title: Non-invasive Quantum dot based Sensors for the Detection of Glucose and Cholesterol in Saliva
Creators: name: Ahmad, I
Publisher: name: University of Liverpool Repository
Year: 2017

description: This project was aimed to develop highly sensitive quantum dots (QDs) based sensors for the detection of glucose and cholesterol. Glutathione (GHS) and mercaptopropionic acid (MPA) capped cadmium-tellurium (CdTe) QDs were used for the development of optical H2O2 glucose and cholesterol sensors. The whole process involves the synthesis of fluorescent QDs, selection of QD via experimental analysis, the sensor measurements via solution phase by equilibrium and kinetic methods, and the fabrication, characterization, and calibrations of a solid state sensor based on encapsulation of QDs in polymer matrix. Initially, thiol-capped CdTe quantum dots were synthesized and characterized. The pH responses of QDs were investigated and it was found that QDs were highly sensitive to pH change. A reversible linear range of pH change was 6.5 to 12. The sensitivity of selected thiols capped QDs to H2O2 were measured, and GHS capped QDs found to be the most sensitive (4243.9 CPS/μM of linear range) with the linear range of 100 to 1200 μM. The sensitivity of MPA QDs was 2624.2 CPS with linear range of 100 to 750. Therefore GHS and MPA QDs were used for further analysis. The initial measurement was done in solution phase. The measuring procedure and conditions were optimized for H2O2 sensing and further applied to measure glucose. The linear range of detection for glucose and cholesterol was 33 to 300 and 1 to 45 μM with the detection limit of 8.2 and 1.5 respectively for glucose and cholesterol. The pseudo-first order kinetic model for H2O2, glucose, and cholesterol analysis was established and verified. The pseudo first order rates constant were found to be a function of H2O2, glucose, or cholesterol concentrations. The linear range of detection for H2O2 measurement was 0.37 to 396 μM with detection limit of 0.2 μM. The linear range of detection of glucose and cholesterol was 8 to 200, and 17 to 136 μM with a detection limit of 2.0 and 3.46 μM respectively. The kinetic analysis was fast (2 - 5 Sec) and sensitive enough to measure glucose at a low level. The methods were validated and verified via bio kinetic stopped flow and the linear range of measurement for H2O2 a glucose was 32 to 2048 and 80 to 2560 μM with detection limit of 14.9 and 75.6 μM respectively. QDs were encapsulated in nafion and polyvinyl alcohol (PVA) polymer membrane to develop a solid-state sensor. The formulation ratio of nafion, polyvinyl alcohol (PVA), quantum QDs, and enzymes were optimized to improve the performance of the sensor. The developed sensor was with improved sensitivity and selectivity and hence the linear range of H2O2 and glucose measurement was 4 to 360 and 6 to 400 μM respectively. The detection limit for H2O2 was 1 μM and 2.5 μM for glucose. The sensor was further used to detect glucose in artificial and human saliva for normal (stimulated and non-stimulated) and diabetic individuals. The results of saliva measurement by proposed solid-solid state sensor and liquid phase sensor were validated, using Gas chromatography (GC). The developed glucose sensor was with high stability and resist to interference and could be applicable for clinics. The glucose oxidase (GOx) was replaced with cholesterol oxidase (ChOx) and hence the glucose sensor was modified to detect cholesterol. The linear range was 9.9 to 150 μM with detection limit of 4.5 μM.