@PEI-BA is an excellent adsorbent for extracting nucleosides from biological samples.

Biosensors with Boronic Acid-Based Materials as the Recognition Elements and Signal Labels

It is of great importance to have sensitive and accurate detection of cis-diol-containing biologically related substances because of their important functions in the research fields of metabolomics, glycomics, and proteomics. Boronic acids can specifically and reversibly interact with 1,2- or 1,3-diols to form five or six cyclic esters. Based on this unique property, boronic acid-based materials have been used as synthetic receptors for the specific recognition and detection of cis-diol-containing species. This review critically summarizes the recent advances with boronic acid-based materials as recognition elements and signal labels for the detection of cis-diol-containing biological species, including ribonucleic acids, glycans, glycoproteins, bacteria, exosomes, and tumor cells. We also address the challenges and future perspectives for developing versatile boronic acid-based materials with various promising applications.

Hierarchical Macroporous Agarose Materials with Polyethyleneimine-Assisted Multiple Boronate Affinity Binding Sites for the Separation of Neomycin

Quantification of neomycin residues in food samples demands an efficient purification platform. Herein, hierarchical macroporous agarose monoliths with multiple boronate affinity sites were established for selective separation of neomycin. The silica core was synthesized by "one-step" Stöber procedures followed by modification with amino group and incorporation of polyethyleneimine. A versatile macroporous agarose monolith was prepared by emulsification strategies and functionalized with epoxy groups. After introducing polyethyleneimine-integrated silica nanoparticles onto the agarose monolith, fluorophenylboronic acids were immobilized. The physical and chemical characteristics of the composite monolith were analyzed systematically. After optimization, neomycin showed high binding ability of 23.69 mg/g, and the binding capacity can be manipulated by changing the pH and adding monosaccharides. The composite monolith was subsequently utilized to purify neomycin from the spiked model aquatic products followed by high-performance liquid chromatography analysis, which revealed a remarkable neomycin purification effect, indicating the great potential in the separation of neomycin from complicated aquatic products.

Analysis of tri-benzeneboronic esters of monosaccharides formed in aqueous solution by MALDI-TOF MS and DFT calculations

The affinity interactions between boronic acids and sugars have been successfully exploited in many fields, such as the sensing of saccharides, selective enrichment of glycoconjugates, and drug delivery. However, despite multiple techniques having been adopted to investigate the reaction of boronate affinity, the pathway of boronate esters formation under aqueous conditions remains controversial. We report a MALDI-MS approach to investigate the interactions between phenylboronic acid and monosaccharides in neutral aqueous solution by using polylevodopa as an innovative substrate instead of conventional matrix. A series of unusual tri-benzeneboronic esters were then revealed. The mass spectrometry data indicate that they bear a dibenzenepyroboronate cyclic ester moiety with seven-membered ring or eight-membered ring. With the aid of theoretical computations, their most likely geometrical structures are elucidated, and these tri-benzeneboronic esters are proposed to be formed via a boroxine binding monosaccharide pathway. This work provides more insight into the mechanism of boronate affinity interaction between boronic acid and sugars and proves the developed MALDI-MS approach is promising for studying interactions between small molecules.

Dually Amplified Electrochemical Aptasensor for Endotoxin Detection via Target-Assisted Electrochemically Mediated ATRP

As the entering of bacterial endotoxin into blood can cause various life-threatening pathological conditions, the screening and detection of low-abundance endotoxin are of great importance to human health. Taking advantage of signal amplification by target-assisted electrochemically mediated atom transfer radical polymerization (teATRP), we illustrate herein a simple and cost-effective electrochemical aptasensor capable of detecting endotoxin with high sensitivity and selectivity. Specifically, the aptamer receptor was employed for the selective capture of endotoxin, of which the glycan chain was then decorated with ATRP initiators via covalent coupling between the diol sites and phenylboronic acid (PBA) group, followed by the recruitment of ferrocene signal reporters via the grafting of polymer chains through potentiostatic eATRP under ambient temperature. As the glycan chain of endotoxin can be decorated with hundreds of ATRP initiators while the further grafting of polymer chains through eATRP can recruit hundreds to thousands of signal reporters to each initiator-decorated site, the teATRP-based strategy allows for the dual amplification of the detection signal. This dually amplified electrochemical aptasensor has the ability to sensitively and selectively detect endotoxin at a concentration as low as 1.2 fg/mL, and its practical applicability has been further demonstrated using human serum samples. Owing to the simplicity, high efficiency, biocompatibility, and inexpensiveness of the teATRP-based amplification strategy, this electrochemical aptasensor holds great application potential in the sensitive and selective detection of low-abundance endotoxin and many other glycan chain-containing bio-targets.

