Detection of Amyloid ß Using a Poly-L-Lysine Mediated Nanobiosensor.

Amyloid ß (Aß) peptide is secreted from the outside of neural cell by a neural signal pathway and it accumulated each other results in the highly toxicity amyloid plaque which is a critical causative factor in the pathogenesis of Alzheimer's Disease (AD). The peptide is considered to be a potential biomarker to diagnose AD. Here we introduce a novel poly-L-lysine (PLL) mediated nanobiosensor to detect Aß in vitro. The PLL molecules were utilized as a signal amplifier of Aß detection. The indirect enzyme-linked immunosorbent assay (ELISA) method and the sandwich ELISA method have tried to the detection of Aß. A commercially available ELISA plate was modified by PLL using a chemical agent and the amplified amino groups were activated by a functional group for the binding of Aß. The bound Aß was further modified with a primary antibody and fluorescence molecules conjugated secondary antibody by the traditional immunochemistry. In the result, the fluorescence intensity was increased by the increasing concentration of Aß, and the best Aß detection results were obtained in the PLL mediated indirect ELISA nanobiosensor. We expected that the present method would be optimized and applied for the detection of Aß in human fluid.

Development of Chemically Signal Amplified Nano-Biosensor Mediated by Poly-L-Lysine.

Amyloid ß (Aß) is considered to be one of a potential biomarker to monitor Alzheimer's Disease (AD) not only for diagnostic purposes but for early detection. Here we describe a novel nano-biosensor for Aß mediated by poly-L-lysine (PLL) which was used for the amplification of detection signal for Aß. The indirect enzyme-linked immunosorbent assay (ELISA) method was modified using PLL for the amplification of the Aß detection signal. A commercially available ELISA plate was modified by PLL using chemical agent and the amplified amino groups were activated by a chemical agent for the detection of Aß. The detection was carried out by the traditional immunochemistry using primary antibody and fluorescence molecules conjugated secondary antibody. In the result, the fluorescence intensity was increased by the increasing treated Aß amount, and the sensitivity was approximately 2 times higher in the concentration of 2 ng/mL Aß treatment, and approximately 4 times higher in the concentration of 200 ng/mL Aß treatment compare with that of indirect ELISA detection method. We suggest our novel signal amplification method for the Aß early detection.

Detection of Actin Filament and Cofilin Interaction Change by Actin Filament Curvature Decreasing.

Actin filament senses mechanical forces and it is transduced into biochemical signals during many cellular processes. In the disassembling process of actin filaments, cofilin plays a central role as the actin filament depolymerization. In this study, we evaluated a quantitative analysis of the actin filament-cofilin interaction change dependent upon the actin filament curvature decrease using atomic force microscopy (AFM) and a fabricated wave-like substrate. A wave-like substrate was fabricated by a maskless photo-lithography of a spin coated film on a glass substrate, and graphene oxide sheet was used for the decreasing of non-specific interaction between protein and the substrate. By single-molecule force spectroscopy, we determined rupture force of actin filament-cofilin binding on the wave-like substrate and a flat substrate. The rupture force of actin filament-cofilin binding at the curvature of -1.35 µm-1 showed a value approximately 4 times higher than the rupture force at the curvature of -0.15 µm-1. The present study will provide the possibility and quantitative evidence that mechanical stress on cytoskeletal filaments can modulate how they interact with their binding proteins.

Probing Amyloid ß and the Antibody Interaction Using Atomic Force Microscopy.

Amyloid ß (Aß) peptide is considered to be the critical causative factor in the pathogenesis of Alzheimer's disease (AD) because the hydrophilic molecules accumulated outside of the neural cells and results in the formation of highly toxicity amyloid plaque. In this study, we probed the interaction between Aß and the antibody using atomic force microscopy (AFM). We compared two kinds of antibodies which are the antibody for Aß 1-42 (antibody42) and the antibody for Aß 1-16 (antibody16). To detect the interaction between Aß and the antibodies, the single molecular force spectroscopy was carried out using Aß modified glass substrate and the antibodies modified AFM probes. In the results, the single Aß-antibody42 dissociation constant was estimated to be 5.2 × 10-3 s-1 and the single Aß-antibody16 dissociation constant was 2.8×10-2 s-1. The Aß-antibody42 showed 5.3 times longer bond life time compare with Aß-antibody16. It suggested that antibody42 is better choice for the Aß sensor development.

