Fructosyl Amino Acid Oxidase Research Articles

Proof-of-Concept Development of a Point-of-Care Direct Quantification of Glycated Albumin Using a Dual Electrochemical Method Approach

Diabetes mellitus is a prevalent chronic metabolic condition characterized by inadequate insulin production or utilization, leading to elevated blood sugar levels (i.e., hyperglycemia). Effective glycemic control is crucial for preventing long-term complications like cardiovascular disease, kidney disease, neuropathy, and retinopathy. Glycated albumin (GA) is a promising biomarker for glycemic control due to its shorter lifespan and broader reliability compared to glycated hemoglobin (HbA1c), which is the gold standard glycated biomarker widely used in clinical practice. By reflecting the average blood glucose level of the previous 2-3 weeks, as opposed to the 2-3 months of HbA1c, GA allows for better tracking of rapidly evolving conditions. Moreover, it is not affected by hematologic disorders which can bias HbA1c measurements. GA is defined as the fraction of glycated human serum albumin (GHSA) to total human serum albumin (HSA). At present, GHSA is assessed at central laboratories using enzymatic assay kits that rely on spectroscopical measurements and include fructosyl amino-acid oxidase, which requires the proteolytic hydrolysis of GHSA to release fructosyl amino acid. Nevertheless, the need for a pre-treatment of GHSA poses a big challenge in the translation of this technique outside a laboratory setting. Therefore, a point-of-care testing (POCT) platform that minimizes the time gap between measurement and clinical decision-making, and expands the tools available to diabetic subjects for self-monitoring of their blood sugar levels management is needed [1, 2].Aptamers are a type of single-stranded oligonucleotide that are able to selectively interact with a wide range of target molecules. They are chemically synthesized, possess great thermal stability and exhibit regenerable binding [3, 4]. The aptamer against intact GHSA has been reported [5], thus eliminating the need for a pre-digestion of the GHSA and empowering POCT applications. Aptamer-based detection of HSA has also been successfully achieved [6].The clinical relevance for GA as a biomarker relies on the percentage ratio quantification of GHSA to the total HSA present in the plasma. Another problem of current spectroscopic techniques is that GHSA and HSA levels are assessed with two distinct assays (i.e., enzymatic for GHSA and bromocresol purple for HSA), which are difficult to combine into a single platform. Hence, for effective implementation of a POCT or personal sensing device it should be able to measure both GHSA and total HSA on the same unit.In this work we aim to expand on a recent design of our research group [7], in which two aptamer-based extended gate field effect transistor (EGFET) sensors were developed in parallel: one dedicated to GHSA measurement and a second one to quantify total HSA. GHSA was successfully detected in concentrations from 0.1 to 10 μM within 20 minutes, even in presence of bovine serum albumin. Total HSA concentrations ranging from 1 to 17 μM were correctly measured. Furthermore, the linear calibration curves obtained with each sensor allowed to correctly quantify glycation ratios in samples with known and clinically relevant GA levels.The aim of this work is to develop a novel GA sensing technique exploiting a single sensor with dual electrochemical modalities, which are based on square wave voltammetry (SWV) and EGFET. In this scenario, separating the signal contribution of each aptamer from the total is of critical importance. To achieve this, we propose to interrogate each recognition element with a different electrochemical technique. SWV is used to detect the change in electron transfer kinetics of the redox probe covalently attached on one aptamer. For the second aptamer, the EGFET configuration that we have already successfully reported is implemented to detect the non-faradaic contribution of charge variations at the surface of the extended gate. The combination of these two techniques could lead to the dual measurement of GHSA and HSA at the single sensor, enabling the development of an all-in-one POCT platform for glycemic control in diabetic subjects.

Enzymatic Deglycation of Damaged Skin by Means of Combined Treatment of Fructosamine-3-Kinase and Fructosyl-Amino Acid Oxidase.

