Investigating the Molecular Mechanisms of In-Plane Mechanochemistry on Cantilever Arrays
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- 作者：Moyu Watari ; Jane Galbraith ; Hans-Peter Lang ; Marilyne Sousa ; Martin Hegner ; Christoph Gerber ; Mike A. Horton ; Rachel A. McKendry
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：January 24, 2007
- 年：2007
- 卷：129
- 期：3
- 页码：601 - 609
- 全文大小：307K
- 年卷期：v.129,no.3(January 24, 2007)
- ISSN：1520-5126
文摘
Free-standing cantilevers, which directly translate specific biochemical reactions into micromechanical motion, have recently attracted much attention as label-free biosensors and micro/nano roboticdevices. To exploit this mechanochemical sensing technology, it is essential to develop a fundamentalunderstanding of the origins of surface stress. Here we report a detailed study into the molecular basis ofstress generation in aqueous environments focusing on the pH titration of model mercaptohexadecanoicacid self-assembled monolayers (SAMs), using in situ reference cantilevers coated with nonionizablehexadecanethiol SAMs. Semiautomated data analysis and a statistical model were developed to quantifycyclic deprotonation/protonation reactions on multiple arrays. In-plane force titrations were found to havethe sensitivity to detect ionic hydrogen bond formation between protonated and nonprotonated carboxylicacid groups in the proximity of the surface pK1/2, which generated a mean tensile differential surface stressof +1.2 ± 0.3 mN/m at pH 6.0, corresponding to 1 pN attractive force between two adjacent MHA molecules.Conversely, the magnitude of compressive differential surface stress was found to increase progressivelywith pH 
7.0, reaching a maximum of -14.5 ± 0.5 mN/m at pH 9.0, attributed to enhanced electrostaticrepulsion between deprotonated carboxylic acid groups. However, striking differences were observed inthe micromechanical responses to different ionic strength and ion species present in the aqueousenvironment, highlighting the critical role of counter- and co-ions on surface stress. Our findings providefundamental insights into the molecular mechanisms of in-plane mechanochemistry, which may be exploitedfor biosensing and nanoactuation applications.
7.0, reaching a maximum of -14.5 ± 0.5 mN/m at pH 9.0, attributed to enhanced electrostaticrepulsion between deprotonated carboxylic acid groups. However, striking differences were observed inthe micromechanical responses to different ionic strength and ion species present in the aqueousenvironment, highlighting the critical role of counter- and co-ions on surface stress. Our findings providefundamental insights into the molecular mechanisms of in-plane mechanochemistry, which may be exploitedfor biosensing and nanoactuation applications.