A Novel Graphene Oxide-Based Protein Interaction Measurement Using Atomic Force Microscopy.

Graphene oxide (GO) is a promising material for biological applications because of its excellent physical/chemical properties such as aqueous processability, amphiphilicity, and surface functionalizability. Here we introduce a new biological application of GO, a novel GO-based technique for probing protein interactions using atomic force microscopy (AFM). GO sheets were intercalated between the protein-modified AFM probe and the polymer substrate in order to reduce the non-specific adhesion force observed during single-molecule force spectroscopy (SMFS). In this study, we used SMFS to probe the interaction of the actin filament and actin-related protein 2/3 complex (Arp2/3), an actin-binding protein. Our results confirm that the GO sheet reduces nonspecific adhesion of the probe to the substrate. Using the GO-based technique, we succeeded in estimating the dissociation constant of the actin filament-binding protein interaction.

A Novel Osteoblast/Osteocyte Selection Method in Primary Isolated Chick Bone Cells by Atomic Force Microscopy.

Selection of bone cells, particularly osteoblasts and osteocytes, for analysis of cellular processes and differentiation is a very important issue because bone remodeling is a highly complex and harmonized process, which includes molecular and cellular interactions and communications. In this study, we introduce a novel osteoblast and osteocyte selection method that uses atomic force microscopy and OB7.3, an antibody of Phex, which is a specific protein marker expressed on the surface of osteocytes. The elasticity and Phex expression levels were simultaneously detected by force spectroscopy using the OB7.3-modified atomic force microscopy probe on the bone cell surface. The elastic modulus was different between osteoblasts and osteocytes. Phex expression level was analyzed by the distribution of Phex-OB7.3 rupturing.

Single-cell manipulation and DNA delivery technology using atomic force microscopy and nanoneedle.

The recent single-cell manipulation technology using atomic force microscopy (AFM) not only allows high-resolution visualization and probing of biomolecules and cells but also provides spatial and temporal access to the interior of living cells via the nanoneedle technology. Here we review the development and application of single-cell manipulations and the DNA delivery technology using a nanoneedle. We briefly describe various DNA delivery methods and discuss their advantages and disadvantages. Fabrication of the nanoneedle, visualization of nanoneedle insertion into living cells, DNA modification on the nanoneedle surface, and the invasiveness of nanoneedle insertion into living cells are described. Different methods of DNA delivery into a living cell, such as lipofection, microinjection, and nanoneedles, are then compared. Finally, single-cell diagnostics using the nanoneedle and the perspectives of the nanoneedle technology are outlined. The nanoneedle-based DNA delivery technology provides new opportunities for efficient and specific introduction of DNA and other biomolecules into precious living cells with a high spatial resolution within a desired time frame. This technology has the potential to be applied for many basic cellular studies and for clinical studies such as single-cell diagnostics.

Probing actin filament and binding protein interaction using an atomic force microscopy.

Actin filaments play essential roles in many kinds of cellular functions by interacting with hundreds of actin binding proteins. Here we probe the interaction between actin filament and a binding protein, α-actinin, using an atomic force microscopy (AFM) and dynamic force spectroscopy (DFS). The distribution of rupturing events including specific and non-specific interactions of actin filament/α- actinin and BSA/α-actinin were analyzed. The rupture force of the actin filament/α-actinin binding was significantly larger than that of the BSA/α-actinin non-specific interaction, and the peaks represent typical multiple parallel bonds. In addition, based on the rupture forces in different loading rate DFS experiments, the dissociation constant of actin filament/α-actinin binding was estimated. The value is in good agreement with a previously reported value obtained by optical tweezer measurement. We expect that the present method will be useful for interaction measurement of actin filaments and many kinds of binding protein.

Real-time monitoring of changes in microtubule mechanical properties in response to microtubule-destabilizing drug treatment.

Microtubules are cylindrical protein polymers that play important roles in a number of cellular functions. The properties of microtubules are dynamically changed by interacting with many microtubule-related proteins and drugs. In this study, we used atomic force microscopy to evaluate the changes in microtubule mechanical properties induced by treatment with nocodazole, which is a microtubule-destabilizing drug. The average spring constant of the microtubules, which was used as a measure of microtubule lateral stiffness, was drastically decreased by treatment with nocodazole within 30 min from 0.052 +/- 0.014 N/m to 0.029 +/- 0.015 N/m. Our findings will aid in the understanding of microtubule dynamics, protein interactions in response to drug treatment, microtubule-related diseases, and drug development.