The consensus in aging is that inflammation, cellular senescence, free radicals, and epigenetics are contributing factors. Skin glycation through advanced glycation end products (AGEs) has a crucial role in aging. Additionally, it has been suggested that their presence in scars leads to elasticity loss. This manuscript reports fructosamine-3-kinase (FN3K) and fructosyl-amino acid oxidase (FAOD) in counteracting skin glycation by AGEs. Skin specimens were obtained (n = 19) and incubated with glycolaldehyde (GA) for AGE induction. FN3K and FAOD were used as monotherapy or combination therapy. Negative and positive controls were treated with phosphate-buffered saline and aminoguanidine, respectively. Autofluorescence (AF) was used to measure deglycation. An excised hypertrophic scar tissue (HTS) (n = 1) was treated. Changes in chemical bonds and elasticity were evaluated using mid-infrared spectroscopy (MIR) and skin elongation, respectively. Specimens treated with FN3K and FAOD in monotherapy achieved an average decrease of 31% and 33% in AF values, respectively. When treatments were combined, a decrease of 43% was achieved. The positive control decreased by 28%, whilst the negative control showed no difference. Elongation testing of HTS showed a significant elasticity improvement after FN3K treatment. ATR-IR spectra demonstrated differences in chemical bounds pre- versus post-treatment. FN3K and FAOD can achieve deglycation and the effects are most optimal when combined in one treatment.

Topical Application of Deglycating Enzymes as an Alternative Non-Invasive Treatment for Presbyopia.

Presbyopia is an age-related vision disorder that is a global public health problem. Up to 85% of people aged ≥40 years develop presbyopia. In 2015, 1.8 billion people globally had presbyopia. Of those with significant near vision disabilities due to uncorrected presbyopia, 94% live in developing countries. Presbyopia is undercorrected in many countries, with reading glasses available for only 6-45% of patients living in developing countries. The high prevalence of uncorrected presbyopia in these parts of the world is due to the lack of adequate diagnosis and affordable treatment. The formation of advanced glycation end products (AGEs) is a non-enzymatic process known as the Maillard reaction. The accumulation of AGEs in the lens contributes to lens aging (leading to presbyopia and cataract formation). Non-enzymatic lens protein glycation induces the gradual accumulation of AGEs in aging lenses. AGE-reducing compounds may be effective at preventing and treating AGE-related processes. Fructosyl-amino acid oxidase (FAOD) is active on both fructosyl lysine and fructosyl valine. As the crosslinks encountered in presbyopia are mainly non-disulfide bridges, and based on the positive results of deglycating enzymes in cataracts (another disease caused by glycation of lens proteins), we studied the ex vivo effects of topical FAOD treatment on the power of human lenses as a new potential non-invasive treatment for presbyopia. This study demonstrated that topical FAOD treatment resulted in an increase in lens power, which is approximately equivalent to the correction obtained by most reading glasses. The best results were obtained for the newer lenses. Simultaneously, a decrease in lens opacity was observed, which improved lens quality. We also demonstrated that topical FAOD treatment results in a breakdown of AGEs, as evidenced by gel permeation chromatography and a marked reduction in autofluorescence. This study demonstrated the therapeutic potential of topical FAOD treatment in presbyopia.

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.

Cloning, expression and purification of fructosyl amino acid oxidase (FAOX) in Escherichia Coli

Introduction: The level of serum HbA1c is an indicator of the average blood sugar level in the last three months. HbA1c can be quantified using assays involving the enzyme fructosyl amino acid oxidase (FAOX). This study aims to produce GST-tagged FAOX-TE (GST/FAOX-TE), a thermal stable and specific variant of FAOX, for future application studies.
 Materials and methods: The E. coli strains DH5α and BL21 (DE3) were used as cloning and expression hosts, respectively. The FAOX-TE sequence was synthesized at IDT (US) and clonned into pGEX-4T3 vector, which was confirmed by Colony PCR. The expression was induced at 16°C, 0.5 mM IPTG in LB media containing 50 µg/ml ampicilin. The protein expression profile was analyzed by SDS-PAGE. The cell pellet was sonicated and purified by Glutathione Sepharose 4 Fast Flow (Cytiva, US). The catalytic activity of GST/FAOX-TE with fructosyl valine was determined using high performance anion exchange chromatography with pulsed amperometry detection (HPAEC-PAD).
 Results: The fusion protein was successfully expressed in Escherichia coli using the plasmid pGEX-4T3 and purified to high purity 93%. Recombinant GST/FAOX-TE was shown to be active on fructosyl valine.
 Conclusions: Active GST/FAOX-TE was successfully expressed in E. coli BL21 (DE3) and purified, which will be used for future development of biosensors for fructosyl valine quantification.

