Caffeine monitoring in biological fluids by solid surface fluorescence using membranes modified with nanotubes

Abstract

BackgroundIn this work, a new methodology based upon enhancement of rhodamine B fluorescent signal is proposed for the quantification of caffeine traces. MethodsMembrane filters treated with multiple wall carbon nanotubes were employed as solid support for determination step by solid surface fluorescence. ResultsExperimental variables that influence the preconcentration step and fluorimetric sensitivity have been optimized using uni-variation assays, presenting linearity from 1.1 to 9.7×103μg/l, with a correlation coefficient of 0.99. At optimal conditions, a limit of detection of 0.3μg/l and a limit of quantification of 1.1μg/l were obtained. The method showed good sensitivity and adequate selectivity and was satisfactorily applied to the determination of trace amounts of caffeine in urine, plasma and serum belonging to subjects with different sex, ages and habit of caffeine intake. ConclusionsChemofiltration step eliminated the highly fluorescent matrix, thus enabling and allowing CF quantification, in the presence of other methylxanthines. The proposed methodology represents an innovative application of the solid surface fluorescence using membrane filters modified with MWCNTs.