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Graphene oxide (GO) is composed of isolated graphene-like sheets containing various oxygen functionalities. The electrochemical reduction of GO enables the direct deposition of the graphene layer on electrode surfaces. Furthermore, a partial reduction of GO can be performed, enabling easy modification of the surface with oxygen-containing groups. In this contribution, the electrochemical reduction of GO is carried out on a gold electrode roughened by electrochemical oxidation-reduction cycles. Such a gold electrode contains nanostructures ranging in size from tens to 300 nm. The electrochemically reduced GO layer is subsequently used for horseradish peroxidase (HRP) immobilization. Two types of electrochemically reduced GOs, partially reduced graphene oxide (ERGOP) and fully reduced graphene oxide (ERGOF), are used in this study. Although HRP immobilized on both types of surfaces directly catalyseselectroreduction of the hydrogen peroxide, the enzyme immobilized on the ERGOP layer exhibits slightly higher current values compared with those of ERGOF. In contrast, HRP adsorbed directly on the roughened gold reveals negligible activity. To evaluate the effect of the roughened gold, HRP immobilized on an ERGOF layer on glassy carbon was studied.Additionally, infrared and Raman spectroscopy were used to investigate the composition of GO, ERGOP, and ERGOF as well as the HRP structure at the studied surfaces. The infrared results indicate a random orientation of the enzyme molecules on the bare roughened gold and ordered HRP layers on the surfaces covered with either ERGOP or ERGOF.

The distribution of acetylcholinesterase (AChE) in oncospheres and developing cysticercoids of Hymenolepis diminuta was examined. The enzyme was localized in the nervous system and in some non-nerve cells of these larvae. In oncospheres AChE was detected in hook muscles and in the binucleated medullar center that is known to enclose two neurons. At early developmental stages of the cysticercoids the enzyme was localized in the post-oncospheral hook muscles and in subtegumental muscle fibers of the cercomer. At medium and late stages of development the activity of AChE was detected in the developing nervous system and in two and, subsequently, in four populations of cells, which gradually spread over the whole internal wall of the cyst, thus forming a thin multilayer AChE-positive lining of the cyst cavity. Following withdrawal of the scolex the lining separates the parenchyma of the turned neck from the cyst tissues and remains AChE-positive during the whole life of the parasite, i.e. up to the death of the infected host. The role played by non-neural AChE associated with the cyst cavity lining is unknown, but seems to regulate both the transport of nutrients and minerals into the scolex and waste substances in the opposite direction.

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