Current Status of HbA1c Biosensors

Label-free electrochemical detection of glycated hemoglobin (HbA1c) and C-reactive protein (CRP) to predict the maturation of coronary heart disease due to diabetes

The pathophysiological link between diabetes and heightened propensity for the development of coronary heart disease (CHD) is well-established. Prevailing evidence confirms that small increases in low concentrations of high-sensitivity C reactive protein (hs-CRP) in the human body can determine the tendency of developing CHD. Additionally, glycated hemoglobin (HbA1c) is a well-recognized biomarker to evaluate diabetes progression. Given the positive correlation between diabetes and CHD, this research presents a notably unprecedented label-free electrochemical approach for the dual detection of %HbA1c regarding Total Hb and hs-CRP, facilitating early CHD prediction and cost-effective point-of-care diagnostics. Furthermore, a novel redox probe O-(4-Nitrophenylphosphoryl)choline (C11H17N2O6P) was used for the electrochemical detection of CRP, a method not documented in scientific literature before. The calibration curves demonstrate a limit of detection (LOD) of 5 mg/mL in PBS (pH 8) and 6 mg/mL in simulated blood (SB) for a linear range of 0-30 mg/mL of HbA1c. Conjointly, a LOD of 0.007 mg/mL and 0.008 mg/mL for measurement in PBS (pH 7.4) and SB are reported for a linear range of 0-0.05 mg/mL of CRP. The electrochemical systems presented could accurately quantify HbA1c and CRP in mixed samples, demonstrating reasonable specificity and practical applicability for complex biological samples.

A comprehensive review on fructosyl peptide oxidase as an important enzyme for present hemoglobin A1c assays

Glycated proteins are generated by binding of glucose to the proteins in blood stream through a nonenzymatic reaction. Hemoglobin A1c (HbA1c) is a glycated protein with glucose at the N-terminal of β-chain. HbA1c is extensively used as an indicator for assessing the blood glucose concentration in diabetes patients. There are different conventional clinical methods for the detection of HbA1c. However, enzymatic detection method has newly obtained great attention for its high precision and cost-effectiveness. Today, fructosyl peptide oxidase (FPOX) plays a key role in the enzymatic measurement of HbA1c, and different companies have marketed HbA1c assay systems based on FPOX. Recent investigations show that FPOX could be used in assaying HbA1 without requiring HbA1c primary digestion. It could also be applied as a biosensor for HbA1c detection. In this review, we have discussed the recent improvements of FPOX properties, different methods of FPOX purification, solubility, and immobilization, and also the use of FPOX in HbA1c biosensors.

Real-time kinetic analysis and detection of glycated hemoglobin A1c using a quartz crystal microbalance-based aptasensor

Glycated hemoglobin (HbA1c) has been an important biomarker for long-term diagnosis and monitoring of diabetes mellitus. The development of a rapid, reliable, and less sophisticated device to measure HbA1c is imperative to facilitate efficient early-care diabetes management. To date, no existing aptamer-based biosensor (aptasensor) for detecting HbA1c has been developed using a quartz crystal microbalance (QCM). In this study, the aptamer specific to HbA1c as a novel biosensing receptor was covalently functionalized onto a QCM substrate via mixed self-assembled monolayers (SAMs). A portable QCM equipped with a liquid-flow module was used to investigate the biospecificity, sensitivity, and interaction dynamics of the aptamer functionalized surfaces. The real-time kinetic analysis of HbA1c binding to the surface-functionalized aptamers revealed "on" and "off" binding rates of 4.19 × 104 M-1 s-1 and 2.43 × 10-3 s-1, respectively. These kinetic parameters imply that the QCM-based aptasensor specifically recognizes HbA1c with an equilibrium dissociation constant as low as 57.99 nM. The linear detection of HbA1c spanned from 13 to 108 nM, with a limit of detection (LOD) of 26.29 nM. Moreover, the spiked plasma sample analysis offered compelling evidence that this aptasensor is a promising technique for developing a point-of-care device for diabetes mellitus.

Clinical Risk Assessment and Comparison of Bias between Laboratory Methods for Estimation of HbA1c for Glycated Hemoglobin in Hyperglycemic Patients

INTRODUCTION

Hemoglobin A1c (HbA1c), also known as glycated hemoglobin, is a blood test used to evaluate and track a patient's blood sugar levels over the previous 2-3 months. We have compared the analytical performance of the D10 hemoglobin (HPLC) testing system to that of the immunoturbidimetric technique, which is a light-scattering immunoassay.

