Graphene Modified Electrode Integrated With Silica Isoporous Film For Direct Electrochemical Analysis In Complex Sample

In the current field of analytical chemistry,the direct and highly sensitive analysis of complex samples is still challenging.Electrochemical analysis methods have attracted much attention because of the merits including rapid response,simple equipment,low cost,and high sensitivity.However,traditional electrochemical electrodes are easy to be stained and interfered by the coexisting particles,macromolecules,and electroactive substances in various complex samples.Therefore,amplifying the current signal while weakening the complex matrix effect is an effective means to achieve direct electrochemical detection in complex samples.Recent studies have shown that vertically-ordered mesoporous silica film(VMSF)is a simple and durable anti-fouling coating,which can be used for direct analysis in complex samples because of its excellent anti-fouling and anti-interference ability.However,due to the limitation of combining stability,most of the current electrochemical analysis of VMSF-based sensors use indium oxide tin(ITO)electrode to support VMSF.Other conventional electrodes such as carbonaceous or metal electrodes exhibit extremely weak binding stability to VMSF.Some recent studies have used organosilanes as adhesive layer to enhance the binding stability of VMSF on these electrodes,however,this non-conductive adhesive layer will cause the surface passivation of the substrate electrodes.Therefore,exploring new adhesive layer with great conductivity and high electrochemical activity,expanding the stable modification of VMSF on various traditional electrode surfaces will greatly enhance its practical application value.Reduced graphene oxide(rGO)is a unique two-dimensional carbon nanomaterial with ?-? conjugated structure and has excellent conductivity and electrocatalytic activity.It is often used as enhanced nanomaterial in the field of preparing high-performance electrochemical sensors.In this paper,electrochemical reduced graphene oxide(ErGO)was applied as a conductive adhesive and electroactive layer on glassy carbon electrode(GCE)and gold electrode(AuE).These modified electrodes are also employed for sensitive detection of electroactive small molecules in complex samples.Combining the high electrochemical activity of ErGO,the extraction and enrichment of hydrophobic micelles(SM),the enrichment of analytes by VMSF nanochannels and the anti-fouling/anti-interference capability of VMSF,the highly sensitive detection of antioxidants,medicinal molecules and environmental pollutants in complex matrix could be achieved respectively.Specific studies were as follows:(1)ErGO was used as adhesive layer to fabricate the highly active VMSF/ErGO/GCE,which could be applied to the direct and highly sensitive electrochemical detection of tert-butyl hydroquinone(TBHQ)(an antioxidant)in complex samples(oil extract and lotion).Graphene oxide(GO)was uniformly coated onto GCE to obtain the ErGO modified electrode by in situ electrochemical reduction.Then we used electrochemically assisted self-assembly(EASA)to grow VMSF on the ErGO/GCE surface.After removal of the micelle template,VMSF/ErGO/GCE was finally prepared.Compared with bare GCE,the VMSF modified on ErGO/GCE showed excellent mechanical stability.ErGO was characterized by X-ray photoelectron spectroscopy(XPS).Transmission electron microscopy(TEM)was used to characterize the VMSF,which showed the VMSF nanochannels were highly ordered and were perpendicular to the electrode substrate.The integrity and selective permeability of VMSF were characterized by electrochemical characterization techniques.Cyclic voltammetry(CV)and differential pulse voltammetry(DPV)were used to investigate the electrochemical detection performance of VMSF/ErGO/GCE towards tert-butyl terephthalate(TBHQ).Compared with bare GCE,VMSF/ErGO/GCE showed excellent electrochemical detection performance for TBHQ,which was mainly attributed to the double signal amplification caused by the high electrochemical activity of ErGO and hydrogen bond enrichment of VMSF nanochannel for TBHQ.In addition,combined with the excellent anti-interference ability of VMSF,we demonstrated that VMSF/ErGO/GCE could be used for direct and highly sensitive detection of TBHQ in complex samples(oil extract and lotion),and this electrode was able to maintain long,stable and high detection sensitivity in complex matrix environment.(2)Based on the previous work,a more convenient and efficient method for the preparation of highly active VMSF/ErGO/GCE was developed.The rapid growth of VMSF and the electrochemical reduction of GO were achieved synchronously by EASA.We used GO as the substrate electrode coating layer,then the highly active VMSF/ErGO/GCE was prepared rapidly in one step and used for the direct and highly sensitive detection of the doxorubicin(DOX)(an antitumor drug)in complex samples(human whole blood).We used XPS,TEM and electrochemical characterization techniques to demonstrate successful electrochemical reduction of GO and modification of VMSF on the electrode.We examined the electrochemical detection performance of VMSF/ErGO/GCE for DOX.Compared with bare GCE,VMSF/ErGO/GCE showed extremely high sensitivity for the detection of DOX,which was mainly attributed to the double signal amplification effect caused by the high electrochemical activity of ErGO and the electrostatic enrichment of VMSF to DOX.In addition,combined with the excellent anti-fouling and anti-interference ability of VMSF,VMSF/ErGO/GCE could be used for direct and highly sensitive detection of DOX in human whole blood.(3)Based on the previous work,we further expanded the application of VMSF on other electrodes.We used AuE as the substrate electrode and modify GO layer on the surface,the reduction of GO and the growth of VMSF could be achieved in one-step process by EASA.Retaining and removing the micelle template in the channel can prepare SM/VMSF/ErGO/AuE and VMSF/ErGO/AuE,respectively.We used TEM,XPS and electrochemical characterization techniques to demonstrate the electrochemical reduction of GO on the electrode as well as the successful modification of VMSF.The as-prepared electrodes were used for the selective detection of two isomers of catechol(CC)and hydroquinone(HQ).We found that the modified electrode showed high potential resolution towards CC and HQ due to the high electrocatalytic activity of ErGO.Moreover,due to the difference in the configuration of CC and HQ and the difference in the hydrogen bonding ability with the nanochannel walls,we found that SM/VMSF/ErGO/AuE showed micelle extraction and enrichment effect on CC,which due to relatively strong hydrophobicity between CC and SM,while VMSF/ErGO/AuE showed a hydrogen bond enrichment effect,which based on the weak hydrophobic between HQ and SM.Therefore,two types of VMSF modified electrodes were prepared by retaining and removing micelle templates,which could realize sensitive and selective detection of CC and HQ respectively.We further studied the simultaneous detection performance of electrodes for HQ and CC.In addition,combined with the excellent anti-fouling and anti-interference capabilities of VMSF,we also investigated the direct and highly sensitive detection performance of the two electrodes for HQ and CC in pond water.