Fig. 1: Preparation and characterization of CA-SBEβCD NPs.

The size distribution (A) and zeta potential (B) of SBEβCD NPs and CA-SBEβCD NPs were determined by laser light scattering. C The morphology of SBEβCD NPs was assessed by negative staining with sodium phosphotungstate solution and examined by transmission electron microscopy. Scale bar: 50 nm. D ¹H-NMR spectra of the components of CA-SBEβCD NPs. Resonance signals corresponding to the characteristic bonds of CA (No.1) appeared at 0.9–3.1 ppm. The characteristic peaks of SBEβCD (No.3) were at 2.88 and 1.71 ppm (peak a and b). NE (No.2), namely, nanoemulsions and auxiliary emulsion components without SBEβCD, presented signals at 2.55 ppm (peak c), 1.95 ppm (peak d), 1.52 ppm (peak e), 1.22 ppm (peak f), 1.09 ppm (peak g) and 0.83 ppm (peak h). The ¹H-NMR spectrum of SBEβCD NPs (No.4) exhibited peaks in similar regions as SBEβCD and NE because the NPs contained SBEβCD and NE groups. Compared with CA-SBEβCD NPs, new peaks at chemical shifts of 0.80 to 1.00 ppm and 1.45 to 1.55 ppm appeared in the ¹H-NMR spectrum of CA-SBEβCD NPs (No.5). Obvious increases in peak intensity at 1.15–1.35 ppm in the resonance signals of CA-SBEβCD NPs confirmed the synthesis of a link between CA and SBEβCD, and the signal peaks disappeared at 2.88 and 1.71 ppm suggests a bonding reaction between SBEβCD and CA. E Molecular docking diagram. CA potentially interacts with SBEβCD through hydrogen bonds: a hydroxyl group of CA respectively forms two intermolecular hydrogen bonds with the hydroxyl group and oxygen atom of SBEβCD; and a hydroxyl group of CA forms a hydrogen bond with a hydroxyl group of SBEβCD. The binding affinity was −21.35 kiloJoules/moL. F CA release from CA-SBEβCD NPs in PBS at pH 7.4 or 6.0 in vitro. CA dissolved in NE was used as control.