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In recent years, food safety concerning food allergy has received increasing attention globally. A simple and sensitive detection method should be developed to measure trace amounts of allergens in foods. Here, we propose a label-free field effect transistor (FET)-based biosensing system for the detection of a buckwheat allergenic protein, BWp16, by surfactant-induced signal amplification. BWp16 could be detected by coupling with an anionic surfactant, sodium dodecyl sulfate (SDS), as this coupling enhanced the net charge of the protein, enough to be detected by FET biosensors. A significant response was observed when the allergen was coupled with SDS, while the responses were decreased or unchanged when it was coupled with a cationic or non-ionic surfactant, suggesting that the SDS coupling maintains the antibody recognition ability of the target allergen, and it would be useful to enhance the sensor responses. The fluorescence spectroscopic measurement revealed that the SDS molecules were successfully coupled with target allergenic protein BWp16, resulting in an increase in its net charge. Furthermore, we demonstrated that the FET biosensor enables specific detection of the allergen in food at the desired concentration levels for food safety analysis, suggesting that it could be used as an alternative food allergen analyzer, both industrially and domestically. [ABSTRACT FROM AUTHOR]

SUMMARY The concept of unobtrusive physiological balance sensing system implementing biosensors is discussed. Biosensors connected with a data system are expected to play a significant role when we extend the sensing objects from body to mind and spirit. Here, we describe the unobtrusive monitoring system using field effect transistor-type sensors and wireless communication devices. Substances subject to the survey of our research will include small ions, immunoglobulins, and hormones. [ABSTRACT FROM AUTHOR]

Abstract: Allergy diagnosis, conducted to determine whether a specific syndrome is attributable to allergy, plays a significant role in the overall health examination. In this paper we report that the detection of allergy-associated protein, immunoglobulin E (IgE), was achieved by using field effect transistors (FETs) immobilized with an antigen as a receptor, which is smaller in size than the conventional receptor (antibody). The antigen-immobilized FETs exhibit a higher response to IgE than the antibody-immobilized FETs, suggesting that the smaller receptor not only makes the more effective use of the charge-detectable region for the FET-based detection in terms of Debye length, but also provides more recognition sites for target molecules and greater ability to block nonspecific adsorption of non-related proteins because of the closely-packed immobilized receptors. In addition, the application of the antigen to FET biosensor gives an advantage in the identification of the specific allergen. These results show that the small receptor of antigen is more effective than the antibody in the allergy detection using FET biosensors. [Copyright &y& Elsevier]

We demonstrate an S-shaped double-spiral microresonator (DSR) for detecting small volumes of analytes, such as liquids or gases, penetrating a microfluidic channel. Optical-ring resonators have been applied as label-free and high-sensitivity biosensors by using an evanescent field for sensing the refractive index of analytes. Enlarging the ring resonator size is a solution for amplifying the interactions between the evanescent field and biomolecules to obtain a higher refractive index sensitivity of the attached analytes. However, it requires a large platform of a hundred square millimeters, and 99% of the cavity area would not involve evanescent field sensing. In this report, we demonstrate the novel design of a Si-based S-shaped double-spiral resonator on a silicon-on-insulator substrate for which the cavity size was 41.6 µm × 88.4 µm. The proposed resonator footprint was reduced by 680 times compared to a microring resonator with the same cavity area. The fabricated resonator exposed more sensitive optical characteristics for refractive index biosensing thanks to the enhanced contact interface by a long cavity length of DSR structures. High quality factors of 1.8 × 104 were demonstrated for 1.2 mm length DSR structures, which were more than two times higher than the quality factors of microring resonators. A bulk sensitivity of 1410 nm/RIU was calculated for detecting 1 µL IPA solutions inside a 200 µm wide microchannel by using the DSR cavity, which had more than a 10-fold higher sensitivity than the sensitivity of the microring resonators. A DSR device was also used for the detection of 100 ppm acetone gas inside a closed bottle. [ABSTRACT FROM AUTHOR]

This article presents information related to the oxygen activation reaction in intact whole mitochondria. The mitochondrial inner membrane contains high concentrations of various functional membrane protein complexes and includes the proteins of the respiratory chain. It has been estimated that three-quarters of the weight of the mitochondrial inner membrane is occupied by membrane proteins. Resonance Raman spectroscopy is a powerful tool for this purpose since, in principle and in practice this technique is generally not influenced by contaminants in the protein sample.

