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

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.