Construction Of Hightly Sensitive Electrochemical Sensors Based On Silica Isoporous Membrane

With the continuous development of analytical chemistry,how to directly,quickly and sensitively analyze complex samples has become the focus of attention of researchers.Electrochemical sensors have become one of the most widely used analytical method due to their high sensitivity,easy operation,rapid response and online monitoring.However,during sample analysis,the electrode is susceptible to contamination by macromolecules or particles in the complex matrix and interference from other electroactive substances.Silica isoporous membranes(also known as vertically ordered mesoporous silica films,VMSF)are a kind of films which has uniform pore size and vertical and highly ordered channels,with molecular level screening ability,by modifying the VMSF on the surface of the electrode,the electrode has excellent anti-fouling and anti-interference performance,realizing the direct analysis of complex samples.The VMSF modified electrode has certain limitations in application due to its poor specificity and non-conductivity of the film.The method of modifying functional groups on the channel or the modified material on the substrate can improve the specific recognition and detection performance of the electrode.This thesis explored three methods of modifying VMSF electrodes,combining the specificity of modified molecules or materials,high electrochemical activity,and VMSF's anti-interference and anti-fouling capabilities is able to directly analyze anions,drug molecules and hormones in complex samples.The specific research content is as follows:(1)Established a method to modify VMSF electrode with phenylboronic acid(PBA),which realized the direct detection of fluoride ion in tap water.The St(?)ber method was used to grow VMSF on the surface of the indium tin oxide(ITO)electrode,and then the channels was functionalized with amino groups and Schiff base reaction grafted with PBA,finally PBA-VMSF/ITO was obtained.Transmission electron microscopy(TEM)proves that the VMSF channels are arranged in order,with a pore diameter of about 2?3 nm;scanning electron microscope(SEM)proves that the VMSF channels are perpendicular to the electrode substrate and have a thickness of 90 nm.Electrochemistry,UV-Vis absorption spectroscopy(UV-Vis)and contact angle characterization proved the modification process of the electrode.Fluoride ions combine with phenylboronic acid molecules to form a tetrahedral borate anion,which enhances the negative charge inside the pores,thereby inhibiting negatively charged electrochemical probe molecules from entering the pores.A fluoride ion sensor is constructed by recording the changes in the probe molecular signal.Its linear range is 10^–9M–10^–3M,10^–3M–2.3×10^–2M,the detection limit is0.83 n M.Combined with VMSF's excellent anti-fouling and anti-interference capabilities,direct and highly sensitive electrochemical detection of fluoride ions in tap water is realized.(2)Established a VMSF/graphene(ErGO)composite film modified ITO electrode method(VMSF/ErGO/ITO)for the highly sensitive electrochemical detection of rutin in drugs and serum.The graphene oxide(GO)was modified on the surface of the ITO electrode by the drop coating method,and VMSF was rapidly grown on the electrochemical surface of the GO/ITO electrode by the electrochemical assisted self-assembly method(EASA),and the electrochemical reduction of GO was realized at the same time.X-ray photoelectron spectroscopy(XPS)and ultraviolet-visible absorption spectroscopy(UV-Vis)proved the successful reduction of GO.Electrochemical characterization proves that the prepared VMSF has good integrity.TEM characterization proves that the VMSF channels are highly ordered and arranged in a hexagonal shape,with a pore size of about 2?3 nm;SEM characterization proves that the thickness of the VMSF and ErGO layers are 50 nm and 218 nm,respectively.Based on the excellent electrocatalytic activity of ErGO and the hydrogen bond enrichment of nanochannels,the VMSF/ErGO/ITO electrode exhibits excellent performance in the detection of rutin.Its linear range is 0.3-2.0?M,2.0-40?M,and the detection limit is 2.3 n M.In addition,the UV-Vis results show that the VMSF/ErGO/ITO electrode can maintain good light transmittance while still having high detection performance.Combined with the anti-fouling and anti-interference ability of VMSF,the direct and sensitive detection of rutin in drugs and serum is realized.(3)A method(HErGO-CNT/VMSF/ITO)of VMSF/graphene-carbon nanotube(HErGO-CNT)nanocomposite film to modify ITO electrode was established,and the preparation process is controllable.The ErGO-CNT composite film was modified on the surface of the ITO electrode by electrochemical deposition,and the rapid growth of VMSF and the further reduction of ErGO were simultaneously realized by the EASA method.XPS characterization proved the reduction of GO during electrode preparation.Electrochemical characterization proved that the prepared VMSF was complete.TEM characterization proves that VMSF pores are distributed in hexagonal shape,arranged in order,and the pore diameter is about 2?3 nm.SEM characterization proves that the thickness of the VMSF and HErGO-CNT layers are152 nm and 260 nm,respectively.CNT intercalation between HErGO sheets improves the electron and material transfer efficiency on the electrode surface,and combines the electrocatalytic activities of the two to construct serotonin(5-HT)and melatonin(MT)detection sensors.The detection range of 5-HT is 0.1-30 u M,and the detection limit is 5.43 n M;the detection range of MT is 1-100 u M,and the detection limit is 14.1 n M.Combined with the anti-fouling and anti-interference ability of VMSF,it can effectively weaken the influence of complex matrix effects and realize direct sensitive electrochemical detection in whole blood and artificial cerebrospinal fluid.