| ObjectiveSince the advent of chemically modified electrodes,they have been active in various research fields,such as clinical,industrial,environmental and agricultural analysis.Carbon paste electrode(CPE)is often used as the base of modified electrodes due to its advantages of simple preparation method,easy modification,cheap and easy access to components,and easy fabrication of microprobes.The organic dye methylene blue(MB)has good electrochemical activity and can be modified on the electrode surface by simple electropolymerization into polymethylene blue(PMB),so it is often used as a modification material for electrodes.In this paper,combining the advantages of CPE and MB,a uric acid(UA)sensor that can be used for actual sample detection is prepared in water and deep eutectic solvents(DESs)medium by means of electropolymerization and electrodeposition,and a sensitive,convenient and stable UA test platform is further built.MethodsIn this paper,the type of adhesive and the proportion of adhesive and carbon powder used to prepare the carbon paste electrode were optimized.Then,the carbon paste electrode prepared under the optimal conditions was used as the substrate to prepare the carbon paste electrode modified by Cu nanoparticles by electrodeposition in an aqueous medium(0.1 mol/L H2SO4)and deep eutectic solvents(DESs,urea∶choline chloride=2∶1,glycerol∶choline chloride=2∶1),and then PMB was modified on the surface of CPE or Cu/CPE by electropolymerization to prepare polymethylene blue modified carbon paste electrode(PMB/CPE)and polymethylene blue composite copper modified carbon paste electrode(PMB-Cu/CPE).According to the difference of medium,the modified electrodes of Cu nanoparticles can be divided into three types: PMB-Cu(w)/CPE,PMB-Cu(u-c)/CPE,PMB-Cu(g-c)/CPE(w:H2O medium,u-c: urea-choline chloride medium,g-c: glycerol-choline chloride medium).Finally,the modified electrodes were electrochemically characterized by cyclic voltammetry(CV)and alternating impedance spectroscopy(EIS).The modified materials were analyzed by infrared spectroscopy(FT-IR),scanning electron microscopy(SEM)and X-ray diffraction(XRD),and the optimal preparation conditions were determined.Results(1)When silicone oil,liquid paraffin and vaseline are used as adhesives,and silicone oil∶graphite powder=1∶5(m∶m),the peak current and peak spacing of CPE prepared are the best,and the electrode effect is the best.(2)The optimum conditions for preparing PMB/CPE were MB concentration of 2.5 mmol/L,polymerization solution ph of 8.2,and 7 cycles of electropolymerization.The optimum conditions for preparing PMB-Cu(w)/CPE by electrodepositing Cu in H2 O medium were as follows: deposition potential of-0.6 V,deposition temperature of 30°C,Cu2+ concentration of 0.05 mol/L,deposition time of 200 s,MB concentration of 1.75 mmol/L,polymerization solution ph of 8.2,and 3 cycles of electropolymerization.Using urea-choline chloride as the medium,the optimum conditions for preparing PMB-Cu(u-c)/CPE by electrodeposition were as follows: deposition potential of-1.2 V,deposition temperature of 50°C,Cu2+ concentration of 0.05 mol/L,deposition time of 600 s,MB concentration of 2.5 mmol/L,polymerization solution ph of 8.2,and 7 cycles of electropolymerization.The optimum conditions for preparing PMB-Cu(g-c)/CPE by electrodepositing Cu in glycerol-choline chloride medium were as follows:deposition potential of-1 V,deposition temperature of 50°C,Cu2+ concentration of 0.075 mol/L,deposition time of 400 s,MB concentration of 2.5 mmol/L,polymerization solution p H of 8.2,10 cycles of electropolymerization.(3)Compared with PMB/CPE,PMB-Cu/CPE has higher current value,lower impedance and better catalytic performance for UA;Compared with PMB-Cu/CPE prepared in three media,PMB-Cu(g-c)/CPE has the highest current value and the lowest impedance.(4)Both PMB/CPE and PMB-Cu(g-c)/CPE modified electrodes can be used for the detection of UA in urine,and within the range of ±5%,they were not affected by interferences.However,when PMB-Cu(g-c)/CPE was used for UA detection,the linear range was wider than that of PMB/CPE,becoming 8 times wider,and the lower detection limit and detection limit were reduced to 10% and2.6% of PMB/CPE,respectively,and the current response value was also increased by 2.6 times.After 20 days of stability test,the UA response value of PMB/CPE decreased by 13.0%,and the UA response value of PMB-Cu(g-c)/CPE decreased by 10.7%,so PMB-Cu(g-c)/CPE has better stability.Conclusions(1)In this paper,the traditional carbon paste electrode was improved by using a 200 μL pipette suction head as the carbon paste container to prepare a small carbon paste electrode,and using this as the working electrode.The PMB/CPE modified electrode prepared by electropolymerization of MB has good selectivity and simple pretreatment,which can be used for the detection of actual urine samples,but the detection range is narrow and the detection limit is high,which needs further improvement.(2)PMB-Cu(w)/CPE prepared by electrodepositing Cu in aqueous medium and then polymerizing MB has higher response current than PMB/CPE,which indicates that the introduction of Cu nanoparticles increases the conductivity of the modified electrode.When DESs was used instead of water as the electrodeposition medium,the morphology of Cu nanoparticles was more uniform and the particle size was smaller;The prepared PMB-Cu DES/CPE has larger response signal and smaller background current.The above results show that using DESs as the medium can not only effectively avoid the side reaction produced when electrodepositing Cu with H2 O as the medium,but also grow Cu nanoparticles with better morphology and performance.(3)Compared with other electrodes prepared in this study,PMB-Cu(g-c)/CPE showed a wider detection range,lower detection limit,improved stability and sensitivity,and better catalytic performance in the detection of UA samples.(4)A sensitive electrode for UA detection was prepared by improved CPE combined with simple electrochemical modification.The overall preparation process was simple and the experimental period was short.On this basis,a new sensing system with stable performance,excellent selectivity and catalytic ability,and suitable for the detection of actual urine samples has been built. |
