Elegant Chemistry to Directly Anchor Intact Saccharides on Solid Surfaces Used for the Fabrication of Bioactivity-Conserved Saccharide Microarrays

Carbohydrate microarrays fabricated on poly(2-methylacrylic acid)-based substrates for analysis of carbohydrate–protein interactions

Carbohydrate microarrays were fabricated on poly(2-methylacrylic acid) (pMAA)-based substrates. They were used for investigating the specific interactions of polysaccharides and SARS-CoV-2 spike protein.

Janus micromotors for motion-capture-lighting of bacteria

The rapid and sensitive identification of bacteria has long been a major challenge in quality control, environmental monitoring and food safety. In the current study, the "motion-capture-lighting" strategy is proposed via integration of motion-enhanced capture of bacteria and capture-induced fluorescence turn-on of micromotors. Compared with the commonly used microtubes and microparticles, micromotors of flexible fiber rods could offer multiple interactions with the bacterial surface with less steric hindrance. Janus fiber rods (JFRs) are prepared by cryocutting of aligned fibers prepared by side-by-side electrospinning. Catalase is grafted on one side of JFRs to produce oxygen bubbles for propulsion of Janus micromotors (JMs), and mannose is conjugated on the other side for specific recognition of FimH proteins from fimbriae on the bacterial surface. The biphasic Janus structure of JFRs and the separate grafting of catalase and mannose on the opposite sides of JMs are confirmed after fluorescent labelling. JMs with aspect ratios of 0.5, 1, 2 and 4 are fabricated, and the aspect ratios of JMs show significant effects on the tracking trajectories and motion speed. JMs with the aspect ratio of 2 exhibit significantly higher magnitudes of mean square displacement (MSD) with a directional motion trajectory, leading to higher bacterial capture and larger fluorescence intensity changes. The bacteria capture leads to lighting up of JMs due to the aggregation-induced emission (AIE) effect of tetraphenylethene (TPE) derivatives. Under an ultraviolet lamp, the fluorescence color of JM suspensions turns from blue to bluish-green and to green after incubation with E. coli of 102 and 105 CFU mL-1, respectively. The fluorescence intensities of JM suspensions could be fitted to an equation versus bacterial concentrations, and the limit of detection (LOD) was around 45 CFU mL-1 within 1 min. Thus, this study demonstrates a motion-capture-lighting strategy for visual, rapid and real-time detection of bacteria without complicated sample pretreatment, expensive apparatus, and trained operators.

Fabrication of carbohydrate microarrays on poly(2-hydroxyethyl methacrylate)-cyanuric chloride-modified substrates for the analysis of carbohydrate–lectin interactions

The pHEMA polymer provides an anti-fouling surface and the CC linker allows the covalent immobilization of intact carbohydrates.

Graphene oxide aggregate-assisted LDI-MS for the direct analysis of triacylglycerol in complex biological samples

Knowledge of blood triacylglycerol (TAG) species is essential to clarify the physiological functions of individual TAG molecules and also to develop potential biomarkers for related diseases. Commonly, lipid samples prepared by organic liquid-liquid extraction contain complex components, thus cannot be directly characterized by mass spectrometry (MS) and often require an additional purification step. Here, we described a laser desorption ionization - mass spectrometry (LDI-MS) method that utilized aggregated graphene oxide (AGO) as both lipid extractant and MS matrix (AGOLDI-MS), to characterize and quantify plasma TAG species without the use of harmful solvent or complex separation step. We first designed and synthesized the AGO material with a multi-layered sheet structure, which could efficiently break up the structure of lipoproteins, and extract plasma TAGs as solid-phase extraction material. Furthermore, in AGOLDI-MS procedure, the AGO could directly act as matrix and selectively produce the MS signals of TAGs without the interferences of phospholipids, which was hardly achieved by using the routine LDI-MS method based on liquid-liquid extraction and small molecular matrix. We confirmed the suitability of AGOLDI-MS as characterization and quantitative tool for TAG species through studying the analysis performances in TAG standards and real plasma samples. To establish potential utility of our method, we characterized 42 human plasmas from healthy and hyperlipemic donators, indicating that the AGOLDI-MS could not only generate comparable quantitative results of total TAGs to current clinical technology, but also monitor the changes of TAG species between different sample groups. This approach could further characterize the compositions of the fatty acid moieties in even low abundant TAGs by the assistance of tandem MS-MS. This concise, specific, and high-throughput approach will facilitate the rapid and precise characterizations of plasma TAGs, and make the MS approach for TAGs more adaptable for clinical uses.

