Duration: 24 months
The aim of the project was to obtain and characterize in detail the physico-chemical, optical and electrical properties of quasi one-dimensional nanostructures such as ceramic electrospun nanofibers and carbon nanotubes. The remarkable geometry, nanometer-scale size and surface area to volume ratio of these materials offer a unique opportunity to prepare sensors and biosensors.
The project was focused on the synthesis and study of polycrystalline ZnO nanofibers obtained by electrospinning and calcination in air, and carbon nanotubes synthesized by the floating catalyst chemical vapor deposition method (FCCVD). The nanofiber consisted of nanometer-size ZnO crystals. The new method resulted in an improved surface area to volume ratio and an active surface area for designing future sensors. Due to the low stability of ZnO in liquids, a facile, one-step method of surface passivation in the gas phase of hydrogen sulfide was developed. The core/shell ZnO/ZnS nanofibers were obtained as a result of the sulfidation process. The nanofibers remained stable in water and buffers at different pH values for several days. The multi-walled carbon nanotubes (MWCNT) demonstrated high chemical and mechanical stability, but their surface oxidation was required to obtain functional groups for further biofunctionalization. The multi-walled carbon nanotubes were oxidized with strong acids using sonication or reflux, or both methods at the same time. Following this, the MWCNT surface was covalently functionalized with poly(ethylene glycol) (PEG). ZnO and ZnO/ZnS nanofibers were wrapped with silane and tiophene compounds.
The optical properties of ZnO, ZnO/ZnS nanofibers and single-walled carbon nanotubes as well as the changes of their optical signals under environmental stimuli were studied in details. Moreover, the multimodal system based on PEGylated multi-walled carbon nanotubes was designed. The nanotube surface was wrapped with organic dyes and Fe particle embedded in nanotube during the synthesis was used as MRI contrast agent. In order to study potential properties of Fe/MWCNT-PEG-organic dye system to detect cancer cells the hybrid was internalized into the HeLa cells.
The project examined the electrical properties of MWCNT/polymer composites, which are stable in liquids and form layers for further application in Extended Gate Field Effect Transistors (EGFET). The electrical properties of ZnO and ZnO/ZnS nanofibers were checked before and after the functionalization processes. Nanofiber conductivity was found to depend on oxygen molecules on the ZnO surface, which trap free carriers, electrons, in an n-type structure. The selectivity of sensors based on ZnO nanostructures is associated with their capacity to remove O2 from the surface and release free electrons. The conductivity increased significantly in the presence of gases and liquids, such as nitrogen, ethanol and water, and UV light. Moreover, DNA and protein biosensors were constructed and their working mechanisms were investigated. The biosensors detected biological molecules at the picomolar level and revealed the behavior of depletion-mode MOSFETs (Metal-Oxide Semiconductor FETs), in which DNA ligonucleotydes and proteins acted as the gate.
The study provided an extensive characterization of the optical and electrical properties of the synthesized quazi-1D nanostructures. The work also extends our understanding of the mechanisms of sensitivity of these structures to various environmental stimuli, such as gases, UV radiation and various chemicals. The impact of surface modifications on the optical and electrical features was elucidated. Our findings will facilitate the construction future electronic and optoelectronic devices for such technological applications as sensors and biosensors.