Optimization of uric acid detection with Au nanorod-decorated graphene oxide (GO/AuNR) using response surface methodology.

A modified glassy carbon electrode (GCE) was developed based on a synthesized graphene oxide (GO) gold nanorod (AuNR) decorated composite (GO/AuNR) for sensitive electrochemical sensing of uric acid (UA). The electrochemical performance of GO/AuNR/GCE for UA detection was investigated employing the differential pulse voltammetry (DPV) technique. Central composite design (CCD) was applied to obtain the optimum composition of the GO and AuNR composite, which provide the highest possible UA oxidation peak current. The optimum composition was obtained at a GO concentration of 5 mg mL-1 and AuNR volume of 10 mL. Under the optimum conditions, GO/AuNR/GCE showed acceptable analytical performance for UA detection with good linearity (concentration range of 10-90 µM) and both a low detection limit (0.4 µM) and quantitation limit (1.0 µM). Furthermore, the proposed sensor exhibits superior stability, reproducibility, and selectivity using ascorbic acid (AA), dopamine (DA), urea, glucose, and magnesium as interferents. Finally, practical use of GO/AuNR/GCE was demonstrated by successfully determining the content of UA in human urine samples with the standard addition approach.

A facile electrochemical sensor based on a composite of electrochemically reduced graphene oxide and a PEDOT:PSS modified glassy carbon electrode for uric acid detection.

A glassy carbon electrode modified with electrochemically reduced graphene oxide (ErGO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was developed for uric acid determination with dopamine as interference in artificial saliva. The electrochemical performance of the fabricated electrode was studied using both techniques of cyclic voltammetry (CV) and differential pulse voltammetry (DPV), under optimized conditions. Using DPV, the sensor based on ErGO/PEDOT:PSS modified GCE displayed a linear relationship in the concentration ranges of 10-100 µM for uric acid. This uric acid sensor exhibited a high sensitivity with detection limits of 1.08 µM and quantitation limit of 3.61 µM. This sensor also showed good reproducibility for uric acid detection in artificial saliva in 5 consecutive days of measurements. This device was successfully used to analyze uric acid in artificial saliva as well as in a human saliva sample using the standard addition method.

Fourier transform infrared spectroscopy combined with chemometrics for discrimination of Curcuma longa, Curcuma xanthorrhiza and Zingiber cassumunar.

Turmeric (Curcuma longa), java turmeric (Curcuma xanthorrhiza) and cassumunar ginger (Zingiber cassumunar) are widely used in traditional Indonesian medicines (jamu). They have similar color for their rhizome and possess some similar uses, so it is possible to substitute one for the other. The identification and discrimination of these closely-related plants is a crucial task to ensure the quality of the raw materials. Therefore, an analytical method which is rapid, simple and accurate for discriminating these species using Fourier transform infrared spectroscopy (FTIR) combined with some chemometrics methods was developed. FTIR spectra were acquired in the mid-IR region (4000-400 cm(-1)). Standard normal variate, first and second order derivative spectra were compared for the spectral data. Principal component analysis (PCA) and canonical variate analysis (CVA) were used for the classification of the three species. Samples could be discriminated by visual analysis of the FTIR spectra by using their marker bands. Discrimination of the three species was also possible through the combination of the pre-processed FTIR spectra with PCA and CVA, in which CVA gave clearer discrimination. Subsequently, the developed method could be used for the identification and discrimination of the three closely-related plant species.