Graphene Quantum Dots Confined In Silica Nanochannels Film Modified Electrode For Highly Sensitive Electrochemical Analysis Of Small Molecules

Direct and highly sensitive detection of complex sample is challenging in the field of analytical chemistry.Electrochemical sensors have the advantages of fast detection,simple operation and low cost.However,substances in the complex matrix will foul and interfer the surface of electrode,further affect the sensitivity and accuracy of detection.Recent researches have proven that silica nanochannel film?also known as vertically-ordered mesoporous silica-nanochannel film,VMSF?can offer electrode with the ability of selectivity at molecular level,that provides the electrode with excellent anti-fouling and anti-interference properties.Thus VMSF-based sensors have great potential in direct electrochemical analysis of complex samples.Graphene quantum dots?GQDs?are usually defined as graphene sheet in single-or few-layers,which lateral demensions are usually less than 10 nm.Modifying VMSF with small-size,single-layered GQDs can achieve in-channel modification without significantly affecting diffiusion and provide extensive chemical recognition and reactivity.In this dissertation,nanochannel-confined GQDs?GQD@VMSF?modified electrode was developed and applied for highly sensitive electrochemical detection of small molecules in complex samples.The recognition,enrichment and signal amplification ablilities of GQDs and the anti-interference and anti-fouling properties of VMSF were combined.Direct and highly sensitive detection of heavy metal ions or dopamine in complex sample were achieved.?1?Hydroxy-functionalized GQDs?OH-GQDs?were prepared and confined in VMSF modified indium tin oxide?OH-GQD@VMSF/ITO?electrode.The modified electrode was applied for sensitive detection of Cu²⁺and Hg²⁺in serum or sea food,respectively.OH-GQDs was synthesized by hydrothermal method under alkaline conditions using 1,3,6-trinitropyrene as carbon source.Transmission electron microscopy?TEM?showed that the size of OH-GQDs were¹.8 nm.Atomic force microscopy?AFM?characterization demonstrated that OH-GQDs were single-layered.The structure and chemical composition of OH-GQDs.was characterized by X-ray photoelectron spectroscopy.?XPS?.Fluorescence spetrum and dynamic light scattering?DLS?were used to prove the interaction between OH-GQDs and Cu²⁺or Hg²⁺.VMSF was decorated on indium tin oxide?ITO?electrode by St?ber-solution growth approach.The porous size was defined as 2.6 nm by TEM.OH-GQD@VMSF/ITO electrode was prepared by confining OH-GQD in VMSF channels through electrophoresis.The successful incorporation of GQDs in the nanochannels was demonstrated by TEM,lased-induced fluoresence and electrochemical probes.Cu²⁺and Hg²⁺were determined by anodic stripping voltammetry.Under optimal conditions,the linear detection range for Cu²⁺and Hg²⁺were 10 pmol/L-1.5?mol/L and 10pmol/L-0.5?mol/L,respectively.The limits of detection?LOD?for Cu²⁺and Hg²⁺were 8.3 pmol/L and 9.8 pmol/L,respectively.In addition,OH-GQD@VMSF/ITO electrode showed potential in simultaneous detemination of multi-metal ions.Owing to the anti-interference/anti-fouling propertities of VMSF,OH-GQD@VMSF/ITO electrodes were applied in sensitive detection of Cu²⁺in human serum or Hg²⁺in sea food.The results were consistent with that of the standard methods.?2?Amine-functionalized GQDs?NH₂-GQDs?were prepared and confined in VMSF modified indium tin oxide?NH₂-GQD@VMSF/ITO?.The electrode was applied for the detection of Cd²⁺in soil leaching solution.The carbon precursor,1,3,6-trinitropyrene,was fused into NH₂-GQDs by hydrothermal method when using ammonia and hydrazine hydrate as alkline medium and nitrogen source.The size,morphology,structure,chemical composition and fluoresence propertities of NH₂-GQDs were characterized by,TEM,AFM,XPS and fluorescence spectroscopy.The size of NH₂-GQDs were¹.9 nm with single-layered graphene structure.NH₂-GQD@VMSF/ITO electrode was prepared by confining NH₂-GQD in nanochannels of VMSF through electrophoresis.The anodic stripping voltammetry was used to detect Cd²⁺using NH₂-GQD@VMSF/ITO electrode.Under optical conditions,the linear detection range for the detection of Cd²⁺was from 20 nmol/L to20?mol/L with LOD of 4.3 nmol/L.The accuracy of detection of Cd²⁺in SLS was tested by spiked recovery method.The recoveries were between 90.4%and 105.0%.?3?OH-GQDs were confined in VMSF modified Au?OH-GQD@VMSF/Au?electrode for the detection of dopmine?DA?in human serum.VMSF decorated on Au electrode was prepared by electrochemical assisted self-assembly?EASA?method.TEM and electrochemical characterization results revealed that the pore size of VMSF was about 2.3 nm.The OH-GQD@VMSF/Au electrode was prepared by the same electrophoresis method.Differential pulse voltammetry?DPV?was applied to detect DA.Under optical conditions,the linear detection range for DA was 0.2?mol/L-100?mol/L with an LOD of 0.12?mol/L.The accuracy of detection of DA in human serum was tested by spiked recovery method.The recoveries were between 100.8%and 101.5%...