Acceleration of deposition of Aβ(1-40) peptide on ultrasonically formed Aβ(1-42) nucleus studied by wireless quartz-crystal-microbalance biosensor.

High-frequency (~ 55 MHz) wireless quartz-crystal microbalance biosensor was used for studying heterogeneous deposition behavior of Aβ(1-40) peptide on Aβ(1-42) nuclei, which were grown under the stirring agitation and 200-kHz ultrasonication at pH 2.2, 4.6, and 7.4. The deposition reaction was monitored over 40 h, and the deposition rate was deduced. Among the agitation nuclei, the maximum deposition rate was observed on the nucleus grown at pH 4.6. However, ultrasonication nucleus grown at pH 7.4 produced much larger deposition rate, despite the same β-sheet concentration. This result indicates that local structural modulation is caused in the nucleus by ultrasonication, which adsorbs the Aβ peptide more actively than other nuclei. The resultant deposits clearly show oligomeric structure.