Simultaneous and combined detection of multiple tumor markers for cancer screening in human serum by an upgraded photonic crystal-encoded suspension array

Combined detection of several tumor markers in serum has attracted attention for cancer screening because it is a much simpler, less expensive, and less invasive method compared with imaging or pathological diagnosis. Optically encoded microsphere-based suspension array technology is an excellent solution for such combined detection, such as xMAP technology owned by the Luminex Corporation and the photonic crystal bead array developed in our previous work. However, the fluorescent coding of xMAP technology has the deficiency of being easy to bleach and quench by environmental factors, whereas photonic crystal coding has great stability. However, what limits the further application of photonic crystal coding is the inert surface for probe immobilization and target detection because of the unreactive surface chemistry and high nonspecific adsorption caused by the periodic pore structure of the beads' carrier. Thus, the creation of novel photonic crystal coding with active composed materials and functional structures is still needed. In this work, we present a simple and cost-effective approach for improving this system with agarose blocking of the pores in the photonic crystal beads, which serves as an amplified molecular sieve effect. It was demonstrated that the silica–agarose photonic bead array has high accuracy, detection reproducibility, and acceptable agreement with a common clinical method for the multiplex assay of the tumor markers carcinoembryonic antigen and α-fetoprotein in practical clinical samples. This cost-effective, easily handled, and sensitive method brings a novel approach to the combined detection of tumor markers in early cancer screening.