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en: Rapid, high-sensitivity detection of biomolecules using dual-comb biosensing

en: Rapid, sensitive detection of biomolecules is important for biosensing of infectious pathogens as well as biomarkers and pollutants. For example, biosensing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still strongly required for the fight against coronavirus disease 2019 (COVID-19) pandemic. Here, we aim to achieve the rapid and sensitive detection of SARS-CoV-2 nucleocapsid protein antigen by enhancing the performance of optical biosensing based on optical frequency combs (OFC). The virus-concentration-dependent optical spectrum shift produced by antigen-antibody interactions is transformed into a photonic radio-frequency (RF) shift by a frequency conversion between the optical and RF regions in the OFC, facilitating rapid and sensitive detection with well-established electrical frequency measurements. Furthermore, active-dummy temperature-drift compensation with a dual-comb configuration enables the very small change in the virus-concentration-dependent signal to be extracted from the large, variable background signal caused by temperature disturbance. The achieved performance of dual-comb biosensing will greatly enhance the applicability of biosensors to viruses, biomarkers, environmental hormones, and so on.

en: Scientific Reports

ja: Scientific Reports


en: Real-time hybrid angular-interrogation surface plasmon resonance sensor in the near-infrared region for wide dynamic range refractive index sensing


en: Highly sensitive detection of nucleocapsid protein from SARS-CoV-2 using a near-infrared surface plasmon resonance sensing system

en: Optics Continuum

ja: Optics Continuum


en: Beam-angle-scanning surface plasmon resonance sensor for rapid, high-precision sensing of refractive index and bio-molecules


en: Ultrasensitive detection of SARS-CoV-2 nucleocapsid protein using large gold nanoparticle-enhanced surface plasmon resonance.

en: The COVID-19 pandemic has created urgent demand for rapid detection of the SARS-CoV-2 coronavirus. Herein, we report highly sensitive detection of SARS-CoV-2 nucleocapsid protein (N protein) using nanoparticle-enhanced surface plasmon resonance (SPR) techniques. A crucial plasmonic role in significantly enhancing the limit of detection (LOD) is revealed for exceptionally large gold nanoparticles (AuNPs) with diameters of hundreds of nm. SPR enhanced by these large nanoparticles lowered the LOD of SARS-CoV-2 N protein to 85 fM, resulting in the highest SPR detection sensitivity ever obtained for SARS-CoV-2 N protein.


en: Molecularly Imprinted Artificial Biointerface for an Enzyme-Free Glucose Transistor.

en: obtained by nonelectrical detection methods. Moreover, the GluMIP-coated gate FET sensor shows an approximately 200-fold higher selectivity for glucose than for fructose. This is because glucose binds to PBA more selectively than fructose in the templates, resulting in the generation of negative charges. The electrical properties of the MIP-coated electrode are also evaluated by measuring capacitance. Our work suggests a new strategy of designing a platform based on the MIP-coated gate FET biosensor, which is suitable for a highly selective, sensitive, enzyme-free biosensing system.

en: ACS Applied Materials & Interfaces

ja: ACS Applied Materials & Interfaces


en: Well-designed dopamine-imprinted polymer interface for selective and quantitative dopamine detection among catecholamines using a potentiometric biosensor.

en: We report a well-designed biointerface enabling the selective and quantitative detection of dopamine (DA) using a potentiometric biosensor. To enhance the detection selectivity of DA, a DA-templated molecularly imprinted polymer (DA-MIP) was synthesized on the extended Au gate electrode of a field-effect transistor (FET) biosensor. For a quantitative DA analysis, the thickness of the DA-MIP was controlled to ca. 60 nm by surface-initiated atom transfer radical polymerization (SI-ATRP). In this process, the DA-MIP was copolymerized with vinylphenylboronic acid (vinyl-PBA), inducing molecular charges at the biointerface of the FET gate electrode. These charges were generated by the diol-binding between PBA and dopamine (a catecholamine), and were directly detected as a change in surface potential. In fact, the surface potential at the gate of the DA-MIP-coated FET responded significantly to DA added at concentrations ranging from 40 nM to 20 μM, whereas that of a non-imprinted polymer (NIP)-coated FET hardly changed over this range. Moreover, by measuring the kinetic parameters and electrochemical properties of well-designed devices with various added catecholamines, we confirmed that the DA-MIP-coated FET biosensor selectively and quantitatively detects DA.

