Studies On Phenolic Compounds And Dopamine Sensor Based On Nanomaterials

Electrochemical biosensing is a new technology which integrates chemistry, biology, physics, and so on. It organically combines the nano materials with electrochemical detection technology, and exhibits the advantages such as high sensitivity, good selectivity, simple operation and fast analysis. Based on the combination of chemiluminescence and electrochemisty, electrogenerated chemiluminescence (ECL) possesses the features of both chemiluminescence and electrochemisty, including high selectivity, fast analysis, simple operation, and good reproducibility. Electrochemical biosensor and ECL detection techniques are not only considered as hot topic in analytical chemistry, but also have been widely used in environmental monitoring, clinical diagnostics, and food industry. This thesis focuses on the study several phenolic compounds and dopamine sensors employing electrochemical as well as ECL detection techniques. A variety of electrochemical characterization techniques were used, such as transmission electron microscopy (TEM), scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS) and ultraviolet-visible (UV-vis) spectroscopy.The main works are included as follows:Part1A sensor of catechol and hydroquinone using Pt-Au-organosilica@chitosan compositesPhenolic biosensors based on the polyphenol oxidase have played a leading role. However, there are disadvantages of these enzymatic biosensors, such as high cost, the chemical and thermal instabilities due to the intrinsic nature of enzymes, as well as the tedious fabrication procedures. Non-enzymatic sensor can overcome those defects. An amperometric non-enzymatic sensor based on Pt-Au-organosilica@chitosan (Pt-Au-OSi@CS) composites has been developed for determining catechol (CC,1,2-dihydroxybenzene) and hydroquinone (HQ,1,4-dihydroxybenzene). The Pt-Au-OSi@CS composites were synthesized using positively charged inorganic-organic core-shell organosilica@chitosan (OSi@CS) crosslinked nanospheres as templates for the assembly of negatively charged1-3nm Au nanoparticles seeds which acted in subsequent step as nucleation sites for the reduction of platinum. Due to the excellent electrocatalytic activity of Pt-Au-OSi@CS for the reduction of CC and HQ, the sensor based on the Pt-Au-OSi@CS exhibited broad linear range of0.06～90.98μmol·L-1for CC and0.03～172.98μmol·L9-1for HQ. The low detection limits of0.02and0.01μmol·L-1(S/N=3) were obtained for CC and HQ, respectively.Part2An electrochemiluminescent sensor for phenolic compounds based on the inhibition of peroxydisulfate electrochemiluminescenceSo far to our knowledge, only few ECL methods have been reported to determine phenolic compounds. An electrochemiluminescent sensor for phenolic compounds based on the quenching effects of phenolic compounds on the electrogenerated chemiluminescence (ECL) of peroxydisulfate solution has been developed. Firstly, gold nanoparticles (AuNPs) were electrodeposited on the surface of glassy carbon electrode (GCE) for assembling L-cysteine (L-cys) through strong binding interactions between AuNPs and the functional groups of-SH and-NH2of L-cys. Then, gold colloidal nanoparticles (nano-Au) and L-cys were assembled to achieve L-cys/nano-Au/L-cys/AuNPs film modified electrode. The ECL behavior of peroxydisulfate solution had been investigated in detail at the L-cys/nano-Au/L-cys/AuNPs/GCE, and phenolic compounds were found to be able to inhibit the ECL of peroxydisulfate solution. Based on this principle, an ECL sensor had been developed for detecting phenolic compounds. Due to the facts that both gold nanomaterials (AuNPs and nano-Au) and L-cys could promote the electron transfer and amplify the ECL signal of peroxydisulfate solution, the combination of them provided a rapid, simple and sensitive method for the detection of a series of phenolic compounds. The resulting sensor showed potential use in the pharmaceutical industry and environmental monitoring. Part3An electrogenerated chemiluminescence sensor prepared with a graphene/multiwall carbon nanotube/gold nanocluster hybrid for the determination of phenolic compoundsSuccessful examples for the construction of ECL phenolic sensors were commonly based on the quenching effects of phenolic compounds on the ECL of Ru complexes and quantum dots (QDs). However, the ECL systems mentioned above suffered the following problems. On the one hand, the challenges for inhibition-based assays for phenolic compounds are the improvement of assay sensitivity. On the other hand, Ru(bpy)32+is an expensive reagent and QDs are not stable enough over time and have inherent toxicity. A dispersible graphene/multiwall carbon nanotube/gold nanocluster (GP/MWCNTs/AuNCs) hybrid in aqueous solution was prepared in situ, and characterized by transmission electron microscopy (TEM) and ultraviolet-visible (UV-vis) spectroscopy. Based on the fact that phenolic compounds can enhance the electrogenerated chemiluminescence (ECL) signal at the GP/MWCNTs/AuNCs modified glassy carbon electrode in the presence of peroxydisulfate, an ECL sensor was proposed for the determination of phenolic compounds with high sensitivity, good repeatability and stability. Due to its fascinating features, such as good water solubility and excellent stability, the GP/MWCNTs/AuNCs hybrid would offer a suitable catalytic platform for phenolic compounds and provide potential promise for the construction of ECL sensors.Part4An ECL sensor for dopamine using reduced graphene oxide/multiwall carbon nanotubes/gold nanoparticlesOnly few enhanced ECL methods have been applied to determine dopamine (DA) and the sensitivity was low. An eletrochemiluminescence (ECL) sensor based on the ECL of peroxydisulfate solution for detecting the DA was proposed using reduced graphene oxide/multiwall carbon nanotubes/gold nanoparticles (rGO/MWCNTs/AuNPs) hybrid modified glassy carbon electrode (GCE). The rGO/MWCNTs/AuNPs was synthesized by an effective and facile in situ chemical reaction using polyethyleneimine (PEI) as a reducing agent for both GO and AuCl4. The ECL behaviors of peroxydisulfate solution have been investigated at the rGO/MWCNTs/AuNPs/GCE, and DA was found to be able to enhance the ECL of peroxydisulfate solution. Under the optimized conditions, the enhanced ECL signal intensity of peroxydisulfate solution was linear with the concentration of DA in the range between0.20and70μmol·L-1(R=0.9902) with a detection limit (S/N=3) of0.067μmol·L-1. Furthermore, the developed sensor exhibited a high sensitivity, good reproducibility, stability for the detection of DA. The applicability of the proposed sensor was also evaluated by detecting DA in dopamine hydrochloride injection, human urine and serum.