Gold Nanostar Colorimetric Detection of Fructosyl Valine as a Potential Future Point of Care Biosensor Candidate for Glycated Haemoglobin Detection.

Diabetes Mellitus is a growing global concern. The current methods used to detect glycated haemoglobin are precise, however, utilise expensive equipment, reagents and consumables. These are luxuries which rural communities cannot access. The nanotechnology methods which have been developed for glycated haemoglobin detection are predominantly electrochemically based, have complicated lengthy fabrication processes and utilise toxic chemicals. Here a fructosyl amino acid oxidase gold nanostar biosensor has been developed as a potential future point of care biosensor candidate for glycated haemoglobin detection. The workup done on this biosensor showed that it was able to give a spectrophotometric readout and colorimetric result with naked eye detection in blank serum spiked with fructosyl valine.

Development of Disposable Single-Use Biosensor for Fructosyl Valine and Glycated Hemoglobin A1c

A novel amperometric biosensor prototype was fabricated using screen printing technique. The disposable single-use strips were made from conductive carbon ink and modified with fructosyl amino acid oxidase. The electrodes and conducting paths were made solely with carbon ink and characterized by conductivity and cyclic voltammetry. The biosensor showed high current output, large linearity, and effectiveness for fructosyl valine as well as human blood samples. Amperometric studies were carried out using both fructosyl valine and human blood samples. With 5 uL sample volume, the biosensor showed strong amperometric response with good linearity for a wide range (0 to 8 mM). Diabetic and healthy blood samples showed sufficient difference in their amperometric responses that correlate well with their different hemoglobin A1c levels. These results demonstrate the feasibility of using this type of inexpensive single-use biosensor strips as the basis for determining hemoglobin A1c levels for diabetic patients.

Gold Nanoparticle‐based Novel Biosensors for Detecting Glycated Hemoglobin

We report here on novel biosensors for the highly sensitive and specific enzymatic analysis of glycated hemoglobin (HbA1c), which we measured primarily to identify three‐month average plasma glucose concentrations. Hydrogen peroxide (H2O2) was generated in this enzymatic measuring of glycated hemoglobin from oxidative cleavage of fructosyl valine by fructosyl amino acid oxidase, and we then used the generated hydrogen peroxide as a reducing agent of gold (III) ion to synthesize gold (0) as a nanoparticle. We were able to measure the gold nanoparticles obtained from this novel approach using colorimetry under a UV–VIS spectrophotometer. For this colorimetric detection, we analyzed 96‐well plates for glycated hemoglobin, and this system worked very well, with a detection limit of 0.142% and coefficient of variation below 10%. Finally, this method can measure glycated hemoglobin in patients with diabetes.

Development of a screen-printed carbon electrode based disposable enzyme sensor strip for the measurement of glycated albumin

Glycated proteins, such as glycated hemoglobin (HbA1c) or glycated albumin (GA) in the blood, are essential indicators of glycemic control for diabetes mellitus. Since GA, compared to HbA1c, is more sensitive to short term changes in glycemic levels, GA is expected to be used as an alternative or together with HbA1c as a surrogate marker indicator for glycemic control. In this paper we report the development of a sensing system for measuring GA by combining an enzyme analysis method, which is already used in clinical practice, with electrochemical principles. We used fructosyl amino acid oxidase, hexaammineruthenium(III) chloride as the electron mediator, and an inexpensive and economically attractive screen-printed carbon electrode. We used chronoamperometry to measure protease-digested GA samples. The developed sensor strips were able to measure protease-digested samples containing GA in very small sample volumes (1.3μL) within about 1min. We also prepared enzyme sensor strips suitable for clinical use in which the enzyme and the mediator were deposited and dried on. This sensor system showed a clear correlation between the GA concentration and the resulting current. The strips were stable following 3 months of storage at 37°C. We conclude that this disposable enzyme sensor strip system for measuring GA is suitable for point-of-care test (POCT) applications.