OBJECTIVES

To assess the clinical risk assessment between two methods (Compare the two Immunoturbidometric methods (AU680) vs. HPLC method (D10)) in hyperglycemic patients and assess the acceptability of the respective methods in the Clinical biochemistry laboratory.

METHODS

The charge of the globins in Hb was used as the basis for the HPLC method used to measure HbA1c. HPLC detects and quantifies even the tiniest Hb fractions and the full spectrum of Hb variants. HbA1c was measured using the immunoturbidimetric (AU 680 Beckmann coulter analyzer) and high-performance liquid chromatography (HPLC) techniques. Experiments also made use of immunoturbidimetric techniques (using an AU 680 Beckmann coulter analyzer equipment).

RESULTS

There is no statistically significant difference in HbA1c readings between male and female patients, as measured by either the Immunoturbidimetric or HPLC techniques.

CONCLUSION

The immunoturbidimetric and high-performance liquid chromatography techniques for estimating HbA1c yielded identical results. From the results of this study, we may deduce that both techniques are valid for estimating HbA1c. As a result, it may be suggested that both approaches can be used to estimate HbA1c in diabetic individuals.

WaveFlex biosensor based on S-tapered and waist-expanded technique for detection of glycosylated hemoglobin

Glycosylated hemoglobin (HbA1c) is considered a new standard for the detection of diabetes mellitus because it is more accurate than regular blood sugar tests and there is no need to take blood on an empty stomach or at a specific time. In this work, we have developed a novel optical fiber biosensor, referred to as the "WaveFlex biosensor," which operates on the principles of localized surface plasmon resonance (LSPR) plasmonic wave. The sensor is fabricated using an innovative S-tapered and waist-expanded technique, enabling it to effectively detect HbA1c. Compared to the HbA1c sensors currently in use, HbA1c optical fiber sensors possess the characteristics of high sensitivity, low cost, and strong anti-interference ability. The gold nanoparticles (AuNPs), cerium oxide (CeO2) nanorods (NRs), and tungsten disulfide (WS2) nanosheets (NSs) are functionalized to improve the effectiveness of the fiber sensor on the probe surface. AuNPs are utilized to generate LSPR by the excitation of evanescent waves to amplify the sensing signal. The CeO2-NRs can have a strong metal-carrier interaction with AuNPs, enhancing the cascade of CeO2-NRs and AuNPs. The WS2-NSs with layered fold structure have a large specific surface area. Therefore, the combination of CeO2-NRs and WS2-NSs is conducive to the binding of antibodies and the addition of sites. The functionalized antibodies on the fiber make the sensor probe capable of specific selection. The developed probe is applied to test the HbA1c solution over concentrations of 0-1000 µg/mL, and the sensitivity and limits of detection of 1.195×10-5 a.u./(µg/mL) and 1.66 µg/mL are obtained, respectively. The sensor probe is also evaluated using assays for reproducibility, reusability, selectivity, and pH. According to the findings, a novel method for detecting blood glucose based on a plasmonic biosensor is proposed.

Point-of-care detection of glycated hemoglobin using a novel dry chemistry-based electrochemiluminescence device

As a good biomarker to reflect the average level of blood glucose, glycated hemoglobin (HbA1c) is mainly used for long-term glycemic monitoring and risk assessment of complications in diabetic patients. Previous analysis methods for HbA1c usually require complex pretreatment processes and large-scale biochemical analyzers, which makes it difficult to realize the point-of-care testing (POCT) of HbA1c. In this work, we have proposed a three-electrode dry chemistry-based electrochemiluminescence (ECL) biosensor and its self-contained automatic ECL analyzer. In this enzymatic biosensor, fructosyl amino-caid oxidase (FAOD) reacts with the hydrolysis product of HbA1c, and the produced hydrogen peroxide further reacts with luminol under the appropriate driving voltage, generating photons to realize the quantitative detection of HbA1c. Under optimized conditions, the biosensors have a good linear response to different concentrations of fructosyl valine (FV) ranging from 0.05 to 2 mM, with a limit of detection of 2 μM. The within-batch variation is less than 15%, and the biosensors still have 78% of the initial response after the accelerated aging test of 36 h at 37 °C. Furthermore, the recoveries for different concentrations of samples in whole blood were within 92.3-99.7%. These results illustrate that the proposed method has the potential for use in POCT of HbA1c.

