Seiji Kamba

Biotinylation of Silicon and Nickel Surfaces and Detection of Streptavidin as Biosensor

The availability of metal mesh device sensors has been investigated using surface-modified nickel mesh. Biotin was immobilized on the sensor surfaces consisting of silicon and nickel via a thiol-ene click reaction, known as the Michael addition reaction. Biotinylation on the maleimidated surface was confirmed by X-ray photoelectron spectroscopy. The binding of streptavidin to the biotinylated surfaces was evaluated using a quartz crystal microbalance and a metal mesh device sensor, with both techniques providing similar binding constant value. The recognition ability of the biotin immobilized using the thiol-maleimide method for streptavidin was comparable to that of biotin immobilized via several other methods. The adsorption of a biotin conjugate onto the streptavidin-immobilized surface via the biotin-streptavidin-biotin sandwich method was evaluated using a fluorescent microarray, with the results demonstrating that the biological activity of the streptavidin remained.

Metal mesh device sensor immobilized with a trimethoxysilane-containing glycopolymer for label-free detection of proteins and bacteria

Biosensors for the detection of proteins and bacteria have been developed using glycopolymer-immobilized metal mesh devices. The trimethoxysilane-containing glycopolymer was immobilized onto a metal mesh device using the silane coupling reaction. The surface shape and transmittance properties of the original metal mesh device were maintained following the immobilization of the glycopolymer. The mannose-binding protein (concanavalin A) could be detected at concentrations in the range of 10(-9) to 10(-6) mol L(-1) using the glycopolymer-immobilized metal mesh device sensor, whereas another protein (bovine serum albumin) was not detected. A detection limit of 1 ng mm(-2) was achieved for the amount of adsorbed concanavalin A. The glycopolymer-immobilized metal mesh device sensor could also detect bacteria as well as protein. The mannose-binding strain of Escherichia coli was specifically detected by the glycopolymer-immobilized metal mesh device sensor. The glycopolymer-immobilized metal mesh device could therefore be used as a label-free biosensor showing high levels of selectivity and sensitivity toward proteins and bacteria.

Detection of

The effectiveness of metallic mesh sensors to quantitatively measure thickness was evaluated by transmission spectra of sub- μm-thick SiO2 layers deposited on a 6-μm-thick metallic mesh. Initially, we simulated the transmission spectra and the localized electric field distribution of different-sized periodic structures using the finite difference time domain method. Both the wavelength of the resonance peak and the decay distance of the localized electric field changed linearly with the size of the geometric parameters of the metallic meshes. These electro-magnetic properties enabled smaller-sized periodic structures to acquire exponentially higher sensitivity for the thin dielectric layer. The experiment resulted in distinct and systematic frequency shifts over 100-nm-thick SiO2 (101 GHz of shift and 61% of CV). Potential of the metallic meshes as label-free and frequency-flexible biosensors was performed, which have high sensitivity for thin target using small size of periodic structures.

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A biosensor for protein detection was developed using antibody-immobilized metal mesh devices. Antihemoglobin antibodies were covalently immobilized on a metal mesh device. Extraordinary transmission with a dipped structure was observed for a metal mesh device immobilized with antihemoglobin antibodies as well as for the original metal mesh device. Hemoglobin in the mixture solution containing albumin at a hundred-fold concentration was detectable using antihemoglobin-immobilized MMDs. The detectability using the antihemoglobin-immobilized metal mesh device was similar to that of a commercially-available kit for the qualitative determination of hemoglobin.

Thin Layer by Using a Metallic Mesh Sensor

Separation and detection of particular cells from culture media and clinical specimens is important for cell engineering and clinical examination. In this paper, we developed a metal mesh device (MMD) in which a thin nickel mesh with periodic microstructures consisting of square apertures plays a pivotal role in cellular fractionation and sensing. The mesh aperture in our 100-THz MMD had a side length of 1.8 μm. This size of aperture was suitable for optically sensing mesh-captured particles by detecting transmittance of the corresponding electromagnetic waves, and simultaneously functioned as a sieve to separate microspheres according to their size. HeLa cells could be selectively captured by filtration through the 100-THz MMD, and the captured cells were detected by infrared transmittance changes. Coating of the mesh with gold improved sensing capability by sharpening of the transmittance peak. Most (98%) HeLa cells captured on the gold-coated mesh were viable and proliferated normally when re-cultured. When a mixture consisting of HeLa cells and an excess number of erythrocytes was filtered, HeLa cells were captured on the mesh, whereas erythrocytes were not, even though the average size of erythrocytes was much larger than the mesh aperture. Thus, gold-coated mesh may be useful for separating solid tumor-derived circulating cancer cells from erythrocytes, a major blood cell type. In addition, metal mesh-aided recovery of mammalian cells from cultures without cellular damage may facilitate the large-scale culture in cell biotechnology, because centrifugation, a laborious process for harvesting cells, becomes dispensable.

