Electrochemical impedance spectroscopy study on polymerization of L-lysine on electrode surface and its application for immobilization and detection of suspension cells.

Poly-L-lysine (PLL), which has been employed as a conductive polymer in the construction of some electrochemical sensors, can be prepared using L-lysine by cyclic voltammetry (CV) with a wide potential range. However, the presented explanation and description about its polymerization mechanism seems oversimplified because the self-reaction of electrode and the electrolysis of solvent at high potential are ignored. This work presents an intensive investigation on the relevant reactions during the process of PLL-polymerization using CV, X-ray photoelectron spectroscopy, Fourier transform-infrared spectroscopy, and electrochemical impedance spectroscopy. At a higher positive potential, the transfer from lysine molecules to cation radicals and the polymerization reaction on the glassy carbon electrode (GCE) could be achieved, accompanied by the activation of GCE, the formation of oxygen-containing functional groups, and the generation of oxygen derived from the oxidation of water. The adsorbed oxygen had a seriously negative effect on the formation of PLL unless it suffered reduction at a lower negative potential. The charge transfer through the electrochemical polymerized PLL film was seriously hindered by the immobilization of suspension cells due to the electrostatic interaction. The charge-transfer resistance difference (ΔR(ct)) was increased with the enhancement of the cell number (N(cells)) and the 1/ΔR(ct) value displayed a linear response with 1/N(cells) in the range of 5.0 × 10(2)-1.0 × 10(5) cells with a detection limit of 180 cells estimated at a signal-to-noise ratio of 3. A sensitive electrochemical sensor for the quantitative detection of suspension cells was developed.

Electrochemical immunoassay for carcinoembryonic antigen using gold nanoparticle-graphene composite modified glassy carbon electrode.

Carcinoembryonic antigen (CEA), which is typically associated with certain tumors and developing fetus, is widely used as a clinical tumor marker for some familiar cancers. In this work, a simple and sensitive electrochemical CEA sensor was developed by employing immunoreaction. Gold nanoparticle-decorated graphene composites (Au-GN) were successfully synthesized based on the reduction of HAuCl4 in the presence of graphene. Horseradish peroxidase-labeled anti-CEA antibody (HRP-anti-CEA) and HRP were successively adsorbed on the Au-GN modified glassy carbon electrode. The stepwise assembly process of the immunosensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The introduction of CEA antigens on the electrode surface reduced the electrochemical response of the electron transfer mediator due to the strong steric effect. Under the optimized conditions, the peak current change derived from the differential pulse voltammetry (DPV) measurements (ΔIDPV) was proportional to the CEA concentration from 0.10 to 80 ng mL(-1) with a detection limit of 0.04 ng mL(-1) (S/N=3). In addition, this new protocol shows good selectivity, stability and reproducibility. The determination of CEA in human serum samples was performed and received in excellent accordance with the results determined by the enzyme-linked immunosorbent assay (ELISA).