Advances in Nanomaterial-Based Biosensors for Determination of Glycated Hemoglobin

Diabetes is a major public health burden whose prevalence has been steadily increasing over the past decades. Glycated hemoglobin (HbA1c) is currently the gold standard for diagnostics and monitoring glycemic control in diabetes patients. HbA1c biosensors are often considered to be cost-effective alternatives for smaller testing laboratories or clinics unable to access other reference methods. Many of these sensors deploy nanomaterials as recognition elements, detection labels, and/or transducers for achieving sensitive and selective detection of HbA1c. Nanomaterials have emerged as important sensor components due to their excellent optical and electrical properties, tunable morphologies, and easy integration into multiple sensing platforms. In this review, we discuss the advantages of using nanomaterials to construct HbA1c sensors and various sensing strategies for HbA1c measurements. Key gaps between the current technologies with what is needed moving forward are also summarized.

A Review of Electrochemical Sensors for the Detection of Glycated Hemoglobin

Glycated hemoglobin (HbA1c) is the gold standard for measuring glucose levels in the diagnosis of diabetes due to the excellent stability and reliability of this biomarker. HbA1c is a stable glycated protein formed by the reaction of glucose with hemoglobin (Hb) in red blood cells, which reflects average glucose levels over a period of two to three months without suffering from the disturbance of the outside environment. A number of simple, high-efficiency, and sensitive electrochemical sensors have been developed for the detection of HbA1c. This review aims to highlight current methods and trends in electrochemistry for HbA1c monitoring. The target analytes of electrochemical HbA1c sensors are usually HbA1c or fructosyl valine/fructosyl valine histidine (FV/FVH, the hydrolyzed product of HbA1c). When HbA1c is the target analyte, a sensor works to selectively bind to specific HbA1c regions and then determines the concentration of HbA1c through the quantitative transformation of weak electrical signals such as current, potential, and impedance. When FV/FVH is the target analyte, a sensor is used to indirectly determine HbA1c by detecting FV/FVH when it is hydrolyzed by fructosyl amino acid oxidase (FAO), fructosyl peptide oxidase (FPOX), or a molecularly imprinted catalyst (MIC). Then, a current proportional to the concentration of HbA1c can be produced. In this paper, we review a variety of representative electrochemical HbA1c sensors developed in recent years and elaborate on their operational principles, performance, and promising future clinical applications.

Associations of Plasma Concentration Profiles of Dapagliflozin, a Selective Inhibitor of Sodium–Glucose Co-Transporter Type 2, with Its Effects in Japanese Patients with Type 2 Diabetes Mellitus

This study was conducted to evaluate the long-term plasma concentration profiles of dapagliflozin and its effects on the glycated hemoglobin (HbA1c) level, body weight, and estimated glomerular filtration rate (eGFR) in 72 Japanese outpatients with type 2 diabetes mellitus (T2DM) receiving metformin and a dipeptidyl peptidase-4 inhibitor. At baseline, HbA1c level, body weight, and eGFR were 6.9 ± 0.6%, 77.9 ± 13.5 kg, and 78.8 ± 20.7 mL/min/1.73 m², respectively. A once-daily oral dose of 5 mg dapagliflozin was administered, and its trough plasma concentrations were evaluated at 1, 3, 6, 9, and 12 months. In this study, the patients with stable dapagliflozin concentrations were defined, based on a well-organized clinical trial, as those with average plasma concentrations of 2–5 ng/mL with a coefficient of variation <30%; these values were achieved if patients complied with their once-daily dosage. Multivariate analysis showed a significant decrease in the HbA1c levels among patients with stable concentrations (−0.6 ± 0.4%, p < 0.01), which was greater than the mean change among all 72 patients (−0.2 ± 0.5%, p < 0.01). The patients’ mean body weight also decreased (−2.3 ± 4.0 kg, p = 0.060). Average plasma concentrations ranged from 1.6 to 11.8 ng/mL; however, multivariate analysis indicated it was unrelated to the HbA1c-lowering effect. In conclusion, the long-term stability of plasma dapagliflozin concentration was important in lowering HbA1c level, and a once-daily oral dose of 5 mg was sufficient in achieving this effect.

