Non-enzyme Sensors Based On Nanocomposites/Polymer Film Composite Material For The Detection Of Small Biomolecules

The development and application of enzyme biosensor has become a research hotspot because of the advantages of high sensitivity, good selectivity and repeatability. However, the enzyme biosensor also has some drawbacks:firstly, the loading of enzyme on the electrode surface is limitied. Secondly, the enzyme is easy to inactivation in the loading process due to its poor internal structure as well as the influence of the environment temperature and pH. So now, we should not only improve enzyme biosensor but also construct non-enzyme sensors to solve these problems mentioned above. Small molecules including small molecule protein, amino acid, polypeptide, amines and lipid mediators, are the material foundation of neuroendocrine and immune network regulation, playing an important role to maintain body homeostasis. Ascorbic acid (AA) is very popular for its antioxidant property, and present in the human diet as a vital vitamin. Moreover, AA is widely used for the prevention of scurvy and treatment of common cold, mental illness, cancer, infertility and aids. In the biological environment, AA and tryptophan (Trp) dopamine (DA) and uric acid (UA) and nitrite (NO2) often coexist in biological samples. So it has become a hot research to detect the four substances respectively or simultaneously. Because of these substances are electrically active, therefore the constructing of a modified electrode to detect these coexisting small biological molecules respectively or simultaneously is very important. In recent years, polymer film has many attractive features:firstly, the polymer film prepared by electropolymerization is a chemically stable homogeneous film with controlled thickness. Secondly, the film is very stable and hard to be taken off from the surface unless the electrode is heavily polished. Thirdly, the polymer film has many the irregularly continuous small wrinkles that endow the biosensor with large surface area and good stability. Nanoparticles have been applied in the fields of chemical modified electrodes arose great attentions due to their large surface areaand good biological compatibility。Based on the above consideration, in this paper, we have constructed a variety of non-enzyme sensors with high sensitivity and selectivity for the detection of small biomolecules. The main works are included as follows: 1. Non-covalent iron(III)-porphyrin functionalized multi-walled carbon nanotubes for the simultaneous determination of ascorbic acid, dopamine, uric acid andnitriteAchloro[3,7,12,17-tetramethyl-8,13-divinylporphyrin-2,18-dipropanoato(2-)] iron(III)/Multi-walled carbon nanotubes (Fe(III)P/MWCNTs) composites and a modified glassy carbon electrode (GCE) was fabricated and successfully used for the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and nitrite (NO2). Fe(III)P/MWCNTs composites were characterized by ultraviolet-visible absorption spectroscopy (UV-vis) and scanning electron microscopy (SEM), and the results revealed a pair of direct redox peaks from the FeⅢ/FeⅡ couple. Moreover, the combination of Fe(III)P and MWCNTs endowed the electrode with a large surface area, good biological compatibility and stability and high selectivity and sensitivity. The linear calibration plots for AA, DA and UA were obtained over the range of14.00μmol·L-1to2.50m mol·L-1,0.70μmol·L-1to3.60mmol·L-1and5.80μmol·L-1to1.30mmol·L-1with detection limits of3.00μmol·L-1,0.09μmol·L-1and0.30μmol·L-1, respectively. Two linear calibrations for NO2-were obtained over ranges of1.00μmol·L-1to0.60mmol·L-1and0.60mmol·L-1to1.60m mol-L"1with detection limits of0.50μmol·L-1. In addition, the modified electrode was successfully applied for the determination of analytes in urine and serum samples using the standard adding method with satisfactory results.2. Au-nanoclusters incorporated3-amino-5-mercapto-1,2,4-triazole film modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitriteA novel biosensor has been constructed by the electrodeposition of Au-nanoclusters (nano-Au) on poly(3-amino-5-mercapto-1,2,4-triazole)(p-TA) film modified glassy carbon electrode (GCE) and employed for the simultaneous determination of dopamine (DA), ascorbic acid (AA), uric acid (UA) and nitrite (NO2-). NH2and SH groups exposed to the p-TA layer are helpful for the electrodeposition of nano-Au. The combination of nano-Au and p-TA endow the biosensor with large surface area, good biological compatibility, electricity and stability, high selectivity and sensitivity and flexible and controllable electrodeposition process. In the fourfold co-existence system, the linear calibration plots for AA, DA, UA and NO2were obtained over the range of2.1-50.1μmol·L-1,0.6-340.0μmol·L-1,1.6-110.0μmol·L-1and15.9-277.0μmol·L-1with detection limits of1.1×10-6mol·L-1,5.0×10-8mol·L-1,8.0×10-8mol-L-1and8.9×10-7mol-L-1, respectively. In addition, the modified biosensor was applied to the determination of AA, DA, UA and NO2-in urine and serum samples by using standard adding method with satisfactory results.3. Simultaneous determination of ascorbic acid, dopamine, uric acid and tryptophan on gold nanoparticles/overoxidized-polyimidazole composite modified glassy carbon electrodeA novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA-DA, DA-UA and UA-Trp were large up to186,165and285mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of210.0-1010.0μmol·L-1,5.0-268.0μmol·L-1and6.0-486.0μmol·L-1with detection limits (S/N=3) of2.0μmol·L-1,0.08μmol·L-1and0.5μmol·L-1, respectively. Two linear calibrations for Trp were obtained over ranges of3.0-34.0μmol·L-1and84.0-464.0μmol·L-1with detection limit (S/N=3) of0.7μmol·L-1. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.