Microfluidic immunoassay with plug-in liquid crystal for optical detection of antibody

•Appearance of liquid crystal (LqC) is dictated by aspect ratio of the microchannel.•Immunobinding events can be detected by LqC signals inside a microchannel.•One-step immunoassay is enabled by using tubing cartridges for liquid delivery.•One-step LqC-based immunoassay is able to detect 1 μg mL−1 anti-IgG in 25 min.•One-step LqC-based immuoassay shows good specificity and quantitation capability.

Recent advance in liquid crystal (LqC) based immunoassays enables label-free detection of antibody, but manual preparation of LqC cells and injection of LqC are required. In this work, we developed a new format of LqC-based immunoassay which is hosted in a microfluidic device. In this format, the orientations of LqC are strongly influenced by four channel walls surrounding the LqC. When the aspect ratio (depth/width) of the channel is smaller than 0.38, LqC orients homeotropically inside the microchannel and appears dark. After antigens bind to immobilized antibodies on the channel walls, a shift of the LqC appearance from dark to bright (due to the disruption of LqC orientation) can be visualized directly. To streamline the immunoassay process, a tubing cartridge loaded with a sample solution, washing buffers and a plug of LqC is connected to the microfluidic device. By using pressure-driven flow, the cartridge allows antigen/antibody binding, washing and optical detection to be accomplished in a sequential order. We demonstrate that this microfluidic immunoassay is able to detect anti-rabbit IgG with a naked-eye detection limit down to 1 μg mL−1. This new format of immunoassay provides a simple and robust approach to perform LqC-based label-free immunodetection in microfluidic devices.

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