A high performance nanocomposite based bioanode for biofuel cell and biosensor application.

Herein, to improve the current density and sensitivity for biofuel cell and glucose sensing application, a bioanode based on redox polymer (PEI-Fc) binding polydopamine (PDA) coated MWCNTs (PEI-Fc/PDA/MWCNTs) nanocomposite and glucose oxidase (GOD) was fabricated. PDA/MWCNTs nanocomposite was prepared by spontaneous self-polymerization of dopamine on MWCNTs surface and the PEI-Fc/PDA/MWCNTs nanocomposite was prepared by a simple self-assembly method. The PEI-Fc/PDA/MWCNTs nanocomposite and the resulting bioanode were fully characterized. A maximum current density of 0.73 mA cm-2 at the resulting bioanode was obtained by linear sweep voltammetry (LSV) at the scan rate of 50 mV s-1 with 20 mM glucose concentration. Moreover, a linear range up to 4 mM, a high sensitivity of 57.2 µA mM-1 cm-2, a fast response time reaching 95% of the steady current (2 s) and a low limit of detection (0.024 mM) were achieved. The amperometric method demonstrated both the sensitivity and the stability of the bioanode for glucose-sensing was improved by the employed PDA layer. Finally, the biosensor was used for glucose detection in human serum samples showing good recoveries. This study proposed an excellent functional material prepared by a facile self-assembled method for applying in biofuel cells and second-generation biosensors.

Electrochemical characteristics of a gold nanoparticle-modified controlled enzyme-electrode contact junction electrode.

Biodevices in which biomolecules such as enzymes and antibodies are immobilized on the surface of electrode materials are capable of converting chemical energy into electrical energy, and are expected to contribute to solving energy problems and developing medical measurements especially as biobatteries and biosensors. Device performance depends on the interface formed between the biomolecule layer and electrode material, and the interface is required to simultaneously achieve a highly efficient enzymatic reaction and electron transfer. However, when enzymes were immobilized on a material surface, the enzymes undergoes a structural change due to the interaction between the enzyme and the electrode surface, making it difficult to maximize the function of the enzyme molecule on the material surface. In this study, we postulate that the structural change of the enzyme would be reduced and the electrochemical performance improved by making the contact area between the enzyme and the electrode extremely small and adsorbing it as a point. Therefore, we aimed to develop a high-power biodevice that retains enzyme structure and activity by interposing gold nanoparticles (AuNPs) between the enzyme and the electrode. The enzymatic and electrochemical properties of pyrroloquinoline quinone-dependent glucose dehydrogenase adsorbed on AuNPs of 5-40 nm diameter were investigated. We found that the characteristics differed among the particles, and the enzyme adsorbed on 20 nm AuNPs showed the best electrochemical characteristics.

Highly Efficient Multi-Step Oxidation Bioanode Using Microfluidic Channels.

With the rapid decline of fossil fuels, various types of biofuel cells (BFCs) are being developed as an alternative energy source. BFCs based on multi-enzyme cascade reactions are utilized to extract more electrons from substrates. Thus, more power density is obtained from a single molucule of substrate. In the present study, a bioanode that could extract six electrons from a single molecule of L-proline via a three-enzyme cascade reaction was developed and investigated for its possible use in BFCs. These enzymes were immobilized on the electrode to ensure highly efficient electron transfer. Then, oriented immobilization of enzymes was achieved using two types of self-assembled monolayers (SAMs). In addition, a microfluidic system was incorporated to achieve efficient electron transfer. The microfluidic system, in which the electrodes were arranged in a tooth-shaped comb, allowed for substrates to be supplied continuously to the cascade, which resulted in smooth electron transfer. Finally, we developed a high-performance bioanode which resulted in the accumulation of higher current density compared to that of a gold disc electrode (205.8 µA cm-2: approximately 187 times higher). This presents an opportunity for using the bioanode to develop high-performance BFCs in the future.

Formation of one-dimensional arrays of nanoparticles using segmented polyurethane nanofibers prepared by electrospinning.