Relationships Among Gut Microbiota, Ischemic Stroke and Its Risk Factors: Based on Research Evidence

Stroke is a highly lethal disease and disabling illness while ischemic stroke accounts for the majority of stroke. It has been found that inflammation plays a key role in the initiation and progression of stroke, and atherosclerotic plaque rupture is considered to be the leading cause of ischemic stroke. Furthermore, chronic inflammatory diseases, such as obesity, type 2 diabetes mellitus (T2DM) and hypertension, are also considered as the high-risk factors for stroke. Recently, the topic on how gut microbiota affects human health has aroused great concern. The initiation and progression of ischemic stroke has been found to have close relation with gut microbiota dysbiosis. Hence, this manuscript briefly summarizes the roles of gut microbiota in ischemic stroke and its related risk factors, and the practicability of preventing and alleviating ischemic stroke by reconstructing gut microbiota.

MicroRNA (miR)-590-3p alleviates high-glucose induced renal tubular epithelial cell damage by targeting C-X3-C motif chemokine ligand 1 (CX3CL1) in diabetic nephropathy

We attempted to analyze the clinical value of microRNA (miR)-590-3p in diabetic nephropathy (DN) patients and its role in high glucose (HG)-induced renal tubular epithelial cell (HK-2) injury. Serum levels of miR-590-3p were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Spearman correlation coefficient analysis of the correlation between miR-590-3p and clinical indicators. The diagnostic value of miR-590-3p was analyzed by the receiver operating characteristic (ROC) curve. Then, the DN cell model induced by HG in HK-2 cells was established. Enzyme-linked immunosorbent assay (ELISA), flow cytometry, and CCK-8 assay were employed to assess cell inflammation, oxidative stress, apoptosis, and proliferation. Dual-luciferase reporter assay confirmed the target of miR-590-3p. Serum miR-590-3p was reduced in patients of DN, which was positively correlated with eGFR and negatively associated with albuminuria. Furthermore, miR-590-3p also can diagnose patients of DN from healthy subjects or patients of T2DM. Furthermore, miR-590-3p was decreased in a concentration- and time-dependent manner during HG-induction. miR-590-3p overexpression bated HG-induced inhibition effect on cell proliferation and promotion effects on apoptosis, oxidative stress, and inflammation. C-X3-C motif chemokine ligand1 (CX3CL1) is the target of miR-590-3p, whose levels were enhanced in DN patients and are negatively regulated by miR-590-3p. Our discoveries offered new insights that reduced miR-590-3p as a potential biomarker for the diagnosis of DN, and elevated miR-590-3p can alleviate renal tubular injury by HG-induced through targeting CX3XL1, which may be a novel target for improving the development of DN.

Electrochemiluminescence paper-based screen-printed electrode for HbA1c detection using two-dimensional zirconium metal-organic framework/Fe3O4 nanosheet composites decorated with Au nanoclusters

Glycated hemoglobin (HbA1c) is one of the most popular biomarkers which can be utilized for the diagnosis and control of diabetes in clinical practice. In this study, a sandwich paper-based electrochemiluminescence (ECL) biosensor has been developed using the zirconium metal-organic framework/Fe₃O₄(trimethyl chitosan)/gold nanocluster (Zr-MOF/Fe₃O₄(TMC)/AuNCs) nanocomposite as tracing tag to label anti-HbA1c monoclonal antibody and reduced graphene oxide (rGO) as immobilization platform of sensing element. The screen-printed electrodes (SPEs) were constructed and modified by sputtering a thick layer of gold on the paper substrate, followed by electrochemical reduction of aminophenylboronic acid (APBA)-functionalized GO to rGO/APBA, respectively. Different types of surface analysis methods were applied to characterize the Zr-MOF/Fe₃O₄(TMC)/AuNCs nanomaterials fabricated. Finally, antibody-labeled Zr-MOF/Fe₃O₄(TMC)/AuNCs nanocomposites were subjected to HbA1c in the sample and on the paper-based SPE. Quantitative measurement of HbA1c was performed using ECL and cyclic voltammetry (CV) over a potential range of - 0.2 to 1.7 V vs gold reference electrode with a sweep rate of 0.2 V.s^-1 in the presence of triethylamine as a co-reactant after sandwiching the HbA1c target between antibody and APBA on the sensing area. This immunosensor demonstrated the desirable assay performance for HbA1c with a wide response range from 2 to 18% and a low detection limit (0.072%). This new strategy provides an effective method for high-performance bioanalysis and opens avenues for the development of high-sensitive and user-friendly device. Graphical abstract.

