Photo- And Electro- Analytical Method Based On ZrO₂ And Its Magnetic Microspheres

It has strong affinity for organic compounds containing phosphorus for ZrO₂, and it has superparamagnetic for nano Fe₃O₄ which can be rapidly separated from the matrix components in an external magnetic field. Thus Fe₃O₄ (core) /ZrO₂ (shell) microspheres (Fe₃O₄ @ ZrO₂) was been formed by modifing ZrO₂ on the surface of Fe₃O₄. Based on the enrichment of organophosphorus by Fe₃O₄@ZrO₂ and inductively coupled plasma-atomic emission spectrometry (ICP-AES), a novel method for the determination of trace organophosphorus pesticides in vegetable was established. Furthermore, nano ZrO₂ was employed to labelα-fetoprotein (AFP) antibody and further been fixed on DNA, then two new ZrO₂ probes were prepared. Based on the probes, two amperometric immunosensors forα-fetoprotein were established based on electrochemical immunoassay method. The detailed materials are shown as follows:1. A novel technique for the determination of trace organphosphorus pesticides in vegetable by ICP-AES was established. The method was based on the paramagnetic advantages and strong affinity of Fe₃O₄ @ ZrO₂ for the phosphoric group, combining with the rapidity, sensitivity, selectivity and strong anti-interference of ICP-AES. The results indicated that protein, pigment and fiber of vegetable had almost no interference to the detection. Thus it could eliminate the process of organic solvent extraction. And this method overcame the shortcomings of conventional detection methods of organophosphorus pesticide residue. Such as gas chromatography is difficult to detect the organic phosphorus pesticide with poor thermal stability. Liquid chromatography has difficulty to detect the organophosphorus pesticides without UV and fluorescence absorption. And electrochemical detection method is not suitable to detect the organic phosphorus pesticides without the electrochemical activity .2. A reagentless amperometric immunosensor for AFP was established based on the layer-by-layer assembly technique using multi-walled carbon nanotubes (MWCNTs), DNA and ZrO₂-Au colloid-poly Lysine (ZrO₂-pLL-Au). Firstly, the phenoxyacetic acid isoniazid schiff base Co(II) complex (referred to as CoL) as electron mediator was intercalated DNA to form DNA-CoL mixture film. The film was casted on surface of MWCNTs modified glassy carbon electrode to prepare the basal electrode (GCE|MWCNTs/DNA-CoL). Then the ZrO₂-pLL-Au was employed to immobilize the antibody of AFP to produce the probes (ZrO₂-pLL -Au-anti AFP). Finally the probes were modified on the GCE|MWCNTs/DNA-CoL electrode through the specific affinity between DNA and ZrO₂ to form a reagentless amperometric immunosensor for AFP (GCE|CNTs/ DNA-CoL/ZrO₂-pLL-Au-anti AFP). After the immunosensor was incubated with AFP solution, the electron transfer access of between horseradish peroxidase (HRP) and CoL was partly inhibited by the immune complexes of AFP and anti AFP, which led to a linear decrease of the catalytic efficiency of CoL by carbamide peroxide (CP) in AFP concentration ranges from 0.05 to 10 ng/mL. The detection limit at a signal to noise ratio of 3 was 0.01 ng/mL under the optimal conditions. The results indicated that the colloidal gold with high density on the surface of the ZrO₂-pLL-Au probes could significantly increase the labeled capacity of antibody and enzyme, which could amplify the detection signal and improve the detection sensitivity. The probes could be readily immobilized on the surface of DNA membrane modified electrode with physical adsorbption. The immunosensor also has good stability, without external electronic mediator in the electrolyte solution. Therefore, it can be easily achieved to detect other tumor markers, which provides a very promising immunoassay method for the clinical diagnosis of malignant tumors.3. A new type of one-dimensional magnetic nanoprobes was fabricated based on a DNA chain fixed with a number of Fe₃O₄ (core) / ZrO₂ (shell) nano-magnetic beads (ZMPs) labeled with secondary antibody. Theα-fetoprotein (AFP) was analyzed by using the probes DNA / (ZMPs-HRP-AFP Ab₂) n and immobilizingα-fetoprotein antibody (AFP Ab₁) onto the glassy carbon electrode modified by nano-gold. The sandwich-type immunocomplex could be formed between the immobilized AFP Ab₁ on the GCE and the probes DNA / (ZMPs-HRP-AFP Ab₂) n and the carried HRP could catalyze the electrochemical reduction of carbamide peroxide (CP) with the help of hydroquinone (HQ). The novel one-dimensional nano structure assembled and sandwich-type amperometric immunosensor was developed. Enhanced sensitivity was achieved by introducing more HRP -AFP Ab₂ onto the electrode surface through the pearl chain structure. Under optimal conditions, the proposed method could respond to 4 pg/ mL AFP with a linear calibration range from 0.01 to 25 ng/mL. The immunosensor was employed to determine AFP in serum samples and the results were satisfactory. The proposed amperometric immunosensor was sensitive, quick, magnetic field controllable. This study provided a platform technology for developing an one-dimensional assembly and highly sensitive immunosensor, which was suitable for screen determination of tumors in serums of normal patients.