Salivary cortisol concentration and its circadian variation were detected by optimizing the ionic concentration of a solution during the immobilization of aptamers on a field-effect transistor biosensor. This was achieved by modifying our previously developed technique of detecting uncharged cortisol using the transformation of negatively charged aptamers by controlling the aptamer spacing. This spacing control was achieved by synthesizing pseudo-cortisol-binding aptamers with a guanine-quadruplex during the immobilization of the aptamers in a highly concentrated solution of K+.

A field effect transistor (FET) biosensor is a promising device for various applications such as medical diagnosis and environmental monitoring. Because characteristics of FET biosensors are directly influenced by the change of gate-insulator surface potential induced by the adsorption of charged molecules, FET biosensors could provide the rapid and label-free biomolecular detection. Recently, mental stress-related diseases, such as integration disorder syndrome and depression, affect people's health, resulting that simple stress monitoring is expected for early stage detection of the disease. Previously, the relation between concentration of stress markers and mental stress has been reported ^[1], and the monitoring of circadian concentration of the markers is found to be important for prediction of the stress condition. Especially, secretory immunoglobulin A (s-IgA), which is an immunity-related molecule present in the human mucus, is one of the candidates to be monitored as a stress marker. However, conventional methods for measuring concentration of s-IgA are restricted in daily use due to complex protocol, time-consuming and expensive equipment.

Nowadays, we have investigated sensitive detection method for various targets by using the FET biosensor ^[2,3]. To achieve improvement of the sensitivity, small receptors have been applied to increase electrical responses owing to the effective use of a charge-recognition region from FET gate surface, Debye length ^[4,5]. In this study, we selected a small plant lectin, jacalin (66 kDa), which specifically binds glycan of hinge region of IgA, as a receptor. Additionally, jacalin was inexpensive compared with antibody due to the purification from jackfruits seeds. From these points, jacalin-immobilized FET biosensor was worth to be investigated to realize a simple, sensitive and low-cost stress monitoring device for stress marker. Thus, we investigated the usefulness of the jacalin as a FET receptor.

The SiO₂ gate insulator of the FET was exposed to O₂ plasma (200 W for 1 min) for introduction of hydroxyl groups reacting with triethoxysilane groups of self-assembled monolayer (SAM). Then, the FET chip was immersed in toluene solvent including 1%(v/w) 3-aminopropyltriethoxysilane in an argon atmosphere (60ºC for 7 min.). Following by the cross-linking by glutaraldehyde, jacalin was immobilized on FET gate surfaces. Finally, ethanolamine capping was performed to prevent the non-specific adsorption of contaminating molecules in analyzed samples, resulting in the fabrication of the jacalin-immobilized FET biosensor. The FET characteristics were measured by sweeping the gate-voltage (V _g) from -2.0 V to 0 V with 0.1 V drain voltage (V _d) in 0.01 × phosphate buffered saline (pH 7.4). Then, the electrical responses (ΔV _g) were analyzed from the FET characteristics before and after the addition of analyte to gate surface.

To evaluate the specificity of jacalin-immobilized FET biosensor, ΔV _g caused by the addition of s-IgA and human serum albumin (HSA) were measured. The FET charactristics was shifted in a positive direction (+53 mV) due to the adsorption of negative-charged s-IgA (Figure 1a), while the responses related with HSA addition were scarcely observed. Thus, specific capture of the s-IgA molecules by the jacalin-immobilized surface was indicated. Moreover, to evaluate the advantage of jacalin, we compared ΔV _g with FET functionalized by antigen binding fragment (Fab), which was obtained by cleaving the anti-s-IgA antibody. An electrical response of Fab-immobilized FET was +24 mV (Figure 1b). The change in ΔV _g values for these two FET sensors using jacalin or Fab could be discussed as follows. Jacalin could capture more s-IgA molecules within Debye length from the gate surface of FET. In addition, the jacalin-immobilized FET responded linearly to s-IgA in a concentration range from 0.1 μg/mL to 100 μg/mL. Finally, sweat samples collected from healthy persons were examined with the developed jacalin-immobilized FET biosensor, and clear responses were obtained. From these results, jacalin was found to be useful as a receptor for FET biosensors to achieve a sensitive, simple and non-invasive detection of s-IgA.

