A graphene oxide coated gold nanostar based sensing platform for ultrasensitive electrochemical detection of circulating tumor DNA†
A high-performance electrochemical sensing platform inspired by a functional ‘green’ electrochemical reduction pathway was developed to identify and detect circulating tumor DNA (ctDNA) of gastric carcinoma in peripheral blood. The assembly of the biosensor, consisting of graphene oxide-wrapped gold nanostars (GO-AuNSs), was fabricated on a glassy carbon electrode using the surface chemistry of ‘layer-by-layer’ modification via an electrochemical route. The electrodeposition of the GO-AuNS nanocomposite on the electrode's surface effectively improved its electrochemical response and enhanced its immobilization pathway. At the same time, it demonstrated the electrochemical phenomena caused by DNA immobilization and hybridization events sans complex labelling or other indicators. The immobilization of the probe DNA occurred due to the π–π (weak) interactions between the GO-AuNS composite and the DNA bases. The hybridization of the probe DNA with ctDNA resulted in the formation of a helix structure, which precipitated the release of the resulting dsDNA from the electrode's surface. The immobilization and hybridization events caused a ‘signal off’ and ‘signal on’ model by respectively decreasing and increasing the signal current. The prepared composite nanostructure and the subsequently modified electrodes were characterized using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The electrochemical response of the biosensor was elucidated using Differential Pulse Voltammetry (DPV), Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS). A linear relationship was established between the oxidation peak currents (DPV) and the different concentrations of ctDNA within the range of 1.0 × 10−20 M to 1.0 × 10−12 M (R2 = 0.998), with a detection limit (LOD) of 1.0 × 10−20 M (S/N = 3). The developed method shows translational prospects in ctDNA detection.