Rapid and simple monitoring of anticancer drug concentrations in blood is important for improving the efficacy of chemotherapeutic cancer treatment. In this study, we demonstrated the detection of 5-fluorouracil (5-FU) in human serum using a field-effect transistor (FET) biosensor with competitive adsorption between uncharged anticancer drugs and charged pseudo-targets. The target 5-FU and 5-FU-modified bovine serum albumin (BSA/5-FU) were competitively adsorbed on the FET sensor surface using antigen-antibody reaction with antigen-binding fragment (Fab) receptor. FET responses to the target 5-FU concentrations were obtained via changes in the amount of negatively charged BSA/5-FU captured by Fab molecules. In addition, the influence of serum components could be suppressed by diluting the samples with a nonionic surfactant solution. As a result, the FET biosensing system was capable of quantitatively detecting 5-FU concentrations in serum. Therefore, the semiconductor-based sensing system could enable the adjustment of anticancer drug dosages and potentially lead to improvements in anticancer drug therapy. [Display omitted] • The FET biosensor was developed for simple monitoring of 5-FU concentrations in blood. • Competitive adsorption enables detection of small uncharged target molecules. • The influence of human serum components was suppressed by dilution treatment with nonionic surfactants. [ABSTRACT FROM AUTHOR]

A robust and applicable strategy of signal amplification for field effect transistor (FET) biosensor is of scientifically and technologically importance to detect wide range of target molecules, particularly for the molecules of low charge density, and to configure highly sensitive analysis. In this communication, we demonstrate a simple technique to modify the net charge of target protein based on the concept of protein conjugation for the detection of prion, which is infectious and transmissible protein in neurodegenerative disorders. The increases of prion net charge after chemical modification generate signal amplification and have remarkably enhanced the sensitivity of FET biosensor below than femtomolar (fM) level. Thus, we suggest that such strategy is promising technique for achieving a highly sensitive detection at very low concentration that is useful for early determination of protein biomarkers. [ABSTRACT FROM AUTHOR]

We have developed a field effect transistor (FET) sensor to sensitively detect copper ions (Cu2+) in a human serum (HS) sample for promising health-care diagnosis. By utilizing a Cu2+-binding prion protein that was immobilized on the FET gate surface, such an FET sensor can provide a simple, label free and highly selective performance, even in HS samples. We demonstrated the sensitivity of the sensor at the nanomolar level, 0–100 nM, which is very useful for the detection range of Cu2+ deficiency in practical applications. [ABSTRACT FROM AUTHOR]

Detection of tumor markers is important for cancer diagnosis. Field effect transistor (FET) has been recognized as a powerful technique for label-free, sensitive, real-time, and multifunctional biosensing. Here, we developed FET biosensors that allow the label-free detection of cytokeratin fragment 21-1 (CYFRA 21-1) and neuron-specific enolase (NSE), useful tumor markers for lung cancer type differentiation. It was found that the FET biosensor was capable of quantitatively detecting these tumor markers in both phosphate-buffered saline and human serum. Additionally, we developed a multianalyte FET biosensor for the selective multiplexed detection of CYFRA 21-1 and NSE at the same time, by integrating two antibody types on the same chip, providing a step towards the realization of sensor arrays. The multianalyte FET biosensor, as described herein, will help for lung cancer differential diagnosis with advantages of simple and rapid detection procedures, low sample consumption, and low cost. [ABSTRACT FROM AUTHOR]

Simple and accurate detection of prion proteins in biological samples is of utmost importance in recent years. In this study, we developed a label-free electrical detection-based field effect transistor (FET) biosensor using thiamine as a probe molecule for a non-invasive and specific test of human prion protein detection. We found that thiamine-immobilized FETs can be used to observe the prion protein oligomer, and might be a significant test for the early diagnosis of prion-related diseases. The thiamine-immobilized FET was also demonstrated for the detection of prion proteins in blood serum without any complex pre-treatments. Furthermore, we designed a dual-ligand binding approach by the addition of metal ions as a second ligand to bind with the adsorbed prion protein on the thiamine-immobilized surface. When the prion attached to metal ions, the additional positive charge was induced on the gate surface of the FET. This approach was capable of amplifying the magnitude of the FET response and of enhancing the sensitivity of the FET biosensor. Detection of prion proteins has achieved the required concentration for clinical diagnosis in blood serum, which is less than 2 nM. In summary, this FET biosensor was successfully applied to prion detection and proved useful as a simple, fast, sensitive and low-cost method towards a mass-scale and routine blood screening-based test. [ABSTRACT FROM AUTHOR]

