Abstract
The use of fluorescence is ubiquitously found in the detection of immunoreaction; though with good sensitivity, this technique requires labeling as well as other time-consuming steps to perform the measurement. An alternative approach involving liquid crystals (LCs) was proposed, based on the fact that an immunocomplex can disturb the orientation of LCs, leading to an optical texture different from the case when only antigen or antibody exists. This method is label-free, easy to manipulate and low-cost. However, its sensitivity was low for practical usage. In this study, we adopted a high-birefringence liquid crystal (LC) to enhance the sensitivity for the immunodetection. Experiments were performed, targeting at the cancer biomarker CA125. We showed that the larger birefringence (Δn = 0.33 at 20 °C) amplifies the detected signal and, in turn, dramatically improves the detection limit. To avoid signal loss from conventional rinsing steps in immunodetection, CA125 antigen and antibody were reacted before immobilized on substrates. We studied the specific binding events and obtained a detection limit as low as 1 ng/ml. The valid temperature ranges were compared by using the typical single-compound LC 5CB and the high-birefringence LC mixture. We further investigated time dependency of the optical textures and affirmed the capability of LC-based immunodetection in distinguishing between specific and nonspecific antibodies.
Highlights
Detection of cancer biomarkers serves as an important measure in cancer prevention and early screening as well as in cancer diagnosis and prognosis
In a study on the liquid crystals (LCs)-based immunoassay of hepatitis B, it is reported that the immunocomplex formed between hepatitis B surface antigen (HBsAg) and hepatitis B antibody disrupts the homeotropic alignment of 5CB, rendering the planar texture observed under crossed polarizing filters
When the optical axis is parallel to the light path, the plane of the polarized light is not rotated, and light is not transmitted by the second polarizer
Summary
Detection of cancer biomarkers serves as an important measure in cancer prevention and early screening as well as in cancer diagnosis and prognosis. The ordering of LCs may serve as a signature to distinguish between lipid bilayer-enveloped and nonenveloped viruses [33], and may be used to identify endotoxins released from Gramnegative bacteria for the detection and diagnosis of sepsis [34] These findings demonstrate the potential of clinical applications with LC biosensing, which is advantageously rapid, label-free, low-cost, and may be developed as point-of-care (POC) diagnostics [20]. In a study on the LC-based immunoassay of hepatitis B, it is reported that the immunocomplex formed between hepatitis B surface antigen (HBsAg) and hepatitis B antibody (anti-HBsAg) disrupts the homeotropic alignment of 5CB, rendering the planar texture observed under crossed polarizing filters. As the change in optical textures of LCs can only provide qualitative description of the immunoreaction, this study is the first to propose a quantification method for the optical response of LCs
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