Glycated Hemoglobin and Methods for Its Point of Care Testing

Glycated hemoglobin (HbA1c) is a product of the spontaneous reaction between hemoglobin and elevated glucose levels in the blood. It is included among the so-called advanced glycation end products, of which is the most important for the clinical diagnosis of diabetes mellitus, and it can serve as an alternative to glycemia measurement. Compared to the diagnosis of diabetes mellitus by glycemia, the HbA1c level is less influenced by a short-term problem with diabetes compensation. Mass spectroscopy and chromatographic techniques are among the standard methods of HbA1c level measurement. Compared to glycemia measurement, there is lack of simple methods for diabetes mellitus diagnosis by means of the HbA1c assay using a point-of-care test. This review article is focused on the surveying of facts about HbA1c and its importance in diabetes mellitus diagnosis, and surveying standard methods and new methods suitable for the HbA1c assay under point-of-care conditions. Various bioassays and biosensors are mentioned and their specifications are discussed.

Digital Health in Cardiac Rehabilitation and Secondary Prevention: A Search for the Ideal Tool

Digital health is becoming more integrated in daily medical practice. In cardiology, patient care is already moving from the hospital to the patients' homes, with large trials showing positive results in the field of telemonitoring via cardiac implantable electronic devices (CIEDs), monitoring of pulmonary artery pressure via implantable devices, telemonitoring via home-based non-invasive sensors, and screening for atrial fibrillation via smartphone and smartwatch technology. Cardiac rehabilitation and secondary prevention are modalities that could greatly benefit from digital health integration, as current compliance and cardiac rehabilitation participation rates are low and optimisation is urgently required. This viewpoint offers a perspective on current use of digital health technologies in cardiac rehabilitation, heart failure and secondary prevention. Important barriers which need to be addressed for implementation in medical practice are discussed. To conclude, a future ideal digital tool and integrated healthcare system are envisioned. To overcome personal, technological, and legal barriers, technological development should happen in dialog with patients and caregivers. Aided by digital technology, a future could be realised in which we are able to offer high-quality, affordable, personalised healthcare in a patient-centred way.

Direct and Label-Free Determination of Human Glycated Hemoglobin Levels Using Bacteriorhodopsin as the Biosensor Transducer

Glycated hemoglobin (HbA1c) levels are an important index for the diagnosis and long-term control of diabetes. This study is the first to use a direct and label-free photoelectric biosensor to determine HbA1c using bacteriorhodopsin-embedded purple membranes (PM) as a transducer. A biotinylated PM (b-PM) coated electrode that is layered with protein A-oriented antibodies against hemoglobin (Hb) readily captures non-glycated Hb (HbA0) and generates less photocurrent. The spectra of bacteriorhodopsin and Hb overlap so the photocurrent is reduced because of the partial absorption of the incident light by the captured Hb molecules. Two HbA0 and HbA1c aptasensors that are prepared by conjugating specific aptamers on b-PM coated electrodes single-step detect HbA0 and HbA1c in 15 min, without cross reactivity, with detection limits of ≤0.1 μg/mL and a dynamic range of 0.1–100 μg/mL. Both aptasensors exhibit high selectivity and long-term stability. For the clinical samples, HbA0 concentrations and HbA1c levels that are measured with aptasensors correlate well with total Hb concentrations and the HbA1c levels that are determined using standard methods (correlation gradient = 0.915 ± 0.004 and 0.981 ± 0.001, respectively). The use of these aptasensors for diabetes care is demonstrated.

The effect of red blood cell transfusion on peripheral tissue oxygen delivery and consumption in septic patients

OBJECTIVES

The impact of blood transfusion on tissue oxygen delivery (DO₂) and tissue oxygen consumption (VO₂) is a subject of current clinical studies. The primary objective of this observational study is to evaluate and measure the parameters involved in determining DO₂ and VO₂, in early phase of septic patients. A secondary objective of this study is to assess the potential benefit of blood transfusion on tissue metabolism by serial measurements of lactic acid (Ac. Lac.).

MATERIAL AND METHODS

A group of 29 patients were studied, each patient received between one to three units of fresh packed red blood cells (pRBC). Clinical and paraclinical criteria for sepsis as well as the plasma value of haemoglobin (Hb) below 10g/dL represented the inclusion criteria in this study. We evaluated Hb, haematocrit (HCT), arterial blood oxigen saturation (SAO₂), central venous oxygen saturation (SCVO₂), parameters which are involved in determination of DO₂ and VO₂, before and after the transfusion of one unit of pRBC. Values of Ac. Lac. were also assessed in order to determine the type of metabolism (aerobic or anaerobic). SCVO₂, SAO₂, Hb, HCT and Ac. Lac. were determined using Epoc blood analyser. The cardiac output (CO) and systemic vascular resistance (SVR) were monitored during blood transfusion, using Vigileo monitor (Edward's Life Science, PreSep catheter kit). SAO₂ was also monitored by pulse-oximetry.

