An electrochemical sensor based on single-stranded DNA-poly(sulfosalicylic acid) composite film for simultaneous determination of adenine, guanine, and thymine.

Poly(sulfosalicylic acid) and single-stranded DNA composite (PSSA-ssDNA)-modified glassy carbon electrode (GCE) was prepared by electropolymerization and then successfully used to simultaneously determine adenine (A), guanine (G), and thymine (T). The characterization of electrochemically synthesized PSSA-ssDNA film was investigated by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The modified electrode exhibited enhanced electrocatalytic behavior and good stability for the simultaneous determination of A, G, and T in 0.1M phosphate buffer solution (PBS, pH 7.0). Well-separated voltammetric peaks were obtained among A, G, and T presented in the analyte mixture. Under the optimal conditions, the peak currents for A, G, and T increased linearly with the increase of analyte mixture concentration in the ranges of 6.5×10(-8) to 1.1×10(-6), 6.5×10(-8) to 1.1×10(-6), and 4.1×10(-6) to 2.7×10(-5)M, respectively. The detection limits (signal/noise=3) for A, G, and T were 2.2×10(-8), 2.2×10(-8), and 1.4×10(-6)M, respectively.

A high-sensitivity electrochemical aptasensor of carcinoembryonic antigen based on graphene quantum dots-ionic liquid-nafion nanomatrix and DNAzyme-assisted signal amplification strategy.

In this work, we have developed an electrochemical aptasensor for high-sensitivity determination of carcinoembryonic antigen (CEA) based on lead ion (Pb2+)-dependent DNAzyme-assisted signal amplification and graphene quantum dot-ionic liquid-nafion (GQDs-IL-NF) composite film. We designed hairpin DNA containing CEA-specific aptamers and DNAzyme chains. In the presence of CEA, hairpin DNA recognized the target and performed a DNAzyme-assisted signal amplification reaction to yield a large number of single-stranded DNA. The GQDs-IL-NF composite film was immobilized on the glassy carbon electrode for the interaction with single-stranded DNA through noncovalent π-π stacking interaction. Therefore, the methylene blue-labeled substrate DNA (MB-substrate) was fixed on the electrode and exhibited an initial electrochemical signal. Under optimal conditions, the response current change was proportional to the concentration of CEA, demonstrating a wide linear range from 0.5fgmL-1 to 0.5ngmL-1, with a low detection limit of 0.34fgmL-1. Furthermore, the proposed aptasensor was successfully applied in determining CEA in serum samples, showing its superior prospects in clinical diagnosis.

Electrochemical properties of catechin at a single-walled carbon nanotubes-cetylramethylammonium bromide modified electrode.

The electrochemical properties of catechin at single-walled carbon nanotubes (SWNTs)-cetylramethylammonium bromide (CTAB) modified glassy carbon electrodes (GCE) were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The SWNTs-CTAB film was characterized with transmission electron microscopy (TEM). A series of parameters including pH of supporting electrolyte, accumulation potential and accumulation time were optimized. There were three peaks of catechin at SWNTs-CTAB/GCE in the potential range of -0.4-1.0 V in PBS (pH 7.0): a reversible pair of peaks and an irreversible peak of the anodic peak. The reductive peak current increased linearly with the concentration of catechin in the range from 3.72 x 10(-10) to 2.38 x 10(-9) M. The detection limit was 1.12 x 10(-10) M. The SWNTs-CTAB/GCE showed good stability and low detection limit, and could be applied to detect trace catechin.