以多尺度模擬分析吸附現象在懸臂樑式生物微感測器的變形行為

Abstract

以感測懸臂樑變形為主的生物微感測器因擁有高靈敏性、不需任何標定物、成本低廉、容易透過標準微機電製程批量生產等特性，近年來越來越受到重視。如能正確分析此微懸臂樑的表面吸附受力與變形行為，不僅能協助我們深入瞭解其力學性質，更能大幅提升設計此元件的能力。本研究目的即是希望發展多尺度模擬，適當地連結微觀的生物分子吸附機制與巨觀的撓曲變形。 本研究推導出一套完整多尺度理論，連接分子吸附的作用與連體懸臂樑之間的關係，對其力學行為做正確之分析與預測。在多尺度分析中推導出一可分析懸臂樑變形行為受吸附影響的解析式，將原子與量子計算中所獲得的吸附特性代入推導求得巨觀撓曲行為。本研究利用原子尺度模擬計算分析自組裝單層分子(alkanethiol)吸附性與金表面的微觀吸附現象。使用VASP進行第一原理計算，正確的模擬自組裝單層分子吸附在金表面上的行為，包含吸附能及吸附位置等皆與文獻值相近，其吸附能的最大誤差範圍在13％以內，並延伸至使用分子模擬正確計算出多碳鏈的吸附行為，誤差在7％以下。 在多尺度計算中，本研究將原子計算中所獲得的吸附特性代入推導，成功分析文獻中實驗數據，發現不同長度自組裝單層分子與懸臂樑的撓度成正比且呈線性關係與實驗結果相似。本研究分析出為金表面原子因受到不同長度自組裝單層分子影響，而使得原子的產生移動以及受力改變，導致表面應力不同。在最後，並提出與本研究相關的議題，作為以後延伸之參考。

Microcantilever-based biosensors are rapidly becoming an enabling sensing technology for a variety of label-free biological applications due to their wide applicability, versatility and low cost. It is thus imperative for us to reveal the physical origin of adsorption-induced deformation, and to further analyze its implication of microscopic mechanisms on macroscopic deformation. The objective of this work is to develop a multi-scale theory that can analyze deformation of micro-cantilever beam subjected to bio-adsorption mechanisms calculated by ab- initio simulation and classical molecular dynamics. The multi-scale theory developed herein has successfully correlated atomistic information (the mechanism of bio-adsorption) and continuum description (bending behavior of a cantilever beam). We have studied the adsorption mechanisms of bio-molecules for SAM (self-assembly monolayer, alkanethiolic molecular for n=1~14) adsorbed on gold through ab-initio and molecular dynamics simulation. The ab-initio simulation results are in a good agreement with the literature, and the error of calculated absorption energy is less than 13％. We then extend to longer SAM simulation by molecular dynamics and the calculated absorption energy is less than 7％ when comparing with the ab-initio results. Adsorption-induced stresses for different SAMs (for n=4, 6, 8, 12 and 14) are calculated by the multi-scale method. Calculated deflection based on the adsorption-induced stress agrees well with experimental measurements. Physical origin of adsorption induced deformation is revealed through the change of atomic positions and forces.