The investigation of recognition interaction between phenylboronate monolayer and glycated hemoglobin using surface plasmon resonance

Emerging biosensor probes for glycated hemoglobin (HbA1c) detection

Glycated hemoglobin (HbA1c), originating from the non-enzymatic glycosylation of βVal1 residues in hemoglobin (Hb), is an essential biomarker indicating average blood glucose levels over a period of 2 to 3 months without external environmental disturbances, thereby serving as the gold standard in the management of diabetes instead of blood glucose testing. The emergence of HbA1c biosensors presents affordable, readily available options for glycemic monitoring, offering significant benefits to small-scale laboratories and clinics. Utilizing nanomaterials coupled with high-specificity probes as integral components for recognition, labeling, and signal transduction, these sensors demonstrate exceptional sensitivity and selectivity in HbA1c detection. This review mainly focuses on the emerging probes and strategies integral to HbA1c sensor development. We discussed the advantages and limitations of various probes in sensor construction as well as recent advances in diverse sensing strategies for HbA1c measurement and their potential clinical applications, highlighting the critical gaps in current technologies and future needs in this evolving field.

Analyzation of the binding mechanism and the isoelectric point of glycated albumin with self-assembled, aptamer-conjugated films by using surface plasmon resonance

Glycated albumin(GA), a biomarker which has great potential to replace glycated hemoglobin in the diagnosis and treatment of diabetes, is being extensively studied by scientists, especially in preventive medicine. Aptamers, as novel probes, have attracted much attention due to their high specificity, wide storage conditions, and simple preparation. However, the interaction mechanism between GA and its aptamer is still unclear, hindering the progress of diabetic aptamer sensors into clinical testing. In this study, the interaction mechanism between GA and its aptamer was evaluated for the first time using surface plasmon resonance by changing the pH value, salt concentration and temperature. The successful preparation of the sensor chip is proved by the water contact angle, Atomic Force Microscope, and the X-ray photoelectron spectroscopy. This study shows that the pH can greatly affect the formation of a complex from the interaction between the aptamer and GA. The interaction mechanism between GA aptamer and GA was caused by electrostatic force. Otherwise, this is the first time to detect protein isoelectric point (pI) using SPR. This study provides an important reference for researchers of aptamer sensors from the perspective of detection environment, and promotes the use of aptamer sensors to the clinic.

Investigation of the recognition interaction between glycated hemoglobin and its aptamer by using surface plasmon resonance

Glycated hemoglobin (HbA1c) has been widely explored as an important marker for monitoring and diagnosing diabetes. Due to the advantages of high selectivity, easy preparation, and convenient preservation of aptamers, research on glycated hemoglobin detection utilizing aptasensors has received much attention in recent years. However, factors such as the pH and the salt concentration of the solution and the structure of the aptamer could influence the interactions between HbA1c and the aptamer. In this study, the factors were evaluated using surface plasmon resonance (SPR). The results show that the pH and the salt concentration can greatly affect the formation of a complex between the aptamer and HbA1c. In the stereostructure of the aptamer, loop L1 may be an important motif for recognizing glycated hemoglobin. In addition, the best condition for detecting HbA1c was at pH 6, with a high sensitivity and a low limit of detection(LOD) (1.06 × 10^-3RUnM /2.55 nM). The results also demonstrated that the use of an SPR aptamer biosensor can be a sensitive technique to improve the accuracy and correctness of HbA1c measurement.

The application of antibody-aptamer hybrid biosensors in clinical diagnostics and environmental analysis

The growing number of various diseases and the increase of environmental contamination are the causes for the development of novel methods for their detection. The possibility of the application of affinity-based biosensors for such purposes seems particularly promising as they provide high selectivity and low detection limits. Recently, the usage of hybrid antibody-aptamer sandwich constructs was shown to be more advantageous in terms of working parameters in comparison to aptamer-based and immune-based biosensors. This review is focused on the usage of hybrid antibody-aptamer receptor layers for the determination of clinically and environmentally important target molecules. In this work, antibodies and aptamer molecules are characterized and the methods of their immobilization as well as analytical signal generation are shown. This is followed by the critical presentation of examples of hybrid sandwich biosensors that have been elaborated in the past 12 years.

