Nanoelectrical characterization of amyloid-β42 aggregates via Kelvin probe force microscopy

Conformation Control of Amyloid Filaments by Repeated Thermal Perturbation

We report that repeated thermal perturbation by thermal cycling (TC) accelerates the formation rate of amyloid filaments at microliter volumes (10-200 μL) and produces a new conformation of zigzag-shaped filaments. The amyloid filaments have been synthesized under different TC conditions, such as temperature variations (ΔT = 0-86 °C) and the number of cycles (C^# = 30-90). In particular, the filament formation was promoted by TC with ΔT ≥ 30 °C. This indicates that the change in binding energy of β-sheets and the breakage of disulfide bonds induced by TC with large ΔT contributed to the increased filament growth. This molecular interaction was investigated by molecular dynamics simulation. We also found that TC leads to the formation of amyloid filaments with peculiar conformation (zigzag-shaped filaments). Moreover, key structural parameters (tortuosity, segment length, and joint angle) of the amyloid filaments could be fine-tuned by selecting certain ΔT conditions. Taken together, we confirmed that the TC not only promotes the formation of amyloid filaments but also affects the conformational changes of the filaments.

Nanoelectrical characterization of individual exosomes secreted by Aβ42-ingested cells using electrostatic force microscopy

Quantifying the physical properties of individual exosomes containing amyloid-β₄₂ (Aβ₄₂) is crucial for a better understanding of an underpinning mechanism of Alzheimer's disease expression which is associated with the Aβ₄₂ transfer. Because of the lack of proper tools, however, there have been very few studies on how the amount of Aβ₄₂ affects the physical properties of exosomes. To answer the question, we investigated the physical properties of exosomes secreted by neuroblastoma by probing individual exosomes using electrostatic force microscopy. Interestingly, we observed that when the higher concentration of Aβ₄₂ oligomers was fed to cells, the higher surface charge of the exosomes appeared. This result indicates that the exosomes contain more Aβ₄₂ with the increase in Aβ₄₂ concentration in cell media, implying that they serve as transport vesicles for Aβ₄₂. Our approach could help to better understand how the neuronal exosomes are related to the propagation of neurodegenerative diseases and to seek how to make an early diagnosis of those diseases.

Peak Force Infrared-Kelvin Probe Force Microscopy

Correlative scanning probe microscopy of chemical identity, surface potential, and mechanical properties provide insight into the structure-function relationships of nanomaterials. However, simultaneous measurement with comparable and high resolution is a challenge. We seamlessly integrated nanoscale photothermal infrared imaging with Coulomb force detection to form peak force infrared-Kelvin probe force microscopy (PFIR-KPFM), which enables simultaneous nanomapping of infrared absorption, surface potential, and mechanical properties with approximately 10 nm spatial resolution in a single-pass scan. MAPbBr₃ perovskite crystals of different degradation pathways were studied in situ. Nanoscale charge accumulations were observed in MAPbBr₃ near the boundary to PbBr₂ . PFIR-KPFM also revealed correlations between residual charges and secondary conformation in amyloid fibrils. PFIR-KPFM is applicable to other heterogeneous materials at the nanoscale for correlative multimodal characterizations.

MoS2 Field-Effect Transistor-Amyloid-β1-42 Hybrid Device for Signal Amplified Detection of MMP-9

The detection of circulating protein (CP) is very important for the diagnosis and therapeutics of cancer. Conventional techniques based on a specific antibody-antigen interaction are still lacking because of a shortage of cost effectiveness, complicated sandwich structure and tagging process, and inconsistent detection of CP due to the inherent instability of antibodies. Herein, we demonstrate a hybrid device consisting of two-dimensional (2D) nanoscale molybdenum disulfide (MoS₂) field-effect transistor (FET) with an amyloid-β_1-42 (Aβ_1-42) functionalized surface, which amplifies electric signals of the FET in order to detect matrix metalloproteinase-9 (MMP-9), which is a certain type of CP that degrades Aβ_1-42. With the hybrid device, we detected the concentrations of MMP-9 in the range from 1 pM to 10 nM. Moreover, using tapping-mode atomic force microscopy and Kelvin probe force microscopy, we verified that the signal amplification corresponding to the MMP-9 concentrations was caused by the reduced length and the decreased surface potential of degraded Aβ_1-42 due to MMP-9. The hybrid device studied in this paper can be very useful for monitoring MMP-9 activity, as well as serving as a sensing platform for the electrical signal amplification of 2D MoS₂ FET-biosensors.

Microwave-induced formation of oligomeric amyloid aggregates

Amyloid aggregates have emerged as a significant hallmark of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Although it has been recently reported that microwave heating induces amyloid aggregation compared with conventional heating methods, the mechanism of amyloid aggregate induction has remained unclear. In this study, we investigated the formation of oligomeric amyloid aggregates (OAAs) by microwave irradiation at microscale volumes of solution. Microwave irradiation of protein monomer solution triggered rapid formation of OAAs within 7 min. We characterized the formation of OAAs using atomic force microscopy, thioflavin T fluorescent assay and circular dichroism. In the microwave system, we also investigated the inhibitory effect on the formation of amyloid aggregates by L-ascorbic acid as well as enhanced amyloid aggregation by silver nanomaterials such as nanoparticles and nanowires. We believe that microwave technology has the potential to facilitate the study of amyloid aggregation in the presence of chemical agents or nanomaterials.

Atomic Force Microscopy Analysis of EPPS-Driven Degradation and Reformation of Amyloid-β Aggregates

Amyloid-β (Aβ) peptides can be aggregated into β-sheet rich fibrils or plaques and deposited on the extracellular matrix of brain tissues, which is a hallmark of Alzheimer’s disease. Several drug candidates have been designed to retard the progression of the neurodegenerative disorder or to eliminate toxic Aβ aggregates. Recently, 4-(2-Hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS) has emerged as a promising drug candidates for elimination of toxic Aβ aggregates. However, the effect of EPPS on the degradation of Aβ aggregates such as fibrils has not yet been fully elucidated. In this article, we investigate the EPPS-driven degradative behavior of Aβ aggregates at the molecular level by using high-resolution atomic force microscopy. We synthesized Aβ fibrils and observed degradation of fibrils following treatment with various concentrations (1–50 mM) of EPPS for various time periods. We found that degradation of Aβ fibrils by EPPS increased as a function of concentration and treatment duration. Intriguingly, we also found regeneration of Aβ aggregates with larger sizes than original aggregates at high concentrations (10 and 50 mM) of EPPS. This might be attributed to a shorter lag phase that facilitates reformation of Aβ aggregates in the absence of clearance system.