Direct electron transfer of Horseradish peroxidase on porous structure of screen-printed electrode.

Disposable hydrogen peroxide biosensor was developed based on the direct electron transfer of horseradish peroxidase (HRP) on porous screen-printed carbon electrodes. Conventional screen-printing process was manually performed to fabricate the planar carbon electrodes, which were endowed with porous surfaces especially after anodizing pretreatment. The cyclic voltammetry experiment indicated a pair of stable and well-defined redox peaks with a formal potential of -0.33 V. And the formal potential was pH-dependent, having a slope of -55.2 mV/pH which indicated one electron transfer. The heterogeneous electron transfer rate constant k(s) was estimated to be 13.28+/-4.80s(-1). Additionally, the sensitivity was 143.3 mAM(-1)cm(-2) and the linear range was from 5.98 to 35.36 microM. In conclusion, the present work achieved the direct electron transfer of HRP on screen-printed electrodes without any promoters. The porous structure of screen-printed carbon electrodes facilitated the direct electron transfer between the active sites of HRP and the electrodes due to large amounts of conductive sites available on the surface for contacting with enzyme molecules. Moreover, the proposed biosensor could be mass-produced at low price, promising for commercial application.

Cytotoxicity of a newly synthesized nitroxide derivative of 4-ferrocenecarboxyl-2,2,6,6-tetramethylpiperidine-1-oxyl in high metastatic lung tumor cells.

Low molecular weight nitroxides are widely used as electron paramagnetic resonance (EPR)-detectable spin labels in the biological and pathological areas. A novel nitroxide derivative, 4-ferrocenecarboxyl-2,2,6,6-tetramethyl piperidine-1-oxyl (FC-TEMPO), was synthesized for evaluating the effects of spin label compounds on tumor cells and firstly its biological effects on tumor and normal cells were evaluated. The cytotoxicity of FC-TEMPO in the high metastatic lung carcinoma cells (95-D) showed that it markedly inhibited the viability of cancer cells in a dose-dependent manner, while it was less toxic to a normal human cell line. Further studies found that FC-TEMPO suppressed the growth of tumor cells by induced apoptosis through activating caspase-3 but not caspase-8 which was proved by caspase inhibitors, and the cell cycle arrest at G1 phase. Moreover, the concomitant increase of superoxide dismutase (SOD) and catalase (CAT) activity was observed. Taken together, these results might provide a base for further anticancer investigations of nitroxides and their potential pharmacological applications.