Successive detection of insulin-like growth factor-II bound to receptors on a living cell surface using an AFM.

In this study, we have developed a method of mechanical force detection for ligands bound to receptors on a cell surface, both of which are involved in a signal transduction pathway. This pathway is an autocrine pathway, involving the production of insulin-like growth factor-II (IGF-II) and activation of the IGF-I receptor, involved in myoblast differentiation induced by MyoD in C3H10T1/2 mouse mesenchymal stem cells. Differentiation of C3H10T1/2 was induced with the DNA demethylation agent 5-azacytidine (5-aza). The etched AFM tip used in the force detection had a flat surface of which about 10 µm(2) was in contact with a cell surface. The forces required to rupture the interactions of IGF-IIs on a cell and anti mouse IGF-II polyclonal antibody immobilized on an etched AFM tip were measured within 5 days of induction of differentiation. The mean unbinding force for a single paired antibody-ligand on a cell was about 81 pN, which was measured at a force loading rate of about 440 nN/s. The percentage of unbinding forces over 100 pN increased to 32% after 2 days from the addition of 5-aza to the medium. This method could be used in non-invasive and successive evaluation of a living cell's behavior.

The effect of amino acid substitution in the imperfect repeat sequences of alpha-synuclein on fibrillation.

Human alpha-synuclein is the causative protein of several neurodegenerative diseases, such as Parkinson's disease (PD) and dementia with Lewy Bodies (DLB). The N-terminal half of alpha-synuclein contains seven imperfect repeat sequences. One of the PD/DLB-causing point mutations, E46K, has been reported in the imperfect repeat sequences of alpha-synuclein, and is prone to form amyloid fibrils. The presence of seven imperfect repeats in alpha-synuclein raises the question of whether or not mutations corresponding to E46K in the other imperfect KTKE(Q)GV repeats have similar effects on aggregation and fibrillation, as well as their propensities to form alpha-helices. To investigate the effect of E(Q)/K mutations in each imperfect repeat sequence, we substituted the amino acid corresponding to E46K in each of the seven repeated sequences with a Lys residue. The mutations in the imperfect KTKE(Q)GV repeat sequences of the N-terminal region were prone to decrease the lag time of fibril formation. In addition, AFM imaging suggested that the Q24K mutant formed twisted fibrils, while the other mutants formed spherical aggregates and short fibrils. These observations indicate that the effect of the mutations on the kinetics of fibril formation and morphology of fibrils varies according to their location.

Analysis of Correlation Between Contrast and Component of Polylatic Acid Composite for Fused Deposition Modeling 3D Printing.

Additive manufacturing or three-dimensional (3D) printing is considered a disruptive technology for producing components with topologically optimized complex geometries as well as functionalities that are not achievable by traditional methods. 3D printing is expected to revolutionize the manufacturing of components. While several 3D printing systems are available, printing based on fused-deposition modeling (FDM) using thermoplastics is particularly widespread because of the simplicity and potential applicability of the method. In this study, we report the analysis of correlation between contrast and component of polylactic acid (PLA) based composite for FDM 3D printing. The pre-fabricated white composite and black composite were mixed in the fraction of 100:0, 90:10, 75:25, 50:50, 25:75, and 0:100% (v/v) and the obtained mixture was extruded using HX-35 3D filament extrusion line. The samples in different contrast were printed in disk like shape, and the gray scale filaments and 3D printed samples were measured the morphology and components using a field emission scanning electron microscope and energy dispersive X-ray spectroscopy. The CIE-lab values of the samples were measured using a colorimeter and the correlation between CIE-lab values and the components were analyzed. Although the component of Ti was linearly increased, the CIE-lab values show a clear exponential increase by increasing the white composite.

Evaluation of the insertion efficiencies of tapered silicon nanoneedles and invasiveness of diamond nanoneedles in manipulations of living single cells.