en: Biosensors and Bioelectronics

ja: Biosensors and Bioelectronics


en: Catecholamine Detection Using a Functionalized Poly(l-dopa)-Coated Gate Field-Effect Transistor.

en: ): 182 mV). Moreover, the limit of detection for each CA was 3.5 nM in LD, 12.0 nM in DA, 7.5 nM in NE, and 12.6 nM in EP. From these results, it is concluded that the poly(PBA-LD/LD)-coated gate FET could become a useful biosensor for neurotransmitters, hormones, and early detection of Parkinson's disease.

en: ACS Omega

ja: ACS Omega


en: Biocompatible Poly(catecholamine)-Film Electrode for Potentiometric Cell Sensing.

en: ) and proteins such as albumin. Thus, the pCA-film electrodes can be used in pH-sensitive and pH-selective biosensors. HeLa cells were cultivated on the surface of the pCA-film electrodes to monitor cellular activities. The surface potential of the pCA-film electrodes changed markedly because of cellular activity; therefore, the change in the hydrogen ion concentration around the cell/pCA-film interface could be monitored in real time. This was caused by carbon dioxide or lactic acid that is generated by cellular respiration and dissolves in the culture medium, resulting in the change of hydrogen concentration. pCA-film electrodes are suitable for use in biocompatible and pH-responsive biosensors, enabling the more selective detection of biological phenomena.

en: ACS Sensors

ja: ACS Sensors


en: Nonoptical Detection of Allergic Response with a Cell-Coupled Gate Field-Effect Transistor.

en: ) with hydroxyl groups is fully responsive to pH on the basis of the equilibrium reaction. The allergic response of RBL-2H3 cells on the gate was also confirmed by estimating the amount of β-hexosaminidase released together with histamine and was analyzed using the electrical properties based on an inflammatory response of secreted histamine with the vascular endothelial cell-based FET. Thus, the allergic responses were monitored in a nonoptical and real-time manner using the cell-based FETs with the cellular layers on the gate, which reproduced the in vivo system and were useful for the reliable detection of the allergic reaction.

en: Analytical Chemistry

ja: Analytical Chemistry


en: Ion Sensitive Transparent-Gate Transistor for Visible Cell Sensing.

en: film gate that includes an indium tin oxide (ITO) film as the source and drain electrodes is utilized. The pH response of the IS-TGT was found to be about 56 mV/pH, indicating approximately Nernstian response. Moreover, the potential signals of the IS-TGT for sodium and potassium ions, which are usually included in biological environments, were evaluated. The optical and electrical properties of the IS-TGT enable cell functions to be monitored simultaneously with microscopic observation and electrical measurement. A platform based on the IS-TGT can be used as a simple and cost-effective plate-cell-sensing system based on thin-film fabrication technology in the research field of life science.


en: Glucose-responsive hydrogel electrode for biocompatible glucose transistor.

en: applications such as eye contact lenses and sheets adhering to the skin.

ja: In this paper, we propose a highly sensitive and biocompatible glucose sensor using a semiconductor-based field effect transistor (FET) with a functionalized hydrogel. The principle of the FET device contributes to the easy detection of ionic charges with high sensitivity, and the hydrogel coated on the electrode enables the specific detection of glucose with biocompatibility. The copolymerized hydrogel on the Au gate electrode of the FET device is optimized by controlling the mixture ratio of biocompatible 2-hydroxyethylmethacrylate (HEMA) as the main monomer and vinylphenylboronic acid (VPBA) as a glucose-responsive monomer. The gate surface potential of the hydrogel FETs shifts in the negative direction with increasing glucose concentration from 10 μM to 40 mM, which results from the increase in the negative charges on the basis of the diol-binding of PBA derivatives with glucose molecules in the hydrogel. Moreover, the hydrogel coated on the gate suppresses the signal noise caused by the nonspecific adsorption of proteins such as albumin. The hydrogel FET can serve as a highly sensitive and biocompatible glucose sensor in

en: Science and Technology of Advanced Materials


en: Self-oriented immobilization of DNA polymerase tagged by titanium-binding peptide motif.

