BSA-Sugar Conjugates as Ideal Building Blocks for SPR-Based Glycan Biosensors

Synthetic pentatrideca-valent triazolylsialoside inhibits influenza virus hemagglutinin/neuraminidase and aggregates virion particles

A synthetic multivalent hemagglutinin and neuraminidase inhibitor was developed by the conjugation of a septa-valent triazolylsialoside to bovine serum albumin using di-(N-succinimidyl) adipate. Matrixassisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) confirmed the attachment of five septa-valent sialyl lactosides to the protein backbone, resulting in a pentatrideca-valent sialyl conjugate. This pseudo-glycoprotein demonstrated a high affinity for hemagglutinin/neuraminidase as well as for the drug-resistant NA mutation on the influenza virus surface due to the cluster effect. The conjugate also exhibited potent antiviral activity against a wide range of virus strains without cytotoxicity at high concentrations. Mechanistic studies revealed that the pentatrideca-valent sialyl conjugate bound strongly to the influenza virion particles through interactions with HA/NA on the virion surfaces. The KD of the interaction was approximately 1 μM, as determined by isothermal calorimetric titration, allowing the capture and trapping of the influenza virions and preventing their further infection of host cells. These findings provide insight into the development of new antiviral agents using multivalent sialic acid clusters.

Probing the interaction of uranyl(VI) complex with bovine serum albumin via in-depth experimental and computational perspectives

Interaction aspects of uranyl(VI) complexes as well as the coordinated ONNO-donor ligand with bovine serum albumin (BSA) were investigated by the fluorescence spectroscopy and computational insights. Under optimal physiological condition, it was observed that there was significant decrease in fluorescence intensity of BSA upon interaction with uranyl(VI) complexes as well as the ligand. The mechanism of interaction between the uranyl(VI) complex and BSA protein was examined by fluorescence measurement. The Stern-Volmer constant, binding affinity, binding constant, standard free energy, and fluorescence lifetime decay profile of BSA in the absence as well as in the presence of uranyl(VI) complex were determined. Furthermore, the conformational binding of uranyl(VI) complexes with BSA protein was explored via molecular docking studies, and confirmed that there is a strong affinity between the Trp-213 residue in the binding pocket of sub-domain IIA and uranyl(VI) complex.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Recent advances in Surface Plasmon Resonance (SPR) biosensors for food analysis: a review

Food safety is the prime area of concern that builds trust. With the prevailing advancements, it has become facile to ensure safety in almost all aspects. Technology has grown from tedious lab techniques to modern chromatographic techniques and immunoassays, progressed with more precise and rapid sensing through the advent of Biosensors. Biosensors provide an automated technology by presenting superfast, nondestructive and cost-effective detection in food analysis. SPR biosensor is an optical biosensor known for its versatility and has wider applications in food testing and analysis. It has an optical system for excitation and interrogation of surface plasmons, and a biomolecular recognition element to detect and seize the target analyte present in a sample. The optical signal detects the binding analyte, on the recognition element, which results in a change in refractive index at the surface and modifies the surface plasmons' propagation constant. SPR aids in label-free detection of various components such as adulterants, antibiotics, biomolecules, genetically modified foods, pesticides, insecticides, herbicides, microorganisms and microbial toxins in food and assures safety. The distinct advancements of SPR in food analysis have been found and discussed. The review also provides knowledge on the advantages and the key challenges encountered by SPR.

Bimetallic Thin-Film Combination of Surface Plasmon Resonance-Based Optical Fiber Cladding with the Polarizing Homodyne Balanced Detection Method and Biomedical Assay Application

