Nanohybrid mediated finely tuned novel ZnO/Au nanostructures for selective bio-capture towards nanodiagnostics
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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.