We have been developing a low invasive cell manipulation technology based on inserting an ultra-thin needle--"nanoneedle"--into a living cell by using an atomic force microscope (AFM). The nanoneedle, made from a silicon AFM tip by focused-ion-beam etching, has a diameter of several hundred nanometers and a length of about 10 microns. Successful insertion of the nanoneedle into the cell can be confirmed by the appearance of a steep relaxation of repulsive force in the force-distance curve as monitored by the AFM system. This technology, termed "cell surgery", can be applied for the detection of intracellular proteins in a living cell or for highly efficient gene transfer. The present study shows that the durability of a tapered nanoneedle is superior to that of a cylindrical nanoneedle, and that a proper aspect ratio for the tapered nanoneedle must be chosen to maintain sufficient insertion efficiency for a particular target cell: tapered nanoneedles of an aspect ratio over 20 showed high insertion efficiency for various kinds of mammalian cells. We then used diamond for the material of the nanoneedle because its specific properties, such as high stiffness, heat conductivity, and electrical conductivity capacitated by boron doping, were deemed useful for the analysis and manipulation of intracellular phenomena. We compared the capability of the diamond nanoneedle in cell manipulation with that of the silicon nanoneedle. Evaluation of the effect of the former on transcription efficiency and localization analysis of p53 expression revealed the low invasiveness for cell manipulation as was also the case for the silicon nanoneedle. We also succeeded in achieving highly efficient plasmid DNA delivery into a mouse fibroblast C3H10T1/2 using the diamond nanoneedle. The diamond nanoneedle is expected to contribute to the versatility of "cell surgery" technology.

High-efficiency DNA injection into a single human mesenchymal stem cell using a nanoneedle and atomic force microscopy.

We describe a low-invasive gene delivery method that uses an etched atomic force microscopy (AFM) tip or nanoneedle that can be inserted into a cell nucleus without causing cellular damage. The nanoneedle is 200 nm in diameter and 6 mum in length and is operated using an AFM system. The probabilities of insertion of the nanoneedle into human mesenchymal stem cells (MSCs) and human embryonic kidney cells (HEK293) were higher than those of typical microinjection capillaries. A plasmid containing the green fluorescent protein (GFP) gene was adsorbed on a poly-L-lysine-modified nanoneedle surface, which was then inserted into primary cultured single human MSCs. A highly efficient gene delivery of over 70% was achieved in human MSCs, which compared very favorably with other major nonviral gene delivery methods (lipofection approximately 50%, microinjection approximately 10 %). The single cells expressing GFP were collected and the amount of delivered DNA in each cell was analyzed. The highest rate of expressed GFP per delivered DNA was achieved using the nanoneedle, because the nanoneedle could be inserted into the nucleus directly without causing significant cell damage.

Real-time TIRF observation of vinculin recruitment to stretched α-catenin by AFM.

Adherens junctions (AJs) adaptively change their intensities in response to intercellular tension; therefore, they integrate tension generated by individual cells to drive multicellular dynamics, such as morphogenetic change in embryos. Under intercellular tension, α-catenin, which is a component protein of AJs, acts as a mechano-chemical transducer to recruit vinculin to promote actin remodeling. Although in vivo and in vitro studies have suggested that α-catenin-mediated mechanotransduction is a dynamic molecular process, which involves a conformational change of α-catenin under tension to expose a cryptic vinculin binding site, there are no suitable experimental methods to directly explore the process. Therefore, in this study, we developed a novel system by combining atomic force microscopy (AFM) and total internal reflection fluorescence (TIRF). In this system, α-catenin molecules (residues 276-634; the mechano-sensitive M1-M3 domain), modified on coverslips, were stretched by AFM and their recruitment of Alexa-labeled full-length vinculin molecules, dissolved in solution, were observed simultaneously, in real time, using TIRF. We applied a physiologically possible range of tensions and extensions to α-catenin and directly observed its vinculin recruitment. Our new system could be used in the fields of mechanobiology and biophysics to explore functions of proteins under tension by coupling biomechanical and biochemical information.

Nanolithography of Amyloid Precursor Protein Cleavage with ß-Secretase by Atomic Force Microscopy.

Cleavage of the amyloid precursor protein (APP) by secretases is critical in neural cell processes including the pathway for neural cell proliferation and that underlying the pathogenesis of Alzheimer's disease (AD). Understanding the mechanism of APP cleavage and development of a convenient tool for the accurate evaluation of APP cleavage intensity by secretases are very important in the development of new AD therapeutic targets. In this study, we developed a sophisticated technology to evaluate the APP cleavage mechanism at the nano-molecular level by atomic force microscopic (AFM) nanolithography. APP was modified on a glass substrate; nanolithography of APP cleavage by ß-secretase-modified AFM probe scanning was achieved. APP cleavage was verified by the AFM imaging and the fluorescent immunostaining. The present method will be very useful in understanding the molecular level of the APP cleavage mechanism by ß-secretase in vitro; this method will facilitate inhibitor screening for the therapeutic target of AD.