[1] K. Obayashi, Clin. Chim. Acta, 425, 196-201 (2013).

[2] S. Hideshima, M. Kobayashi, T. Wada, S. Kuroiwa, T. Nakanishi, N. Sawamura, T. Asahi, T. Osaka, Chem. Commun., 50, 3476-3479 (2014).

[3] S. Hideshima, K. Fujita, Y. Harada, M. Tsuna, Y. Seto, S. Sekiguchi, S. Kuroiwa, T. Nakanishi, T. Osaka, Sens. Bio-Sens. Res., 7, 90–94 (2016).

[4] S. Cheng, K. Hotani, S. Hideshima, S. Kuroiwa, T. Nakanishi, M. Hashimoto, Y. Mori, T. Osaka, Materials, 7, (4), 2490-2500 (2014).

[5] S. Hideshima, H. Hayashi, H. Hinou, S. Nambuya, S. Kuroiwa, T. Nakanishi, T. Momma, S.-I. Nishimura, Y. Sakoda, T. Osaka, Sci. Rep., 9, 11616 (2019).

Figure 1 V _g-I _d characteristics of (a) jacalin or (b) Fab-immobilized FET biosensor before and after the addition of 100 μg/mL s-IgA.



Figure 1

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The dosage of 5-fluorouracil (5-FU), which is a widely used for cancer medication, is determined based on body surface area, although efficacy largely depends on the liver function of the individual, resulting that only 21% patients are given an optimal dose of 5-FU in these years. The measurement of the 5-FU concentration in the blood enables us to adjust individual dose adjustment. Conventional methods for 5-FU detection such as an enzyme-linked immunosorbent assay (ELISA) and liquid chromatography are not very suitable for clinical applications because they need time-consuming procedure with expensive equipments. Detection of 5-FU using a field effect transistor (FET) biosensor, which enables rapid and simple measurement, is expected to solve such problems. However, FET biosensor, which detects changes in its surface density due to the adsorption of charged molecules, was unable to detect uncharged 5-FU. In this study, a method for the FET biosensing to detect 5-FU exploiting sequential adsorption of 5-FU modified bovine serum albumin (BSA/5-FU) was proposed. By using this method, FET responses caused by the adsorption of negatively charged BSA/5-FU depending on the 5-FU concentration were detected.

The SiO₂ surface of the FET gate insulator was exposed to O₂ plasma to introduce hydroxyl groups. After the exposure, the surface was exposed to 3-aminopropyltriethoixysilane (APTES), followed by the modification of the cross-linker, glutaraldehyde (GA). A single chain variable fragments (ScFv) and antigen binding fragments (Fab) were allowed to react with each activated GA-modified FET. After the immobilization, the residual aldehyde-groups were treated by ethanolamine to suppress the non-specific adsorption. V _g-I _d characteristics were measured before and after dripping of both 5-FU and BSA/5-FU on the ScFv- and Fab-immobilized FET biosensors. Finally, threshold voltage shifts (∆V _g) caused by the adsorption of BSA/5-FU were obtained.

To compare the capture capability of ScFv and Fab, the electrical responses of the FET biosensors functionalized with the two receptors due to the adsorption of BSA/5-FU were measured. The responses of ScFv- and Fab-immobilized FET biosensor caused by dripping of 25 μg/mL BSA/5-FU were +25 mV and +40 mV, respectively. The difference between ΔV _g values for these two FET sensors using ScFv or Fab can be ascribed to the difference of affinity ^[1]. To verify the specificity of Fab-immobilized FET biosensor, ∆V _g was measured when human serum albumin (HSA) was dropped on the FET biosensor, and the ∆V _g was hardly observed. Additionally, the atomic force microscopic (AFM) images on the FET gate surface shows that the size of observed particles matches the size of BSA/5-FU, while the surface morphology and roughness are not significantly changed. These results indicated that Fab-immobilized surface specifically captured BSA/5-FU. To investigate the quantitative detectability of the Fab-immobilized FET biosensor, we measured the FET responses corresponding to the amount of adsorbed BSA/5-FU, which was related with the concentrations of 5-FU. As a result, the magnitude of ∆V _g by dripping of 1000 ng/mL 5-FU and 25 μg/mL BSA/5-FU was reduced to +12 mV compared with the response of 25 µg/mL BSA/5-FU (Figure 1). These results can be attributed to that the adsorbed 5-FU inhibited the adsorption of BSA/5-FU to the Fab-immobilized surface. Therefore, we conclude that the detection of 5-FU using the FET biosensors by applying the charged BSA/5-FU is a promising simple method for monitoring the concentration of 5-FU.