Influence Of Zinc Oxide Nanorods On The Sensitivity Of A Glycated Hemoglobin Biosensor

The glucose level measurement in the blood of diabetic patients without significant variations is important. The level of glycated hemoglobin (HbA1c) in the blood provides an authentic tool for glucose level measurement. In our study, a biosensing system established on properly aligned single-crystal zinc oxide (ZnO) nanorods structures grown on indium-tin oxide coated glass plate (ITO) electrode. ZnO nanorods were immobilized with fructosyl amino-acid oxidase (FAO) enzyme through physical adsorption integrated with cross linking molecules N-5-azido-2-nitro-benzoyloxysuccinimide (ANB-NOS). Whole blood samples were first hemolyzed & then properly digested with protease prior to measuring the HbA1c through the sensor. This enzyme biosensor reported an optimum response at +0.2 V. This biosensor displayed a significant sensitivity and detection limit (0.1μM), fast response time (4s) and wide linear range (from 0.1 to 2000 μM). The enzyme/working electrode is stable for about 4 months, when kept at 4 oC. This recommended biosensor method may apply for detecting HbA1c in blood samples obtained from apparently healthy as well as diabetic patients.

Titania nanotubes decorated with gold nanoparticles for electrochemiluminescent biosensing of glycosylated hemoglobin

A glycated hemoglobin (HbA1c) biosensor with high performance has been constructed in this work. Here the fructosyl amino acid oxidase was immobilized onto a pre-functionalized indium tin oxide glass with titania nanotubes decorated with gold nanoparticles. The property of nanocomposite was characterized by transmission electromicroscopy, scanning electron microscopy, electrochemistry and spectroscopy. Under the optimum conditions, fructosyl valine was detected by this biosensor. It exhibited a linear detection range from 4.0 × 10−9 M to 7.2 × 10−7 M, and a limit of detection for 3.8 × 10−9 M at the signal-to-noise ratio of 3. Thus the HbA1c level in whole blood samples of healthy individuals or diabetic patients were evaluated with designed biosensor after pre-treatment of hydrolysis. The results of our detection were closely consistent with that of the standard method. At the same time, our biosensor has some advantages including high sensitivity, disposable usage and low cost, which implies its great promising application in point-of-care testing of HbA1c.

Glycated hemoglobin detection with electrochemical sensing amplified by gold nanoparticles embedded N-doped graphene nanosheet

In the diabetic patients the level of glucose must be determined without any short term fluctuations. The level of Glycated hemoglobin (HbA1c) is accordingly examined for checking diabetes mellitus. HbA1c is considered one of the primarily factor to discern the concentration of average plasma glucose over a long-drawn-out period. In our work, we describe a construction of biosensor which is based on fructosyl amino-acid oxidase (FAO) immobilized nitrogen-doped graphene/gold nanoparticles (AuNPs)/fluorine doped tin oxide (FTO) glass electrode. This constructed biosensor exhibits a wide linear range of 0.3 to 2000μM in response to HbA1c at +0.2V. Consequently, the detection limit of 0.2μM and good stability (4 months) were achieved. The electrocatalytic activity of this sensor was good as a result of synergistic effect of graphene and AuNPs (2D and 0D nanomaterials). The charge transfer resistance was decreased which was observed by electrochemical impedance spectroscopy (EIS) study. The graphene/AuNPs composites film reveals a distinguished electrochemical response to fructosyl valine (FV) which demonstrates a promising application for electrochemical detection of HbA1c in human blood samples.

Advancing the development of glycated protein biosensing technology: next-generation sensing molecules.

Research advances in biochemical molecules have led to the development of convenient and reproducible biosensing molecules for glycated proteins, such as those based on the enzymes fructosyl amino acid oxidase (FAOX) or fructosyl peptide oxidase (FPOX). Recently, more attractive biosensing molecules with potential applications in next-generation biosensing of glycated proteins have been aggressively reported. We review 2 such molecules, fructosamine 6-kinase (FN6K) and fructosyl amino acid-binding protein, as well as their recent applications in the development of glycated protein biosensing systems. Research on FN6K and fructosyl amino acid-binding protein has been opening up new possibilities for the development of highly sensitive and proteolytic-digestion-free biosensing systems for glycated proteins.