Molecularly Imprinted Polymers as Synthetic Antibodies for Protein Recognition: The Next Generation

Molecularly imprinted polymers (MIPs) are chemical antibody mimics obtained by nanomoulding the 3D shape and chemical functionalities of a desired target in a synthetic polymer. Consequently, they possess exquisite molecular recognition cavities for binding the target molecule, often with specificity and affinity similar to those of antigen-antibody interactions. Research on MIPs targeting proteins began in the mid-90s, and this review will evaluate the progress made till now, starting from their synthesis in a monolith bulk format through surface imprinting to biocompatible soluble nanogels prepared by solid-phase synthesis. MIPs in the latter format will be discussed more in detail because of their tremendous potential of replacing antibodies in the biomedical domain like in diagnostics and therapeutics, where the workforce of antibodies is concentrated. Emphasis is also put on the development of epitope imprinting, which consists of imprinting a short surface-exposed fragment of a protein, resulting in MIPs capable of selectively recognizing the whole macromolecule, amidst others in complex biological media, on cells or tissues. Thus selecting the 'best' peptide antigen is crucial and in this context a rational approach, inspired from that used to predict peptide immunogens for peptide antibodies, is described for its unambiguous identification.

Boronate Affinity-Amplified Electrochemical Aptasensing of Lipopolysaccharide

As lipopolysaccharide (LPS) is closely associated with sepsis and other life-threatening conditions, the point-of-care (POC) detection of LPS is of significant importance to human health. In this work, we illustrate an electrochemical aptasensor for the POC detection of low-abundance LPS by utilizing boronate affinity (BA) as a simple, efficient, and cost-effective amplification strategy. Briefly, the BA-amplified electrochemical aptasensing of LPS involves the tethering of the aptamer receptors and the BA-mediated direct decoration of LPS with redox signal tags. As the polysaccharide chain of LPS contains hundreds of cis-diol sites, the covalent crosslinking between the phenylboronic acid group and cis-diol sites can be harnessed for the site-specific decoration of each LPS with hundreds of redox signal tags, thereby enabling amplified detection. As it involves only a single-step operation (∼15 min), the BA-mediated signal amplification holds the significant advantages of unrivaled simplicity, rapidness, and cost-effectiveness over the conventional nanomaterial- and enzyme-based strategies. The BA-amplified electrochemical aptasensor has been successfully applied to specifically detect LPS within 45 min, with a detection limit of 0.34 pg/mL. Moreover, the clinical utility has been validated based on LPS detection in complex serum samples. As a proof of concept, a portable device has been developed to showcase the potential applicability of the BA-amplified electrochemical LPS aptasensor in the POC testing. In view of its simplicity, rapidness, and cost-effectiveness, the BA-amplified electrochemical LPS aptasensor holds broad application prospects in the POC testing.

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.

One, two, many: Strategies to alter the number of carbohydrate binding sites of lectins

Carbohydrates are more than an energy-storage. They are ubiquitously found on cells and most proteins, where they encode biological information. Lectins bind these carbohydrates and are essential for translating the encoded information into biological functions and processes. Hundreds of lectins are known, and they are found in all domains of life. For half a century, researchers have been preparing variants of lectins in which the binding sites are varied. In this way, the traits of the lectins such as the affinity, avidity and specificity towards their ligands as well as their biological efficacy were changed. These efforts helped to unravel the biological importance of lectins and resulted in improved variants for biotechnological exploitation and potential medical applications. This review gives an overview on the methods for the preparation of artificial lectins and complexes thereof and how reducing or increasing the number of binding sites affects their function.

