Electronically Type-Sorted Carbon Nanotube-Based Electrochemical Biosensors with Glucose Oxidase and Dehydrogenase

An electrochemical enzyme biosensor with electronically type-sorted (metallic and semiconducting) single-walled carbon nanotubes (SWNTs) for use in aqueous media is presented. This research investigates how the electronic types of SWNTs influence the amperometric response of enzyme biosensors. To conduct a clear evaluation, a simple layer-by-layer process based on a plasma-polymerized nano thin film (PPF) was adopted because a PPF is an inactive matrix that can form a well-defined nanostructure composed of SWNTs and enzyme. For a biosensor with the glucose oxidase (GOx) enzyme in the presence of oxygen, the response of a metallic SWNT-GOx electrode was 2 times larger than that of a semiconducting SWNT-GOx electrode. In contrast, in the absence of oxygen, the response of the semiconducting SWNT-GOx electrode was retained, whereas that of the metallic SWNT-GOx electrode was significantly reduced. This indicates that direct electron transfer occurred with the semiconducting SWNT-GOx electrode, whereas the metallic SWNT-GOx electrode was dominated by a hydrogen peroxide pathway caused by an enzymatic reaction. For a biosensor with the glucose dehydrogenase (GDH; oxygen-independent catalysis) enzyme, the response of the semiconducting SWNT-GDH electrode was 4 times larger than that of the metallic SWNT-GDH electrode. Electrochemical impedance spectroscopy was used to show that the semiconducting SWNT network has less resistance for electron transfer than the metallic SWNT network. Therefore, it was concluded that semiconducting SWNTs are more suitable than metallic SWNTs for electrochemical enzyme biosensors in terms of direct electron transfer as a detection mechanism. This study makes a valuable contribution toward the development of electrochemical biosensors that employ sorted SWNTs and various enzymes

Characterization of Nitrogen-Rich Coating Films with Atmospheric-Pressure Plasma Generated by Re-Entrant Microwave Cavity

The deposition and characterization of nitrogen-rich coating films using atmospheric-pressure plasma generated with a re-entrant cylindrical microwave cavity is presented. This system enables simple matching, stable plasma, and free space under the orifice of plasma steam. Allylamine and acetonitrile are employed as monomers, whereas argon is used as the carrier gas. The effective area of the hydrophilic coating film is 55 mm in diameter and the deposition rate is 10 nm min^–1. X-ray photoelectron spectroscopy measurements show that the surfaces of these films contain a high concentration of nitrogen atoms and primary amine groups. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry shows that the coating films have a large molecular weight (>200 kDa). The surface morphology is very flat (ca. 1 nm). The experimental results indicate that a highly cross-linked three-dimensional polymer matrix is formed and atmospheric-pressure plasma deposition is successfully achieved

Electrochemical Study of Dopamine at Electrode Fabricated by Cellulose-Assisted Aqueous Dispersion of Long-Length Carbon Nanotube

A long-length (hundred micrometers) carbon nanotube is successfully dispersed in aqueous solution with surfactant cellulose while maintaining its length. An electrochemical study of the synthetic pathway of dopamine (DA), dopamine-<i>o</i>-quinone (DAQ), leucodopaminechrome (LDAC), and dopaminechrome (DAC) at the electrode fabricated by the long-length carbon nanotube dispersed solution is presented. The sequence DA ⇌ DAQ ⇀ LDAC ⇌ DAC for the reaction is electron transfer-chemical reaction-electron transfer (ECE)-type, which is a chemical reaction (DAQ ⇀ LDAC, C) interposed between two electron transfer reactions (DA ⇌ DAQ and LDAC ⇌ DAC, E). The salient electrochemical signals due to both DA ⇌ DAQ and LDAC ⇌ DAC can be obtained at the long-length carbon nanotube electrode, unlike other carbon electrodes such as carbon paste, graphene, fullerene, nanofiber, and graphite. The overall reaction is dominated by step DAQ ⇀ LDAC and is sensitive to pH. With cyclic voltammetry in acidic media, the peak current due to LDAC ⇀ DAC disappeared at a higher scan rate because the reaction rate for DAQ ⇀ LDAC was so slow that DAQ was completely consumed in the electron transfer of DAQ ⇀ DA before the chemical reaction of DAQ ⇀ LDAC could go forward. In alkaline media, the peak height due to DAC ⇀ LDAC became as high as that due to DA ⇀ DAQ because the DAQ ⇀ LDAC rate became fast enough that a sufficient amount of LDAC was generated for the subsequent reaction of LDAC ⇀ DAC. Concomitantly, the reaction DAQ + LDAC ⇌ DA + DAC was generated. Quantitative and selective detection of dopamine based on the signal due to LDAC ⇀ DAC is possible just as in the conventional strategy of direct oxidation of dopamine (DA ⇀ DAQ)