Label-free detection of antigen protein using a metal mesh device surface-modified by an antibody

We demonstrated specific and rapid detection of Escherichia coli (E. coli) without culturing and labeling, using a metallic mesh sensor. Streptavidin and biotinylated antibody, specific for E. coli, were immobilized on the metallic mesh surface via amination and maleimidation. E. coli in PBS were captured, and attached to the surface of the metallic mesh, by immunoreaction with the antibody for E. coli. Transmission spectra of these samples were then measured around 10 THz, where the size of the generated, localized, electric field is the same as that of E. coli. After demonstrating a significant relationship between the frequency shift on the metallic mesh sensor and antibody for E. coli concentration, we then went on to specifically and quantitatively measure E. coli concentration. As E. coli concentration increased so did the spectral frequency shift, with detection limit being observed at 106 mL-1.

Surface Coating of a Metal Mesh Device Sensor With Gold to Improve the Separation and Sensing of Mammalian Cells

Metamaterial meshes are artificial thin metal film structures with a periodic arrangement of holes. Here we describe the development of metamaterial meshes for applications as sensors, using high-accuracy and low-cost fabrication methods to enable disposable devices. Small liquid droplets from dispensers were used to characterize the devices. The results demonstrate that detection of sub-microliter liquid specimens is possible. The process was considerably simpler than conventional techniques, such as staining or mass balance measurements. Our results show that these metamaterial meshes have potential applications as sensors, in particular for rapid tests and calibration of multi-channel dispensers.

Specific detection of Escherichia coli by using metallic mesh sensor in THz region

Aggregation of amyloid-β (Aβ) peptides is believed to play a key role in the mechanism of molecular pathogenesis of Alzheimers disease (AD). To inhibit the aggregation and prevent AD, numerous compounds have been synthesized. A previous experimental study elucidated that a triazine derivative AA3E2 has anti-amyloidogenic ability, while a triazine derivative AA3D2 having a different substituent has no inhibitory effect. However, the reason for this remarkable difference in the ability cannot be explained by the chemical structures of these derivatives. In the present study, we present stable structures of the solvated complexes with Aβ and AA3E2/AA3D2 obtained by classical molecular mechanics method. The specific interactions between Aβ and AA3E2/AA3D2 in the complexes are investigated by ab initio fragment molecular orbital calculations. Based on the results obtained, we attempt to propose new potent inhibitors for the Aβ aggregation.

Detection of sub-microliter liquid droplets using a metamaterial mesh sensor

When proteins are attached to microstructures such as a metal mesh device, changes in their optical properties occur. These changes have been characterized based on actual measurements in the infrared region of the spectrum. We have previously theoretically and experimentally demonstrated the optical changes associated with streptavidin. Here, we investigate three types of proteins: avidin, BSA, and lysozyme. The three proteins were adsorbed onto three types of metal mesh devices having different resonant frequencies, and the corresponding spectra were measured in the infrared region. The change in the frequency of the dip point in the spectrum was extracted to quantitatively determine the quantity of protein; these results were correlated with the quantitative measurements obtained by electrophoresis. By examining three types of different proteins, it was verified that a variety of proteins can be measured based on the optical characteristics of metal mesh devices.

Proposal for an inhibitor of Alzheimer's disease blocking aggregation of amyloid-β peptides: ab initio molecular simulations

A metal mesh device has a structure in which through-holes of the same shape are periodically placed on a thin metal film, and the selection of such a structure makes it possible to sense objects of various sizes. In this study, we showed the structure of the metal mesh device and the relationship between the detectable optical domain and the size of the objects to be measured. In addition, from measurement of changes in electromagnetic wave transmission characteristics of the metal mesh device due to specific adsorption of particles with a mean diameter of 100 nm with surface modification with Streptavidin to a metal mesh device fixed with biotin, we showed that even large particles can be sensed. Based on these examinations, we showed that, by using a metal mesh device with detectable optical domain corresponding to the size of objects, even objects that are larger than protein can be sensed.