In this work, we present the optical birefringence properties of the optical fiber cladding that exists as an evanescent field where the refractive index (RI) of the analysis solution is applied for optical sensor aspiration. To enhance the performance of the sensor, we have investigated the sensor with different thicknesses of TiO₂ coating and bimetallic (Ag-Al) film alloy combinations by thermal evaporation coating. We described a special balanced homodyne detection method for the intensity difference change between the p- and s-polarization lights in the surface plasmon resonance sensing systems, which is strongly determined by the RI of the test medium. The plasmonic optical fiber can measure a very small change of the RI of a glycerol solution, which is a resolution of 4.37 × 10^-8 RI unit (RIU). This method has great advantages of a small-sized optical setup, high stability, high selectivity, easy chemical modification, and low cost. Furthermore, because of the experiment results, we observe that our approach can also eliminate the surrounding noise in the Mach-Zehnder interferometer, which shows the feasibility of this proposed technique. We demonstrate the fluorescence enhancement in detecting the C-reactive protein antibody conjugated with fluorescein isothiocyanate by means of near-field coupling between surface plasmons and fluorophores at spectral channels of emission. This technique can also be extended for application in a biomedical assay and in biochemical science, including molecular diagnostics relying on multichannels that require a small volume of the analyte at each channel which would suffer from the weakness of fluorescence if it were not for the enhancement technology.

Glycan Nanobiosensors

This review paper comprehensively summarizes advances made in the design of glycan nanobiosensors using diverse forms of nanomaterials. In particular, the paper covers the application of gold nanoparticles, quantum dots, magnetic nanoparticles, carbon nanoparticles, hybrid types of nanoparticles, proteins as nanoscaffolds and various nanoscale-based approaches to designing such nanoscale probes. The article covers innovative immobilization strategies for the conjugation of glycans on nanoparticles. Summaries of the detection schemes applied, the analytes detected and the key operational characteristics of such nanobiosensors are provided in the form of tables for each particular type of nanomaterial.

Multivalent glycan arrays

Glycan microarrays have become a powerful technology to study biological processes, such as cell-cell interaction, inflammation, and infections. Yet, several challenges, especially in multivalent display, remain. In this introductory lecture we discuss the state-of-the-art glycan microarray technology, with emphasis on novel approaches to access collections of pure glycans and their immobilization on surfaces. Future directions to mimic the natural glycan presentation on an array format, as well as in situ generation of combinatorial glycan collections, are discussed.

Direct immobilization of sugar probes on bovine serum albumin-coated gold substrate for the development of glycan biosensors

Glycan biosensors based on surface plasmon resonance (SPR) spectroscopy have attracted a great deal of interest due to their potential applications in numerous biological and biomedical fields. Controlled immobilization of sugar probes on a gold substrate is believed to be critical for the performance of these SPR biosensors. In this regard, herein the authors report a direct coupling of mannose probes with bovine serum albumin (BSA) layer on the gold substrate via a squaric acid-mediated reaction under mild conditions, in which the BSA layer provides not only reactive amine groups but also a nonfouling surface property. SPR measurements show that the resultant biosensor with an appropriate amount of mannose probes exhibits high affinity to its corresponding lectin (i.e., concanavalin A) and at the same time could resist nonspecific adsorption of other lectins. The limit of detection of the current SPR biosensor is 1.9 nM. Thus, the squaric acid-mediated immobilization strategy appears to be effective and useful for the fabrication of bioanalytical devices.

Fundamentals and commercial aspects of nanobiosensors in point-of-care clinical diagnostics

Among various problems faced by mankind, health-related concerns are prevailing since long which are commonly found in the form of infectious diseases and different metabolic disorders. The clinical cure and management of such abnormalities are greatly dependent on the availability of their diagnoses. The conventional diagnostics used for such purposes are extremely powerful; however, most of these are limited by time-consuming protocols and require higher volume of test sample, etc. A new evolving technology called "biosensor" in this context shows an enormous potential for an alternative diagnostic device, which constantly compliments the conventional diagnoses. In this review, we have summarized different kinds of biosensors and their fundamental understanding with various state-of-the-art examples. A critical examination of different types of biosensing mechanisms is also reported highlighting the advantages of electrochemical biosensors for its great potentials in next-generation commercially viable modules. In recent years, a number of nanomaterials are extensively used to enhance not only the performance of biosensing mechanism, but also obtain robust, cheap, and fabrication-friendly durable mechanism. Herein, we have summarized the importance of nanomaterials in biosensing mechanism, their syntheses as well as characterization techniques. Subsequently, we have discussed the probe fabrication processes along with various techniques for assessing its analytical performances and potentials for commercial viability.

