With the expected characteristics of both promoting electric transfer rate and immobilizing -NH2 labeled probe for the construction of electrochemical sensing platform for DNA determination, the carboxyl functionalized graphene (CFGR-COOH) was carried out from the carboxylation of graphene oxide (GO), partly reduction, addition of cyan groups (-CN). The X-ray photoelectron spectroscopy (XPS) results indicated the successfully prepared expected materials. Three kinds of novel electrochemical DNA biosensors were developed at CFGR-COOH modified glassy carbon electrode (CFGR-COOH/GCE), targeting at identifying specific DNA, the CFGR-COOH and PANI modified platinum electrode (CFGR-COOH/PANI/Pt), aiming at the further increase for the electrochemical performance of the prior biosensor with the synergistic effect between those two materials, and the hairpin probe/horseradish peroxidase (HRP) labeled CFGR-COOH/GCE, which was constructed to prove the promise utilization of CFGR-COOH in various sensing platforms. Through the differential pulse voltammetry (DPV) detection, the linear ranges of 1.0 x 10(-6) to 1.0 x 10(-13) mol.L-1, 1.0 x 10(-6) to 1.0 x 10(-14) mol.L-1 and 1.0 x 10(-6) to 1.0 x 10(-10) mol.L-1 were obtained for the above biosensors, coupling with the detection limits of 4.0 x 10(-14) mol.L-1, 5.8 x 10(-15) mol.L-1 and 7.0 x 10(-11) mol.L-1, respectively. The as-prepared CFGR-COOH showed potential application prospect as a valuable modification material in DNA sensing platforms. (C) 2017 The Electrochemical Society. All rights reserved.