Reversible and Highly Ordered Biointerfaces for Efficient Capture and Nondestructive Release of Circulating Tumor Cells

The engineering strategy of artificial biointerfaces is vital for governing their performances in bioanalysis and diagnosis. Highly ordered arrangement of affinity ligands on the interface surface facilitates efficient interaction with target molecules, whereas biointerfaces aimed at drug delivery or rare cell isolation require sophisticated stimuli-response mechanisms. However, it is still challenging to facilely fabricate biointerfaces possessing the two features. Herein, we endow a biointerface with both reversibility and capability to orderly assemble affinity ligands by introducing boronic acid moieties alone. By boronate conjugation via glycosylation sites, avidin was well arranged at the surface of boronic acid-decorated carbon nitride nanosheets for the assembly of biotinylated aptamers. The ordered orientation of aptamers largely relieved their inactivation caused by inter-strand entanglement, facilitating significant increase in cell affinity for the isolation of circulating tumor cells (CTCs). The reversible boronate conjugation also facilitated mild release of CTCs by acid fructose with high cell viability. This engineered interface was capable of isolating CTCs from the peripheral blood of tumor-bearing mice and cancer patients. The successful utilization of the isolated CTCs in the downstream drug susceptibility test and mutation analysis demonstrated the clinical potential of this biointerface for the early diagnosis of cancers and precision medicine.

Veni, Vidi, Vici: Immobilized Peptide-Based Conjugates as Tools for Capture, Analysis, and Transformation

Analysis of peptide biomarkers of pathological states of the organism is often a serious challenge, due to a very complex composition of the cell and insufficient sensitivity of the current analytical methods (including mass spectrometry). One of the possible ways to overcome this problem is sample enrichment by capturing the selected components using a specific solid support. Another option is increasing the detectability of the desired compound by its selective tagging. Appropriately modified and immobilized peptides can be used for these purposes. In addition, they find application in studying the specificity and activity of proteolytic enzymes. Immobilized heterocyclic peptide conjugates may serve as metal ligands, to form complexes used as catalysts or analytical markers. In this review, we describe various applications of immobilized peptides, including selective capturing of cysteine-containing peptides, tagging of the carbonyl compounds to increase the sensitivity of their detection, enrichment of biological samples in deoxyfructosylated peptides, and fishing out of tyrosine–containing peptides by the formation of azo bond. Moreover, the use of the one-bead-one-compound peptide library for the analysis of substrate specificity and activity of caspases is described. Furthermore, the evolution of immobilization from the solid support used in peptide synthesis to nanocarriers is presented. Taken together, the examples presented here demonstrate immobilized peptides as a multifunctional tool, which can be successfully used to solve multiple analytical problems.

HILIC-MS/MS for the Determination of Methylated Adenine Nucleosides in Human Urine

N6-methyl-2'-deoxyadenosine (m6dA) is a newly discovered DNA epigenetic mark in mammals. N6-methyladenosine (m6A), 2'-O-methyladenosine (Am), N6,2'-O-dimethyladenosine (m6Am), and N6,N6-dimethyladenosine (m62A) are common RNA modifications. Previous studies illustrated the associations between the aberrations of these methylated adenosines in nucleic acids and cancer. Herein, we developed Fe3O4/graphene-based magnetic dispersive solid-phase extraction for the enrichment and hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS/MS) for the measurements of m6dA, m6A, Am, m6Am, and m62A in human urine samples. We found that malic acid could improve the HILIC-based separation of these modified nucleosides and markedly enhance the sensitivity of their MS detection. With this method, we accurately quantified the contents of these modified adenine nucleosides in urine samples collected from gastric and colorectal cancer patients as well as healthy controls. We found that, relative to healthy controls, urinary m6dA and Am levels are significantly lower for gastric and colorectal cancer patients; while gastric cancer patients also exhibited lower levels of urinary m6A, the trend was opposite for colorectal cancer patients. Together, we developed a robust analytical method for simultaneous measurements of five methylated adenine nucleosides in human urine, and our results revealed an association between the levels of urinary methylated adenine nucleosides and the occurrence of gastric as well as colorectal cancers, suggesting the potential applications of these modified nucleosides as biomarkers for the early detection of these cancers.

