Design of a 3D interfacial SERS liquid sensing platform based on Au-nanobones for discrimination and quantitation of quercetin loaded nanoemulsions

Characterization, and discrimination between free quercetin and quercetin-loaded nanoemulsions (Q-NEs) are described, as well as the design of a plasmonic metal liquid platform for their quantitation. First, reproducible Q-NEs synthesis using GRAS (Generally Recognized as Safe) components and a low-energy method as phase inversion temperature was used. Q-NEs were fully characterized being the resulting droplet size of 73.1 ± 2.4 nm and 69.7 ± 2.3 nm by DLS and SEM, respectively, with spherical morphology and encapsulation efficiency of 96.5%. Based on UV-Vis, Raman and SERS characterization studies, a discrimination between free quercetin and Q-NEs was achieved. Secondly, a new 3D-platform was developed based on tuned gold nanorods-bone shaped with fitted aspect ratios for Q-NEs quantification without altering its native nanostructure using the enhanced stretching at 1600 cm-1 as analytical signal. The developed plasmonic sensing platform allows to reach intensification factors up to 103 and 105 for the target analyte and methylene blue as Raman reporter, respectively. It was also submitted to an exhaustive evaluation of analytical performance characteristics in terms of linear dynamic range (0.5 – 30 µM), detection limit (0.2 µM) with good precision (RSD = 2.6%). The nanometrological 3D SERS approach was reliably implemented and validated on commercial nutritional supplements containing declared encapsulated quercetin as nanosized formulations by means of a statistical comparison with those ones obtained by a µHPLC-DAD method.