Mechano-adaptive sensory mechanism of α-catenin under tension.

The contractile forces in individual cells drive the tissue processes, such as morphogenesis and wound healing, and maintain tissue integrity. In these processes, α-catenin molecule acts as a tension sensor at cadherin-based adherens junctions (AJs), accelerating the positive feedback of intercellular tension. Under tension, α-catenin is activated to recruit vinculin, which recruits actin filaments to AJs. In this study, we revealed how α-catenin retains its activated state while avoiding unfolding under tension. Using single-molecule force spectroscopy employing atomic force microscopy (AFM), we found that mechanically activated α-catenin fragment had higher mechanical stability than a non-activated fragment. The results of our experiments using mutated and segmented fragments showed that the key intramolecular interactions acted as a conformational switch. We also found that the conformation of α-catenin was reinforced by vinculin binding. We demonstrate that α-catenin adaptively changes its conformation under tension to a stable intermediate state, binds to vinculin, and finally settles into a more stable state reinforced by vinculin binding. Our data suggest that the plastic characteristics of α-catenin, revealed in response to both mechanical and biochemical cues, enable the functional-structural dynamics at the cellular and tissue levels.

A molecular delivery system by using AFM and nanoneedle.

We developed a new low invasive cell manipulation and gene or molecule transfer system in a single living cell by using an atomic force microscope (AFM) and ultra thin needle, a nanoneedle. DNA was immobilized on the surface of the nanoneedle by covalent bonding and avidin-biotin affinity binding. Immobilization of DNA on the nanoneedle was confirmed by measuring the unbinding force between avidin and biotin. The DNA-immobilized nanoneedle was successfully inserted into HEK293 cells. Though TO-PRO-3 iodide staining experiments using confocal microscopy, we observed the immobilized DNA on the surface of the nanoneedle, which was retained after 10 times insertions to and evacuations from a living cell.

External mechanical cues trigger the establishment of the anterior-posterior axis in early mouse embryos.

Mouse anterior-posterior axis polarization is preceded by formation of the distal visceral endoderm (DVE) by unknown mechanisms. Here, we show by in vitro culturing of embryos immediately after implantation in microfabricated cavities that the external mechanical cues exerted on the embryo are crucial for DVE formation, as well as the elongated egg cylinder shape, without affecting embryo-intrinsic transcriptional programs except those involving DVE-specific genes. This implies that these developmental events immediately after implantation are not simply embryo-autonomous processes but require extrinsic factors from maternal tissues. Moreover, the mechanical forces induce a breach of the basement membrane barrier at the distal portion locally, and thereby the transmigrated epiblast cells emerge as the DVE cells. Thus, we propose that external mechanical forces exerted by the interaction between embryo and maternal uterine tissues directly control the location of DVE formation at the distal tip and consequently establish the mammalian primary body axis.

Development of a novel biosensing system based on the structural change of a polymerized guanine-quadruplex DNA nanostructure.

By inserting an adenosine aptamer into an aptamer that forms a G-quadruplex, we developed an adaptor molecule, named the Gq-switch, which links an electrode with flavin adenine dinucleotide-dependent glucose dehydrogenase (FADGDH) that is capable of transferring electron to a electrode directly. First, we selected an FADGDH-binding aptamer and identified that its sequence is composed of two blocks of consecutive six guanine bases and it forms a polymerized G-quadruplex structure. Then, we inserted a sequence of an adenosine aptamer between the two blocks of consecutive guanine bases, and we found it also bound to adenosine. Then we named it as Gq-switch. In the absence of adenosine, the Gq-switch-FADGDH complex forms a 30-nm high bulb-shaped structure that changes in the presence of adenosine to give an 8-nm high wire-shaped structure. This structural change brings the FADGDH sufficiently close to the electrode for electron transfer to occur, and the adenosine can be detected from the current produced by the FADGDH. Adenosine was successfully detected with a concentration dependency using the Gq-switch-FADGDH complex immobilized Au electrode by measuring response current to the addition of glucose.