The number density and the arrangement of metal nanoparticles in composite materials have a significant effect on their performance and hence their suitability for use in sensors and devices. Forming one-dimensional arrays of metal nanoparticles is one way of controlling their number density and arrangement in the devices. In this study, we fabricated one-dimensional arrays of gold nanoparticles by adsorbing them on linearly distributed hard segments present on the surfaces of segmented polyurethane nanofibers, which were produced by electrospinning under a stretching force. The length of the one-dimensional array was approximately 500 nm. Furthermore, the interparticle distance was almost constant at approximately 14 nm. Thus, the proposed method is suitable for fabricating one-dimensional arrays of metal nanoparticles with high precision.

Effects of multicopper oxidase orientation in multiwalled carbon nanotube biocathodes on direct electron transfer.

In this study, multicopper oxidase (MCO) was immobilized on multiwalled carbon nanotubes (MWCNTs) at two different orientations, and the electrochemical properties of the resulting cathodes were investigated. Using N- or C-terminal His-tagged MCO and MWCNTs, we constructed two types of cathodes. We assumed that the distance between the type 1 (T1)Cu of the C-terminal His-tagged MCO and the MWCNT surface was lesser than that between the T1Cu of the N-terminal His-tagged MCO and the MWCNT surface. In addition, in the C-terminal His-tagged MCO, T1Cu was expected to be closer to the MWCNT surface than the type 2/type 3 Cu site. The current density of the modified electrode with a C-terminal His-tagged MCO immobilized on an MWCNT surface was 1.3-fold higher than that of the electrode with an N-terminal His-tagged MCO immobilized on an MWCNT surface. In addition, the amount of H2 O2 produced by the N-terminal His-tagged MCO immobilized MWCNT modified electrodes was 2.3-fold higher than that produced by the C-terminal His-tagged MCO immobilized MWCNT electrodes. In direct electron transfer (DET)-type biocathodes, both the MCO orientation and the distance between the T1Cu of MCO and the electrode surface are important. The authors succeeded in constructing highly efficient DET-type electrodes.

Development of Biofuel Cell Using a Complex of Highly Oriented Immobilized His-Tagged Enzyme and Carbon Nanotube Surface Through a Pyrene Derivative.

For increasing the output of biofuel cells, increasing the cooperation between enzyme reaction and electron transfer on the electrode surface is essential. Highly oriented immobilization of enzymes onto a carbon nanotube (CNT) with a large specific surface area and excellent conductivity would increase the potential for their application as biosensors and biofuel cells, by utilizing the electron transfer between the electrode-molecular layer. In this study, we prepared a CNT-enzyme complex with highly oriented immobilization of enzyme onto the CNT surface. The complex showed excellent electrical characteristics, and could be used to develop biodevices that enable efficient electron transfer. Multi-walled carbon nanotubes (MWCNT) were dispersed by pyrene butyric acid N-hydroxysuccinimide ester, and then N-(5-amino-1-carboxypentyl) iminodiacetic acid (AB-NTA) and NiCl2 were added to modify the NTA-Ni2+ complex on the CNT surface. Pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH) was immobilized on the CNT surface through a genetically introduced His-tag. Formation of the MWCNT-enzyme complex was confirmed by monitoring the catalytic current electrochemically to indicate the enzymatic activity. PQQ-GDH was also immobilized onto a highly ordered pyrolytic graphite surface using a similar process, and the enzyme monolayer was visualized by atomic force microscopy to confirm its structural properties. A biofuel cell was constructed using the prepared CNT-enzyme complex and output evaluation was carried out. As a result, an output of 32 µW/cm² could be obtained without mediators.

Construction of a novel bioanode for amino acid powered fuel cells through an artificial enzyme cascade pathway.

