An effective, green, and facile approach to synthesize gold nanoparticle-loaded protein–polysaccharide nanogels was developed in this study. Biocompatible gold nanoparticle-loaded lysozyme–dextran (Au@Lys–Dex) nanogels were produced using lysozyme–dextran nanogels as reducing and stabilizing agents. Lysozyme–dextran nanogels have a size of about 200 nm and a structure of lysozyme core and dextran shell. At pH around 4, AuCl₄ ⁻ ions are attracted and locally enriched by lysozyme due to the electrostatic and coordination interactions. When the solution is under UV irradiation, the AuCl₄ ⁻ ions are reduced to gold nanoparticles in situ by solvated electrons and reactive radicals produced from aromatic amino acid residues in the lysozyme. The produced gold nanoparticles with a size of about 8 nm are trapped inside the nanogels and the Au@Lys–Dex nanogels are well dispersible by virtue of the dextran shell. Antitumor drug, doxorubicin, can be loaded effectively inside Au@Lys–Dex nanogels via diffusion. In vitro study demonstrates the doxorubicin loaded Au@Lys–Dex nanogels have the same antitumor activity as free doxorubicin. The nanogels can be used as a contrasting agent in optical cell imaging, in which direct visual images of the subcellular distributions of the gold nanoparticles and the released doxorubicin are presented synchronously. The dual functional drug loaded Au@Lys–Dex nanogels are a promising system for simultaneous drug delivery and biomedical imaging.

Diabetes mellitus is the most common metabolic disease in the world. Herein, insulin- and cholic acid-loaded zein nanoparticles with dextran surfaces were fabricated to enhance the oral absorptions of insulin in the intestine and in the liver which is the primary action organ of endogenous insulin. In the nanoparticles, zein acted as cement to embed insulin, cholic acid and casein by hydrophobic interactions. The hydrophilic dextran conjugated to casein by the Maillard reaction was located on the nanoparticle surface. The nanoparticles had an insulin loading efficiency of 74.6%, a cholic acid loading efficiency of 55.1% and a hydrodynamic diameter of 267 nm. The dextran significantly increased the disperse stability of the nanoparticles, protected the loaded insulin from hydrolysis in digestive juices, and increased the trans-mucus permeability of the insulin. The embedded cholic acid molecules were consecutively exposed to the surface when the nanoparticles were gradually eroded by proteases. The exposed cholic acid promoted the absorptions of the nanoparticles in the ileum and liver via bile acid transporters. The effect of pretreated lymphatic transport inhibitor cycloheximide revealed that about half of the nanoparticles were transported via the intestinal lymphatic transport pathway and the other half of the nanoparticles were transported via portal blood absorption. The oral pharmacological bioavailability of the nanoparticles in type I diabetic mice was 12.5–20.5%. This study demonstrates that nanoparticles are a promising oral delivery system for insulin.