1. Full name: DO PHUC TUYEN 2. Sex: Male
3. Date of birth:July 28, 1980 4. Place of birth: Thaibinh city, Vietnam
5. Admission decision number: 3614/QĐ-SĐH dated on October 22, 2009 issued by the President of Vietnam National University, Hanoi.
6. Changes in academic process: None
7. Official thesis title: Fabrication modified electrodes based on the nanocomposites of conducting polymers and nanocarbon materials for electrochemical determination of dopamine in pharmaceutical or physiological samples
8. Major: Analytical Chemistry 9. Code: 62440118
10. Supervisors: Doc. Do Phuc Quan
Prof. Doc. Tu Vong Nghi
11. Summary of the new findings of the thesis
- A novel modified electrode was fabricated by modifying the surface of the glassy carbon electrode with a composite film NF-SWCNT/P3MT of Nafion (NF), single-walled carbon nanotubes (SWCNT) and poly (3-methylthiophene) (P3MT) for highly selective and sensitive determination of dopamine (DA).
- The NF-SWCNT/P3MT composite film modified electrode shows excellent electrocatalytic activity toward the oxidation of DA in a phosphate buffer solution. The two linear ranges of 1 to 20 µM and 20 to 60 µM, limit of detection and limit of quantitation of 0.18 µM and 0.5 µM respectively was observed in 0.1 M and pH 4.0 phosphate buffer solutions.
- The interference studies show that the modified electrode exhibits excellent selectivity in the presence of ascorbic acid (AA) and uric acid (UA) with a concentration 2000- and 500-times higher than that of DA, respectively. No interference was observed for the following compounds with a concentration hundreds times higher than that of DA: CaCl2, NaCl, NH4NO3, MgCl2, NaNO3, starch, citric acid, metabisulfite, urea, glucose.
- Another novel modified electrode has been developed for selectively and sensitively detecting DA by electrochemically prepared on glassy carbon electrodes a nanocomposite film of graphene (Gr), overoxided dopamine-imprinted polypyrrole (OPPy-MIP) and gold nanoparticles (AuNPs).
- The resulting modified electrodes have a dramatic electrocatalytic effect combining the excellent electrochemical reactivity of graphen and gold nanoparticles with cation perm-selectivity of dopamine-imprinted polypyrrole films. In 0.1 M phosphate buffer solution (PBS) of pH 7.0, the differential pulse voltammetric peak heights are linear with DA concentration in interval 0.5–8.0 µM, with correlation coefficient of 0.990. The limit of detection and limit of quantitation of 0.1 µM and 0.3 µM respectively could be estimated.
- The interferences of ascorbic acid (AA) and uric acid (UC) are effectively diminished. The interference studies showed that no signal arises from AA in the presence of large excess of AA while separate peaks were observed for DA and UA. No interference also was observed for the following compounds with a concentration hundreds times higher than that of DA: CaCl2, NaCl, NH4NO3, MgCl2, NaNO3, starch, citric acid, metabisulfite, urea, glucose.
- The practical application of the two modified electrodes were demonstrated by the determination of dopamine in dopamine hydrochloride injection and human urine samples with satisfactory results:
- DA in dopamine hydrochloride injection (40 mg/L, 5 mL per injection) was determined. The ralative percentage difference was relatively low, under 5%. The relative standard deviation (n = 7) was less than 3 %. The results are acceptable, showing that the proposed method could be effectively used for the determination of DA in commercial samples.
- The proposed method in real sample analysis was also investigated by direct analysis of DA in human urine samples. The standard addition method was used for testing recovery. The results are in accordance with the results found by the Elisa method, the ralative percentage difference was relatively low, under 5 %, indicating the detection procedures are free from interferences of the urine sample matrix. The proposed method can be applied to the determination of DA in real samples with satisfactory results.
12. Paratical applicability, if any:
This work provides a voltammetric method for selectively and sensitively detecting dopamine in real pharmaceutical or biological samples.
13. Further research directions, if any
The potential applications of nano metarials such as nano carbon, nano particles, and molarcular imprinting polymer recognization materials in electrochemical sensing are well documented. Therefore, continued efforts could yield new generations of miniaturized sensing devices for selectively and sensitively detecting different molecules in real pharmaceutical or biological samples.
14. Thesis-related publications:
[1]. Do Phuc Tuyen, Do Phuc Quan, Nguyen Hai Binh, Van Chuc Nguyen, Tran Dai Lam, Le Trong Huyen, Le Huy Nguyen, Pham Hung Viet, Nguyen Thai Loc,Tran Quang Huy (2014), "A highly sensitive electrode modified with graphene, gold nanoparticles, and molecularly imprinted over-oxidized polipyrrole for electrochemical determination of dopamine", Journal of Molecular Liquids 198 p. 307-312.
[2]. Do Phuc Tuyen, Do Phuc Quan, Tu Vong Nghi, Pham Hung Viet (2013), "Using the Nafion/poly(3-methylthiophene) modified glassy carbon electrode for selective determination of dopamine in the presence of ascorbic acid", Journal of Analytical Sciences 18 (1), p. 26-31.
[3]. Do Phuc Tuyen, Do Phuc Quan, Tu Vong Nghi, Pham Hung Viet (2012), "Electrochemically selective determination of dopamine in the presence of ascorbic and uric acids on the surface of the glassy carbon electrode modified by a thin film of Nafion/poly(3-methylthiophene) composite", Journal of Analytical Sciences 17 (4), p. 72-76.
[4]. Do Phuc Quan, Do Phuc Tuyen, Tran Dai Lam, Phan Thi Ngoc Tram, Nguyen Hai Binh, Pham Hung Viet (2011), "Electrochemically selective determination of dopamine in the presence of ascorbic and uric acids on the surface of the modified Nafion/single wall carbon nanotube/poli(3-methylthiophene) glassy carbon electrodes", Colloids and Surfaces B: Biointerfaces 88 p. 764-770.