Mediatorless Direct Electron Transfer between Flavin Adenine Dinucleotide-Dependent Glucose Dehydrogenase and Single-Walled Carbon Nanotubes

The flavoenzymes flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) and oxidase (FAD-GOx) do not undergo direct electron transfer (DET) at conventional electrodes, because the flavin adenine dinucleotide (FAD) cofactor is buried deeply (∼1.4 nm) below the protein surface. We present a mediator-less DET between oxygen-insensitive FAD-GDH and single-walled carbon nanotubes (SWCNTs). A glucose-concentration-dependent current (GCDC) is observed at the electrode with the combination of glycosylated FAD-GDH and debundled SWCNTs; the GCDC, because of an increase in the polarized potential during potential sweep voltammetry, increases steeply (+0.1 V of onset, 1.2 mA cm^–2 at +0.6 V 48 mM glucose) without the appearance of the FAD redox peak at −0.45 V. In the control experiment, the GCDC is not observed at the counterpart with either bundled SWCNTs or debundled multiwalled carbon nanotubes (MWCNTs). In the control experiment, the GCDC is observed at an analogous electrode based on oxygen-sensitive FAD-GOx with all CNT types (bundled SWCNTs, debundled SWCNTs, and debundled MWCNTs) in the presence of oxygen because oxygen acts as a natural and mobile mediator. Therefore, observation of the GCDC at the electrode with oxygen-insensitive FAD-GDH and debundled SWCNTs provides evidence of mediator-less DET, even though oxygen is present. Details of the DET are discussed with respect to the recently reported crystallographic model of FAD-GDH. The three-dimensional globular FAD-GDH molecule is 4.5 nm × 5.6 nm × 7.8 nm, which is larger than the 1.2 nm diameter of an individual SWCNT and smaller than the 10 nm diameter of an individual MWCNT and the 1 μm size of a SWCNT bundle. Only individual SWCNTs can be plugged into the groove of FAD-GDH, which is close to and within 1.0 nm of FAD, while maintaining their catalytic activity. Images obtained using transmission electron and atomic force microscopies support the stated configuration of FAD-GDH molecules and debundled SWCNTs. We demonstrate that DET can be explained by quantum tunneling theory. Electrochemical experiments with various FAD-GDHs suggest that (i) DET with debundling SWCNT can be applied to any type of FAD-GDH, (ii) the electrode with various types of FAD-GDH implements superior functions (compared to an analogous electrode with FAD-GOx and nicotineamide adenine dinucleotide-GDH), and (iii) glycan chains present on FAD-GDH prevent denaturation when the SWCNT is close to FAD

Thermophilic <i>Talaromyces emersonii</i> Flavin Adenine Dinucleotide-Dependent Glucose Dehydrogenase Bioanode for Biosensor and Biofuel Cell Applications

Flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (GDH) was identified and cloned from thermophilic filamentous fungi Talaromyces emersonii using the homology cloning method. A direct electron transfer bioanode composed of T. emersonii FAD-GDH and a single-walled carbon nanotube was produced. Enzymes from thermophilic microorganisms generally have low activity at ambient temperature; however, the T. emersonii FAD-GDH bioanode exhibits a large anodic current due to the enzymatic reaction (1 mA cm^–2) at ambient temperature. Furthermore, the T. emersonii FAD-GDH bioanode worked at 70 °C for 12 h. This is the first report of a bioanode with a glucose-catalyzing enzyme from a thermophilic microorganism that has potential for biosensor and biofuel cell applications. In addition, we demonstrate how the glycoforms of T. emersonii FAD-GDHs expressed by various hosts influence the electrochemical properties of the bioanode

Erratum: Yoshimi, Y., et al. Size of Heparin-Imprinted Nanoparticles Reflects the Matched Interactions with the Target Molecule. Sensors 2019, 19, 2415

The authors wish to make the following erratum to this paper [1]: The affliation 5 of co-author Ewa Moczko should be corrected into: “Departamento de Química Ambiental, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Concepción 4090541, Chile”. The authors would like to apologize for any inconvenience caused to the readers by these changes