OBJECTIVE: The construction of a novel bioanode based on L-proline oxidation using a cascade reaction pathway comprised of thermostable dehydrogenases. RESULTS: A novel multi-enzymatic cascade pathway, containing four kinds of dehydrogenases from thermophiles (dye-linked L-proline dehydrogenase, nicotinamide adenine dinucleotide (NAD)-dependent Δ1-pyrroline-5-carboxylate dehydrogenase, NAD-dependent L-glutamate dehydrogenase and dye-linked NADH dehydrogenase), was designed for the generation of six-electrons from one molecule of L-proline. The current density of the four-dehydrogenase-immobilized electrode, with a voltage of + 450 mV (relative to that of Ag/AgCl), was 226.8 µA/cm2 in the presence of 10 mM L-proline and 0.5 mM ferrocene carboxylate at 50 °C. This value was 4.2-fold higher than that of a similar electrode containing a single dehydrogenase. In addition, about 54% of the initial current in the multi-enzyme cascade bioanode was maintained even after 15 days. CONCLUSIONS: Efficient deep oxidation of L-proline by multiple-enzyme cascade reactions was achieved in our designed electrode. The multi-enzyme cascade bioanode, which was built using thermophilic dehydrogenases, showed high durability at room temperature. The long-term stability of the bioanode indicates that it shows great potential for applications as a long-lived enzymatic fuel cell.

Construction of a biocathode using the multicopper oxidase from the hyperthermophilic archaeon, Pyrobaculum aerophilum: towards a long-life biobattery.

OBJECTIVES: The life of biobatteries remains an issue due to loss of enzyme activity over time. In this study, we sought to develop a biobattery with a long life using a hyperthermophilic enzyme. RESULTS: We hypothesized that use of such hyperthermophilic enzymes would allow for the biofuel cells to have a long battery life. Using pyrroloquinoline quinone-glucose dehydrogenase and the multicopper oxidase from Pyrobaculum aerophilum, we constructed an anode and cathode. The maximum output was 11 µW at 0.2 V, and the stability of the both electrode was maintained at 70 % after 14 days. CONCLUSION: The biofuel cells that use hyperthermophilic enzymes may prolong their life.

Selective miR-21 detection technology based on photocrosslinkable artificial nucleic acid-modified magnetic particles and hybridization chain reaction.

Recently, microRNA (miRNA) detection in blood has attracted attention as a new early detection technology for cancer. The extraction of target miRNA is a necessary preliminary step for detection; however, currently, most extraction methods extract all RNA from the blood, which limits the detection selectivity. Therefore, a method for the selective extraction and detection of target miRNA from blood is very important. In this study, we utilized photocrosslinkable artificial nucleic acids and the hybridization chain reaction (HCR) in an attempt to improve upon the current standard method RT-qPCR, which is hampered by problems with primer design and enzymatic amplification. By introducing photocrosslinkable artificial nucleic acids to oligonucleotide probes modified with magnetic particles with a sequence complementary to that of the target miRNA and irradiating them with light, covalent bonds were formed between the target miRNA and the oligonucleotide probes. These tight covalent bonds enabled the capture of miRNA in blood, and intensive washing ensured that only the target miRNA were extracted. After extraction, two types of DNA (H1 and H2) modified with fluorescent dyes were added and the fluorescence signals were amplified by the HCR in the presence of the target miRNA bound to the photocrosslinkable artificial nucleic acids, allowing for isothermal and enzyme-free miRNA detection. The novel method is suitable for selective miRNA detection in real blood samples. Because the reaction proceeds isothermally and no specialized equipment is used for washing, this detection technology is simple and selective and suitable for application to point-of-care technology using microfluidic devices.

A Biochemical Corrosion Monitoring Sensor with a Silver/Carbon Comb Structure for the Detection of Living Escherichia coli.

