Continuous glucose monitoring (CGM) systems are most important in the current Type I diabetes care and as component for the development of artificial pancreas systems because the amount of insulin ...being supplied is calculated based on the CGM results. Therefore, to stably and accurately control the blood glucose level, CGM should be stable and accurate for a long period. We have been engaged in the biomolecular engineering and application of FAD dependent glucose dehydrogenase complex (FADGDH) which is capable of direct electron transfer. In this study, we report the development of the third-generation type open circuit potential (OCP) principle-based glucose sensor with direct electron transfer FADGDH immobilized on gold electrodes using a self-assembled monolayer (SAM). We developed a novel algorithm for OCP-based glucose sensors. By employing this new algorithm, high reproducibility of measurement and sensor preparation were achieved. In addition, the signal was not affected by the presence of acetaminophen and ascorbic acid in the sample solution. The thus optimized third-generation OCP-based glucose sensor could be operated continuously for more than 9 days without significant change in the signal, sensitivity and dynamic range, indicating its potential application for CGM systems.
•The third-generation type open circuit potential principle-based glucose sensor was developed.•A novel OCP measurement protocol, which discharge charged electron before measurement, was proposed.•This sensor showed high reproducibility in the measurement and electrode preparation.•This sensor signal was not affected by the presence of 340 µM ascorbic acid or 2.6 mM of acetaminophen in the sample solution.•This sensor could measure the glucose concentration stably and continuously during 9 days.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The evolution from first-generation through third-generation glucose sensors has witnessed the appearance of a number of very diverse oxidoreductases, which vary tremendously in terms of origin, ...structure, substrate specificity, cofactor used as primary electron acceptor, and acceptable final electron acceptor. This article summarizes our present knowledge of redox enzymes currently utilized in commercially available glucose monitoring systems to promote a fuller appreciation of enzymatic properties and principles employed in blood glucose monitoring to help avoid potential errors.
Full text
Available for:
NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
In order to construct an aptasensor, aptamers that show high affinity for target molecules are required. While the systematic evolution of ligands by exponential enrichment (SELEX) is an efficient ...method for selecting aptamers, it sometimes fails to obtain aptamers with high affinity and so additional improvements are required. We applied a genetic algorithm (GA) to post-SELEX screening as an
in silico maturation of aptamers. First, we pre-selected DNA aptamers against prostate specific antigen (PSA) through three rounds of SELEX. To improve the PSA-binding ability of the aptamers, we carried out post-SELEX screening using GA with the pre-selected oligonucleotide sequences. For screening using GA, we replicated the oligonucleotide sequences obtained through SELEX, crossed over and mutated
in silico resulting in 20 sequences. Those oligonucleotide sequences were synthesized and assayed
in vitro. Then, the oligonucleotides were ranked according to PSA-binding ability and the top sequences were selected for the next cycle of GA operation. After GA operations, we identified the aptamer showing a 48-fold higher PSA-binding ability than candidates obtained by SELEX. The dissociation constant (
K
D) of the obtained aptamer was estimated to be several tens of nM. We demonstrated sensing of PSA using the obtained aptamer and succeeded in sensing PSA concentrations between 40 and 100
nM. This is the first report of a DNA aptamer against PSA and its application to PSA sensing.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The development of wearable multiplexed biosensors has been focused on systems to measure sweat l-lactate and other metabolites, where the employment of the direct electron transfer (DET) principle ...is expected. In this paper, a fusion enzyme between an engineered l-lactate oxidase derived from Aerococcus viridans, AvLOx A96L/N212K mutant, which is minimized its oxidase activity and b-type cytochrome protein was constructed to realize multiplexed DET-type lactate and glucose sensors. The sensor with a fusion enzyme showed DET to a gold electrode, with a limited operational range less than 0.5 mM. A mutation was introduced into the fusion enzyme to increase Km value and eliminate its substrate inhibition to construct “b2LOxS”. Together with the employment of an outer membrane, the detection range of the sensor with b2LOxS was expanded up to 10 mM. A simultaneous lactate and glucose monitoring system was constructed using a flexible thin-film multiplexed electrodes with b2LOxS and a DET-type glucose dehydrogenase, and evaluated their performance in the artificial sweat. The sensors achieved simultaneous detection of lactate and glucose without cross-talking error, with the detected linear ranges of 0.5–20 mM for lactate and 0.1–5 mM for glucose, sensitivities of 4.1 nA/mM∙mm2 for lactate and 56 nA/mM∙mm2 for glucose, and limit of detections of 0.41 mM for lactate and 0.057 mM for glucose. The impact of the presence of electrochemical interferants (ascorbic acid, acetaminophen and uric acid), was revealed to be negligible. This is the first report of the DET-type enzyme based lactate and glucose dual sensing systems.
