Neodymium 3 oxide

A single lot (Aldrich-634611) of neodymium (III) oxide (purity: 99.9%) was purchased from Sigma-Aldrich (St. Louis, Mo, USA). The surface area of nano-sized Nd₂O₃ used in the present study was measured to be 17.45 m²/g using the Brunauer-Emmett-Teller (BET) method (ASAP 2420, Micromeritics Inc., Norcross, GA, USA), and the particle size was calculated to be 49.05 nm. Nano-sized Nd₂O₃ was suspended in distilled water at a concentration of 0.09 to 1.50% and sonicated for 30 min (5 s sonication/3 s rest cycle) using a probe-type ultrasonicator (VC750, Sonics & Materials Inc., Newtown, CT, USA). The hydrodynamic diameter was then measured using the dynamic light scattering method (Zetasizer Nano ZS 90, Malvern, UK) to check particle size and dispersity. The dispersed suspension was aerosolized through a 0.6~0.8 mm diameter orifice at an airflow of 4~8 L/min in a nose-only inhalation chamber (NITC system, HCT Co., Icheon, Korea) under constant agitation. The total airflow for each chamber was set at 20 L/min to achieve a 1.0 L/min flow per rat. Temperature, relative humidity, pressure, and air ventilation in the chambers were recorded automatically.

Strontium carbonate (SrCO₃, 99.9%), neodymium(iii) oxide (Nd₂O₃, 99.9%), 1-octadecene (ODE, 90%), oleic acid (OA, 90%), trifluoroacetic acid (TFA, 99%), trichloroacetic acid (TCA, 99%), ammonium hydroxide solution (28–30% in H₂O), and dopamine hydrochloride were purchased from Sigma-Aldrich (Sigma-Aldrich, St. Louis, MO). Hexane (95%), ethanol (95% with 5% methanol) and isopropanol (IPA, 99.7%) were purchased from Aik Moh (Aik Moh Chemicals, SG). All chemicals were used as received without any further purification.