Vertically aligned carbon nanotubes (VA-CNTs) have attracted the attention of researches in recent years due to their unique physical properties. The extraordinary electrical properties of carbon nanotubes, the porous nature and the large surface area of their 3D structures combined with the ability to synthesize them in relatively controlled fashion have open up new possibilities of using them as an excellent nanomaterial to develop electrodes for analytical sensing devices. In comparison to the conventional 2D microelectrodes, such 3D structures provide a very large and developed surface area, excellent for detection of low concentrations of biomolecules with higher signal-to-noise ratio. Functionalization of the surface of VA-CNTs brings new additional possibilities to develop sensitive and highly specific miniaturized chemical sensors and biosensors. In this work we applied a novel technology in the synthesis of VA-CNT. Metal catalyst (Fe) was used to grow VA-CNTs on a chip. In contrast to many existing chip fabrication technologies, metal was used as a buffer layer between the substrate and the catalyst. This resulted in an excellent electrical conductivity of the VA-CNTs. The height of the VA-CNTs grown on a chip varies from a few hundreds µm to 1 mm. We demonstrate that the electrochemical pre-treatment of the electrode surface led to the improved analytical signal obtained from the tested electrochemical species (ferrocyanide, ferrocene methanol and dopamine). VA-CNTs were functionalized with cellobiose dehydrogenase from Neurospora crassa (NcCDH) by a simple physical adsorption of the enzyme on the chip surface. NcCDH is capable of transfer the reaction electrons from oxidizing mono- and disaccharides to electrodes without the need of mediators. We demonstrated that VA-CNTs, in contrast to other electrode materials, showed an improved direct electron transfer between the immobilized enzyme and the electrode surface. The catalytic current was clearly observed in the presence of substrate starting from -100 mV vs. Ag/AgCl electrode. The experiments have shown that the chip is reusable, i.e. multiple immobilizations of the fresh portions of the enzyme do not deteriorate the working features of VA-CNTs. Different VA-CNTs based working surfaces (hydrophilic, hydrophobic) were tested with respect to their capabilities to adsorb the enzyme and keep its catalytic properties. The surface of the functionalized nanotubes on a chip was investigated using SEM and EDX. The chip may be integrated in a flow cell or microfluidic system. Further, modification of the VA-CNTs with other molecules is under progress. The preliminary data that we obtained demonstrate that on chip functionalized VA-CNTs are excellent and versatile platform for construction of electrochemical sensors and biosensors.

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