Development and validation of immunoassay for whole cell detection of Brucella abortus and Brucella melitensis

Brucella is alpha-2 Proteobacteria mainly responsible for multi-factorial bacterial zoonotic disease brucellosis with low concentration (10–100 CFU) required to establish the infection. In this study, we developed sandwich ELISA with detection range of 10² to 10⁸ cells mL⁻¹ and limit of detection at 10³ cells mL⁻¹ by employing polyclonal rabbit IgG (capture antibody, 10 µg mL⁻¹) and mice IgG (detection antibody, 50 µg mL⁻¹) antibody for its detection. Surface Plasmon Resonance evaluated the interaction of detection antibody with whole cell spiked serum samples at LOD of 10² cells mL⁻¹ along with non co-operative interaction of protein albumin. Further, kinetic evaluation study using detection antibody against cell envelope antigen was performed whereby, Equilibrium Dissociation Constant (K_D) and Maximum Binding Capacity (B_max) were found to be 16.48 pM and 81.67 m° for Brucella abortus S99 and 0.42 pM and 54.50 m° for Brucella melitensis 16 M, respectively. During interference study, sandwich ELISA assay cross-reacted with either of the polyclonal antibody of above Brucella species. Upon validation, no cross-reactivity observed with bacteria-closely related to Brucella. In conclusion, developed semi-quantitative sandwich immunoassay is sensitively rapid in whole cell detection of Brucella and will be useful in development of detection assays from environmental and clinical matrices.

Surface plasmon resonance sensing of Ebola virus: a biological threat

Here, different monoclonal antibodies (mAb1, mAb2 and mAb3) of Ebola virus were screened in a real-time and label-free manner using surface plasmon resonance (SPR) to select an appropriate antibody for biosensor applications against a biological warfare agent. For this purpose, a gold SPR chip was modified with 4-mercaptobenzoic acid (4-MBA), and modification was confirmed by FTIR-ATR and EIS. The 4-MBA-modified gold SPR chip was used for immobilization of the recombinant nucleoprotein of Ebola (EBOV-rNP), and the interactions of mAb1, mAb2 and mAb3 were then investigated to determine the best mAb based on the affinity constant (K_D), expressed as equilibrium dissociation constant. K_D values of 809 nM, 350 pM and 52 pM were found for the interaction of mAb1, mAb2 and mAb3 of Ebola with the immobilized EBOV-rNP, respectively, thus reflecting the high affinity of mAb3. This was confirmed by ELISA results. The thermodynamic parameters (ΔG, ΔH and ΔS) for the interaction between mAb3 and EBOV-rNP were also determined, which revealed that the interaction was spontaneous, endothermic and driven by entropy. The SPR limit of detection of EBOV-rNP with mAb3 was 0.5 pg ml^-1, showing mAb3 to be the best high-affinity antibody in our study. This study has opened up new possibilities for SPR screening of different monoclonal antibodies of BWA through the convergence of materials science and optical techniques.

Lossy Mode Resonance-Based Glucose Sensor with High-κ Dielectric Film

In the past, high-κ dielectrics gained much attention because of the constant demand for increasingly smaller semiconductors. At the same time, in the field of optical sensing, high-κ dielectrics are key materials. This study presents the experimental investigations on a lossy mode resonance-based optical planar waveguide (LMROPW) sensor coated with a high-κdielectric of an indium tin oxide (ITO) layer. Two types of sensing structures were fabricated by coating (i) only a single-layer ITO (or bared LMROPW) and (ii) an ITO layer with glucose probes onto the optical planar waveguide (or boronic LMROPW) to detect glucose molecules. The sensing characteristics of these two types of sensors toward the surrounding analyte were determined using different concentrations of glucose solutions. It was found that the bared LMROPW sensor is only suitable for a higher concentration of glucose; the boronic LMROPW sensor with glucose probes on ITO could be applied to a lower-concentration solution to monitor glucose adsorption onto the sensing surface. Furthermore, with the advantages of a simple structure, easy alignment, and suitable production, the LMROPW sensor with a high-κ dielectric surface could be applied in clinical testing and diagnostics.

Current Status of HbA1c Biosensors

Glycated hemoglobin (HbA1c) is formed via non-enzymatic glycosylation reactions at the α–amino group of βVal1 residues in the tetrameric Hb, and it can reflect the ambient glycemic level over the past two to three months. A variety of HbA1c detection methods, including chromatography, immunoassay, enzymatic measurement, electrochemical sensor and capillary electrophoresis have been developed and used in research laboratories and in clinics as well. In this review, we summarize the current status of HbA1c biosensors based on the recognition of the sugar moiety on the protein and also their applications in the whole blood sample measurements.

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.