Abstract: The effect of surface modification of indium tin oxide (ITO) electrode on its potential response to tryptophan was investigated for ITO substrates with different surface roughness. It was found that a small difference in surface roughness, between ∼1 and ∼2nm of R a evaluated by atomic force microscopy, affects the rest potential of ITO electrode in the electrolyte. A slight difference in In:Sn ratio at the near surface of the ITO substrates, measured by angle-resolved X-ray photoelectron spectrometry and Auger electron spectroscopy is remarkable, and considered to relate with surface roughness. Interestingly, successive modification of the ITO surface with aminopropylsilane and disuccinimidyl suberate, of which essentiality to the potential response to indole compounds we previously reported, improved the stability of the rest potential and enabled the electrodes to respond to tryptophan in case of specimens with R a values ranging between ∼2 and ∼3nm but not for those with R a of ∼1nm. It was suggested that there are optimum values of effective work function of ITO for specific potential response to tryptophan, which can be obtained by the successive modification of ITO surface. [Copyright &y& Elsevier]

Abstract: In this paper, we present a method of fabricating a rigid antibody-immobilized surface using electric activation of a glutaraldehyde (GA)-modified aminopropylsilyl surface for stable antibody-modified field effect transistors (FETs). Electric activation of the GA-modified gate surface of the FET reduces Schiff bases, which are easily hydrolyzed and collapsed, formed between GA and 3-aminopropyltriethoxysilane, resulting in preventing the immobilized antibodies from desorbing from the surface. The lack of Raman peaks that could be assigned to a Schiff base after the electrical activation of the GA-modified surface indicated that the electric activation had reduced the Schiff base. The use of the antibody-modified FETs has three advantages for the detection of antigens: increased sensitivity, distinct recognition ability, and improved reproducibility. A tumor marker, alpha-fetoprotein (AFP), was quantitatively detected up to a concentration of 10ng/mL using the antibody-modified FET. The detection ability of the FET accomplished a cutoff value of hepatic cancer. The quantitative detection of AFP in a solution with contaminating proteins was also demonstrated. This electric activation method is applicable to other antibody-modified FETs. [ABSTRACT FROM AUTHOR]

Electrical detection of RNAs using transistor-based biosensors has attracted attention as a strategy for medical diagnosis and environmental monitoring. Herein, we demonstrated a proof-of-concept for specific, sensitive, and label-free RNA detection using a field-effect transistor (FET) biosensor with signal amplification by ternary initiation complexes (SATIC), which is an isothermal one-step nucleic acid amplification initiated by the combination of target RNA, circular DNA template and DNA primer. The SATIC system-applied FET biosensor specifically and quantitatively detected the target RNA with a single-nucleotide difference via the negative charges derived from the amplification products formed by a nucleic acid amplification reaction with φ29 DNA polymerase on the gate surface. In particular, the control of the amplification time allowed the detection of target RNA molecules over a wide concentration range, resulting in a detection limit of up to 6 copies/μL. Therefore, a transistor-based bioassay using the SATIC system could be useful for simple and sensitive nucleic acid analysis. [Display omitted] • Field-effect transistor biosensor was developed to detect attomolar RNA molecules. • The FET surface was designed for nucleic acid amplification by SATIC system. • A wide RNA concentration was detected by controlling the amplification time. [ABSTRACT FROM AUTHOR]

A Fe2+ ion on the acceptor side of plant photosystem II has been substituted by Zn2+ and an anion radical of the primary acceptor quinone, Q-A, has been studied by electron spin echo method. The electron spin echo modulation shows the interaction of the unpaired electron of Q-A with nitrogen nuclei of the histidine and, probably, alanine residues situated nearby. The comparison of the modulation spectra of Q-A with those of the anion radical of plastoquinone-9 stabilized in protonated and deuterated isopropanol matrices allows one to distinguish between the spectrum lines due to the quinone protons and due to the protons of other molecules that form hydrogen bonds with the oxygen atoms of the quinones. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electrodeposition–annealing route to fabricating thin film of the promising photocatalyst material anatase-titanium dioxide (anatase-TiO 2 ) has been studied. The sample was deposited with a solution of N,N-dimethylformamide containing titanium compound by controlled-potential technique. SEM image showed the annealed sample at 600 °C for 1 h under air provided a continuous film with a thickness of ca. 350 nm. In this sample, X-ray photoelectron spectrum corresponding to the Ti 2p peak assigned to a chemical bond of TiO 2 and X-ray diffraction peaks assigned to the anatase phase were observed, respectively. Electrochemical oxidation in sodium sulfate solution on this annealed film was enhanced in the presence of UV light radiation. These results confirm the successful synthesis of photocatalytic anatase-TiO 2 film by the electrodeposition and annealing process. [ABSTRACT FROM AUTHOR]

