Detection Of Heavy Metal Ions And P-Aminophenol Using Electrodes Decorated With Vertically-Ordered Silica Nanochannels Film

The practical application of electrochemical sensors in chemical and biochemical detection,environmental and biomedical monitoring and clinical diagnostics has attracted wide attentions owing to low cost,ease of fabrication and portable operation.However,direct detection in complex media without sample pre-treatment remains challenging.This is mostly due to fouling and non-specific adsorption caused by such as proteins on the sensing surface,that hinder the effective electrical communication between analytes of interest and the underlying electrode,leading to poor accuracy,sensitivity and reproducibility.Therefore,overcoming the problem of contamination or fouling on sensing interface and realizing the direct detection in complex samplesare still an object of intense scientic researches.Considerable evidences confirm that electrode with mesoporous silica films consisted of vertically-ordered silica nanochannels film?VMSF?demonstrate great potential in direct electrochemical detection in real samples.On the one hand,VMSF favor the transfer of molecules?or reactants?from the solution to mesochannels and subsequently to the underlying electrode surface.On the other hand,charge and size screening effect of nanochannels endow VMSF with excellent anti-fouling property.In this thesis,preparation of indium tin oxide coated glass?ITO?decorated with ertically-ordered silica nanochannels film?VMSF/ITO?was developed.VMSF/ITO was applied as electrochemical sensor for simultaneous label-free and pretreatment-free detection of Pb²⁺,Cu²⁺,and Cd²⁺in human serum and soil leaching solution,as well as the detection of p-aminophenol in drug tablet.Detailed researches were summarized as following.?1?The Vertically-ordered mesoporous silica film?VMSF?was prepared on ITO surface through St?ber-solution growth approach.The initially obtained VMSF/ITO was filled with CTAB micelle?SM@VMSF/ITO?and SM could be easily removed in HCl ethanol solution.Scanning electron microscopy?SEM?and transmission electron microscopy?TEM?were used to characterize the morphology and structure of the electrodes before and after removing micelles.It was found that the VMSF thin films were smooth and the thickness was about 86 nm.The removal of SM had no significant effects on the structure of VMSF.The obtained VMSF are continuous and uniform with mesopores?².6 nm?homogeneously distributed over the entire film.The vertical channels can be seen from the cross-section TEM image of VMSF.The VMSF/ITO electrode was characterized by Zeta potential.It was proved that in the solution of pH>3,the film was negative,and the negative potential increased significantly with the increase of pH.Using the three standard electrochemical probe-anion probe Fe?CN?₆^3-,neutral probe ferrocene derivatives?Fc MeOH?and cationic probe Ru?NH₃?₆³⁺,the electrochemical properties of SM@VMSF/ITO or VMSF/ITO electrodes were investigated.It was confirmed that the pore was open after removal of SM.Owing to the surface negative charge,the electrochemical response of cationic electrochemical probe was promote and the electrochemical response of anion probe was inhibitted.?2?VMSF/ITO was applied as electrochemical sensor for simultaneous label-free and pretreatment-free detection of Pb²⁺,Cu²⁺,and Cd²⁺in human serum and soil leaching solution.The electrochemical detection consists of electro-deposition of metal species and subsequent anodic stripping in the silica nanochannels.In the following electrochemical stripping scanning,Separation of the striping potentials promises simultaneous detection of multiple ion species.In order to achieve high sensitivity for simultaneous determination of Pb²⁺,Cu²⁺and Cd²⁺,the experimental conditions including deposition potentials,pH value and deposition time were optimized.The pH and electrodeposition time of metal ions were optimized.The optimum pH was 5.0 and the optimum deposition time was 300 s.VMSF/ITO can be used for individual and simultaneous detection of Cd²⁺,Cu²⁺,and Pb²⁺.When the single ion is detected,good linear correlation is found between the stripping current and the centration from 25.0nM to 40.0?M for Pb²⁺,100.0 nM to 30.0?M for Cu²⁺,1.0?M to 20.0?M for Cd²⁺.The limits of detection?LOD?of Pb²⁺,Cu²⁺and Cd²⁺ions are determined as low as 2.4nM,20 nM and 140 nM respectively.Simultaneous detection of one ion type with varying concentrations in the presence of a fixed concentration of the other two ions type is investigated.The VMSF/ITO sensor is able to detect Pb²⁺?25.0 nM⁴0.0?M?,Cu²⁺?100.0 nM³0.0?M?and Cd²⁺?1.0?M²0.0?M?with LOD of 2.6 nM,32 nM and 230 nM,respectively.Comparing to the individual analysis,the liner range and sensitivity for the detection of Cu²⁺and Pd²⁺remain unchanged.However,reduction in sensitivity is observed for Cd²⁺.This may be caused by the formation of Cu-Cd and Pb-Cd alloys when Cd,Cu and Pb co-electrodeposited on electrode surface.The VMSF/ITO could be reused.?3?The application of VMSF/ITO for the electrochemical detection of aminophenol was established.The oxidation-reduction mechanism of p-aminophenol on the electrode was preliminarily investigated and the pH for detection was optimized.The results show that the redox process of p-aminophenol is the process of electron and proton equilibrium,and the optimal detection pH is 7.0.The electrochemical process of p-aminophenol on the electrode was diffusion-controlled.The linear range for the detection of p-aminophenol by VMSF/ITO electrode was 0.5?M-400?M,and the detection limit was 0.32?M.The VMSF/ITO electrode can be used to determine the content of p-aminophenol in drug tablets,and the results are in agreement with those obtained by high-performance liquid chromatography?HPLC?.