Polydopamine/Graphene Composite Films For Dopamine And Acetaminophen Permselective Sensing

Membranes with permselectivity have been widely used in various fields,such as seawater desalination,gas separation,and sensing applications.Improving the selectivity in the analysis of complex biological samples plays an important role in sensing technology and has always been a frontier subject of sensing research.When poly(phenylenediamine)combined with enzymes began to selectively determine target substances(such as glucose),the use of permselective films for electrochemical sensors was developed.Based on this,this dissertation is devoted to the permselectivity of electrode modification materials for electrochemical sensor of acetaminophen and dopamine in biological samples.The main contents are as follows:(1)Preliminary study on the permeation selectivity of polydopamine/graphene compositesPolydopamine(PDA)is a synthetic analogue of natural eumelanin,with permselectivity,but its insulation will reduce the detection sensitivity of the electrode.In order to improve the sensitivity of polydopamine,a composite film of electrochemically reduced graphene oxide(er GO)and polydopamine was prepared.The composite film was characterized by scanning electron microscope(SEM),atomic force microscope(AFM),cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS).The results showed that the electropolymerized dopamine film can be uniformly deposited on the electrode surface under neutral conditions.With the increase of the number of PDA deposition cycles and the increase of monomer concentration,the permeability of PDA gradually decreases.The composite has high cation permeability to dopamine,and has a good inhibitory effect on ascorbic acid(AA)and uric acid(UA).The dopamine concentration and the oxidation peak current showed a good linear relationship,and the good selectivity of the polydopamine/graphene is expected to be used for biological sample analysis.(2)Determination of acetaminophen based on the permselectivity of polydopamine/graphene filmAlthough good permselectivity of composite films has achieved,the sensitivity of the film is not high,and the permselectivity has not been quantitatively evaluated.Based on previous work,the sensitivity of the film was enhanced by the method of direct electrodepositing graphene,and differential pulse voltammetry(DPV)was used to determine the apparent permeability and selectivity of the film.The results show that the PDA composite film has good permselectivity,and has no obvious permeation to high concentrations of ascorbic acid(above 10 mmol/L);the selectivity coefficient to uric acid is about-1.6,indicating that it has a good inhibitory to anions.The potential of the characteristic peak of p-nitrophenol(4-NP)does not affect the determination of the target,as the interference can be eliminated by potential selection.The possibility of the films for the selective determination of acetaminophen(AP)was showed in samples.EIS and CV were used to investigate the relationship between analytes with different charges and permselectivity.In order to investigate the long-term stability of the film,the composite was continuously monitored in urine and saliva samples for 12 hours.The low background value demonstrated the composite’s long-term stability and anti-fouling ability.(3)Investigation about the electrodepositing methods of polydopamine on permselectivity and simultaneous determinationThe permselectivity of the composite is mainly derived from polydopamine,and the enhanced sensitivity is attributed to the good conductivity of graphene.Therefore,it is necessary to compare different deposition methods of polydopamine and optimize the preparation of graphene.Three electrodepositing methods of PDA: constant potential deposition,cyclic voltammetric deposition and pulse deposition were investigated.It was found that the different electrodeposition methods of polydopamine did not particularly affect the permeability of the films.Given the uniformity and stability of the film and the lifespan of the electrode,cyclic voltammetric deposition was finally selected as the deposition method of polydopamine.The deposition conditions of the graphene film were optimized to improve the sensitivity of the film.In order to examine the application,a polydopamine/graphene composite membrane was used to simultaneously determine dopamine and acetaminophen in urine and saliva.The peak potential difference between dopamine and acetaminophen(～200 mV)is sufficient to ensure that the determination of the two will not interfere with each other.