Enhancement of sensitivity of glucose sensors from alizarin–boronic acid adducts in aqueous micelles

The sensitivity of glucose sensors fabricated from alizarin–boronic acid adducts was improved by an assistance of surfactants. Basically, Alizarin Red S (ARS) is not a fluorescence active compound. However, the fluorescence emission can be observed when forming an adduct with 2-formylphenyl boronic acid (2-FPBA). Using displacement strategy, the fluorescence intensity of the ARS/2-FPBA adduct decreased as a linear function of the glucose concentration. A simple and sensitive method was developed by incorporating the ARS/2-FPBA adduct in the hydrophobic core of micelles. Various parameters that could possibly affect the fluorescence quenching ability including solution pH, concentration of 2-FPBA, types of surfactants and concentrations of surfactants were investigated. The optimum condition for the determination of glucose by the proposed assay was 2 mM cetyltrimethylammonium bromide (CTAB) in 0.05 M phosphate buffer pH 7.0. The fluorescence intensity of the ARS/2-FPBA adduct in the presence of CTAB was remarkably 13 times higher than that in the buffer solution. Moreover, the linear working concentration range was found to be 1.2–80 mM, and the calibration sensitivity was 14 times higher than that from the system containing only buffer solution.     

New approach for evaluation of the antioxidant capacity based on scavenging DPPH free radical in micelle systems

A simple and sensitive method was developed to evaluate the antioxidant capacity using a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) incorporated in surfactants. Parameters possibly affected the DPPH scavenging activity were investigated including the type of surfactant, concentration of surfactant, solution pH and concentration of buffer. The optimum micelle system for determining the antioxidant capacity was 2 mM CTAB in 0.1 M acetate buffer (pH 4.6). The IC₅₀ values of various antioxidants were calculated and compared to those prepared in methanol. Furthermore, the rate of the reaction between DPPH and antioxidants was investigated. The rate constants observed in the micelle system were significantly faster than those in methanol, and this allowed shorter analysis time. This method was validated through linearity, limit of detection and precision by comparing with conventional methanolic assay. The purposed method was applied to evaluate the antioxidant capacity from aqueous extracted plant samples with satisfactory results.