Phenylboronic acid-functionalized cross-linked chitosan magnetic adsorbents for the magnetic solid-phase extraction of benzoylurea pesticides

In this study, a 4-formylphenylboronic acid-modified cross-linked chitosan magnetic nanoparticle (FPBA@CCHS@Fe₃ O₄ ) was fabricated. The synthesized material was utilized as the magnetic solid-phase extraction adsorbent for the enrichment of six benzoylurea pesticides. In addition to B-N coordination, FPBA@CCHS@Fe₃ O₄ interacts with benzoylureas through hydrogen bonds and π-π stacking interaction on account of rich active groups (amino and hydroxyl) and aromatic rings in structure. Compared to traditional extraction methods, less adsorbent (20 mg) and reduced extraction time (3 min) were achieved. The adsorbent also exhibited good reusability (no less than 10 times). Coupled with a high-performance liquid chromatography-diode array detector, satisfactory recoveries (89.1-103.9%) and an acceptable limit of detection (0.2-0.7 μg/L) were obtained. Under optimized conditions, the established method was successfully applied to the tea infusion samples from six major tea categories with acceptable recoveries ranging from 76.8 to 110%, indicating its application potential for the quantitative detection of pesticides in complex matrices.

A Universal Boronate-Affinity Crosslinking-Amplified Dynamic Light Scattering Immunoassay for Point-of-Care Glycoprotein Detection

Herein, we report a universal boronate-affinity crosslinking-amplified dynamic light scattering (DLS) immunoassay for point-of-care (POC) glycoprotein detection in complex samples. This enhanced DLS immunoassay consists of two elements, i.e., antibody-coated magnetic nanoparticles (MNP@mAb) for target capture and DLS signal transduction, and phenylboronic acid-based boronate-affinity materials as crosslinking amplifiers. Upon the addition of targets, glycoproteins are first captured by MNP@mAb and amplified by target-induced crosslinking stemming from the selective binding between the boronic acid ligand and cis-diol-containing glycoprotein, thereby resulting in a remarkably increased DLS signal in the average nanoparticle size. Benefiting from the multivalent binding and fast boronate-affinity reaction between glycoproteins and crosslinkers, the proposed immunosensing strategy has achieved the ultrasensitive and rapid quantitative assay of glycoproteins at the fM level within 15 min. Overall, this work provides a promising and versatile design strategy for extending the DLS technique to detect glycoproteins even in the field or at POC.

Fabrication of hydrophilic zwitterionic microspheres via inverse suspension polymerization for the enrichment of N-glycopeptides

A kind of zwitterionic microsphere was prepared via one-step inverse suspension polymerization employing 3-[N,N-dimethyl-[2-(2-methylpropyl-2-enyloxy) ethyl] ammonium] propane-1-sulfonate (MSA) and N,N-methylene bisacrylamide (BIS) as the precursors. The preparation conditions were carefully investigated and optimized by regulating the content of total monomers, ratio of MSA to BIS, ratio of water to oil, and content of stabilizer. The properties of microspheres were characterized by helium ion microscopy (HIM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), N₂ adsorption/desorption measurement, and water contact angle measurement. The particle size of resulting polydisperse microspheres ranged from 15-25 μm, exhibiting high specific surface area of 138 m² g^-1. Owing to great hydrophilicity, the resulting zwitterionic microspheres could be directly used as hydrophilic interaction chromatography (HILIC) sorbent to enrich glycopeptides from biosamples without any chemical modification. A total of 19 N-glycopeptides was enriched from 10 μg of IgG digest. Besides, up to 383 N-glycopeptides and 224 N-glycosylation sites were unambiguously identified from 2 μL of human serum digest by cLC-MS/MS after enrichment with zwitterionic microspheres, indicating their great enrichment performance to N-glycopeptides. The approach of preparing hydrophilic zwitterionic microspheres contains only one synthesis reaction and is suitable for large-scale preparation.