檢測水中甲醛之液晶感測器

Liquid Crystal Sensor System for Detecting Formaldehyde in Aqueous Solutions

何宗洋(Tsung-Yang Ho)

指導教授 ： 陳志欣

淡江大學/理學院/化學學系碩士班/碩士(2020年)

https://doi.org/10.6846/TKU.2020.00227

摘要

此研究以向列型液晶–5CB為基礎，參雜了含有胺基的兩親性分子–PBA，開發了檢測水中甲醛的液晶感測器。由於PBA具有兩親性，可以在液晶／水溶液界面誘導液晶的排列形成垂直配向，在此狀態下以偏光顯微鏡可觀察到暗的光學訊號，當甲醛存在於系統時會與PBA發生反應，導致其結構由胺基變為亞胺基，失去誘導液晶排列的能力，此時液晶排列狀態改變並呈現亮訊號，由這個暗變亮的訊號轉換，我們可以得知系統是否檢測到水溶液中甲醛的存在。
起初我們以Hantzsch反應為檢測機制設計感測器，隨著進一步的討論，我們修改了對檢測機制的假說，並證明了其檢測機制為醛胺縮合反應，以此機制在酸性條件下，感測器可以檢測到1 mM的甲醛，具有高度的選擇性，也可應用於檢測化妝水樣品中30 mM濃度的甲醛含量。
液晶感測器具有低成本、簡單操作且肉眼即可辨識訊號的特性，因此適合開發為個人護理用品之甲醛檢測器。

關鍵字

液晶 ； 甲醛 ； 感測器

並列摘要

We developed a liquid crystal (LC)-based sensor system for detecting formaldehyde in aqueous solutions. In this sensor, nematic LCs were doped with 4'-pentyl-4-biphenylamine (PBA), which acts as the amphiphilic molecule to align at LC/aqueous interface. Such alignment induced the homeotropic orientation of LCs and a dark signal was observed under polarized light. When formaldehyde was presented in the aqueous solutions, formaldehyde reacted with PBA to produce corresponding imine, which was not able to align at LC/aqueous interface such that the orientation of LCs was disrupted. As a result, a dark-to-bright transition of the LC signals was observed.
At first, we supposed the detection mechanism was involved Hantzsch reaction. Based on the evidences of each discussion, we discarded our hypothesis and proved that the mechanism was amine-aldehyde reaction. By using this mechanism, 1 mM of formaldehyde can be detected in real-time with good selectivity. Moreover, we demonstrated that this system can be applied to detect formaldehyde in commercial facial toners with the limit of detection (LOD) of 30 mM. Because the LC-based sensor system is cost-effective and easy to use, while its signals can be simply differentiated through the naked-eye under ambient light, it shows great potential for the applications of formaldehyde detection in the daily necessities for general family.

並列關鍵字

Liquid crystal ； Formaldehyde ； Sensor

參考文獻

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