Judul: Aktivitas glukosa dehidrogenase pada tiga isolat bakteri Indonesia terpilih yang diimobilisasi untuk pengembangan biosensor glukosa darah
Abstrak: Biosensor mengkombinasikan selektivitas komponen pengenal hayati dan sensitivitas transduser. Aplikasi biosensor sebagai alat pengukur glukosa darah pada pasien penderita diabetes melitus menggunakan enzim murni sebagai sensor hayati. Penggantian enzim murni dengan sel mikrob penghasil enzim sebagai sensor hayati dilakukan untuk mengatasi kelemahan yang dimiliki enzim murni seperti stabilitas yang rendah dan harga yang mahal. Penelitian bertujuan mengukur aktivitas glukosa dehidrogenase (GDH)–enzim yang bereaksi secara spesifik dengan substrat glukosa dan menggunakan pyrolloquinoline quinone (PQQ) sebagai gugus prostetik serta ion Mg2+ sebagai zat pengaktif –yang dihasilkan oleh tiga jenis bakteri, yaitu Escherichia coli KRGS, Bacillus subtilis KRGL, dan Thermus sp. 1K dengan menggunakan metode spektrofotometri dan elektrokimia. Studi juga dilakukan terhadap kondisi optimum (pH larutan bufer fosfat, konsentrasi PQQ, dan konsentrasi glukosa) aktivitas GDH E. coli KRGS serta kestabilan aktivitas GDH ketiga bakteri dengan menggunakan metode elektrokimia.
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Judul: Stabilitas dan efektivitas biosensor glukosa berbasis Escherichia coli menggunakan imobilisasi glutaraldehida
Abstrak: The immobilization glucose dehydrogenase (GDH) cells from Escherichia coli cross-linking glutaraldehyde on a carbon paste electrode were studied. Cyclic voltammetry are employed to investigate the catalytic behavior of the biosensor. The analysis used for the optimization of GDH activity was response surface method. Optimum conditions for GDH activity was at temperature 30 oC, pH 6, glucose 10.25 mM, and pyrroloquinoline quinone (PQQ) 3.05μM for E. coli cells without cross-link with glutaraldehyde. On the other hand, the optimum conditions for GDH activity of E. coli cells cross-linked with glutaraldehyde was at temperature 30 oC, pH 6, glucose 10.25 mM, PQQ 3.05 μM, and glutaraldehyde 12.5 μL. Dehydrogenase reaction kinetics of GDH catalyzed by glucose followed the Lineweaver-Burk kinetics. KM app value of bacterial E. coli cells cross-linked with glutaraldehyde at 1.1162 mM was smaller than without cross-link, which was 1.9007 mM. Stability of activity GDH E. coli cells cross-linked with glutaraldehyde was 68% higher than that without cross-link.
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Judul: The Effects of Variance of Interest rate to Variance of Annuity Future Values
Abstrak: Time value of money is a concept that refers to the difference of the value of money due to time difference. The value of money for present time would not be the same as the value of money in the future. The value of money for present time is called as Present Value (PV) of the money and the value of money for future time is called Future Value (FV) of the money. Determination the value of money, for present and future time, depends on the time and rate of return. The value of money is determined by several factors such as inflation, fluctuation of interest rates, and government policy in securities and taxation. Due to fluctuation of the value of money we need a FV formulation, it is useful for knowing whether an investment can be profitable or not, and this information is useful also in budget analysis. Annuity is defined as a series of payments made for a specific period. The payment, fixed or varied, can be made at the beginning or at the end of the period. Annuity paid at the beginning of the period is called annuity-due and annuity paid at the end of the period is called immediate annuity-certain. The accumulated value of the annuity after few years later is called as a final value or a future value. Burnecki et al. (2003) have discussed about the FV of a fixed-rate annuity in which payments are made according to the arithmetic or geometric series. They have also examined FV for annuities in which payments are made according to arithmetic or geometric series with random rates of interest. This paper examines FV for annuity-due in which payments are made according to arithmetic or geometric series with interest rates as a random variable, which is normal distribution ,  . Future value formula is expressed in recursive form. FV for annuity-due which payments are made according to the arithmetic or geometric series with random rates of interest is calculated by theoretical way and simulation way. The random rates of interest is denoted as k k i  i  , where k i an independent random variable; i is a constant and k  is a random variable which has normal distribution ,  . By using the determined parameters, a sequence of random rates of interest are generated for theoretical calculation. Meanwhile for the simulation, the random rates of interest is generated 1000 times for the simulation. The generated data give mean value, variance, and standard deviation. Moreover, error of mean value, variance, and standard deviation from the theoretical and simulation results are calculated. Error calculation uses Symmetric Mean Absolute Percentage Error (SMAPE). The smaller the value of SMAPE is the more accurate the simulation. The interest rate variances are varied from 0.000036 to 0.0001 to study the relationship between variance of rates of interest and variance of future value. The theoretical and simulation results show that when the variance of random rates of interest increases, then the variance of FV increases linearly. FV of the annuity-due in
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