Phenol Electrochemical Sensors Based On Plant Tissue

1. A novel amperometric biosensor based on sponge cucumber tissue homogenate for the determination of phenolic compoundsA composite matrix consisting of the inorganic laponite and chitosan (CHT) was used for the immobilization of sponge cucumber tissue homogenate to form a novel biosensor for the detection of catechol. Amperometric detection of catechol was evaluated by holding the tissue-homogenate electrode at– 0.2V (versus SCE). Due to the laponite's special properties, such as high porosity due to easy swelling of laponite in aqueous solutions, chemical inertia, better adsorptivity, and good anionic exchange ability between layers, the sponge cucumber tissue homogenate was well immobilized in the composite matrix. Constructing this tissue biosensor has the optimum parameters being as follows: the mass ratio of laponite to CHT (w/w) was 2:1; the volume ratio of the immobilized carrier to tissue homogenate(v/v) ratio was 1:4; the tissue homogenate amount deposited on the electrode surface was 5μl. The tissue biosensor showed an optimum current response under the following conditions: the pH of the phosphate buffer solution was 5.5, temperature was controlled at 25℃, the applied potential was set at– 0.2 V. The results from the measurements of four phenolic compounds demonstrated: catechol and phenol have obvious current response; however, no current response was detected for m-cresol and p-chlorophenol. An apparent Michaelis constants of polyphenol oxidase in immobilized sponge cucumber tissue are 3.48mM and 2.905 mM for catechol and phenol, respectively. 2. A biosensor based on potato tissue homogenate for the determination of phenolic compoundsThe calcium carbonate nanoparticles have large specific surface area, lager surface energy, and good biocompatibility, so it is a good immobilized material for immobilization of biomolecules. The experimental results of FTIR and scanning electron microscope (SEM) indicated that the potato tissue homogenate can be well immobilized on the glassy carbon electrode using laponite/chitosan composite, which formed a high sensitivity and selectivity biosensor to detect the catechol. This tissue biosensor has a fast and sensitive current response to catechol (sensitivity is 139.14 mA M-1cm-2), but low response to m-cresol, phenol, p-chlorophenol (less than 3% of catechol). Therefore, this biosensor has a good selectivity to the determination of catechol. The potato tissue biosensor provided a linear response to catechol over a concentration range from 4.49×10-6 to 4.00×10-5 with a detection limit of 5.00×10 -7 M at S/N of 3. The apparent Michaelis constant of the enzyme-catalyzed reaction for polyphenol oxidase from potato tissue homogenate is 1.005 mM. In addition, we studied the optimum conditions for the construction and use of this potato tissue biosensor in details.3. Development of a mushroom tissue-homogenate biosensor and investigation of the inhibition effectDue to the high content of polyphenol oxidase in mushroom, we built a highly sensitive biosensor based on the mushroom tissue. In the work, we have used the laponite/chitoson composite to immobilize the mushroom tissue homogenate on the glassy carbon electrode to fabricate a biosensor. Using the FTIR and scanning electron microscope (SEM) to characterize the composition, the morphology of the laponite/chitoson composite, and the interaction between the carrier and biomaterials. The electrochemical measurements were performed with a conventional three-electrode system and amperometric method. Under optimization of the fabrication and using conditions of the biosensor, this tissue biosensor expressed an excellent analytical performance: high sensitivity (886.62 mA M-1cm-2 for catechol), low detection limit (4.99×10-8M), and good stability. The tissue biosensor has obvious response to different phenolic compounds, the order of sensibility is as follows: catechol>phenol> p-chlorophenol >m-cresol. The apparent Michaelis constants are 0.256, 0.157, 0.043, 0.063 and 0.03mM for catechol, phenol, p-chlorophenol and m-cresol, respectively. In this report, the inhibition of polyphenol oxidase, arising from mushroom tissue homogenate immobilized in laponite/chitosan composite, was investigated using benzoic acid. The experimental result demonstrated that this inhibition is a quasi-reversible competitive type.