Boronate-functionalized hydrogel as a novel biosensing interface for the glycated hemoglobin A1c (HbA1c) based on the competitive binding with signaling glycoprotein

According to recent increases in public healthcare costs associated with diabetes mellitus, the development of new glycemic monitoring techniques based on the biosensing of glycated hemoglobin A1c (HbA_1c), a promising long-term glycemic biomarker, has become a major challenge. In the development of HbA_1c biosensors for point-of-care applications, the selection of an effective biorecognition layer that provides a high reaction yield and specificity toward HbA_1c is regarded as the most significant issue. To address this, we developed a novel HbA_1c biosensing interfacial material by the integration of boronate hydrogel with glass fiber membrane. In the present study, a new boronate-functionalized hydrogel was designed and spatio-selectively photopolymerized on a hydrophilic glass fiber membrane by using N-hydroxyethyl acrylamide, 3-(acrylamido)phenylboronic acid, and bis(N,N'-methylene-bis-acrylamide). Using this approach, the boronic acid group, which specifically recognizes the cis-diol residue of glucose on the HbA_1c molecule, can be three-dimensionally coated on the surface of the glass fiber network with a high density. Because this network structure of boronate hydrogel-grafted fibers enables capillary-driven fluid control, facile HbA_1c biosensing in a lateral flow assay concept could be accomplished. On the proposed HbA_1c biosensing interface, various concentrations of HbA_1c (5-15%) in blood-originated samples were sensitively measured by a colorimetric assay using horseradish peroxidase, a glycoenzyme can generate chromogenic signal after the competitive binding against HbA_1c to the boronic acid residues. Based on the demonstrated advantages of boronate hydrogel-modified membrane including high analytical performance, easy operation, and cost-effectiveness, we expect that the proposed biorecognition interfacial material can be applied not only to point-of-care HbA_1c biosensors, but also to the quantitative analysis of other glycoprotein biomarkers.

DNA-probe-target interaction based detection of Brucella melitensis by using surface plasmon resonance

Surface plasmon resonance (SPR) immunosensor using 4-mercaptobenzoic acid (4-MBA) modified gold (4-MBA/Au) SPR chip was developed first time for the detection of Brucella melitensis (B. melitensis) based on the screening of its complementary DNA target by using two different newly designed DNA probes of IS711 gene. Herein, interaction between DNA probes and target molecule are also investigated and result revealed that the interaction is spontaneous. The kinetics and thermodynamic results derived from the experimental data showed that the interaction between complementary DNA targets and probe 1 is more effective than that of probe 2. Equilibrium dissociation constant (K_D) and maximum binding capacity of analyte (B_max) values for the interaction of complementary DNA target with the immobilized DNA probes were calculated by using kinetic evaluation software, and found to be 15.3 pM (K_D) and 81.02m° (B_max) with probe 1 and 54.9pM and 55.29m° (B_max), respectively. Moreover, real serum samples analysis were also carried out using immobilized probe 1 and probe 2 with SPR which showed the applicability of this methodology and provides an alternative way for the detection of B. melitensis in less than 10min. This remarkable sensing response of present methodology offer a real time and label free detection of biological warfare agent and provide an opportunity to make miniaturized sensor, indicating considerable promise for diverse environmental, bio-defence, clinical diagnostics, food safety, water and security applications.

Development of a label-free SPR sensor for detection of matrixmetalloproteinase-9 by antibody immobilization on carboxymethyldextran chip

Surface plasmon resonance (SPR) immunosensor has been widely utilized for monitoring antigen-antibody interactions. The sensor measures changes of refractive index upon binding of analyte molecules to specific ligand immobilized on the sensor chip. This effort reports development of SPR immunosensor for real-time and label-free detection of recombinant human matrix metalloproteinases-9 (MMP-9), which has been associated with malignant tumor progression and metastasis by matrix degradation. MMP-9 was expressed in Escherichia coli BL21 and purified by Ni-NTA agarose column. CMD 50 D was activated by EDC/NHS for immobilization of monoclonal anti-MMP-9. Atomic force microscopy images showed uniform distribution of anti-MMP-9 over the sensor chip. Equilibrium constant (KD), maximum binding capacity (Rmax) and ∆Gb values for interaction of MMP-9 and anti-MMP-9 were 0.4nM, 680 µRIU and -53.51kJ/mol, respectively. Concentration of MMP-9 in saliva samples was determined, with linearity in the range of 10-200ng/mL. The limit of detection was found to be 8pg/mL, being lower than most of the previously reported techniques.