Immobilization of glycans on solid surfaces for application in glycomics

Carbohydrates are an important class of biomolecules which are involved in a multitude of cellular functions. In the field of glycomics, the structure and function of various carbohydrates, oligosaccharides, glycans and their conjugates are constantly under investigation. In the continuing quest to understand the roles of carbohydrates in their interactions with proteins, immunogens, and other cell-surface carbohydrates, scientists have developed methods for observing the effects of specific saccharide sequences on various cellular components. Carbohydrate immobilization has allowed researchers to study the impact of specific sequences, leading to a deeper understanding of many cellular processes. The goal of this review is to highlight the chemical reactions and interactions that have been used for glycan immobilization.

Sugared biomaterial binding lectins: achievements and perspectives

Lectins, a distinct group of glycan-binding proteins, play a prominent role in the immune system ranging from pathogen recognition and tuning of inflammation to cell adhesion or cellular signalling. The possibilities of their detailed study expanded along with the rapid development of biomaterials in the last decade. The immense knowledge of all aspects of glycan-lectin interactions both in vitro and in vivo may be efficiently used in bioimaging, targeted drug delivery, diagnostic and analytic biological methods. Practically applicable examples comprise photoluminescence and optical biosensors, ingenious three-dimensional carbohydrate microarrays for high-throughput screening, matrices for magnetic resonance imaging, targeted hyperthermal treatment of cancer tissues, selective inhibitors of bacterial toxins and pathogen-recognising lectin receptors, and many others. This review aims to present an up-to-date systematic overview of glycan-decorated biomaterials promising for interactions with lectins, especially those applicable in biology, biotechnology or medicine. The lectins of interest include galectin-1, -3 and -7 participating in tumour progression, bacterial lectins from Pseudomonas aeruginosa (PA-IL), E. coli (Fim-H) and Clostridium botulinum (HA33) or DC-SIGN, receptors of macrophages and dendritic cells. The spectrum of lectin-binding biomaterials covered herein ranges from glycosylated organic structures, calixarene and fullerene cores over glycopeptides and glycoproteins, functionalised carbohydrate scaffolds of cyclodextrin or chitin to self-assembling glycopolymer clusters, gels, micelles and liposomes. Glyconanoparticles, glycan arrays, and other biomaterials with a solid core are described in detail, including inorganic matrices like hydroxyapatite or stainless steel for bioimplants.

Stability of Polydopamine Coatings on Gold Substrates Inspected by Surface Plasmon Resonance Imaging

Polydopamine (PDA)-based surface modification has been used in a variety of fields. However, a vague impression on the stability of PDA still exists due to a lack of systematic studies. To ascertain the issue and make better use of this surface modification method, a technique of surface plasmon resonance imaging (SPRi) was exploited to study the stability of PDA coated on gold surface. The results showed that PDA-coating stability was largely dependent on the pH of aqueous solutions, giving detachment ratios up to 66% and 80% at pH 1.0 and pH 14.0, respectively. However, increasing the ionic strength of aqueous solutions could reduce the detachment of PDA in strong acid and strong alkali conditions. Besides, organic solvents also made a difference on the PDA-coating stability. Among the tested 10 kinds of organic solvents, including n-hexane, toluene, ethyl ether, tetrahydrofuran, ethyl acetate, isopropanol, acetone, acetonitrile, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), DMSO caused the most serious detachment of PDA, up to 56%, followed by DMF with a detachment ratio of 31%. Ultrasonication caused less than 10% detachment of the coated PDA. It should be mentioned that the PDA coatings deposited on gold surface were not detached completely in all the test conditions, even at pH 14.0 (ca. 20% PDA retained). In alkaline conditions, detachment competes with further polymerization, which gave a slight increase of the SPRi signals at pH 9.0-11.0. Based on the obtained information about PDA-coating stability, thickness-controllable and alkali-resistant PDA coatings were prepared. Moreover, the alkali-resistant PDA coatings remained reactive to biomolecules, supporting further functionalization of PDA coatings.

