Preparation Of Small Biological Molecules Nanocomposites Modified Electrodes For Electrochemical Sensing Applications

As an important branch of the sensor,electrochemical sensor is one of the most important research areas in modern analytical science due to its highly sensitive,excellent selectivity,simple operation and low cost.Electrochemical sensor has been widely used in many fields,such as biological analysis,food industry,environmental analysis,military medicine and medical research.Small biological molecules are often used in electrochemical sensor due to distinct properties such as non-toxic,biodegradable,highly active group,good electrocatalytic activity and so on.Small biological molecules such as thymine,phytic acid,cysteine and chitosan are often used for electrochemical detection of heavy-metal,dopamine and glucose.This thesis includes mainly two aspects:Electrochemical mercury ion sensor based on thymine-mercury-thymine structure was fabricated;preparation of phytic acid nanocomposites modified electrodes for sensitive and selective determination of copper ions and dopamine.The main contents of this thesis include:(1)Functionalized gold nanoparticles/reduced graphene oxide nanocomposites for ultrasensitive electrochemical sensing of mercury ions based on thymine-mercury-thymine structureGold nanoparticles/reduced graphene oxide(AuNPs/rGO)nanocomposites were used as a template for signal magnification,and the carboxylic group of the thymine-1-acetic acid was covalently coupled with the amine group of the cysteamine which self-assembled onto AuNPs,then an electrochemical biosensor for the determination of mercury ions(Hg2+)has been obtained based on thymine(T)modified AuNPs/rGO nanocomposites.The structural features of the T bases functionalized AuNPs/rGO electrode were confirmed by attenuated total reflection infrared spectroscopy and scanning electron microscopy spectroscopy.Each step of the modification process was characterized by cyclic voltammetry and electrochemical impendence spectroscopy.With the presence of Hg2+,the specific binding of T bases and Hg2+ forming T-Hg2+-T complexes in aqueous solution and the electrochemical response was measured by differential pulse voltammetry measurement.As a result,the T bases modified AuNPs/rGO biosensor was found to be highly sensitive to Hg2+ in the range of 10 ng L-1-1.0 mg L-1.The detection limit is 1.5 ng L-1,demonstrating that T/AuNPs/rGO modified electrode has the high sensitivity to Hg2+.The biosensor afforded excellent selectivity for Hg2+ against other heavy metal ions.Furthermore,the developed sensor exhibited a high reusability through a simple washing.In addition,the prepared biosensor was successfully applied to assay Hg2+in real environmental samples.(2)Phytic acid/graphene oxide nanocomposites modified electrode for electrochemical sensing of dopamineAn electrochemical sensor for determining dopamine was developed by modifying phytic acid/graphene oxide nanocomposites onto a glassy carbon electrode.Graphene oxide was synthesized from natural graphite powder using a modified Hummer’s method and further treated by means of ultra-sonication with phytic acid to form a stable phytic acid/graphene oxide nanocomposites suspension by the π-πinteraction.The structural feature of the phytic acid/graphene oxide modified glassy carbon electrode was confirmed by attenuated total reflection infrared spectroscopy and scanning electron microscopy spectroscopy.The proposed electrochemical sensor was applied to detect various concentrations of dopamine by differential pulse voltammetry.The results showed that the fabricated sensor exhibited high electro-catalytic activities toward the detection of dopamine,and presented a wider linear range and a lower detection limit.In addition,the phytic acid/graphene oxide/glassy carbon electrode demonstrated high electrochemical selectivity toward dopamine in the presence of ascorbic acid and uric acid.Moreover,the sensor also displayed good reproducibility and stability and availability.The phytic acid/graphene oxide nanocomposites can be successfully used for the detection of dopamine in dopamine hydrochloride injection and human urine samples and offer a new platform for selective dopamine determination.(3)Determination of copper ions using a phytic acid/polypyrrole nanowires modified glassy carbon electrodeA phytic acid/polypyrrole nanowires modified electrode was developed for the determination of copper ions.The phytic acid/polypyrrole nanowires were prepared by an electrostatic adsorption and ultrasonic mixing,and then the nanocomposites were drop-casted on a glassy carbon substrate.The phytic acid/polypyrrole nanowires modified glassy carbon electrodes was applied to detect various concentrations of copper ions by differential pulse voltammetry.The results showed that,because of the synergistic effect between the phytic acid and polypyrrole nanowires,the phytic acid/polypyrrole nanowires/glassy carbon electrode revealed the higher sensitivity to detect copper ions than polypyrrole nanowires/glassy carbon electrode.The Phytic acid/polypyrrole nanowires composites functionalized electrodes showed a good linear relationship with copper ions at concentration ranges of 10-60 μg·L-1,and the limit of detection(S/N = 3)was 3.33 μg·L-1.In addition,the electrochemical sensor has good reproducibility and stability,and can be applied to assay copper ions in real water samples.