Construction And Application Of Micro/nanoelectrode Sensors Based On Carbon-based Composites

Carbon-based composite materials have been intensively studied in the field of electrochemical sensors due to their low cost,high electrical conductivity,good stability,abundant electroactive sites,and safety and reliability.However,its large-scale application faces bottlenecks such as complicated preparation processes,the use of toxic reagents,dependence on expensive equipment,and poor stability of electrocatalytic performance.It is difficult to meet the technical needs of high sensitivity,high selectivity,and miniaturized electrochemical sensors.Therefore,through a simple and environmentally friendly synthesis strategy,the composition of the composite material and the electroactive sites are adjusted to prepare a new carbon-based composite material with high conductivity and electrocatalytic performance,and it is coupled with an optimized electrode structure to improve the electrochemical sensor performance.This thesis focuses on the simple,adjustable and environment-friendly preparation of carbon-based nanocomposites with abundant electroactive sites.Based on 0D nanoparticles,1D carbon nanotubes,2D graphene oxide,and3D nanopipette as a carrier,a reasonable electrode structure was designed.The relationship between the composition and structure of carbon-based composite materials and the electrochemical performance of the sensor was systematically studied,and the detection mechanism and structure-activity relationship of the new sensor were revealed.The main research contents of this thesis are as follows:?1?Based on a simple and green synthesis strategy,3D structured copper nanoparticles?Cu NPs?modified nitrogen-doped graphene composites?GR-CN-Cu?were successfully prepared.The multiple effects of polydopamine?PDA?in the preparation of materials were discussed.It is not only an important binder for composite materials,but also a nitrogen source for nitrogen-doped graphene?GR-CN?,or an adsorbent or reducing agent for in-situ adsorption or reduction of Cu²⁺.Based on the composite material with excellent conductivity,electron transfer ability and electrocatalytic activity,an electrochemical sensor for detecting dihydroxybenzene isomers was constructed,which exhibits high sensitivity,good selectivity,wide linear range(0.5-720?mol L^-1)and low detection limit(81-131 nmol L^-1).In addition,the electrochemical sensor can be used for the simultaneous detection of hydroquinone isomers in actual water samples?wastewater?,and the detection results are consistent with the HPLC method,showing satisfactory application value.The results confirmed that the excellent redox performance of GR-CN-Cu is attributed to the difference in the electronegativity of the carbon and nitrogen atoms in the 3D GR-CN and the synergistic effect of Cu NPs and 3D GR-CN.?2?Based on the above synthesis strategy,nitrogen?N?and iron phosphide?FeP?co-doped carbon nanotubes?N/FeP-CNT?were successfully prepared and characterized,showing multi-element co-doping,multiple active sites and good dispersion performance.The study reveals that the synergistic effect of nitrogen-doped carbon nanotubes?N-CNT?as electron transport channels and uniformly dispersed active sites?FeP?significantly improves the conductivity and electrical conductivity of the modified electrode?N/FeP-CNT/GCE?Catalytic performance.To provide a new analytical platform for the simultaneous detection of dihydroxybenzoic acid?DHBA?isomers,the results show that the linear range of 2,4-DHBA,3,4-DHBA and 2,5-DHBA are 0.5-600?mol L^-1.0.5-560?mol L^-1 and 0.5-820?mol L^-1,the corresponding detection limits are 124,65 and 221 nmol L^-1,respectively.In addition,the electrochemical sensor showed good anti-interference performance and stability in the detection of DHBA isomers in actual samples.?3?Based on the unique electrical properties of multi-doped composite materials,it is possible to develop portable sensing devices with reliable performance.Nitrogen?N?and tungsten phosphide?WP?doped carbon nanotubes?WP/N-CNT?were used as electrode materials.And a new portable and reusable electrochemical analysis platform for anti-cancer drug methotrexate?MTX?was also proposed.Studies have confirmed that WP with high electrocatalytic activity as a reactive site not only forms a synergistic effect with N-CNT as an electron transport channel,but also provides an electronegativity difference to help MTX adsorption and desorption,making electrode reuse possible.Using a portable screen-printed electrode?SPE?as a carrier,it realizes a small sample size,which can meet the analysis platform of on-site testing,and achieve faster,simpler,and cheaper testing of MTX.The experimental results show that the constructed portable electrochemical sensor has a low detection limit of MTX(45 nmol L^-1),high sensitivity,wide linear range(0.01-540?mol L^-1),good stability and satisfactory reproducibility.It also demonstrated the reliable detection of in vitro blood samples and is expected to become a new low-cost on-site cancer diagnosis and treatment platform.?4?Based on the simplicity,green synthesis strategy and research on high-performance electrode materials,the electrochemical sensor detection mode is expected to be revolutionized.Using the recyclable characteristics of magnetic nanoparticles,PDA functionalized its surface,rationally designed active recognition sites and signal sources,and proposed an electrochemical sensor based on monodisperse functional magnetic micro-nanoparticles?Fe₃O₄@PDA/Cu_xO?electrode unit.An ultrasensitive electrochemical method for the detection of D-cysteine?D-Cys?was established.The experiment reveals that D-Cys and Cu²⁺form a stable D-Cys-Cu²⁺-D-Cys structure,thereby shielding the detection mechanism of the redox current of the signal indicator(Cu²⁺).And the enrichment mechanism of covalently combining the PDA layer on the surface of Fe₃O₄@PDA/Cu_xO electrode unit with the Cys enantiomer.The results confirmed the feasibility of the proposed magnetic micro-nano electrode unit sensor for identification and quantification of D-Cys strategy,with high sensitivity(102?A?M^-1 cm^-2)and a low detection limit of 83 pmol L^-1.Compared with the traditional electrode structure,this strategy is expected to promote the development of new electrochemical sensing models.?5?Based on a simple,green synthesis strategy,combined with customizable micro-nano size carriers,carbon based micro-nano electrodes will be endowed with diversity.PDA and graphene oxide?GO?achieve layer-by-layer self-assembly on the surface of the nanopipette through electrostatic interaction.After pyrolysis at high temperature,a nitrogen-doped graphene microelectrode?NGR ME?can be obtained.A novel preparation strategy of carbon based micro-nano electrodes fills the gap in the development of in-situ nitrogen-doped carbon based microelectrodes.The electrical conductivity and electrocatalytic performance of NGR ME were investigated,and a biosensor that simultaneously detected multiple neurotransmitters was constructed with NGR ME.It has high electrocatalytic activity,good selectivity and stability for dopamine?DA?and serotonin?5-HT?,with detection limits reaching 0.69 nmol L^-1and 6.5 nmol L^-1,respectively.Taking advantage of the size of NGR ME,a new type of self-priming portable micro-volume sensor device was designed to detect neurotransmitters in human serum and obtain reliable analysis results.The research on the performance of surface self-adsorption/reduction and in-situ multi-doped carbon-based composite materials and their micro-nano electrodes deepened the understanding of the coupling of high-performance electrode materials and suitable electrode structures to promote the analysis performance of electrochemical sensors.At the same time,this research also expands the application of portable and miniaturized electrochemical sensors in the field of analytical chemistry,laying the foundation for further research on integrated and intelligent sensing devices.