Reference:

[1] Y. Reiter, et al., J. Biol. Chem., 269, 28, 18327-18331 (1994).

Figure 1 V _g-I _d characteristics of Fab-immobilized FET biosensor before and after dripping of (a) 0 ng/mL 5-FU and 25 µg/mL BSA/5-FU or (b) 1000 ng/mL 5-FU and 25 µg/mL BSA/5-FU.



Figure 1

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Introduction

People have felt that their mind controls the body. Advances in immunology and neuroscience are scientifically elucidating this experience. For example, it has been clarified that the mechanism by which changes in the activity of the central nervous system due to stress regulate the immune response through sympathetic nerves. If these latest medical knowledge and electronic advances can be used to provide a simple monitoring system for stress-related substances, it is hoped that it will help prevent mental and physical diseases. Nevertheless, performing a blood draw to detect the stress hormones cortisol and catecholamine has the challenge that the act of drawing blood itself causes stress. Instead, cortisol concentration measurement from saliva has been developed as a non-invasive detection, but catecholamines cannot be detected from saliva. Salivary cortisol concentration measurements have been developed as an alternative non-invasive detection method, but catecholamines are unable to obtain the necessary information from saliva. Salivary α-amylase and chromogranin A (CgA) have also been studied and used in part as alternatives to catecholamines. Secretary immunoglobulin A (s-IgA) in saliva is also a good stress marker that reflects suppression of the immune system by stress. Simultaneous monitoring of the time-dependence of these stress markers of different origins is expected to help elucidate the complex mental stress mechanisms [1].

Sensor module platform

Accurate and inexpensive biomaterial detectors are required for IoT biosensing systems and monitoring over time has not been realized until now. Field-effect transistor (FET) biosensors are small devices that detect various types of biomarkers at low power consumption without disturbing the system under test [2]. The biggest challenge of FET biosensors when used in electronics systems is instability due to current drift. We have succeeded in developing a method that minimizes drift using only the normal silicon fab process. This manufacturing process does not use tantalum pentoxide or other special materials.

Figure 1 shows a picture of a newly developed four element FET sensor chip with extremely low instability. The electronics part of the developed biosensor module consists of this chip and a Bluetooth Low Energy (BLE)-type communication circuit. We selected four types of aptamers as sensor receptors on the gate insulator on the chip [3]. The aptamers can be stored and used at room temperature for a long period of time. They also have the advantages of being reversible to thermal denaturation and can be produced inexpensively and industrially. Finally, as a technique for producing biosensors with less variation, such as commercial physical sensors, we developed a tool for uniformly immobilizing the receptor monolayer in a narrow range of fixed positions on the chip.

Simultaneous detection of multiple stress markers in saliva

When n types of receptors are immobilized on n FET elements, n-1 types of independent signals can be extracted. The effects of non-specifically adsorbed substances and pH in saliva, temperature fluctuation, optical noise, and crosstalk between elements can be eliminated from the original signals of multiple FET elements. Using this technique, we succeeded in obtaining multiple stress marker concentrations such as cortisol, a-amylase, s-IgA, and CgA [4], at the same time just by dropping saliva on the sensor. The signal time constant is less than 1 minute, which indicates that a continuous monitor is realized substantially.

Operability equivalent to physical sensor

Internet of Things (IoT) systems require many low-cost sensors. FET sensor chips manufactured using only the conventional silicon fab process can achieve a low cost of about $1 per chip. However, even with such cheap biosensors, if they are disposable, the cost burden on the user will increase significantly in the long run. As a result, it becomes difficult to secure good customers as fixed users. In addition, disposable chips are not suitable for continuous monitoring required for medically important data. We are developing biosensors that are as easy to operate as conventional physical sensors by introducing reusable cleaning methods and recycled precision cleaning methods.

References

[1] L. Steinman, Annu. Rev. Immunol., 32, 257-281, (2014).

[2] K. Ohashi, T. Osaka, ECS Transactions, 75, 39, 1-9, (2017).

