Immobilization of a bio-recognition element to the surface of a functional working electrode is fundamental for effective biosensor development. In this study, the enzyme glutathione-s-transferase (GST) that constitutes a protein superfamily involving various distinct chemical transformations was introduces as a versatile tool for the sensing of environmental toxicants. Functional electrode surface was made by selfassembly of a great bioscaffold chitosan onto screen-printed carbon electrode surface concerning to its excellent covalent bonding binding of biomolecules. To enhance the enzyme proximity, glutaraldehyde was employed as an assisting bifunctional cross-linker. The self assembled chitosan layer and the GST immobilizing nanostructural features were explored by morphological imaging and several quantitative analyses such as surface grain size and distribution, power spectrum density (PSD) algorithm, fractal dimension character and other important surface roughness parameters via atomic force microscopy (AFM). Vertical aggregation of the successive layer was clearly verified in all quantitative approaches. Exceedingly, a better understanding in the direction of aggregation along with the growth mechanism was obtained by PSD analysis and the fractal dimension values gained around 2.27 for modified chitosan surface and 2.02 for GST immobilized chitosan modified screen-printed carbon basement could thus imply for the diffusion limited model in this growth mechanism.

The evidence of DNA immobilization and hybridization on a functional surface is demonstrated in this presentation following the high-resolution atomic force microscopic (AFM) direct observation. A planar functional surface was fabricated by self-assembly of a biopolymer chitosan onto screen-printed carbon electrode (SPCE) concerning to its excellent covalent bonding binding of biomolecules. The target DNA molecules were extracted from important phytoplasma diseased plants such as sugarcane white leaf (SCWL), burmuda grass white leaf (BGWL) and sesame phyllody (SP). The real image in actual posture of long chain natural DNA and the well-known structure of the DNA double helix were obviously visualized following the DNA immobilization and subsequent transitional hybridization with their complementary DNA. The coordinate quantitative parameters of AFM images such as line profile analysis, surface roughness, power spectrum density (PSD) algorithm and fractal dimension were also determined. The width size of double stranded DNA and the specific hybrid DNA were apparently almost 2 folds bigger than their single stranded DNA. Whereas an aggregation and growth mechanism of those DNAs on chitosan modified SPCE surfaces were mainly stacked in vertical direction and grown beyond a diffusion limited model as indicated by their fractal dimension values around 2 to 3. This phenomenon is hence valuable for the verification and the efficient development of diagnostic DNA-based devices.