| dc.description.abstract | Nanoscale structures combined with noble metals are expected to yield novel materials
that will create new avenues for diagnosis and therapeutics. Among various types of
nanostructured metal/semiconductor hybrid that have been developed, nanostructured
Zinc oxide (ZnO) has been intensively studied because of its unique nano-morphological,
functional bio-compatible, chemical stability, sensitivity, non-toxicity, and high catalytic
properties. The biocompatibility characteristics of ZnO make this material a convenient
choice for conducting surface functionalization and interfacing with chemical and
biological compounds at pH extremes. Nanohybrids that comprise ZnO and noble metal
nanoclusters have attracted tremendous interest in recent years owing to their potential
for improved catalytic activity, excellent surface area-to-volume ratio and several
functionalities that are superior to those of pure ZnO nanomaterials. The objective of this
research is to synthesize different type of Au doped ZnO nanostructures using simple solgel
spin coating and low-temperature hydrothermal method to tract the profile of biomolecule
(DNA) that lead to pathogenic leptospirosis and cholerae detection. Firstly, a
thin seed layer of ZnO prepared by sol-gel method was deposited on the gold
interdigitated electrode to provide the nucleation sites for growth of ZnO nanostructures.
Next, ZnO NRs were grown using simple low temperature hydrothermal growth method.
Consequently, ZnO NRs were sputtered with Au to form ZnO/Au nanostructures.
Therefore, the fabricated ZnO/Au nanostructure was examined through various
characterization for surface morphology (FESEM, TEM, AFM), structural (XRD, XPS),
optical (PL, UV-VIS) and electrical properties (EIS, IV) investigation. Thus, the research
has successfully demonstrated the application of novel two-step method, the combination
of sol-gel and hydrothermal process to synthesize different nanostructures. Secondly, we
have studied the effect of Au on the localized surface plasmonic of ZnO thin film.
Incorporation through sputtering of Au into a ZnO thin film resulted in changes in the
surface morphology as well as the optical and electrical behaviour. It was observed that
the AuNPs tends to grow along with the ZnO thin film and the density of the AuNPs
increases forming a continuous layer as the Au thickness increased from 10 nm to 50 nm.
Based on the structural, optical and electrical analyses, incorporation of Au substantially
improves the ZnO thin film. Furthermore, the effect of sputtered AuNPs on the
conduction mechanism of ZnO Nanorods was also studied. It was observed that different
sputtered thickness of AuNPs greatly affects the dielectric constant of ZnO Nanorods as
well the conductivity of the device. Thirdly, we have selected novel spotted nanoflower
structure among the different structure of nanowire fabricated to investigate the
biosensing properties for impedance sensing to distinguish pathogenic and nonpathogenic
leptospira species. Selective capture of molecular probes onto the seeded
AuNPs was evidence for the specific interaction with DNA from pathogenic
leptospirosis-causing strains via hybridization and mis-match analyses. The attained
detection limit was 100 fM as determined via impedance spectroscopy. Furthermore,
stability, reproducibility and regeneration of this sensing surface were demonstrated.
Finally, we created a new worm like nanostructure with ZnO/Au hybrid through aqueous
hydrothermal method, by doping Au-nanoparticle (AuNP) on the growing ZnO lattice.
Further, the ability to create Au-decorated hybrid nano-worm structure for impedance
sensing was proved to distinguish serovars of cholera. It was observed that the sensor was
more sensitive over the literature documented AuNP incorporated doped ZnO nanorods xvii
in detecting DNA at ambient temperature (10 fM). The fabricated sensor displayed the
increment in grain boundary resistance from 0.17 to 1.13 MΩ when the target DNA
concentration was increased from 1 μM to 10 fM. The biosensor based on Au-decorated
hybrid nano-worm structure exhibited excellent linearity over a wide range of target DNA
concentrations. Further, higher stability, reproducibility and regeneration on this sensing
surface were demonstrated. The worm like nanostructure with ZnO/Au hybrid has
superior sensitivity and selectivity compared to novel spotted nanoflower due to the
improvement over structural defects such as Zinc- and/or Oxygen-vacancies. Such
improvement facilitates the chemisorption of organic molecules towards the substrate,
which is beneficial for the high loading of DNA during immobilization and hybridization
processes. In addition, the AuNPs nano-radii in combination with the increased surface
area due to random curving, significantly enhances the detection efficiency due to
increased immobilization rates and enhanced hybridization efficiency. In conclusion, this
research successfully demonstrated the process to synthesize, fabricate, characterize and
validation of Au doped ZnO nanostructures based biosensor. | en_US |
