Mucoadhésion (article en préparation)

 Synthesis of gold nanoparticles

Gold nanoparticles coated with PEG 2000 (referred to as AuNP 2000) were synthesized using a single phase Brust method modified from a technique previously published.45 A significant advantage of this procedure is the absence of tetraoctylammonium bromide, thus avoiding residual ionic contamination of this toxic compound. First, a stock solution of aqueous gold chloride was prepared by dissolving 1 g of HAuCl4∙3H2O to a final concentration of 0.1 mg/mL.

Then, 0.5 mL (0.127 mmol) of this stock solution was added to 30 mL of a 1:1 methanol:water solution. 0.048 g (0.024 mmol) of PEG 2000 and 20 mL of methanol were then added, and the solution was agitated during 90 minutes. 0.040 g (1.057 mmol) of NaBH4 dissolved in 20 mL of ice-cold water was then added dropwise under vigorous stirring using a peristaltic pump. The solution was left to agitate for 3h to ensure proper particle growth and stabilization.

The methanol was then evaporated under reduced pressure, and the nanoparticles were extracted with dichloromethane using a minimal amount of a saturated NaCl solution. AuNP were then dissolved in 10 mL of water and dialysed over two days. The nanoparticles were recovered and kept in solution in water in amber glass bottles in the dark. Unless otherwise specified, all the AuNP 2000 used in this paper came from this synthesis method.

A second synthesis, called synthesis #2, was performed using a different ratio of PEG 2000 to gold and different solvents compared the one previously described (data not shown). These AuNP were only used in one specific experiment for comparison (PAS coloration; sections 2.11 and 3.2.6) and their synthesis will be discussed in a further publication. 

Ligand exchange 8 molar equivalents of PEG 1000 double thiol, with respect to the amount of PEG 2000 used for the initial synthesis, were dissolved in the AuNP solution. The mixture was left to agitate for 5 days in the dark. The AuNP were then purified by extensive dialysis over 4 days. The resulting nanoparticles, referred to as AuNP double thiol, were recovered and kept in solution in amber glass bottles in the dark.

Elemental analysis

The samples were sent to Saskatchewan Research Council (SRC) Geoanalytical Laboratories. Sulfur and gold content of the AuNP were determined by induction furnace and fire assay, respectively. 2.4 Preparation of the mucins solution Typically, a stock solution of mucins from bovine submaxillary glands was prepared by dissolving the crude powder in water to a final concentration of 0.40 mg/mL. The solution was sonicated for 30 minutes and the pH was adjusted to 7.4.

The solution was then kept at 4 °C if not used immediately. A sonication of 30 minutes was realized before each new dilution. 2.5 TEM After leaving a droplet of AuNP solution to dry on a carbon grid for at least 5 days, TEM images were taken with the JEOL JEM 1230. The zoom factor was 50 000x. The images were then analyzed with ImageJ to determine the number and the diameter of the gold cores