[3] N Kaneko, H Minagawa, J Akitomi, K Ohashi, S Kuroiwa, S Wustoni, S Hideshima, T Osaka, K Horii, I Waga, The 43rd International Symposium on Nucleic Acids Chemistry, 2P-55, (2016).

[4] S. Kuroiwa, R. Takibuchi, A. Matsuzaka, S. Hideshima, N. Kaneko, H. Minagawa, K. Horii, I. Waga, T. Nakanishi, K. Ohashi, T. Momma, T. Osaka, 232nd ECS Meeting, 2115, (2017).



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Nature-inspired flexible electrochromic devices have been fabricated using electrochromic metallo-supramolecular polymer for the first time in the world. The use of Ru(II)-based polymer, which changes the color between red and green, and the multi-layer coating method have enabled to reproduce the nature of a real fallen leaf by the devices

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.

Recent statistics show that the incidence and mortality of cancer are on the rise. Among all types of cancer, lung cancer and liver cancer arc the most prevalent. We have many biomarkers for these two cancers, among which the cytokeratin fragment 21-1 (CYFRA 21-1) and a-fetoprotein (AFP) are the most common and widely used. Among the various detection methods, the field effect transistor (FET) biosensor is one of the most attractive approaches, providing a label-free, fast, and low-cost electrical detection of biomarkers with high specificity and sensitivity. In previous work, we applied biomarkers for a single cancer type. With the detection of CYFRA 21-1 and neuron-specific enolase (NSE), lung cancer was differentiated in the early stages. Compared with the early work, the biomarkers for the two cancer types, CYFRA 21-1 for lung cancer and AFP for liver cancer, were prepared in this work. The detection of CYFRA 21 1 and AFP in human serum was achieved at the same time with the limits of detection of 1 and 10 ng mL(-1), while the cut-off values were 4 and 10 ng mL(-1). The method featured short analytical time, small sample volume, and low cost. With its good selectivity and appropriate sensitivity, clinical application will become popular in the future.

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. (C) 2017 The Authors. Published by Elsevier B.V.

The concept of unobtrusive physiological balance sensing system implementing biosensors is discussed. Biosensors connected with a data system is 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 FET-type sensors and wireless communication devices. Substances subject to the survey of our research will include small ions, immunoglobulins, and hormones.

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. (C) 2016 Elsevier B.V. All rights reserved.

The electrodeposition-annealing route to fabricating thin film of the promising photocatalyst material anatase-titanium dioxide (anatase-TiO2) 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 degrees C for 1 h under air provided a continuous film with a thickness of ca. 350 nm. In this sample, X-ray photoelectron spectrumcorresponding to the Ti 2p peak assigned to a chemical bond of TiO2 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-TiO2 film by the electrodeposition and annealing process. (C) 2016 Elsevier B.V. All rights reserved.

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. (C) 2015 Elsevier B.V. All rights reserved.

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.

We fabricated dye-sensitized solar cells (DSSCs) with synthetic quartz nanoparticle (SQNP)-supported Pt/fluorine doped tin oxide counter electrodes to utilize an adsorptive capacity of synthetic quartz. The amperage of I-3(-) reduction was 1.6 times higher with SQNP than that without SQNP. SQNP also improved the photocurrent density-voltage characteristics and the incident photon to current conversion efficiency spectra in the visible region. These suggest that SQNP enhances the I-3(-) reduction activity on the counter electrode and the electron transfer to the photoanode. The SQNP-supported counter electrode is expected to be useful to raise the efficiency of a DSSC. (C) The Electrochemical Society of Japan, All rights reserved.

Detection of tumor markers is important for cancer diagnosis. Field-effect transistors (FETs) are a promising method for the label-free detection of trace amounts of biomolecules. However, detection of electrically charged proteins using antibody-immobilized FETs is limited by ionic screening by the large probe molecules adsorbed to the transistor gate surface, reducing sensor responsiveness. Here, we investigated the effect of probe molecule size on the detection of a tumor marker, α-fetoprotein (AFP) using a FET biosensor. We demonstrated that the small receptor antigen binding fragment (Fab), immobilized on a sensing surface as small as 2-3 nm, offers a higher degree of sensitivity and a wider concentration range (100 pg/mL-1 μg/mL) for the FET detection of AFP in buffer solution, compared to the whole antibody. Therefore, the use of a small Fab probe molecule instead of a whole antibody is shown to be effective for improving the sensitivity of AFP detection in FET biosensors. Furthermore, we also demonstrated that a Fab-immobilized FET subjected to a blocking treatment, to avoid non-specific interactions, could sensitively and selectively detect AFP in human serum. © 2014 by the authors.

