| Electrochemical sensors are of considerable interest because of their special characteristics,such as relative simplicity,specificity,direct detection and fast response time.The key of the electrochemical sensor is to develop new materials for electrode surface modification to enhance sensitivity and selectivity.Nanomaterials,especially graphene and nobel metal nanoparticles,including palladium,platinum,gold and silver,have been extensively used to enhance sensitivity and electrocatalytic activity due to their special electrochemical properties.Therefore,the research presented in this dissertation is focused on the design and fabrication of electrochemical sensors for the detection of neurotransmitter dopamine and amino acid.1.Simultaneous electrochemical detection of ascorbic acid,dopamine and uric acid based on graphene anchored with Pd-Pt nanoparticlesMany biomolecules are ubiquitous in nature and play important roles in a variety of biological processes.Ascorbic acid(AA),a water-soluble vitamin,is an essential nutrient for human beings and extensively used as the antioxidant for the prevention or treatment of scurvy,cancer,mental illness and common cold.Dopamine(DA)is a catecholamine neurotransmitter,which belongs to the excitatory neurotransmitter family.Abnormal levels of DA may cause schizophrenia and Parkinson’s disease.Uric acid(UA)is the primary end product of purine metabolism and long-standing elevated uric acid levels may lead to several diseases such as hyperuricemia,gout and pneumonia.Usually,AA,DA and UA are co-existing substances in real biological matrixes.Thus,the development of novel methods for the simultaneous determination of them with sensitivity,selectivity and low costs is highly desirable for diagnostic and analytical applications.A number of studies based on various analytical methods for detection of dopamine have been reported,such as capillary electrophoresis,high-performance liquid chromatography,mass spectrometry,fluorescence spectroscopy,and gas chromatography-mass spectrometry.Electrochemical methods,which can be easily implemented in electronic devices,attract much.attention owe to simple,fast,low-cost,high sensitivity without time-consuming pretreatment.However,these three molecules(AA,DA,UA)are oxidized at almost the same potential of 0-0.2 V at the traditional electrode,which resulted in the overlap of voltammetric response.To overcome these problems,various materials have been used to modify electrode surfaces for the simultaneous determination of AA,DA and UA.To improving the sensitivity and selectivity determination of DA,a novel modified electrode based on graphene anchored with Pd-Pt bimetallic nanoparticles has been studied in this research.The details are categorized as following:Pd-Pt bimetallic nanoparticles anchored on functionalized reduced graphene oxide(RGO)nanomaterials were synthesized via a one-step in situ reduction process,in which Pt and Pd ions were first attached to poly(diallyldimethylammonium chloride)(PDDA)functionalized graphene oxide(GO)sheets,and then the encased metal ions and GO were subjected to simultaneous reduction by ethylene glycol.The as-prepared Pd3Pti/PDDA-RGO nanocomposites were characterized by transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy and electrochemical methods.Three well-separated voltammetric peaks along with remarkable increasing electro-oxidation currents were obtained in differential pulse voltammetry(DPV)measurements.Under the optimized conditions,there were linear relationships between the peak currents and the concentrations in the range of 40-1200 μM for AA,4-200 μM for DA and 4-400 μM for UA,with the limit of detection(LOD)(based on S/N = 3)of 0.61,0.04 and 0.10μM for AA,DA and UA,respectively.Furthermore,the practical electroanalytical utility of the sensor was demonstrated by the determination of AA,DA and together with UA in human urine and blood serum samples with satisfactory results.2.Gold nanoparticles doped molecularly imprinted polymer of dopamine for the electrochemical determination of L-tyrosineAmino acids and their derivatives are extensively found in nature.Besides building blocks of proteins and polypeptides,amino acids can regulate key metabolic pathways,which are necessary for maintenance,growth,reproduction and immunity.With the characteristics of predetermination,recognition and practicability,molecularly imprinted polymers(MIPs)are used in many fields,such as catalysis,solid phase extraction,chemical bionics sensor and film separation.Inspired by mussel adhesive protein,the dopamine aqueous solution was discovered to self-polymerize into thin adherent polydopamine(PDA)films,which can be coated on various inorganic and organic substrates.There are plenty of phenolic hydroxyl groups and amino groups in polydopamine,which can be used as cross-linker reagents for the immobilization of biomolecules via Michael addition or Schiff base reaction.The use of polydopamine presents several advantages over traditional polymers(polyaniline,polypyrrole,poly(o-aminophenol),polyphenol),such as high hydrophilicity,high stability,excellent biocompatibility,robust adhesion onto various substrates,abundant functional groups,ease in preparation and controllable thickness,which would make it attractive as a promising materials for construction of novel molecular imprinted polymers.A novel molecularly imprinted electrochemical sensor(MIES),constructed by molecular imprinting technique combined with electrochemical technique,was fabricated by using dopamine as functional monomer.The electrochemical behaviors of L-tyrosine(L-Tyr)at MIES have been investigated.The details are categorized as following:Molecularly imprinted polymer of dopamine was electropolymerized on glassy carbon electrode surface by using L-Tyr as the template molecule,gold nanoparticles(AuNPs)as dopant,dopamine as the functional monomer.The obtained MIES was successfully used to determination of L-Tyr.Under the optimal conditions,the MIES exhibited good sensitivity.A good linearity was obtained in the range of 0.6 to 70 μM with the limit of detection(LOD)of 0.05 μM for L-Tyr(based on S/N = 3). |
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