For the detection and monitoring of live bacteria, we propose a biochemical corrosion monitoring (BCM) sensor that measures galvanic current by using a Ag/C sensor comprising silver and carbon comb electrodes. The deposition of an Escherichia coli suspension containing an LB liquid medium on the Ag/C sensor increased the galvanic current. The time required for the current to reach 20 nA is defined as T20. T20 tends to decrease as the initial number of E. coli in the E. coli solution increases. A linear relationship was obtained between the logarithm of the E. coli count and T20 in a bacterial count range of 1-108 cfu/mL under culture conditions in which the growth rate of the bacteria was constant. Hence, the number of live E. coli could be determined from T20. Ag2S precipitation was observed on the surface of the Ag electrode of the Ag/C sensor, where an increase in the current was observed. This generation of galvanic current was attributed to the reaction between a small amount of free H2S metabolized by E. coli in the bacterial solution during its growth process and Ag-the sensor anode. The Ag/C sensor can detect a free H2S concentration of 0.041 µM in the E. coli solution. This novel biochemical sensor can monitor the growth behavior of living organisms without damaging them.

Photo-Cross-Linked Probe-Modified Magnetic Particles for the Selective and Reliable Recovery of Nucleic Acids.

Polymerase chain reaction (PCR) assays are used to diagnose various infectious diseases such as Coronavirus disease 2019 by detecting the nucleic acids of the pathogen. However, in practice, the yield of the extraction process and the inhibition of the reverse transcription reaction and PCR by foreign substances reduce the sensitivity and may yield false negative results. The sensitivity of the PCR test can be improved by using technologies that can reliably capture the target nucleic acid and remove foreign substances. In this study, we developed photo-cross-linkable probe-modified magnetic particles (PPMPs) for the sequence-specific recovery of target nucleic acids using photo-cross-linkable artificial nucleic acid probes and magnetic particles. Nucleic acid probes modified with photo-cross-linkable artificial nucleic acids can hybridize with the target nucleic acids in a sequence-specific manner and then securely capture the target nucleic acids by UV irradiation-mediated covalent bonding. Then the target nucleic acid is detected by trapping the target-bound probe on the surface of the magnetic particles and subjecting these collected magnetic particles to PCR. Recovery of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) N gene pseudo-DNA (120 bp) was performed using PPMPs. We confirmed that the PPMPs captured the target consistently even after washes were done with denaturing agents and surfactants. Even in the presence of foreign DNA fragments, PPMPs were able to specifically recover the target DNA. This method allows for a more accurate detection by recovering only the target DNA for PCR. Hence, PPMPs can be successfully used for PCR-mediated detection of SARS-CoV-2 and other pathogens whose nucleic acid sequences are known.

Biocathode design with highly-oriented immobilization of multi-copper oxidase from Pyrobaculum aerophilum onto a single-walled carbon nanotube surface via a carbon nanotube-binding peptide.

Biofuel cells generate electric energy using an enzyme as a catalyst for an electrode but their stability and low battery output pose problems for practical use. To solve these problems, this study aimed to build a long-lasting and high-output biocathode as a catalyst using a highly stable hyperthermophilic archaeal enzyme, multi-copper oxidase, from Pyrobaculum aerophilum (McoP). To increase output, McoP was oriented and immobilized on single-walled carbon nanotubes (SWCNT) with a high specific surface area, and the electrode interface was designed to achieve highly efficient electron transfer between the enzyme and electrode. Type 1 copper (T1Cu), an electron-accepting site in the McoP molecule, is located near the C-terminus. Therefore, McoP was prepared by genetically engineering a CNT-binding peptide with the sequence LLADTTHHRPWT, at the C-terminus of McoP (McoP-CBP). We then constructed an electrode using a complex in which McoP-CBP was aligned and immobilized on SWCNT, and then clarified the effect of CBP. The amounts of immobilized enzymes on McoP-SWCNT and (McoP-CBP)-SWCNT complexes were almost equal. CV measurement of the electrode modified with both complexes showed 5.4 times greater current density in the catalytic reaction of the (McoP-CBP)-SWCNT/GC electrode than in the McoP-SWCNT/GC electrode. This is probably because CBP fusion immobilize the enzyme on SWCNTs in an orientational manner, and T1Cu, the oxidation-reduction site in McoP, is close to the electrode, which improves electron transfer efficiency.

