Measurement of a Bubble-Free Chemical Oscillator Using QCMs Treated with Self-Assembled Monolayers

Minoru Yoshimoto; Shigeru Kurosawa; Mutsuo Tanaka

doi:10.1021/acs.jpcb.4c00002

Measurement of a Bubble-Free Chemical Oscillator Using QCMs Treated with Self-Assembled Monolayers

J Phys Chem B. 2024 Apr 11;128(14):3360-3367. doi: 10.1021/acs.jpcb.4c00002. Epub 2024 Apr 3.

Authors

Minoru Yoshimoto¹, Shigeru Kurosawa², Mutsuo Tanaka³

Affiliations

¹ Department of Information Science and Biomedical Engineering, Graduate School of Science and Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan.
² Health and Medical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
³ Department of Life Science & Green Chemistry, Saitama Institute of Technology, 1690, Fusaiji, Fukaya, Saitama 369-0293, Japan.

PMID: 38567983
DOI: 10.1021/acs.jpcb.4c00002

Abstract

The oscillation of a 1,4-cyclohexanedione-bromate (CHD-bromate) system was investigated by using a quartz crystal microbalance (QCM) without or with a self-assembled monolayer (SAM), where gold and platinum were used for QCM electrodes and SAMs were composed of HS(CH₂)₁₁CH₃, HS(CH₂CH₂O)₅H, and HS(CH₂CH₂O)₅CH₃. The CHD-bromate system is well-known as a bubble-free oscillator and oscillates without or with a catalyst. In the CHD-bromate system without a catalyst, the oscillation of a resonant frequency shift (ΔF) of the QCM was observed in the Au-electrode QCMs without a SAM or with SAMs formed from HS(CH₂)₁₁CH₃ and HS(CH₂CH₂O)₅H. On the other hand, the HS(CH₂CH₂O)₅CH₃ SAM suppressed the ΔF oscillation. The results revealed that in the CHD-bromate system without a catalyst, hydrophobic CH₃ terminal and helical conformation were important to prevent nonspecific adsorption of substances on a gold surface and its dissolution. In the CHD-bromate system with a catalyst (ferroin), the ΔF oscillation was observed in the Au-electrode QCM with the HS(CH₂CH₂O)₅CH₃ SAM. The results suggest evidence that the change of the solution viscosity and density led to the ΔF oscillation. These results for Au-electrode QCMs were also corroborated by those for Pt-electrode QCMs.