We propose, as an alternative to conventional spectroscopic assays, a simple method for discriminating fibrous amyloid proteins by using a label-free semiconductor-based biosensor. The highly sensitive assay is expected to be useful for accelerating amyloid related research. [ABSTRACT FROM AUTHOR]

A field-effect transistor (FET) biosensor that can directly detect target molecules is a promising diagnostic tool for healthcare and medical applications. However, the immersion of FET sensors in aqueous physiological environments for the long-term stability might damage the insulating layer of silicon dioxide, resulting in the degradation of the sensor response reproducibility. In this study, to improve the durability of the sensor response for long-term immersion in aqueous solution, we examined the effectiveness of reduced graphene oxide (rGO) coating on the gate insulator of FET sensors. The rGO coating was applied to the gate surface of the FET biosensor modified with an amino-terminated self-assembled monolayer by two steps: deposition of graphene oxide (GO) dispersion onto the monolayer-modified surface and subsequent thermal reduction of GO. The transconductance of both GO-coated and rGO-coated FETs remained unchanged after incubation under physiological conditions, suggesting that graphene prevents cations in the electrolytes from invading the gate insulator of the FET. Furthermore, functionalizing the rGO-coated FET surface enabled specific detection of target molecule. [Display omitted] • The stability of the FET biosensor in biological environments was developed. • Reduced graphene oxide as a coating layer could effectively prevent the invasion of the cations. • The biosensing ability of the FET biosensor based on specific interaction between molecules was demonstrated. [ABSTRACT FROM AUTHOR]

Influenza virus, through cell invasion and propagation with the interaction between hemagglutinin (HA) present on its surface and glycans on the host cell, causes a rapidly spreading infection throughout the world. In the present investigation, we succeeded for the first time in the attomolar-level sensing and discrimination of influenza A viral HA molecules H1 and H5 by using a glycan-immobilized field effect transistor (FET) biosensor. The small ligand glycans immobilized on the FET device, which make effective use of the charge-detectable region for FET-based detection in terms of Debye length, gave an advantage in the highly sensitive detection of the proteins. Two kinds of trisaccharides receptors terminating in sialic acid-α2,6-galactose (6'-sialyllactose) and in sialic acid-a2,3-galactose (3'-sialyllactose) were conjugated directly with the SiO2 surface of FET devices by a simple glycoblotting method using the self-assembled monolayer (SAM) of aminooxy terminated silane-coupling reagent, 3-aminooxypropyltriethoxysilane. Furthermore, it was demonstrated that the FETs with densely immobilized glycans, which possess the high capture ability by achieving the glycoside cluster effect, clearly distinguish HA molecules between their subtypes H1 (human) and H5 (avian) at the attomolar level, while the conventional method based on HA antibodies achieves only picomolar-level detection. Our findings indicate that the glycan-immobilized FET is a promising device to detect various pathogenic bacteria and viruses through glycan-protein interaction found ubiquitously in many infectious diseases. [ABSTRACT FROM AUTHOR]

Abstract: This paper demonstrates that antibody-modified field effect transistors (FETs), which were treated with bovine serum albumin (BSA) blocking, had quantitative capability for tumor marker detection in blood serum. Antibody-modified surface covered with 0.1% BSA effectively minimized nonspecific adsorption of blood proteins. Tumor markers with their isoelectric points of around 5 generated strong signals in body environmental pH (pH 7.4) in proteins with isoelectric points ranging from 3 to 10. Detection of a tumor marker alpha-fetoprotein in blood serum at required level for clinical diagnosis (10ng/mL) was achieved. The obtained results suggest that the fabricated FETs be expected to practical application in medical fields for direct detection of multi-tumor markers from blood. [Copyright &y& Elsevier]