Immune-enrichment of insulin in bio-fluids on gold-nanoparticle decorated target plate and in situ detection by MALDI MS

BACKGROUND

Detection of low-abundance biomarkers using mass spectrometry (MS) is often hampered by non-target molecules in biological fluids. In addition, current procedures for sample preparation increase sample consumption and limit analysis throughput. Here, a simple strategy is proposed to construct an antibody-modified target plate for high-sensitivity MS detection of target markers such as insulin, in biological fluids.

METHODS

The target plate was first modified with gold nanoparticle, and then functionalized with corresponding antibody through chemical conjugation. Clinical specimens were incubated onto these antibody-functionalized target plates, and then subjected to matrix assisted laser desorption ionization mass spectrometry analysis.

RESULTS

Insulin in samples was enriched specifically on this functional plate. The detection just required low-volume samples (lower than 5 µL) and simplified handling process (within 40 min). This method exhibited high sensitivity (limit of detection in standard samples, 0.8 nM) and good linear correlation of MS intensity with insulin concentration (R² = 0.994). More importantly, insulin present in real biological fluids such as human serum and cell lysate could be detected directly by using this functional target plate without additional sample preparations.

CONCLUSIONS

Our method is easy to manipulate, cost-effective, and with a potential to be applied in the field of clinical biomarker detection.

Fabrication of Bio-function-Preserved Saccharide Microarray Chips with Cyanuric Chloride as a Rotatable Linker

Microarray-based saccharide chips possess an inherent property of high throughput but remain hard to use in practice due mainly to their fabrication problems, which have led to many strategies proposed but nearly none can immobilize small saccharides without losing their bio-affinity. Herein introduced is an easy strategy able to directly immobilize all intact saccharides on solid surface with excellent preservation of their molecular recognition ability. The core idea is to anchor a saccharide molecule on a universally rotatable molecular frame to free its spatial adjustment during molecular recognition process. This strategy can simply be realized by use of cyanuric chloride as a rotatable linker which offers three reactive chlorines pointing at 120°. The first chlorine can readily react with hydroxyl groups at only 0-5 °C, enabling one to "plant" a layer of Y-shaped rotatable linker on hydroxyl-terminated surfaces. This facilitates the second chlorine on one of the upper "Y-branch" to react with saccharides at ca. 25 °C, a very convenient room temperature for practical manipulation. The third chlorine can further react with saccharides but at ca. 50 °C which is not too difficult to manipulate but commonly is not utilized. This chemical strategy has been exploited to dot various intact hydroxyl substances on either gold or glass surfaces, and the recognition ability of the anchored saccharides with their right lectins was validated to be well preserved according to surface plasmon resonance and/or laser-induced fluorescence imaging data. Furthermore the method is extendable to amines and other substances able to be hydroxylated and/or aminated.

A universal strategy for direct immobilization of intact bioactivity-conserved carbohydrates on gold nanoparticles

Carbohydrate-functioned gold nanoparticles have been highlighted for sensing complicated carbohydrates but their performance is far from ideal due to the lack of bioaffinity-conserved ways to function the particles with intact carbohydrates.

