以分子動力模擬探討烷基硫醇分子於金表面之吸附與自組裝行為

Abstract

微懸臂梁生物感測器的便利、高精確度和低成本，使之近年來漸受關注。烷基硫醇分子是常用於連結微懸臂梁與感測分子的自組裝單層分子，不同碳鏈長度硫醇自組裝單層分子排列的特性相異，並且會對微懸臂梁生物感測結果與靈敏度造成影響，然而微觀尺度的實驗觀察不易，且多為對單一長度的碳鏈長度進行研究，因此本研究欲以分子動力模擬觀察不同碳鏈長度硫醇自組裝單層分子之吸附，希望透過模擬了解其吸附的機制，進而改善微懸臂梁感測器之設計。 本研究以分子動力模擬分析自組裝烷基硫醇分子於微懸臂梁之金(1 1 1)表面之吸附，探討兩種濃度(0.540M、1.080M)和四種碳鏈長度(2、6、10、14)時，覆蓋率對吸附行為和吸附硫醇分子傾斜角度的影響。我們觀察到硫醇自組裝單層分子膜的形成過程可分為三個階段，第一階段為當表面的覆蓋率極低時，吸附的硫醇分子會在表面移動。第二階段時，平躺於表面不移動但無規則排列。當表面的覆蓋率高時，則幾乎不動，僅小幅度的偏移。當平躺的覆蓋率達飽和時進入第三階段，此時傾斜角度的分布開始改變，可以看到傾斜角度θ較小的硫醇分子散布於金表面，並且此覆蓋率極限隨碳鏈長度增加而下降。此外，觀察到短碳鏈硫醇分子的排列較無規律，且沒有不同的形成階段。

Microcantilever-based biosensors have received much attention because of the features of convenience, high precision, and low cost. Alkanethiol is a common self-assembled monolayer used to link the surface of microcantilever-based biosensors and biorecognition elements. The adsorption and chain length effects of alkanethiols on gold affect the sensing results and sensitivity of microcantilever-based biosensors. The objective of this work is to understand the kinetics and mechanisms of alkanethiols adsorption with varying chain length. The understanding will shed light on the design of microcantilever-based biosensors in the future.. Molecular dynamics simulations are used to analyze the adsorption of alkanethiol self-assembled monolayers on Au(111). The influence of adsorption coverage on tilting angle of alkanethiols and formation of self-assembled monolayers is observed. Two different concentrations (0.540M、1.080M) and four different chain lengths (2、6、10、14) of alkanethiols are also discussed. The simulation results show that alkanethiols are mobile on gold surface with low coverage and immobile with higher coverage. In the process of adsorption, the distribution of alkanethiols tilting angle changes when certain coverage is reached, and this coverage decreased with longer chain length of alkanethiols. While the coverage exceeds the limit of lying phase, alkanethiols with small tilting angle begin to be scattered on gold surface. Moreover, the structure is more disordered and no distinct formation phases are observed for alkanethiols with short chain length.