Gold nanoparticles biofunctionalized (grafted) with chiral amino acids: a practical approach to determining the enantiomeric percentage of racemic mixtures

Abstract

The importance of stereochemistry in chiral drugs is due to the different pharmacological behavior of enantiomers. Enantioseparation methods based on nanoparticles have gained interest recently. Different interactions of enantiomers with chiral nanoparticles encouraged us to determine the enantiomeric percentage of racemic mixtures with modified gold nanoparticles. In this work we applied L-cysteine capped gold nanoparticles (chiral environment) as a colorimetric sensor for enantio-selective detection of naproxen (NAP) racemic mixtures. The selective and rapid aggregation of modified gold nanoparticles in the presence of R-naproxen allowed us to construct a visual chiral sensor. The results were characterized by TEM, UV-visible, zeta potential and FT-IR measurements. L-Cysteine group functionalized gold nanoparticles (L-Cys-Au NPs) had a cooperative effect on visual inspection of R-naproxen in aqueous solution resulting in sensible changes in color and absorption specifications over S-naproxen. The effect can be monitored by the naked eye or using a UV-vis spectrometer. The developed method was utilized for the determination of enantiomeric percentage of racemic mixtures of NAP in aqueous and plasma samples with satisfactory results. Under optimum conditions, the chiral biosensor exhibited a good linear response to naproxen enantiomers in the concentration range of 10 to 200 μM with a limit of detection of 6.02 μM (S/N = 3). The relative standard deviation (R.S.D.) in water was 3.8% (n = 7).