可檢測氨氣的液晶感測器

以往的氨氣檢測方法是依靠比色法、半導體式感測器，但有些方法會使用到危險的試劑、感測器毒化等問題，另外在比色法的結果判斷，會因為環境、人為因素造成分析的誤差，所以在本研究中，我們以5CB基礎，將甲基紅摻雜入其中，開發出檢測氨氣的感測器。因為甲基紅是一種酸鹼指示劑，在接觸氨氣後，會使甲基紅解離，生成陰離子，吸附於銅網上，擾亂液晶排列，訊號由暗轉亮，我們可以藉由光學訊號的變化得知氨氣的濃度區間。另外我們也解決比色法容易受環境干擾的缺點，使用相互垂直的偏光片觀察液晶光學訊號，排除環境光，把訊號簡單化，並且分析色彩飽和度，定義氨氣檢測的濃度區間，我們的感測器最低檢測濃度為22 ppm。液晶感測器具有低成本、容易觀察、操作簡單等特性，對未來氣體檢測很有潛力。

關鍵字

液晶感測器；甲基紅；氨氣

並列摘要

In the past, ammonia gas detection methods were mainly based on colorimetric and semiconductor sensors. However, some methods may use dangerous reagents and sensor poisoning. In addition, the results of colorimetric sensors may be influenced by environmental and personal errors. In this research, we use methyl red-doped 5CB as a sensing matrix to develop a sensor for ammonia gas detection. Because methyl red is an acid-base indicator, it will dissociate and generate anions when it exposes to ammonia gas. These anions further adsorb on the copper gird and disturb the original alignment of liquid crystal, which changes the image of liquid crystals from dark to bright. Therefore, we can define the concentration range of ammonia gas by the changes in optical signals. Besides, we also solve the disadvantage of colorimetric assay that are easily affected by environmental interference. We use polarizers to observe the optical signal of the liquid crystal, eliminate the ambient light, and simplify the signal. Next, we analyze the color saturation to define the concentration range of ammonia detection. The minimum detectable concentration is 22 ppm for our sensor. The liquid crystal sensor has the characteristics of low cost, easy observation, simple operation, which has great potential for gas detection in the future.