Printed photonic crystal biochips for rapid and sensitive detection of biomarkers in various body fluids.

There is an urgent requirement to improve accessibility to diagnostic tools in remote areas. This requires assays that are easy to use, are cost-effective and produce rapid results. Important public health applications include early disease diagnosis, real-time monitoring, epidemic control and medical cost control. This protocol describes the fabrication of all-printed photonic crystal (PC) biochips for point-of-care testing of biomarkers. The photonic crystal material is prepared by the self-assembly of latex nanospheres that are printed onto a polyethylene terephthalate substrate. Photonic crystals composed of latex nanospheres of different sizes enhance the fluorescent signal emitted at different wavelengths, resulting in remarkably higher detection sensitivity. PC microarrays enable mass-printed preparation (up to 2,700 pieces can be printed per hour by one printer), and each microarray can be stored for a long time (>6 months) after heating. Biomarker specificity is achieved by the biofunctionalization of the nanospheres, for example, attaching capture antibodies. The detection involves the use of a fluorescently labeled detection antibody and a simple point-of-care detection device. This universal approach can be applied to the detection of many biomarkers, and the simultaneous detection of multiple biomarkers is also possible. Here we demonstrate describing how to prepare a chip that can be used to detect three inflammatory biomarkers in 10 min at low sample volumes at a cost of less than 3 CNY (~US$0.41) per PC codetection biochip. The biofunctionalization process including capture antibody coupling and blocking takes 3-4 h, and the detection process takes 20 min.