Multivalent oleanolic acid human serum albumin conjugate as nonglycosylated neomucin for influenza virus capture and entry inhibition

We report the synthesis of multivalent oleanolic acid (OA) protein conjugates as nonglycosylated neomucin mimic for the capture and entry inhibition of influenza viruses. Oleanolic acid derivatives bearing an amine-terminated linker were synthesized by esterification of carboxylic acid and further grafted onto the human serum albumin (HSA) via diethyl squarate method. The binding of hemagglutinin (HA) on the virion surface to the synthetic neomucin was evaluated by hemagglutination inhibition assay. The influenza virus capture ability of the PEGylated OA-HSA conjugate was further investigated by Dynamic Light Scattering (DLS), virus capture assay and Isothermal Titration Calorimeter (ITC) techniques. The pronounced agglutination of viral particles, the high capture efficiency and affinity constant indicate that this neoprotein is comparable to natural glycosylated mucin, suggesting that this material could potentially be used as anti-infective barriers to prevent virus from invading host cells. The study also rationalizes the feasibility of antiviral drug development based on OA or other antiviral small molecules conjugated protein strategies.

Magnetite-Quantum Dot Immunoarray for Plasmon-Coupled-Fluorescence Imaging of Blood Insulin and Glycated Hemoglobin

New microarray chip strategies that are sensitive and selective and that can measure low levels of important biomarkers directly in a blood sample are significant for improving human health by allowing timely diagnosis of an abnormal condition. Herein, we designed an antibody-aptamer immunoarray chip to demonstrate simultaneous measurement of blood insulin and glycated hemoglobin (HbA1c) levels relevant to diabetic and prediabetic disorders using a surface plasmon microarray with validation by fluorescence imaging. To accomplish both surface plasmon and fluorescence imaging on the same sample, we decorated magnetite nanoparticles with quantum dots for covalent immobilization of aptamers for subsequent capture and isolation of the aptamers specific for insulin and HbA1c markers from 20-times diluted whole blood samples. Direct clinically relevant analysis, along with fluorescent imaging of the two markers, was achieved by this new immunoarray platform. The limit of detection was 4 pM for insulin and 1% for HbA1c. Examination of cross-talk using thrombin and platelet-derived growth factor confirmed that the designed immunoarray was highly selective for insulin and HbA1c. Surface plasmon kinetic analysis provided apparent binding constants of 0.24 (±0.08) nM and 37 (±3) μM, respectively, for the binding of insulin and HbA1c onto their surface immobilized monoclonal antibodies. Thus, quantitative imaging of ultralow levels of blood biomarker levels with binding kinetics is uniquely obtained in the designed immunoarray chip. In conclusion, this report demonstrates considerable significance of the developed magnetite-quantum dot-bioconjugate strategy for clinical diagnostics of whole blood biomarkers with characterization of molecular binding interactions.

Modification of bovine serum albumin with aminophenylboronic acid as glycan sensor based on surface plasmon resonance and isothermal titration calorimetry

Aminophenylboronic acid (ABA) modified bovine serum albumin (BSA) was prepared as neolectin and its interactions with oligosaccharides and glycopolymer were studied by surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). The conjugation between the primary amine group of the ABA molecule and lysine residues on BSA was performed with an adipate-based strategy to afford the synthetic neoprotein. The number of ABA molecules loaded to BSA surface was determined by matrix-assisted laser desorption/ionization – time of flight (MALDI-TOF) mass spectrometry. In the BSA-ABA and sugar interaction study, no signal was observed for both the SPR and ITC sensor platform using monosaccharides as the analyte, indicating a weak binding affnity, while the galactose modified polymer showed an enhanced response. The binding affinities of the galactosyl-polymer to BSA-ABA from SPR and ITC data were in the micromolar range.