Genetically engineering of Escherichia coli and immobilization on electrospun fibers for drug delivery purposes

Engineered EcN bacteria were entrapped in core-sheath fibersviacoaxial electrospinning or grafted on the fiber surfaceviacovalent binding or affinity adsorption.

Protecting group-free immobilization of glycans for affinity chromatography using glycosylsulfonohydrazide donors

A variety of applications in glycobiology exploit affinity chromatography through the immobilization of glycans to a solid support. Although several strategies are known, they may provide certain advantages or disadvantages in how the sugar is attached to the affinity matrix. Additionally, the products of some methods may be hard to characterize chemically due to non-specific reactions. The lack of specificity in standard immobilization reactions makes affinity chromatography with expensive oligosaccharides challenging. As a result, methods for specific and efficient immobilization of oligosaccharides remain of interest. Herein, we present a method for the immobilization of saccharides using N'-glycosylsulfonohydrazide (GSH) carbohydrate donors. We have compared GSH immobilization to known strategies, including the use of divinyl sulfone (DVS) and cyanuric chloride (CC), for the generation of affinity matrices. We compared immobilization methods by determining their immobilization efficiency, based on a comparison of the mass of immobilized carbohydrate and the concentration of active binding sites (determined using lectins). Our results indicate that immobilization using GSH donors can provide comparable amounts of carbohydrate epitopes on solid support while consuming almost half of the material required for DVS immobilization. The lectin binding capacity observed for these two methods suggests that GSH immobilization is more efficient. We propose that this method of oligosaccharide immobilization will be an important tool for glycobiologists working with precious glycan samples purified from biological sources.

Electrospun fibrous mats with conjugated tetraphenylethylene and mannose for sensitive turn-on fluorescent sensing of Escherichia coli

A rapid and sensitive detection of microbes in water and biological fluids is a key requirement in water and food safety, environmental monitoring, and clinical diagnosis and treatment. In the current study, electrospun polystyrene-co-maleic anhydride (PSMA) fibers with conjugated mannose and tetraphenylethylene (TPE) were developed for Escherichia coli (E. coli) detection, taking advantage of the high grafting capabilities of ultrafine fibers and the highly porous structure of the fibrous mat to entrap bacterial cells. The specific binding between mannose grafts on PSMA fibers and FimH proteins from the fimbriae of E. coli led to an efficient "turn-on" profile of TPE due to the aggregation-induced emission (AIE) effect. Poly(ethylene glycol) diamine was used as hydrophilic tethers to increase the conformational mobility of mannose grafts, indicating a more sensitive change in the fluorescence intensity against bacteria concentrations, a lower fluorescence background of fibers without bacteria incubation, and a sufficient space for bacteria binding, compared with the use of hexamethylenediamine or poly(ethylene imine) as spacers for mannose grafting. The addition of bovine serum albumin, glucose, or both of them into bacteria suspensions showed no significant changes in the fluorescence intensity of fibrous mats, indicating the anti-interference capability against these proteins and saccharides. An equation was drafted of the fluorescence intensities of fibrous mats against E. coli concentrations ranging from 10(2) to 10(5) CFU/mL. The test strip format was established on mannose-conjugated PSMA fibers after exposure to E. coli of different concentrations, providing a potential tool with a visual sensitivity of bacteria concentrations as low as 10(2) CFU/mL in a matter of minutes. This strategy may offer a capacity to be expanded to exploit electrospun fibrous mats and other carbohydrate-cell interactions for bioanalysis and biosensing of pathogenic bacteria.

Are glycan biosensors an alternative to glycan microarrays?

Complex carbohydrates (glycans) play an important role in nature and study of their interaction with proteins or intact cells can be useful for understanding many physiological and pathological processes. Such interactions have been successfully interrogated in a highly parallel way using glycan microarrays, but this technique has some limitations. Thus, in recent years glycan biosensors in numerous progressive configurations have been developed offering distinct advantages compared to glycan microarrays. Thus, in this review advances achieved in the field of label-free glycan biosensors are discussed.