Development And Applications Of Non-enzyme Electrochemical Sensor

There are four chapters in this thesis. Three new and simple strategies wereestablished for fabricating of electrochemical sensor based on immobilization ofelectron mediators (Prussian blue and Thionine) by electrodeposition (Chapter1),diazotization-coupling reaction (Cchapter2) and electrochemically pretreatment(Chapter3). A reagentless ascorbic acid (AA) sensor was also fabricated based ongraphene doped carbon paste electrode in the four chapter1. A sensitive non-enzyme sensing platform for D-glucose based on the specificboronic acid–diol binding was established. Prussian blue (PB) which was co-depositedwith gold nanoparticles (AuNPs) to form Au–PB nanocomposite on gold electrodesurface was employed to be the electrochemical indicator. To further improve thesensitivity of the sensor, a second AuNPs layer was assembled on the Au–PBnanocomposite via electroless metallization induced by catechol group ofpolydopamine. The in situ generated AuNPs afforded multiple binding sites for4-mercaptophenylboronic acid (MPBA) self-assembly on the electrode surface viaAu–S interaction. MPBA reacted with the1,2-diol of D-glucose to form a stable5-membered cyclic boronate ester and the binding event was monitored by thedecreased current signal of PB moiety. Due to the high affinity of MPBA forD-glucose and high stability of the resulting sensing platform as well as the existenceof AuNPs, the fabricated sensor exhibited high selectivity, good sensitivity, and widelinear range from1.0×107to1.35×105M with a low detection limit of5.0×108M towards D-glucose.2. A novel electrochemical sensing platform by modification of electroactivethionine (Th) onto gold electrode surface was constructed, which was realized bydiazotization of4-aminothiophenol (ATP) selfassembled monolayer, followed bycoupling of Th with the diazonium group to form a covalent diazo bond. A pair ofwell-defined redox peaks of Th was observed in the cyclic voltammetric measurement. The resulting diazo-ATP monolayer displayed superior electrical conductivity, whichcontributed to the sensitive detection of hydrogen peroxide (H2O2). The immobilizedTh also showed a remarkable stability, which may benefit from the π–π stacking forceand the covalent diazo bond between diazo-ATP and Th molecules. Under theoptimized experimental conditions, the current fabricated non-enzyme and reagentlesssensor could show a rapid response to H2O2within3s and a linear calibration plotranged from1.0×106to6.38×103M with a detection limit of6.7×107M. Thecurrent fabrication strategy of electroactive interface is expected to be used as aversatile route for the immobilization of more electroactive molecules and offer moreopportunities for the applications in electrochemical sensor, biosensor, electrocatalysis,etc.3. A novel protocol for effectively covalent immobilization of thionine (Th) wasproposed, which was based on Schiff-base reaction between–NH2of Th and–COHwhich was in situ generated on glassy carbon electrode (GCE) via simple potentiostaticactivation in diluted nitric acid. GCE pretreated by potentiostatic activation possessedCHO-riched surface and microporous structure with high distribution density ofelectron transfer sites, and thus it became a good candidate for effectiveimmobilization of Th through imine bond with high stability. The application of theresulting Th modified electrode in hydrogen peroxide sensor was also investigated andit exhibited rapid response to H2O2within3s. The linear calibration ranged from5.0×107to5.8×103M with a detection limit of1.0×107M.4. The graphene doped carbon paste electrode (CPE) was firstly prepared with theaddition of graphene into the carbon paste mixture. Compared with conventional CPE,an improved electrochemical response of graphene doped CPE toward the redoxcouple of Fe(CN)63/4was demonstrated owing to the excellent electrical conductivityof graphene. The graphene doped CPE was further used for the successfuldetermination of ascorbic acid (AA), and it showed an excellent electrocatalyticoxidation activity toward AA with a lower overvoltage, pronounced current response,and good sensitivity. Under the optimized experimental conditions, the proposedelectrochemical AA sensor exhibited a rapid response to AA within5s and a linearcalibration plot ranged from1.0×107to1.06×104M was obtained with a detectionlimit of7.0×108M.