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Title:	New urea and DNA biosensors from water soluble ZnS quantum dots (QDs)
Authors:	Eka Safitri (P45143)
Supervisor:	Lee Yook Heng, Prof. Dr.
Keywords:	Electrochemical urea DNA biosensors Water soluble Zinc sulphide quantum dots Dissertations, Academic -- Malaysia
Issue Date:	3-Sep-2016
Description:	Water soluble zinc sulphide quantum dots (ZnS QDs) have been synthesized via a direct method at room temperature. The ZnS QDs were aimed to fabricate new optical urea biosensors, new electrochemical urea and DNA biosensors. For the construction of the biosensors, the ZnS QDs were modified to produce ZnS QD bioconjugated urease enzyme and DNA (ZnS QDs-urease and ZnS QDs-DNA). The ZnS QD-urease was used as a bioassay to detect urea. Furthermore, it was entrapped in an acrylic membrane to create a new fluorescence urea biosensor. The fluorescence intensity of the biosensor changed linearly at urea concentrations between 1 x 10-5 to 1 mM (R2 = 0.997). The limit of detection (LOD) was 1 x 10-5 mM and the response was not influenced by alkaline metal ions such as Na+ , K+, Ca+2, and Mg+2. The fluorescence urea biosensor exhibited good repeatability and reproducibility which have relative standard deviation (RSD) of < 5%. The construction of the electrochemical urea biosensor was through binding of ZnS QD-urease with cysteamine, which was selfassembled onto gold nanoparticles that were immobilised on a carbon screen-printed electrode (SPE). Methylene blue (MB), used as a redox indicator was also immobilized on the SPE. The biosensor was able to detect a wide dynamic range of urea concentrations between 1 x 10-6 and 1 x 10-1 mM with a LOD of 1 x 10-6 mM. The biosensor showed repeatability with RSD of 8.94%. This similar concept was used to fabricate a new electrochemical DNA biosensor utilizing ZnS QD-DNA and the redox DNA hybridization indicator anthraquinone sulphonic acid. The electrochemical DNA biosensor was able to detect DNA target of concentrations ranging from 1 x 10-9 to 1 x 10-3 μM (R2 = 0.982), with the LOD at 9.08 x 10-11 μM. This study has confirmed that ZnS QD can function as a good matrix for the immobilization of biological molecules such as DNA and urease. When attached to self-assembled cysteamine, it could also act as a medium to facilitate electron transfer in electrochemical urea and DNA biosensors. These properties enable the performance of the biosensors to be improved especially for the electrochemical urea and DNA biosensors, where the dynamic response range becomes wider and the LOD becomes lower compared with similar biosensors reported before.,Certification of Master's/Doctoral Thesis" is not available
Pages:	219
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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