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The focus of the research is the first step of fibrillogenesis of amyloid beta protein. |
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In our study, the conjugation of various sequences of amyloid beta protein solution with gold or silver colloidal nanoparticles were confirmed. For gold colloidal particles, a color changes from red to blue was clearly seen as the pH decreased from pH 7. Particularly, the addition of the amyloid beta caused the color change to take place at the higher pH values. While the color of bear gold colloidal nanoparticles (size of 20 nm) at pH 3-5 were red, the mixture of gold colloidal nanoparticles and amyloid beta exhibited bluish color at these pHs. We also found that hydrophobic amyloid beta 1-42 in pH 2-6 range presented the precipitates after about a day. However, the color of the solution still remained the same even with precipitates present (Figure 3-ii). |
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Absorption spectroscopy exhibited proof of the changes in the optical property of both metal colloid for pHs, ranging from pH 2 to pH 10. This SPR band clearly showed a shoulder band as amyloid beta was added and pH was adjusted to the lower values. Therefore, our study utilized the absorption spectra to characterize the color change in the solution as a function of pHs.Quite interestingly, all tested proteins in this study showed the color change at a higher pH than where bare gold colloid exhibited its color change at pH =3.69(2). All tested Amyloid beta sequences except for 1-42 exhibited color changes around pH =5. The Amyloid beta 1-42 exhibited precipitants in all pH lower than pH 7 and showed the color change around pH 3.96(5). Overall, we did not get good correlation between pI (isoelectric point) and pHo for the smaller segments of amyloid beta sequences (Amyloid beta 12-28 and 31-35). It indicates that the color change does not necessary happen when the net charge of the proteins are neutralized for these sequences. Since these pH values are much smaller than pI, the electrostatic interaction between anionic gold surface and positive net charge of amyloid protein must take place. |
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The conjugation onto the silver colloidal nanoparticles were tested. A slight color change from yellow to dark orange was confirmed for the amyloid beta 1-40 coated silver colloid nano particles with the sizes of 20, 40, and 60 nm. They showed higher pHo values than that obtained for gold colloidal nanoparticles. In the case of silver colloidal particles, the pHo shifts to higher values as the amyloid beta was added, indicating that the interaction of conjugation may be different in nature from that exists in gold colloid-amyloid beta bonding. |
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Interestingly, only Amyloid beta 1-40・coated gold colloidal nanoparticles of 20 nm size exhibited a reversible color change as the pH was externally altered between pH 4 and 10 among all tested amyloid beta sequences. Demo-clip |
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The AFM study conducted on the dried sample of Amyloid beta 1-40 and gold colloidal nanoparticles 20 nm of size. The topology of the amyloid beta on mica and graphite surface was drastically different as the gold colloid was mixed. The Amyloid beta 1-40 themselves showed a granular cluster of the monomer unit, while the thin homogeneous layer was formed as the gold colloid was mixed in the solution. The different topology was found in the dried sample started from pH 4, 7, and 10 solutions. |
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