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. © 2013 Elsevier Ltd. All rights reserved..

Matrix metalloproteinase (MMP) is known to be involved in chronic inflammation, tumor invasion, and carcinogenesis. To detect MMP-2, we examined the use of field effect transistors (FETs). After the addition of MMP-2 to a fibronectin (FN)-immobilized gate, negative value of FET response was observed, which indicates MMP-2 decreased the amount of negative charges arising from FN molecules. This FET device successfully detected MMP-2 by utilizing degradation of FN on the gate.

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 (10 ng/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. (C) 2011 Elsevier B.V. All rights reserved.

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 similar to 1 and similar to 2 nm 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 similar to 2 and similar to 3 nm but not for those with R(a) of similar to 1 nm. 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. (C) 2011 Elsevier Ltd. All rights reserved.

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 10 ng/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. (C) 2010 Elsevier B.V. All rights reserved.

This paper describes a practical method for predicting signals of an adsorbed protein detected by field effect transistors (FETs). The FETs detect the change of the surface charge caused by protein adsorption. The sensing signals strongly depend on an ionic strength of the buffer solution. The prediction of signals is useful for optimizing the strength. A calculation method using three-dimensional conformation structure of proteins was proposed for the prediction tool in the latest paper citing biotin-avidin interaction as an example. To verify availability of the method for alternative adsorbed protein, an adsorption model of streptavidin, which also has a binding ability to biotin, was investigated. Streptavidin has little charge in a buffer solution at pH 7.4 calculated from the method. The results suggest that the signals caused by adsorption of streptavidin were barely detectable using a biotinylated FET.

Determination of protein charges under physiological conditions by field effect transistors (FETs) is challenging because of the screening effect by solution counter ions We showed that sugar-chain-modified FETs can detect proteins under physiological conditions Protein charges are detectable on the gate interface by applying sugar chains as receptors these sugar chains are short and highly flexible Threshold voltage shifts caused by adsorption of SSA lectin from Sambucus sieboldiana onto sialylglycan-modified FET showed a linear relationship with SSA concentrations under physiological conditions

Fabricating reference field effect transistor (FET) sensors instead of reference electrodes are important for the miniaturization and variegated applications of FET sensors. To make a reference FET, the gate surface of FET was modified with the self-assembled monolayer (SAM) of n-octadecyltrimethoxysilane (ODS). Though an ODS-SAM FET had low pH-sensitivity, it was cation-sensitive. This work demonstrates the relation between the surface morphology and the cationic and pH-sensitivity of ODS-SAM FETs. A roughness parameter of atomic force microscope images. the mean summit curvature (Ssc) has correlation with the cationic and pH-sensitivity of ODS-SAM FETs.

Field effect transistors (FETs) may respond to charge variations occurring when proteins are adsorbed to the gate surface. The electrolyte electrostatic screening allows a practical detection of charges that are only within a distance of approximately the double layer thickness, which is related to the Debye length in the electrolyte. Hence, operating the FET biomolecular sensors at the highest possible ionic concentration improves reproducibility; however, it may reduce the signal if the concentration is too high. Here, we propose an optimization method of the buffer ionic concentration using a figure of merit "charge number," Z(d), which is defined as the ratio between the effective number of the surface charges and the number of immobilized molecules. The theoretical Z(d) was calculated using a three-dimensional conformation data taken from the Protein Data Bank. The Z(d) was obtained from the total number of four charged amino acids of avidin, arginine (positive), lysine (positive), aspartic acid (negative), and glutamic acid (negative), which are within the double layer length from the surface. To verify this model, we chose avidin-biotin interaction. The experimental Z(d), which was obtained for three buffer concentrations, matched the theoretical Z(d). This method shortens the solution calibration time and reduces the analyte amount. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3491764] All rights reserved.