Superparamagnetic nanoparticles as versatile carriers and supporting materials for enzymes

Abstract Enzymes are highly efficient catalysts extensively employed in biotechnology. Among the many challenging aspects in this area, enzymes are yet difficult to obtain and purify, which makes them extremely expensive. Therefore, the industrial use of such expensive biocatalysts suffers from a critical point, which is the lack of efficient recovery processes. As a very promising strategy, superparamagnetic nanoparticles based on magnetite (Fe3O4) and maghemite (γ-Fe2O3) have been recently employed as supporting materials for enzymes, exhibiting striking characteristics, such as large surface area, mobility and high mass transference. More than that, they can be easily recovered by applying an external magnetic field. In addition to their excellent environmental compatibility, the use of such superparamagnetic nanoparticles represents an effective green chemistry approach, since it prolongs, through the successive recovery cycles, the useful lifetime of the biocatalyst. Several enzymes and biomolecules, including antibodies, albumin, α-chymotrypsin, aminopeptidase, acetylcholine esterase, amylase, amyloglucosidase, celullase, epoxide hydrolases, esterase, lipase, lysozyme, pectinases, phosphatase, pyruvate phosphate dikinase, trypsin, subtilisin, urease, chitosanase, haloalkane dehalogenase, RNA polymerase, lactate dehydrogenase, alcohol dehydrogenase, galactosidase, catalase, cholesterol oxidase, d -amino acid oxidase, cathecol dioxygenase, fructosyl amino acid oxidase, l -lactate dehydrogenase, xanthine oxidase, glucose oxidase, glucosidase, laccase, peroxidases, tyrosinase and so on, have been successfully immobilized onto magnetic nanoparticles, and the recent progress in this area is focused on this review.

An amperometric hemoglobin A1c biosensor based on immobilization of fructosyl amino acid oxidase onto zinc oxide nanoparticles–polypyrrole film

Measurement of hemoglobin A1c (HbA1c, glycated hemoglobin) level in blood provides the long-term glucose level in diabetic patients without the influence of short-term fluctuations. The existing methods for HbA1c determination, including biosensors, suffer from insufficient sensitivity, detection limit, response time, and storage stability. These problems were overcome in the current biosensor. A method is described for construction of an amperometric HbA1c biosensor by immobilizing a fructosyl amino acid oxidase (FAO) onto zinc oxide nanoparticles/polypyrrole (ZnONPs/PPy) hybrid film deposited onto gold (Au) electrode and using it as working electrode, Ag/AgCl as reference electrode, and platinum (Pt) as auxiliary electrode. The whole blood samples were hemolyzed and digested by protease before measuring their HbA1c level by the biosensor. The enzyme electrode detected fructosyl valine (FV) as low as 50μM at a signal-to-noise ratio of 3 within 2s at +0.27V versus Ag/AgCl, pH7.0, and 35°C with a linear working range of 0.1 to 3.0mM for FV and sensitivity of 38.42μAmM−1. The electrode showed only a 30% loss of its initial response over a period of 160days when stored at 4°C. The biosensor measured HbA1c in whole blood of apparently healthy individuals and diabetic patients and found it to be in the ranges of 4.0% to 5.6% and 5.7% to 12.0%, respectively.

Tuning Fructosyl Peptidyl Oxidase into Dehydrogenase and Its Application for the Construction of an Enzyme Electrode

Fructosyl valyl-histidine, which is released from protease digestion of the major diabetes indicator HbA1c, is recognized as a target molecule for HbA1c sensors. The flavoenzyme fructosyl amino acid oxidase (FAOD) is an enzyme catalyzing the oxidative deglycation of fructosyl amino acids, with those also possessing high activity towards fructosyl dipeptides being referred to as fructosyl peptidyl oxidases (FPOXs). The high oxygen reactivity of FAODs and FPOXs limits their potential utility in amperometric enzyme sensors employing artificial electron mediators. We successfully modified the proton relay system of Pichia N1-1 FAOD, significantly decreasing its catalytic ability to employ oxygen as the electron acceptor, while having little effect on the dye-mediated dehydrogenase activity employing artificial electron acceptors instead of oxygen. We expect that similar engineering of a recently discovered FPOX will produce an enzyme that is ideally suited for HbA1c sensing.

