A facile and rapid aptasensor based on split peroxidase DNAzyme for visual detection of carcinoembryonic antigen in saliva

Aptamers have been used as recognition elements in various sensors, called aptasensors. In this study, a facile colorimetric aptasensor was designed based on only two un-labeled oligonucleotides including carcinoembryonic antigen (CEA) aptamer and split peroxidase-mimicking DNAzyme. The halves of DNAzyme were connected by the complementary sequence of aptamer. In the absence of CEA, aptamer and its complementary hybridized and helped to pull DNAzyme halves apart which could decrease catalytic reaction. When CEA was recognized by aptamer, the duplex of oligonucleotide was not formed so the peroxidation rate increased. In the first step, three types of CEA aptamer were applied to select the more applicable one. In addition, UV-vis spectroscopy, CD technique and fluorescence spectroscopy were also used for monitoring structural changes. The cost-effective aptasensor enables to detect CEA over a range from 1 to 50 ng ml−1 and the detection limit of CEA was 1 ng ml−1. The controlled experiments demonstrated that CEA signal was not interfered with other existing proteins. Moreover, it was revealed that the aptasensor could detect CEA in saliva. It is noticeable that the CEA level in saliva increases much more than blood in patients with oral and salivary malignant tumors.