Siti Fauziyah Rahman

Selective determination of dopamine with an amperometric biosensor using electrochemically pretreated and activated carbon/tyrosinase/Nafion®-modified glassy carbon electrode

Dopamine, the most important neurotransmitter in the human brain, controls various functions. Dopamine deficiency causes fatal neurological disorders such as Parkinson’s disease. Even though various types of electrochemical sensors have been studied to measure dopamine levels, they often have poor selectivity for dopamine due to co-existence of interfering substances (e.g. ascorbic acid). Herein, we aimed to develop a highly sensitive dopamine detection method in the co-existence of ascorbic acid, a major interfering substance in real sample by designing an electrochemically pretreated and activated carbon/tyrosinase/Nafion®-modified GCE as an amperometric dopamine biosensor. To maximize the biosensor performance, pH, volume of Nafion®, and scan rate were optimized. This electrochemically pretreated and activated carbon/tyrosinase/ Nafion®-modified GCE could detect as low as 50 μM of dopamine with a wide linear range (50 ~ 1,000 μM) within a few seconds. In addition, it had a sensitivity of 103mAM/cm2, which was higher than all previously reported tyrosinasebased dopamine biosensors. In addition, interference effect caused by 4 mM of ascorbic acid was negligible in the co-existence of 1 mM of dopamine. Consequently, this electrochemically pretreated and activated carbon/tyrosinase/ Nafion®-modified GCE might be applicable as amperometric biosensor for selective detection of dopamine in real samples with interfering substances.

Highly sensitive and selective dopamine detection by an amperometric biosensor based on tyrosinase/MWNT/GCE

Dopamine (3,4-dihydroxylphenyl ethylamine) is the most significant neurotransmitter in the human nervous system. Abnormal dopamine levels cause fatal neurological disorders, and thus measuring dopamine level in actual samples is important. Although electrochemical methods have been developed for detecting dopamine with high accuracy, certain substances (e.g., ascorbic acid) in actual samples often interfere with electrochemical dopamine detection. We developed tyrosinase-based dopamine biosensor with high sensitivity and selectivity. An electrochemically pretreated tyrosinase/multi-walled carbon nanotube-modified glassy carbon electrode (tyrosinase/MWNT/GCE) was prepared as an amperometric biosensor for selective dopamine detection. For optimizing the biosensor performance, pH, temperature, and scan rate were investigated. The electrochemically pretreated tyrosinase/MWNT/GCE exhibited not only the highest sensitivity (1,323 mAM−1 cm−2) compared to previously reported tyrosinase-based dopamine sensors, but also good long-term stability, retaining 90% of initial activity after 30 days. Additionally, ascorbic acid, a major interfering substances, was not oxidized at the potential used to detect dopamine oxidation, and the interfering effect of 4mM ascorbic acid was negligible when monitoring 1mM dopamine. Consequently, the electrochemically pretreated tyrosinase/MWNT/GCE is applicable for highly selective and sensitive dopamine detection in actual samples including interfering substances, thereby extending the practical use to monitor and diagnose neurological disorders.

Production and characterization of cellulase from E. coli EgRK2 recombinant based oil palm empty fruit bunch

Oil Palm Empty Fruit Bunch (OPEFB) is an abundant biomass resource in Indonesia, which contains 41.3 ~ 46.5% (w/w) of cellulose. This research examined the production of cellulase by the E. coli EgRK2 recombinant strain using an OPEFB substrate. The production of the enzyme was initially examined to identify optimum growth conditions, by observing the growth and activity of E. coli EgRK2 compared to its wild type. Our results showed that the optimum production time, pH and temperature of the recombinant growth and cellulase activity were achieved at 24 h, and at 7 and 40°C, respectively. Using these optimum conditions, the enzyme was produced, and experiments were carried out to examine the enzyme characteristics, produced from both strains, on hydrolysis of cellulose from OPEFB. Our results showed that the activity of the enzyme produced by the recombinant almost doubled compared to that of the wild type, although the optimum pH for both strains was pH 6. Higher activity was achieved by the recombinant compared to the wild type strain, and values were 1.905 and 1.366 U/mL, respectively. The optimum temperature for hydrolysis by cellulase occurred at 50°C for Bacillus sp. RK2, and 60°C for Bacillus sp. EgRK2. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) for OPEFB degradation by E. coli EgRK2 were 0.26% and 1.750 μmol/mL/sec, which were significantly better values than those of the wild type. Control experiments for the degradation test using CMC also showed a better Vmax value for E. coli EgRK2 compared to the wild type, which is 2.543 and 1.605 μmol/mL/sec, respectively.

Column chromatography isolation of nicotine from tobacco leaf extract (Nicotiana tabaccum L.)

Restrictions on the use of dried tobacco leaf for cigarette production must be accompanied by the development of non-cigarette alternative products that are made from tobacco leaves. One of the alternative that can be done is to use the nicotine compound in tobacco leaf extract as medical product, such as Parkinson’s medication or to be used as active substance in biopesticide. Nicotine was isolated using column chromatography method with the variation of mobile phase mixture ratio (petroleum ether and ethanol), started from 8:2, 6:4, 4:6, 2:8, to 0:10. All of the chromatographic fraction from each mobile phase’s ratio was then tested qualitatively using thin layer chromatography (TLC) and also quantitatively using HPLC instrument. The column chromatography process could isolate 4.006% of nicotine compound from 4.19% tobacco leaf extract’s nicotine. It is also known that ethanol is a good solution to be used as chromatography’s mobile phase for nicotine isolation from tobacco leaf extract.Restrictions on the use of dried tobacco leaf for cigarette production must be accompanied by the development of non-cigarette alternative products that are made from tobacco leaves. One of the alternative that can be done is to use the nicotine compound in tobacco leaf extract as medical product, such as Parkinson’s medication or to be used as active substance in biopesticide. Nicotine was isolated using column chromatography method with the variation of mobile phase mixture ratio (petroleum ether and ethanol), started from 8:2, 6:4, 4:6, 2:8, to 0:10. All of the chromatographic fraction from each mobile phase’s ratio was then tested qualitatively using thin layer chromatography (TLC) and also quantitatively using HPLC instrument. The column chromatography process could isolate 4.006% of nicotine compound from 4.19% tobacco leaf extract’s nicotine. It is also known that ethanol is a good solution to be used as chromatography’s mobile phase for nicotine isolation from tobacco leaf extract.