Selective label-free electrochemical impedance measurement of glycated haemoglobin on 3-aminophenylboronic acid-modified eggshell membranes

We propose a novel alternative approach to long-term glycaemic monitoring using eggshell membranes (ESMs) as a new immobilising platform for the selective label-free electrochemical sensing of glycated haemoglobin (HbA1c), a vital clinical index of the glycaemic status in diabetic individuals. Due to the unique features of a novel 3-aminophenylboronic acid-modified ESM, selective binding was obtained via cis-diol interactions. This newly developed device provides clinical applicability as an affinity membrane-based biosensor for the identification of HbA1c over a clinically relevant range (2.3 - 14 %) with a detection limit of 0.19%. The proposed membrane-based biosensor also exhibited good reproducibility. When analysing normal and abnormal HbA1c levels, the within-run coefficients of variation were 1.68 and 1.83%, respectively. The run-to-run coefficients of variation were 1.97 and 2.02%, respectively. These results demonstrated that this method achieved the precise and selective measurement of HbA1c. Compared with a commercial HbA1c kit, the results demonstrated excellent agreement between the techniques (n = 15), demonstrating the clinical applicability of this sensor for monitoring glycaemic control. Thus, this low-cost sensing platform using the proposed membrane-based biosensor is ideal for point-of-care diagnostics.

Glucose-responsive polymer vesicles templated by α-CD/PEG inclusion complex

Polymeric nanoparticles with glucose-responsiveness are of great interest in developing a self-regulated drug delivery system. In this work, glucose-responsive polymer vesicles were fabricated based on the complexation between a glucosamine (GA)-containing block copolymer PEG45-b-P(Asp-co-AspGA) and a phenylboronic acid (PBA)-containing block copolymer PEG114-b-P(Asp-co-AspPBA) with α-CD/PEG45 inclusion complex as the sacrificial template. The obtained polymer vesicles composed of cross-linked P(Asp-co-AspGA)/P(Asp-co-AspPBA) layer as wall and PEG chains as both inner and outer coronas. The vesicular morphology was observed by transmission electron microscopy (TEM), and the glucose-responsiveness was investigated by monitoring the variations of hydrodynamic diameter (Dh) and light scattering intensity (LSI) in the polymer vesicle solution with glucose using dynamic light scattering (DLS). Vancomycin as a model drug was encapsulated in the polymer vesicles and sugar-triggered drug release was carried out. This kind of polymer vesicle may be a promising candidate for glucose-responsive drug delivery.

Recent Progress in Electrochemical HbA1c Sensors: A Review

This article reviews recent progress made in the development of electrochemical glycated hemoglobin (HbA1c) sensors for the diagnosis and management of diabetes mellitus. Electrochemical HbA1c sensors are divided into two categories based on the detection protocol of the sensors. The first type of sensor directly detects HbA1c by binding HbA1c on the surface of an electrode through bio-affinity of antibody and boronic acids, followed by an appropriate mode of signal transduction. In the second type of sensor, HbA1c is indirectly determined by detecting a digestion product of HbA1c, fructosyl valine (FV). Thus, the former sensors rely on the selective binding of HbA1c to the surface of the electrodes followed by electrochemical signaling in amperometric, voltammetric, impedometric, or potentiometric mode. Redox active markers, such as ferrocene derivatives and ferricyanide/ferrocyanide ions, are often used for electrochemical signaling. For the latter sensors, HbA1c must be digested in advance by proteolytic enzymes to produce the FV fragment. FV is electrochemically detected through catalytic oxidation by fructosyl amine oxidase or by selective binding to imprinted polymers. The performance characteristics of HbA1c sensors are discussed in relation to their use in the diagnosis and control of diabetic mellitus.

Characterization of the binding strengths between boronic acids and cis-diol-containing biomolecules by affinity capillary electrophoresis

The affinity of boronic acids toward cis-diol-containing biomolecules has found wide applications in many fields, such as sensing, separation, drug delivery, and functional materials. A sound understanding of the binding interactions will greatly facilitate exquisite applications of this chemistry. Traditional techniques are associated with some apparent drawbacks, so they are only applicable to a limited range of boronic acids and cis-diol-containing biomolecules. This chapter describes an affinity capillary electrophoresis (ACE) method for the characterization of the binding strengths between boronic acids and cis-diol-containing biomolecules. As compared with existing approaches, such as (11)B NMR, the ACE method exhibits several significant advantages: (1) possibility of simultaneous study of multiple interactions, (2) low requirement on the purity of the binding species, (3) widely applicable to almost all types of cis-diol-containing compounds and boronic acids, and (4) high accuracy and precision.