An electrochemical biosensor for fructosyl valine for glycosylated hemoglobin detection based on core–shell magnetic bionanoparticles modified gold electrode

A high-performance amperometric fructosyl valine (FV) biosensor was developed, based on immobilization of fructosyl amino-acid oxidase (FAO) on core–shell magnetic bionanoparticles modified gold electrode. Chitosan was used to introduce amino groups onto the surface of core–shell magnetic bionanoparticles (MNPs). With FAO as an enzyme model, a new fructosyl valine biosensor was fabricated. The biosensor showed optimum response, when operated at 50 mV s −1 in 0.1 M potassium phosphate buffer, pH 7.5 and 35 °C. The biosensor exhibited excellent sensitivity [the detection limit is down to 0.1 mM for FV], fast response time (less than 4 s), wide linear range (from 0 to 2 mM). Analytical recovery of added FV was 95.00–98.50%. Within batch and between batch coefficients of variation were <2.58% and <5.63%, respectively. The enzyme electrode was used 250 times over 3 months, when stored at 4 °C.

Engineering of dye-mediated dehydrogenase property of fructosyl amino acid oxidases by site-directed mutagenesis studies of its putative proton relay system

The flavoenzyme fructosyl amino acid oxidase (FAOD) catalyzes the oxidative deglycation of fructosyl amino acids, model compounds of glycated proteins. The high oxygen reactivity of FAODs limits their potential utility in amperometric enzyme sensors employing artificial electron mediators. To alter their electron acceptor availability, site-directed mutagenesis was carried out on conserved residues predicted to be involved in the proton relay system (PRS) of two eukaryotic FAODs, the FAOD from the marine yeast Pichia sp. N1-1 and amadoriase II from the fungus Aspergillus fumigatus. The substitution of a single conserved Asn residue in the putative PRS, Asn47Ala of N1-1 FAOD and Asn52Ala of amadoriase II, resulted in significant loss in the catalytic ability to employ O(2) as the electron acceptor, while having little effect on the dye-mediated dehydrogenase activity employing artificial electron acceptors instead of O(2).

Motif‐based search for a novel fructosyl peptide oxidase from genome databases

The measurement of glycated hemoglobin A1c (HbA1c) has important implications for diagnosis of diabetes and assessment of treatment effectiveness. We proposed specific sequence motifs to identify enzymes that oxidize glycated compounds from genome database searches. The gene encoding a putative fructosyl amino acid oxidase was found in the Phaeosphaeria nodorum SN15 genome and successfully expressed in Escherichia coli. The recombinant protein (XP_001798711) was confirmed to be a novel fructosyl peptide oxidase (FPOX) with high specificity for alpha-glycated compounds, such as HbA1c model compounds fructosyl-(alpha)N-valine (f-(alpha)Val) and fructosyl-(alpha)N-valyl-histidine (f-(alpha)Val-His). Unlike previously reported FPOXs, the P. nodorum FPOX has a K(m) value for f-(alpha)Val-His (0.185 mM) that is considerably lower than that for f-(alpha)Val (0.458 mM). Based on amino acid sequence alignment, three dimensional structural modeling, and site-directed mutagenesis, Gly60 was found to be a determining residue for the activity towards f-(alpha)Val-His. A flexible surface loop region was also found to likely play an important role in accepting f-(alpha)Val-His.

Review of fructosyl amino acid oxidase engineering research: a glimpse into the future of hemoglobin A1c biosensing.

Glycated proteins, particularly glycated hemoglobin A1c, are important markers for assessing the effectiveness of diabetes treatment. Convenient and reproducible assay systems based on the enzyme fructosyl amino acid oxidase (FAOD) have become attractive alternatives to conventional detection methods. We review the available FAOD-based assays for measurement of glycated proteins as well as the recent advances and future direction of FAOD research. Future research is expected to lead to the next generation of convenient, simple, and economical sensors for glycated protein, ideally suited for point-of-care treatment and self-monitoring applications.