RESULTS

Changes in Hb, HCT and SCVO₂ before and after pRBC transfusion (which further determine VO₂) were statistically significant (P<0.001). A statistically significant increase (P<0.001) was obtained in Ac. Lac. values, before and after pRBC transfusion. SAO₂ and CO directly involved in producing DO₂, were clinically monitored during blood transfusion and the results remained constant.

CONCLUSION

Results obtained in this clinical study show an increase in DO2 in critically ill septic patients and also an increase in oxygen tissue uptake which is similar to VO2, clearly pointing out the benefit of pRBC transfusion. The benefits of pRBC transfusion on tissue metabolism in critically ill septic patients remain elusive because of lactic acid values increase during and after transfusion. Based on our findings we recommend that Hb values used as a single trigger for pRBC transfusion should be further studied and that additional parameters such as SCVO₂ and lactic acid should be considered as possible triggers for transfusion. Values of Hb and HCT should never be neglected.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Analytical techniques for the detection of glycated haemoglobin underlining the sensors

The increase in concentrations of blood glucose results arise in the proportion of glycated haemoglobin. Therefore, the percentage of glycated haemoglobin in the blood could function as a biomarker for the average glucose level over the past three months and can be used to detect diabetes. The study of glycated haemoglobin tends to be complex as there are about three hundred distinct assay techniques available for evaluating glycated haemoglobin which contributes to some differences in the recorded values from the similar samples. This review outlines distinct analytical methods that have evolved in the recent past for precise recognition of the glycated - proteins.

An amperometric biosensor for specific detection of glycated hemoglobin based on recombinant engineered fructosyl peptide oxidase

Here, we present a specific biosensor based on the detection of glycated hemoglobin (HbA1c) proteolytic digestion product, fructosyl valyl histidine (Fru-ValHis). A recombinant engineered fructosyl peptide oxidase (FPOX) enzyme with improved specificity was immobilized on the electrode surface modified by chitosan (CHIT), graphene oxide (GO) and gold nanoparticles (AuNPs). The biosensor exhibited a linear response toward different concentrations of Fru-ValHis ranging from 0.1 to 2 mM with a sensitivity of 8.45 µA mM^-1 cm^-2. Detection limit of the current biosensor for Fru-ValHis was 0.3 µM as the lowest quantity required giving a signal to a background. Analytical recovery of added Fru-ValHis in whole blood was 95.1-98.35% for FPOX/AuNPs/GO/CHIT/FTO electrode. For Fru-ValHis determination by FPOX-AuNPs-GO-CHIT/FTO electrode, within-run coefficient of variation (CV) was between 1.3% and 2.4% and between run CV was between 2.1% and 3.5%. A significant change in electron transfer resistance after the incubation of FPOX-modified electrode with Fru-ValHis was observed, while no response was achieved with control, indicating specific measurement of Fru-ValHis. Moreover, designed biosensor measured HbA1c in human blood samples and the results were well agreed with that obtained with NORUDIA™ N HbA1c diagnostic kit. Overall, suitable specificity of the engineered FPOX made the bioelectrode responded well to the Fru-ValHis level, which demonstrates a promising application for specific detection of HbA1c biomarker.

Different strategies for detection of HbA1c emphasizing on biosensors and point-of-care analyzers

Measurement of glycosylated hemoglobin (HbA1c) is a gold standard procedure for assessing long term glycemic control in individuals with diabetes mellitus as it gives the stable and reliable value of blood glucose levels for a period of 90-120 days. HbA1c is formed by the non-enzymatic glycation of terminal valine of hemoglobin. The analysis of HbA1c tends to be complicated because there are more than 300 different assay methods for measuring HbA1c which leads to variations in reported values from same samples. Therefore, standardization of detection methods is recommended. The review outlines the current research activities on developing assays including biosensors for the detection of HbA1c. The pros and cons of different techniques for measuring HbA1c are outlined. The performance of current point-of-care HbA1c analyzers available on the market are also compared and discussed. The future perspectives for HbA1c detection and diabetes management are proposed.