| The need for specific, simplicity, rapid, low cost, sensitive and easy determination of biomolecules is vast. Electrochemical biosensors are essential for health monitors to help diagnose and detection of diseases. Enzyme adsorptions on biosensor electrodes and direct electron transfer between them have been recognized as key factors to affect biosensor performance. Electrodes play a crucial role in H2O2 electrochemical biosensors performance. Depending on the selection function of the electrode, material of the electrode, its surface modification, such as dimension, structure parameters and doping, significantly influence its sensing ability.The nanomaterials are broadly utilized in various fields and applications including biosensors applications, whereas nanomaterials showed improving in the efficiency of the devices.Horseradish peroxidase was selected to be as protein model for all modified biosensor electrodes. By physical adsorption approach, the Nafion solution was used to immobilize the enzyme and make the biosensor more biocompatible.This thesis delivers the possibilities of tailoring and doping the nanostructured titanium dioxide biosensor that is able to improve the biosensor performance to detect H2O2 with low limit of detection, wide linear range of H2O2 concentration, stable and high sensitivity.The TiO2 nanodots films were prepared on Ti substrate through a phase separation induced self-assemble method. Field emission scanning electron microscope (FESEM) was used to characterize the morphology of TiO2 nanodots. An electrochemical work-station (CHI660D) was used to characterize the sensing property.For TiO2 nanodots modified electrodes, the sensitivities of (TND-1, TND-2, TND-3) electrodes with different nanodots films were calculated to be 349.1,404.8 and 897.8 μA-mM/cm2, respectively. Electrode with TND-3 showed the best sensitivity and detection limits. Such property could be ascribed to the improved enzyme immobilization on TND-3 electrode, since it has the largest specific area of all the samples. Fortheremore, TND-3 has lowest detection limit than others, whereas it has 0.26μM with linear range 1-850 mM and the apparent Michaelis-Menten constant ) was 1.27 mM.For Mg doped TiO2 nanodots modified electrodes, Mg ions are introduced into TiO2 nanodots in order to further improve electrode performance because Mg ions are considered to have good affinity with proteins or enzymes. Mg doped TiO2 nanodots on Ti substrates were prepared by spin coating and calcining. The effects of Mg doping on the nanodots morphology was studied via SEM and TEM, the density and size of TiO2 nanodots were obviously changed with Mg doping. Compared with un-doped TiO2 nanodots, the density of TiO2 nanodots was inversely proportional to Mg concentration, and the size of TiO2 nanodots was proportional to the Mg concentration. The performance of 2% Mg doped TiO2 nanodots modified biosensor electrode was studied and displayed that sensitivity was increased to 1377.64 from 897.8μAmM-1 c-"2 and its KMapp decreases to 0.83 from 1.27 mM, implying that the enzyme achieves higher catalytic efficiency due to better affinity of the enzyme with the Mg doped TiO2. Such doping approach could provide an effective way to improve performance of the electrode of amperometric biosensors through chemical modifications.For TiO2 nanorods modified electrodes, anatase TiO2 nanorods were synthesized on Ti substrate by three stages, hydrothermal, alkali and heat treatments. The morphology of TNR-A/Ti electrode was characterized via XRD and FESEM. It could be clearly seen that all of the diffraction peaks fit well with anatase TiO2 phase (JCPDS No.21-1272). FESEM images of the anatase TiO2 nanorods on Ti substrates showed that the film has a highly oriented 1D structure with a typical column diameter of 30 nm. And the surface of the anatase TiO2 nanorods is smooth. The cyclic voltammograms (CVs) was used to study the electrochemical behavior of Nafion/HRP/TNR-A/Ti electrode towards hydrogen peroxide (H2O2). The performance of the Nafion/HRP/TNR-A/Ti biosensor was investigated by using the amperometric technique. Whereas the investigations showed that Nafion/HRP/TNR-A/Ti biosensor has better performance than the previous biosensors, with high sensitivity reached up to 5332.11 μA mM-1 cm-2, low detection limit of 0.01 μM H2O2, wide linear range of (0.05-700) μM and small Michael-Menten KMapp of 0.029 mM.For electrochemical reduction pre-treatment, the pre-treatment was adopted to reduce the TiO2 surface to form more Ti3+ ions, trying to enhance direct electron transfer of working enzyme with electrode through increasing electrical conductance of the TiO2 mediator in the electrodes. After the pre-treatment, the increase in Ti3+on the surface for all TiO2 nanostructures was proven by XPS characterization. All TiO2 nanostructure modified electrodes showed higher response to H2O2 and better direct electron transfer, also had higher detection sensitivity, indicating that the pre-treatment works very well for improving the performance. Nafion/HRP/Ti3+-TNR-A/Ti biosensor electrode was exhibited the best electrochemical behavior and performance with the sensitivity of 6096.4 μA mM-1 cm-2, detection limit of 0.008 μM, linearity of (0.04-700) μM and KMapp of 0.0027 μM, which is higher than that of other reported TiO2 or similar nanostructure modified biosensor electrodes.The present research could be potentially a good candidate to modify electrodes to have high performance amperometric biosensors. |
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