To photomodulate the interaction of the phosphatidylinositol 3-kinase SH3 domain with a peptide ligand, a cyclic peptide (cyclic-1)with a photolabile side chain-to-side chain linker was synthesized. The conformation of cyclic-1 differs from that of the parent linear peptide, but becomes identical by UV-irradiation. Accordingly, the binding affinity of cyclic-1 to the SH3 domain increased upon conversion of the cyclic to a linear flexible structure by irradiation (Kd: 3.4 +/- 1.7 and 0.9 +/- 0.3 mm, respectively). These results confirm the usefulness of a photocleavable peptide for photocontrol of peptide-protein interactions. Copyright (C) 2009 European Peptide Society and John Wiley & Sons, Ltd.

The use of Tb3+ as a center ion and media to introduce more exogenously negative charges onto double-stranded DNA (dsDNA), can greatly enhance potentiometric signals produced by the shift of gate voltage of field effect transisitor (FET). Furthermore, different affinities of Tb3+ to normal and mismatched dsDNAs amplified the signal difference between their detections, which can improve the discrimination of single nucleotide polymorphism.

For completion of on-chip field effect transistor (FET) biosensors, it is essential to produce a reference FET instead of a reference electrode that uses an inner electrolyte. In this study, a light-addressable potentiometric sensor (LAPS) modified by a self-assembled monolayer (SAM) of octadecylsilane (ODS) was pH-insensitive (-1.5 mV/pH), but it was sensitive to ionic strength as was reported in polymer-gate FETs. Our purpose was to make clear the problems of the evaluation methods of ODS-SAM FETs concerning pH and ionic responses and the effect of the surface morphology to improve a reference SAM-FET. An ODS-SAM LAPS and FET were deposited under different conditions. pH and ionic responses, roughness measured by atomic force microscope, and contact angle (CA) were greatly changed by the difference in morphology of the ODS-SAM. ODS coagulation raised the CA. It is difficult to distinguish the ODS-SAM with and without ODS coagulation only by CA, but CA is utilizable for observing the state of hydroxyl groups on the surface without ODS coagulation. ODS coagulation caused the pH response with the ODS-SAM but decreased the ionic response of the LAPS. Controlling the surface morphology of the ODS-SAM is important to suppress the pH and ionic sensitivities for an in vivo applicable reference FET.

The electron-electron double resonance (ELDOR) method was applied to measure the dipole interaction between cytochrome (Cyt) b(559)(+) and the primary acceptor quinone (Q(A)(-)), observed at g = 2.0045 with the peak to peak width of about 9 G, in Photosystem II (PS II) in which the non-heme Fe2+ was substituted by Zn2+. The paramagnetic centers of Cyt b(559)(+)Y(D)(.)Q(A)(-) were trapped by illumination at 273 K for 8 min, followed by dark adaptation for 3 min and freezing into 77 K. The distance between the pair Cyt b(559)(+)-Q(A)(-) was estimated from the dipole interaction constant fitted to the observed ELDOR time profile to be 40 +/- 1 Angstrom. In the membrane oriented PS II particles the angle between the vector from Q(A) to Cyt b(559) and the membrane normal was determined to be 80 +/- 5 degrees. The position of Cyt b559 relative to Q(A) suggests that the heme plane is located on the stromal side of the thylakoid membrane. ELDOR was not observed for Cyt b(559)(+) Y-D(.) spin pair, suggesting the distance between them is more than 50 Angstrom. (C) 2000 Elsevier Science B.V. All rights reserved.

The electron spin echo envelope modulation spectra of the reduced primary acceptor quinone, Q(A), in two preparations of plant photosystem II, have been studied. In one of these preparations the Fe2+ ion in the quinone-iron complex has been substituted by diamagnetic Zn2+. In the other preparation this iron ion has been converted into the diamagnetic state using a potassium cyanide treatment. A comparative analysis of two-dimensional three-pulse electron spin echo envelope modulation spectra has shown similar structure of the binding site of QA in both preparations. Two nitrogen nuclei have been found to contribute to the spectra in both preparations. One of these nitrogens is, most probably, an amino nitrogen in the imidazole ring of histidine 215 of the D2 protein. The other nitrogen has been assigned to the peptide group of alanine 261 of the D2 protein. The numerical simulations of the electron spin echo envelope modulation spectra have shown that both nitrogens are simultaneously bound to Q(A). (C) 1998 American Institute of Physics.