Signal amplification in electrochemical detection of buckwheat allergenic protein using field effect transistor biosensor by introduction of anionic surfactant

AbstractFood allergens, especially buckwheat proteins, sometimes induce anaphylactic shock in patients after ingestion. Development of a simple and rapid screening method based on a field effect transistor (FET) biosensor for food allergens in food facilities or products is in demand. In this study, we achieved the FET detection of a buckwheat allergenic protein (BWp16), which is not charged enough to be electrically detected by FET biosensors, by introducing additional negative charges from anionic surfactants to the target proteins. A change in the FET characteristics reflecting surface potential caused by the adsorption of target charged proteins was observed when the target sample was coupled with the anionic surfactant (sodium dodecyl sulfate; SDS), while no significant response was detected without any surfactant treatment. It was suggested that the surfactant conjugated with the protein could be useful for the charge amplification of the target proteins. The surface plasmon resonance analysis revealed that the SDS-coupled proteins were successfully captured by the receptors immobilized on the sensing surface. Additionally, we obtained the FET responses at various concentrations of BWp16 ranging from 1ng/mL to 10μg/mL. These results suggest that a signal amplification method for FET biosensing is useful for allergen detection in the food industry

Improved Water-stable Protected Anodes with Low Resistance for Aqueous Energy Storage Devices

Multi-component anodes, fabricated by assembling lithium metal or pre-lithiated graphite negative electrode, a lithium-ion conducting solid electrolyte with water stability and a polymer or gel electrolyte in between the negative electrode and solid electrolyte, are promising as water-stable protected anodes for next-generation batteries and hybrid capacitors. By applying the protected anode to hybrid capacitors, operating voltage of 4 V can be achieved in aqueous electrolytes. However, the protected anode suffers from large resistance due to its multi-component structure, leading to insufficient power density and energy conversion efficiency. Here we analyze various protected anodes by using electrochemical impedance spectroscopy (EIS) to evaluate the bottleneck components in order to reduce the overall resistance. Protected anodes with different polymers or gel membranes, lithium salts and ionic liquid additives, negative electrode materials, binders, and solid electrolytes, were fabricated and the impedance components were analyzed. The resistance of the protected anode was successfully reduced by selecting proper materials

Origin of the Adsorption-Controlled Redox Behavior of Quinone-Based Molecules: Importance of the Micropore Width

Redox-active organic materials have emerged as promising alternatives to inorganic electrode materials in electrochemical devices owing to advantages such as low cost and flexible design. However, the kinetics of their electrochemical reactions are typically slow due to the slow diffusion of organic materials dissolved in the electrolyte. Generally, peak separation of the redox reaction is observed (mass-transfer-controlled system), while no peak separation is obtained when the active molecules, such as high surface carbon material, are adsorbed onto the electrode material (adsorption-controlled system). Aromatic compounds confined in activated carbon (AC) micropores exhibit an adsorption-controlled reaction, improving the reaction kinetics. To elucidate this behavior, a well-defined and accurate understanding of the pore geometry is required. Although various synthetic techniques have been used to tune the micropore size, these afford different surface properties. This study reports an approach to achieve an adsorption-controlled redox reaction of quinone-based molecules and a tool to analyze their reaction environment. AC micropores sized <1 nm were filled with n-nonane without any change occurring in the AC surface properties. It was thus concluded that AC micropores in the sub-nanometer scale are necessary for an adsorption-controlled redox reaction to occur. This study reveals new insights on the micropore confinement effect in electrochemistry

Synergetic Effect of RuO2 Nanosheets as a Redox Active Binder for Aqueous Electrochemical Capacitors: The Case of MnO2

MnO2 has been considered as a promising positive electrode material for aqueous electrochemical capacitors combined with activated carbon negative electrodes. Owing to the low electronic conductivity of MnO2, carbon is usually added in large quantities, in particular, for high power applications. In this study, we have pursued the possibility of using RuO2 nanosheets with high electronic conductivity and specific capacitance as a redox active binder. By adding only 20 mol% RuO2 nanosheets to MnO2, an increase in specific capacitance per total mass of composite electrode was observed. Notably, the enhancement effect was particularly pronounced at high scan rates with an increase in specific capacitance of 6.7 times at 50 mV s−1 by using RuO2 nanosheet binder, while at 2 mV s−1 the enhancement was 1.3 times. The cause of the enhancement in specific capacitance and rate performance is discussed based on RuO2 nanosheets acting as redox active conductive binder and MnO2 particles acting as spacers to suppress re-stacking of RuO2 nanosheets

Effect of human serum on the electrical detection of amyloid-β fibrils in biological environments using azo-dye immobilized field effect transistor (FET) biosensor

As amyloid-β peptide 1–42 (Aβ42) was found to be an emerging and important biomarker for Alzheimer's disease, the detection of this peptide in biological samples such as human serum (HS) has become very important for evaluating the potential disease state and determining the appropriate treatment. In this study, we developed an electrical analysis strategy based on a field effect transistor (FET) biosensor as a simple and reliable technique for confirming the presence of Aβ42 aggregates (fibrils) in biological samples. By utilizing Congo red immobilized on the FET gate surface as a biorecognition element, we observed remarkable sensitivity and specificity for detecting Aβ42 fibrils. Furthermore, we optimized the procedure to minimize the interference of abundant human serum albumin for the detection system using HS samples. The optimized system of Congo red-immobilized FET enables measurement of Aβ42 fibrils in the 100-pM level in HS samples, which is lower than its clinical concentration. The FET device can be applied as a biosensing system for mass and routine screening of peptide biomarkers related to Alzheimer's disease. Keywords: Field effect transistor biosensor, Amyloid beta fibrils, Alzheimer's disease, Human serum albumin, Albumin-amyloid beta complexe

Field Effect Transistor Biosensor Using Antigen Binding Fragment for Detecting Tumor Marker in Human Serum

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

Immobilization of Target-Bound Aptamer on Field Effect Transistor Biosensor to Improve Sensitivity for Detection of Uncharged Cortisol

Field effect transistor (FET) biosensors are capable of detecting various biomolecules, although challenges remain in the detection of uncharged molecules. In this study, the detection of uncharged cortisol was demonstrated by interfacial design using a technique to immobilize target-bound aptamers. The target-bound aptamers, which formed a higher-order structure than target-unbound aptamers, expanded the distance between adjacent aptamers and reduced the steric hindrance to the conformational change. The density-controlled aptamers efficiently induced their conformational changes with the cortisol binding, which resulted in the improvement of the sensitivity of FET biosensors