Electrochemical biosensors based on ferroceneboronic Acid and its derivatives: a review

We review recent progress in the development of electrochemical biosensors based on ferroceneboronic acid (FcBA) and ferrocene (Fc)-modified boronic acids. These compounds can be used to construct electrochemical biosensors because they consist of a binding site (i.e., a boronic acid moiety) and an electrochemically active part (i.e., an Fc residue). By taking advantage of the unique properties of FcBA and its derivatives, electrochemical sensors sensitive to sugars, glycated hemoglobin (HbA1c), fluoride (F(-)) ions, and so forth have been widely studied. FcBA-based sugar sensors rely on the selective binding of FcBA to 1,2- or 1,3-diol residues of sugars through the formation of cyclic boronate ester bonds. The redox properties of FcBA-sugar adduct differ from those of free FcBA, which forms the basis of the electrochemical determination of sugars. Thus, non-enzymatic glucose sensors are now being actively studied using FcBA and Fc-modified boronic acids as redox markers. Using a similar principle, HbA1c can be detected by FcBA-based electrochemical systems because it contains hydrocarbon chains on the polypeptide chain. HbA1c sensors are useful for monitoring blood glucose levels over the preceding 8-12 weeks. In addition, FcBA and Fc-modified boronic acids have been used for the detection of F(-) ions due to the selective binding of boronic acid to F(-) ions. F(-)-ion sensors may be useful alternatives to conventional ion-selective electrodes sensitive to F(-) ion. Furthermore, FcBA derivatives have been studied to construct lectin; steroids; nucleotides; salicylic acid; and bacteria sensors. One of the limitations of FcBA-based sensors comes from the fact that FcBA derivatives are added in sample solutions as reagents. FcBA derivatives should be immobilized on the surface of electrodes for developing reagentless sensors.

Selective detection of carbohydrates and their peptide conjugates by ESI-MS using synthetic quaternary ammonium salt derivatives of phenylboronic acids

We present new tags based on the derivatives of phenylboronic acid and apply them for the selective detection of sugars and peptide-sugar conjugates in mass spectrometry. We investigated the binding of phenylboronic acid and its quaternary ammonium salt (QAS) derivatives to carbohydrates and peptide-derived Amadori products by HR-MS and MS/MS experiments. The formation of complexes between sugar or sugar-peptide conjugates and synthetic tags was confirmed on the basis of the unique isotopic distribution resulting from the presence of boron atom. Moreover, incorporation of a quaternary ammonium salt dramatically improved the efficiency of ionization in mass spectrometry. It was found that the formation of a complex with phenylboronic acid stabilizes the sugar moiety in glycated peptides, resulting in simplification of the fragmentation pattern of peptide-derived Amadori products. The obtained results suggest that derivatization of phenylboronic acid as QAS is a promising method for sensitive ESI-MS detection of carbohydrates and their conjugates formed by non-enzymatic glycation or glycosylation.

Development of a highly specific amine-terminated aptamer functionalized surface plasmon resonance biosensor for blood protein detection

This paper presents a generally applicable approach for the highly specific detection of blood proteins. Thrombin and thrombin-binding aptamers are chosen for demonstration purposes. The sensor was prepared by immobilizing amine-terminated aptamers onto a gold modified surface using a two-step self-assembled monolayer (SAM) immobilization technique and the physical detection is performed using Surface Plasmon Resonance (SPR). The developed sensor has an optimal detectable range of 5-1000 nM and the results show the sensor has good reversibility, sensitivity and selectivity. Furthermore, the sensor shows the potential of being improved and standardized for direct detection of other blood proteins for clinical applications.

Assessment of glycoprotein interactions with 4-[(2-aminoethyl)carbamoyl]phenylboronic acid surfaces using surface plasmon resonance spectroscopy

Reported here are analyses of the interactions between a select group of solution-phase glycoproteins and a unique boronic acid capture surface. The boronic acid derivative, 4-[(2-aminoethyl)carbamoyl]phenylboronic acid, AECPBA, was synthesized and then immobilized on carboxymethyl dextran surfaces using simple coupling methods. From surface plasmon resonance spectroscopy responses, it is found that model glycoproteins interact strongly with the AECPBA surface and subsequently can be readily released from the AECPBA surface using borate buffer. A striking difference between the glycoproteins fetuin and asialofetuin (desialylated fetuin), in terms of glycoprotein binding to the AECPBA surface, indicates that the interaction of glycoproteins with the immobilized AECPBA is dictated by the terminal saccharide of the heteroglycan chain. Surprisingly, secondary interactions of glycosylated and nonglycosylated proteins with the carboxymethyl dextran hydrogel matrix are observed. Importantly, it is demonstrated that use of tris(hydroxymethyl)aminomethane buffer allows for decreased secondary interactions of nonglycosylated proteins on the AECPBA/dextran surface, as noted with the model protein ExtrAvidin.