Dual-density formulations devices and methods for intranasal drug delivery or sampling

A method of delivering a therapeutic agent to an olfactory region of a nasal cavity of a subject, the method comprising:

• a. delivering a formulation to the olfactory region of the nasal cavity, the formulation configured to form:
• i. an upper fluid comprising the therapeutic agent;
• and
• ii. a lower fluid, immiscible with the upper fluid at intranasal environmental conditions and having a greater density than that of the upper fluid, such that the upper fluid amasses on top of the lower fluid;
• wherein the upper fluid and the lower fluid are delivered simultaneously,
• wherein the formulation delivered to the olfactory region of the nasal cavity forms an upper layer comprising the upper fluid and a separate lower layer comprising the lower fluid, the upper layer impacting the olfactory region and the separate lower layer supporting the upper layer, thereby concentrating the upper fluid against the olfactory region of the nasal cavity and delivering the therapeutic agent to the olfactory region of the nasal cavity.