使用高複折射率液晶以提升癌症生物標記CA125之液晶免疫檢測靈敏度

Abstract

本研究提出使用高複折射率液晶之癌症生物標記免疫偵測技術，吾人使用液態晶體這種對於可以將玻璃表面上的分子大小以及分子間作用力轉換成光訊號的特性，將各種不同之蛋白質溶液滴於以矽烷DMOAP （N,N-dimethyl-n-octadecyl-3-aminopropyltrimethoxysilyl chloride）作為配向層的玻璃基板上，並且陰乾形成一小塊薄膜，使蛋白質薄膜具有擾動液晶配向層的效果，最後製作成液晶盒，藉由偏光顯微鏡觀察各種不同蛋白質薄膜擾動液晶配向層，使液晶分子在偏光顯微鏡下產生散亂排列的蛋白質光學紋理，來進行各種蛋白質分子之檢測。研究結果發現，使用高複折射率之液晶HDN進行蛋白質分子之偵測，其靈敏度較常用於生物感測之5CB液晶來的高且量測溫寬也有飛躍性的提升。藉由檢測靈敏度之提升，吾人進一步發展出較快速的液晶免疫檢測技術，將癌症生物標記CA125與CA125抗體溶液預先於試管中混合後形成CA125抗體抗原免疫複合體（immunocomplex），再以HDN液晶進行免疫偵測。在HDN液晶檢測下，CA125免疫複合體之光學紋理亮度明顯高於相同蛋白質濃度之CA125抗體或CA125抗原，因此可快速檢測樣本中有無CA125抗體抗原複合體之形成，此實驗手法簡易且再現性高，並藉由高複折射率液晶提高CA125免疫複合體與未結合之CA125抗體或CA125抗原光學訊號之差異，使CA125偵測極限降低至1 ng/ml。因此吾人藉由此一技術的發展，冀望能夠達到癌症臨床檢驗的標準，並發展出癌症生物標記之液晶免疫檢測技術。

This study proposed a method of immunodetection using high-birefringence liquid crystals for the immunoassay of cancer biomarker CA125. Liquid crystals can transduce the interaction between molecules into optical signals. Exploiting this transducing nature, we coated glass substrates with an alignment layer consisting of N,N-dimethyl-n-octadecyl-3-aminopropyltrime-thoxysilyl chloride (DMOAP) and dispensed droplets of different protein solutions on the DMOAP-coated glass surface to form a thin film, which was then covered with another glass substrate to construct liquid crystal cells. The protein film induced disturbance in the alignment of liquid crystals, and the disturbance can be measured quantitatively through the resultant change in optical signals. Through observation under polarized optical microscope, we analyzed cancer biomarker CA125 in various concentrations and binding conditions. A more significant change in optical texture was obtained for the highly birefringent LCs compared to 5CB, which is commonly used in LC-based biosensing in the literature. With the improvement in detection sensitivity, we further proposed to simplify the detection procedure of liquid crystal-based immunoassay. Instead of immobilizing the CA125 antibody on a DMOAP-coated glass substrate, CA125 antibody was mixed with CA125 antigen in a reaction tube prior to interaction with the DMOAP alignment layer on the glass substrate. The immunocomplex resulted in higher optical signal compared to CA125 antibody or antigen alone at the same concentration, and the detection limit for the CA125 cancer biomarker was as low as 1 ng/ml. This method allows fast detection of the immunocomplex and is easy to implement, with good reproducibility and high signal-to-noise contrast using highly birefringent LCs. We hope, with future developments, a practical cancer screening assay based on liquid crystals can be established for clinical application.