Human myoglobin (Mb) possesses a unique cysteine (Cys1 10), whereas other mammalian Mbs do not. To investigate the effect of a cysteine residue on Mb, we introduced cysteine to various sites on the surface of sperm whale Mb (K56C, V66C, K96C, K102C, A125C, and A144C) by mutation. The cysteines were inserted near the end of α-helices, except for V66C, where the cysteine was introduced in the middle of an α-helix. Reduction of the heme was observed for each mutant metMb by incubation at 37 °C under carbon monoxide atmosphere, which was much faster than reduction of wild-type metMb under the same condition. Heme reduction did not occur significantly under nitrogen or oxygen atmospheres. The rate constant for heme reduction increased for higher mutant Mb concentration, whereas it did not change significantly when the CO concentration was reduced from 100% CO to 50% CO with 50% O2. The similarity in the rate constants with different CO concentrations indicates that CO stabilizes the reduced heme by coordination to the heme iron. SDS—PAGE analysis showed that mutant Mb dimers were formed by incubation under CO atmosphere but not under air. These dimers were converted back to Mb monomers by an addition of 2-mercaptoethanol, which showed formation of a Mb dimer through a disulfide bond. The rate constant decreased in general as the heme-cysteine distance was increased, although V66C Mb exhibited a very small rate constant. Since V66 is placed in the middle of an α-helix, steric hindrance would occur and prevent formation of a dimer when the cysteine residues of two different V66C Mb molecules interact with each other. The rate constants also decreased for K56C and A144C Mbs presumably because of the electrostatic repulsion during dimer formation, since they are relatively charged around the inserted cysteine. [ABSTRACT FROM AUTHOR]

Secretory immunoglobulin A (s-IgA), found in biological fluids, is useful for monitoring condition on mental health to prevent depression. In this study, the non-invasive detection of s-IgA in human sweat was demonstrated using field effect transistor (FET) biosensors modified with a plant lectin, jacalin, as a receptor. The s-IgA molecules were detected with greater sensitivity using the jacalin-immobilized FET biosensors as compared to the sensitivity shown by Fab-immobilized FET biosensors. Jacalin, which is a small lectin tetramer, has four glycan-binding sites and can capture a large number of s-IgA molecules within the charge-detectable region in terms of Debye length. Moreover, the jacalin-immobilized FET biosensor could detect s-IgA at concentrations ranging from 0.1 μg/mL to 100 μg/mL. Additionally, by using a filtration process to eliminate the interference of other components found in human sweat, our FET sensing system could specifically and quantitatively detect s-IgA. Therefore, our results show the utility of this device in monitoring mental stress. Unlabelled Image • A field effect transistor (FET) biosensor modified with jacalin was developed to detect secretory immunoglobulin A (s-IgA). • Jacalin can be inexpensively extracted from the seeds of jackfruits. • The FET biosensor could quantitatively detect s-IgA at the concentrations ranging from 0.1 μg/mL to 100 μg/mL. • The concentration of s-IgA in human sweat, treated by filtration process, was determined by the FET biosensor. [ABSTRACT FROM AUTHOR]

Pandemic influenza, triggered by the mutation of a highly pathogenic avian influenza virus (IFV), has caused considerable damage to public health. In order to identify such pandemic IFVs, antibodies that specifically recognize viral surface proteins have been widely used. However, since the analysis of a newly discovered virus is time consuming, this delays the availability of suitable detection antibodies, making this approach unsuitable for the early identification of pandemic IFVs. Here we propose a label-free semiconductor-based biosensor functionalized with sialic-acid-containing glycans for the rapid identification of the pandemic IFVs present in biological fluids. Specific glycans are able to recognize wild-type human and avian IFVs, suggesting that they are useful in discovering pandemic IFVs at the early stages of an outbreak. We successfully demonstrated that a dual-channel integrated FET biosensing system, which were modified with 6′-sialyllactose and 3′-sialyllactose for each gate area, can directly and specifically detect human H1N1 and avian H5N1 IFV particles, respectively, present in nasal mucus. Furthermore, to examine the possibility of identifying pandemic IFVs, the signal attributed to the detection of Newcastle disease virus (NDV) particles, which was selected as a prime model of a pandemic IFV, was clearly observed from both sensing gates. Our findings suggest that the proposed glycan-immobilized sensing system could be useful in identifying new pandemic IFVs at the source of an outbreak. [ABSTRACT FROM AUTHOR]