Electrochemical detection of protein by using magnetic graphene-based target enrichment and copper nanoparticles-assisted signal amplification

In this paper, we propose a new method for protein detection by making use of magnetic graphene for enrichment and separation of the targets and duplex DNA-templated copper nanoparticles for amplification of electrochemical signals. Because the binding of the target protein (e.g. folate receptor) and small molecule (e.g. folate) can protect complementary DNA (cDNA) from exonuclease III-catalyzed degradation, duplex DNA from the hybridization of probe DNA and cDNA can act as the template for the formation of copper nanoparticles (CuNPs). Afterward, CuNPs-coated DNA can be enriched on the surface of magnetic graphene through the 3'-overhanging end of probe DNA, and then separated from the reaction mixture with the aid of magnet. As a result, copper ions released from acid-dissolution of CuNPs can catalyze the oxidation of o-phenylenediamine (OPD) by dissolved oxygen, resulting in an amplified electrochemical response. Our method can sensitively detect target protein over a wide linear range and with a low detection limit of 7.8 pg mL(-1), which can easily distinguish the targets even in complex serum samples. Therefore, this method may be promising for the clinical diagnosis of protein biomarkers by changing the recognition elements in the future.