Site-Directed Mutagenesis of Multicopper Oxidase from Hyperthermophilic Archaea for High-Voltage Biofuel Cells.

Enzymes from hyperthermophilic archaea are potential candidates for industrial use because of their superior pH, thermal, and long-term stability, and are expected to improve the long-term stability of biofuel cells (BFCs). However, the reported multicopper oxidase (MCO) from hyperthermophilic archaea has lower redox potential than MCOs from other organisms, which leads to a decrease in the cell voltage of BFCs. In this study, we attempted to positively shift the redox potential of the MCO from hyperthermophilic archaeon Pyrobaculum aerophilum (McoP). Mutations (M470L and M470F) were introduced into the axial ligand of the T1 copper atom of McoP, and the enzymatic chemistry and redox potentials were compared with that of the parent (M470). The redox potentials of M470L and M470F shifted positively by about 0.07 V compared with that of M470. In addition, the catalytic activity of the mutants towards 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) increased 1.2-1.3-fold. The thermal stability of the mutants and the electrocatalytic performance for O2 reduction of M470F was slightly reduced compared with that of M470. This research provides useful enzymes for application as biocathode catalysts for high-voltage BFCs.

Activity enhancement of multicopper oxidase from a hyperthermophile via directed evolution, and its application as the element of a high performance biocathode.

Although multicopper oxidase from the hyperthermophilic archaeon Pyrobaculum aerophilum (McoP) can be particularly useful in biotechnological applications, e.g., as a specific catalyst at the biocathode of biofuel cells (BFCs), owing to its high stability against extremely high temperatures and across a wide range of pH values, this application potential remains limited due to the enzyme's low catalytic activity. A directed evolution strategy was conducted to improve McoP catalytic activity, and the No. 571 mutant containing four amino acid substitutions was identified, with specific activity approximately 9-fold higher than that of the wild type enzyme. Among the substitutions, the single amino acid mutant F290I was essential in enhancing catalytic activity, with a specific activity approximately 12-fold higher than that of the wild type enzyme. F290I thermostability and pH stability were notably comparable with values obtained for the wild type. Crystal structure analysis suggested that the F290I mutant increased loop flexibility near the T1 Cu center, and affected electron transfer between the enzyme and substrate. Additionally, electric current density of the F290I mutant-immobilized electrode was 7-fold higher than that of the wild type-immobilized one. These results indicated that F290I mutant was a superior catalyst with potential in practical biotechnological applications.

Electrochemical characteristics of a hyperthermophilic enzyme in microdroplets stirred and heated by surface acoustic waves.

Micro total analysis system (µTAS) is expected to be applied in various fields. In particular, since electrochemical measurement is inexpensive and easy, electrochemical measurement can be integrated with a microchannel. However, electrochemical detection sensitivity in a microchannel is lowered because the diffusion of the detection target is limited. In an ordinary electrochemical detection system, using a stirrer in a beaker can overcome limited diffusion. We previously proposed a new detection system that combines a microliquid solution agitation technology using surface acoustic waves (SAWs) with the µTAS. The SAWs function as microstirrers, thus making electrochemical detection possible by overcoming limited diffusion of the sample. However, when the solution is stirred by the SAWs, the temperature of the solution increases to 70°C due to vibrational energy. This leads to enzyme inactivation and impaired electrochemical response. Therefore, in this study, we used a hyperthermophile-derived enzyme. Temperature and electrochemical characteristics of the detection system using SAWs and a multi-copper oxidase (MCO) derived from the hyperthermophilic archaea Pyrobaculum aerophilum were studied. Laccase, which is an MCO derived from the thermophilic fungus Trametes versicolor, was also studied. We also characterized the enzyme-electrochemical reaction using SAWs by comparing the magnitude of the reduction current obtained using the two enzymes with different heat resistances. We observed an increase in the electrochemical response with the SAWs, without impaired enzyme activity. Thus, the use of a thermostable enzyme is suitable for the development of a biosensor that uses SAWs for agitation.