Quantitative analysis of liquid crystal-based immunoassay using rectangular capillaries as sensing platform

In past studies, liquid crystal (LC)-based immunoassays were accomplished by fabricating an LC cell with two pieces of glass slides after immunobinding, which makes the determination of the immunoassay not in real-time and requires trained personnel. Herein, we developed the LC-based immunoassay by using rectangular capillaries as the substrate for immunobinding. The inner surface of rectangular capillaries was decorated with a long alkyl saline, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP), followed by immobilization of human serum albumin (HSA) as the probe. In this situation, the orientation of LC was homeotropic and dark LC image was observed under polarized light. When the solution containing anti-human serum albumin (anti-HSA) were dispensed into the capillary through capillary action, the specific immunobinding between HSA and anti-HSA formed an immunocomplex on the inner surface of capillary, which disrupted the original orientation of LC and led to a dark-to-bright transition of the LC images. The quantification of anti-HSA can be achieved by measuring the length of the bright LC image in the rectangular capillary. By using this immunoassay, the limit of detection (LOD) for anti-HSA is 1 μg/mL, and it did not respond to HSA and anti-human immunoglobulin G (anti-h-IgG). On the other hand, the diversity of the LC-based immunoassay can be extended for HSA detection when we immobilized anti-HSA in the capillary. Because the post-fabrication of LC cell was waived by using rectangular capillaries to develop the LC-based immunoassay, it is more convenient for users to handle and collect more reliable data. Moreover, the results of the immunoassay were visualized through naked-eye and could be recorded by a smartphone; it is more suitable for portable and point-of-care applications.