•The direct electron transfer (DET) type lactate and glucose enzyme sensor was developed.•Oxygen insensitive lactate oxidase (LOx) mutant was fused with b-type cytochrome protein to construct DET-type LOx.•A mutation was introduced in DET-type LOx to relieve the substrate inhibition and low Km value.•A flexible thin-film multiplexed electrodes with DET-type LOx and a DET-type glucose dehydrogenase were constructed.•Simultaneous lactate and glucose detection was achieved in the artificial sweat.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Antibody–enzyme complexes (AECs) are ideal sensing elements, especially when oxidoreductases are used as the enzymes in the complex, with the potential to carry out rapid electrochemical ...measurements. However, conventional methods for the fabrication of AECs, including direct fusion and chemical conjugation, are associated with issues regarding the generation of insoluble aggregates and production of homogeneous AECs. Here, we developed a convenient and universal method for the fabrication of homogeneous AECs using the SpyCatcher/SpyTag system. We used an anti-epidermal growth factor receptor (EGFR) variable domain of a heavy chain antibody (VHH) and a glucose dehydrogenase (GDH) derived from Aspergillus flavus (AfGDH) as the model antibody and enzyme, respectively. Both SpyTag-fused VHH and SpyCatcher-fused AfGDH were successfully prepared using an Escherichia coli expression system, whereas anti-EGFR AECs were produced by simply mixing the two fusion proteins. A bivalent AEC, AfGDH with two VHH at both terminals, was also prepared and exhibited an increased affinity. A soluble EGFR was successfully detected in a dose-dependent manner using immobilized anti-EGFR immunoglobulin G (IgG) and bivalent AEC. We also confirmed the universality of this AEC fabricating method by applying it to another VHH. This method results in the convenient and universal preparation of sensing elements with the potential for electrochemical measurement.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Electrochemical aptamer-based biosensors (E-ABs) are attractive candidates for use in biomarker detection systems due to their sensitivity, rapid response, and design flexibility. There are only ...several redox probes that were employed previously for this application, and a combination of redox probes affords some advantages in target detection. Thus, it would be advantageous to study new redox probes in an E-AB system. In this study, we report the use of amine-reactive phenazine ethosulfate (arPES) for E-AB through its conjugation to the terminus of thrombin-binding aptamer. The constructed E-AB can detect thrombin by square-wave voltammetry (SWV), showing peak current at -0.15 V vs. Ag/AgCl at pH 7, which differs from redox probes used previously for E-ABs. We also compared the characteristics of PES as a redox probe for E-AB to methylene blue (MB), which is widely used. arPES showed stable signal at physiological pH. Moreover, the pH profile of arPES modified thrombin-binding aptamer revealed the potential application of arPES for a simultaneous multianalyte detection system. This could be achieved using different aptamers with several redox probes in tandem that harbor various electrochemical peak potentials. Our findings present a great opportunity to improve the current standard of biological fluid monitoring using E-AB.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We report the first three-dimensional structure of fungus-derived glucose dehydrogenase using flavin adenine dinucleotide (FAD) as the cofactor. This is currently the most advanced and popular enzyme ...used in glucose sensor strips manufactured for glycemic control by diabetic patients. We prepared recombinant nonglycosylated FAD-dependent glucose dehydrogenase (FADGDH) derived from Aspergillus flavus (AfGDH) and obtained the X-ray structures of the binary complex of enzyme and reduced FAD at a resolution of 1.78 Å and the ternary complex with reduced FAD and D-glucono-1,5-lactone (LGC) at a resolution of 1.57 Å. The overall structure is similar to that of fungal glucose oxidases (GOxs) reported till date. The ternary complex with reduced FAD and LGC revealed the residues recognizing the substrate. His505 and His548 were subjected for site-directed mutagenesis studies, and these two residues were revealed to form the catalytic pair, as those conserved in GOxs. The absence of residues that recognize the sixth hydroxyl group of the glucose of AfGDH, and the presence of significant cavity around the active site may account for this enzyme activity toward xylose. The structural information will contribute to the further engineering of FADGDH for use in more reliable and economical biosensing technology for diabetes management.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In this review, recent progress in the engineering of the oxidative half-reaction of flavin-dependent oxidases and dehydrogenases is discussed, considering their current and future applications in ...bioelectrochemical studies, such as for the development of biosensors and biofuel cells. There have been two approaches in the studies of oxidative half-reaction: engineering of the oxidative half-reaction with oxygen, and engineering of the preference for artificial electron acceptors. The challenges for engineering oxidative half-reactions with oxygen are further categorized into the following approaches: (1) mutation to the putative residues that compose the cavity where oxygen may be located, (2) investigation of the vicinities where the reaction with oxygen may take place, and (3) investigation of possible oxygen access routes to the isoalloxazine ring. Among these approaches, introducing a mutation at the oxygen access route to the isoalloxazine ring represents the most versatile and effective strategy. Studies to engineer the preference of artificial electron acceptors are categorized into three different approaches: (1) engineering of the charge at the residues around the substrate entrance, (2) engineering of a cavity in the vicinity of flavin, and (3) decreasing the glycosylation degree of enzymes. Among these approaches, altering the charge in the vicinity where the electron acceptor may be accessed will be most relevant.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
PDF