en: We developed a titanium-binding-peptide-1 (TBP-1)-tagged DNA polymerase, for self-oriented immobilization onto a titanium oxide (TiO2) substrate. The enzymatic function of a polymerase immobilized on a solid state device is strongly dependent on the orientation of the enzyme. The TBP-tagged DNA polymerase, which was derived from a hyperthermophilic archaeon, was designed to incorporate the RKLPDA peptide at the N-terminus, and synthesized by translation processes in Escherichia coli (E. coli). The specific binding of the TBP-tagged DNA polymerase onto a TiO2 substrate was clearly monitored by surface plasmon resonance spectroscopy (SPR) and by surface potential detection with an extended-gate field effect transistor (FET). In the SPR analyses, constant quantities of the DNA polymerase were stably immobilized on the titanium substrate under flow conditions, regardless of the concentration of the DNA polymerase, and could be completely removed by a 4 M MgCl2 wash after measurement. The FET signal showed the contribution of the molecular charge in the TBP motif to the binding with TiO2. In addition, the TBP-tagged DNA polymerase-tethered TiO2 gate electrode enabled the effective detection of the positive charges of hydrogen ions produced by the DNA extension reaction, according to the FET principle. Therefore, the self-oriented immobilization platform based on the motif-inserted enzyme is suitable for the quick and stable immobilization of functional enzymes on biosensing devices.

en: Langmuir

ja: Langmuir


en: Purification, identification and molecular cloning of glycoside hydrolase family 15 glucoamylase from the brown-rot basidiomycete Fomitopsis palustris.

en: The brown-rot basidiomycete Fomitopsis palustris produces a major extracellular enzyme of 72 kDa when the fungus is incubated in cellulose culture with 0.2% cellobiose. This protein was purified by column chromatography, and the amino acid sequences of its proteolytic fragments were analyzed. The N-terminal amino acid sequence of one of the fragments showed high identity with fungal glycoside hydrolase family 15 glucoamylases. As its kinetic efficiency increased in proportion to the degree of polymerization of the substrate, the protein was identified as a glucoamylase. A cDNA encoding the glucoamylase (gla) was cloned by reverse transcriptase PCR.

en: FEMS Microbiology Letters

ja: FEMS Microbiology Letters


en: Characterization and molecular cloning of cellobiose dehydrogenase from the brown-rot fungus Coniophora puteana.

en: Cellobiose dehydrogenase (CDH) was purified from the brown-rot fungus Coniophora puteana grown in culture containing crystalline cellulose as a carbon source. The purified enzyme gave a single band at 115 kDa on SDS-PAGE and showed a typical flavocytochrome absorption spectrum. The enzyme oxidized both cellobiose and cellooligosaccharides, but not their monomer, glucose, suggesting typical kinetic features of CDH. A cDNA encoding CDH was cloned by RT-PCR using primers designed from the consensus sequences of known CDHs from white-rot fungi. The cDNA consists of 2448 bp, including an open reading frame encoding the 18 amino acids of the putative signal peptide and the 756 amino acids of the mature protein. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) data for tryptic fragments of the purified C. puteana CDH were consistent with partial amino acid sequences of the mature protein deduced from the cloned cDNA. Moreover, the sequences contained common characteristics of CDH, i.e., two possible residues for a heme ligand (Met 64 and His 160), a flavin-binding motif, and two glucose-methanol-choline oxidoreductase motifs. This is the first cloning of CDH from a brown-rot fungus, and the results suggest structural and kinetic similarity of C. puteana CDH to white-rot fungal CDHs.

en: Journal of Bioscience and Bioengineering