Mimicking peroxidase activity of Co₂(OH)₂CO₃-CeO₂ nanocomposite for smartphone based detection of tumor marker using...

We present a paper-based microfluidic colorimetric immunosensor for the detection of carcinoembryonic antigen (CEA), using Co₂(OH)₂CO₃-CeO₂ nanocomposite with extraordinary intrinsic peroxidase like activity. The morphology and composition of the nanocomposite characterized with Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The proposed immunosensor facilely fabricated by loading mixture of ionic liquid and chitosan functionalized primary antibodies (Ab₁) on the surface of paper. Compared to traditional paper based immunodevice, when ionic liquid was used the nonspecific binding protein from the paper surface was more effectively removed. Secondary antibodies (Ab₂) were stacked on the surface of the carboxylated Co₂(OH)₂CO₃-CeO₂ nanocomposite. The immunosensor response was obtained by a color change resulting from Co₂(OH)₂CO₃-CeO₂ nanocomposite catalyzing the oxidation of 3,3',5,5'-tetramethyl benzidine in the presence of H₂O₂. The colorimetric sensing was accomplished on the paper, using smartphone for taking a photo and then analyzing the colors with an installed application. Detection of CEA was performed by this method with a linear range from 0.002 to 75.0 ng mL^-1 and a detection limit of 0.51 pg mL^-1. In this paper we developed simple, cost-effective and portable design for sensitive immunoassay and point-of-care diagnostics of cancer marker.